Merge pull request #140 from storytold/pr/release-0.2.1

Release: LightCraft v0.2.1

.github/workflows/packaging-lint.yml

@@ -47,6 +47,10 @@ jobs:
       - name: XML, desktop entry, AppStream, Flatpak manifest
         run: |
           xmllint --noout packaging/windows/lightcraft.wxs packaging/macos/*.plist* packaging/linux/*.xml*
+          # Windows Installer needs Icon ids ending in .ico or .exe, or shortcuts show a blank icon.
+          if grep -oE '<Icon Id="[^"]*"' packaging/windows/lightcraft.wxs | grep -vE '\.(ico|exe)"$'; then
+            echo "::error::Icon Id must end in .ico or .exe"; exit 1
+          fi
           desktop-file-validate packaging/linux/ai.storyteller.lightcraft.desktop
           sed -e 's/@VERSION@/0.0.0/' -e 's/@DATE@/2026-01-01/' packaging/linux/ai.storyteller.lightcraft.metainfo.xml.in >"$RUNNER_TEMP/ai.storyteller.lightcraft.metainfo.xml"
           appstreamcli validate --no-net --explain "$RUNNER_TEMP/ai.storyteller.lightcraft.metainfo.xml"

.github/workflows/release.yml

@@ -221,8 +221,9 @@ jobs:
       - name: Install wasm-bindgen CLI
         run: |
           # Must match the wasm-bindgen version in Cargo.lock exactly (cargo xtask web checks it).
-          command -v wasm-bindgen >/dev/null && wasm-bindgen --version | grep -q "$WASM_BINDGEN_VERSION" \
-            || cargo install wasm-bindgen-cli --version "$WASM_BINDGEN_VERSION" --locked
+          if ! { command -v wasm-bindgen >/dev/null && wasm-bindgen --version | grep -q "$WASM_BINDGEN_VERSION"; }; then
+            cargo install wasm-bindgen-cli --version "$WASM_BINDGEN_VERSION" --locked
+          fi
           wasm-bindgen --version
       - name: Apply version override
         if: inputs.version != ''

Cargo.lock

@@ -2073,7 +2073,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "eframe",
  "egui",
@@ -2091,7 +2091,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-catalog"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "crc32fast",
  "lightcraft-develop",
@@ -2105,7 +2105,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-cli"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "dhat",
  "lightcraft-codecs",
@@ -2120,7 +2120,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-codecs"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "bytemuck",
  "image",
@@ -2145,7 +2145,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-color"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "lightcraft-geom",
  "proptest",
@@ -2154,7 +2154,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-develop"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "lightcraft-color",
  "lightcraft-geom",
@@ -2165,7 +2165,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-engine"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "ab_glyph",
  "libc",
@@ -2193,7 +2193,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-geom"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "proptest",
  "serde",
@@ -2201,7 +2201,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-gpu"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "bytemuck",
  "lightcraft-color",
@@ -2217,7 +2217,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-mcp"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "lightcraft-codecs",
  "lightcraft-engine",
@@ -2228,7 +2228,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-merge"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "lightcraft-codecs",
  "lightcraft-color",
@@ -2244,7 +2244,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-meta"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "lightcraft-geom",
  "lightcraft-tiff",
@@ -2256,7 +2256,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-pipeline"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "image",
  "lightcraft-color",
@@ -2272,7 +2272,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-preview"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "jpeg-encoder",
  "lightcraft-raster",
@@ -2284,7 +2284,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-raster"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "libc",
  "lightcraft-color",
@@ -2296,7 +2296,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-raw"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "jpeg-encoder",
  "lightcraft-color",
@@ -2315,7 +2315,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-scenes"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "image",
  "lightcraft-color",
@@ -2326,11 +2326,11 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-sysmem"
-version = "0.2.0"
+version = "0.2.1"
 
 [[package]]
 name = "lightcraft-tiff"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "proptest",
  "serde",
@@ -2339,7 +2339,7 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-ui-egui"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "egui",
  "lightcraft-catalog",
@@ -2359,8 +2359,9 @@ dependencies = [
 
 [[package]]
 name = "lightcraft-web"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
+ "crc32fast",
  "eframe",
  "egui",
  "js-sys",
@@ -5127,7 +5128,7 @@ checksum = "e450f9b2ed1dff33c94c12589a87338689467b9c4f5d8a5710bd09a847d2c8a7"
 
 [[package]]
 name = "xtask"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "brotli",
  "flate2",

Cargo.toml

@@ -3,7 +3,7 @@ resolver = "3"
 members = ["crates/*", "apps/*", "xtask"]
 
 [workspace.package]
-version = "0.2.0"
+version = "0.2.1"
 edition = "2024"
 license = "MIT OR Apache-2.0"
 rust-version = "1.90"

ROADMAP.md

@@ -24,19 +24,19 @@ duplicate Local entries #22, black GPU exports on an Intel iGPU #78).
 |---|---:|---|---|
 | **Feature checklist** | 79% | P0 core and P1 nearly complete: import (Add / Copy / Move, templates, devices), library, grid/loupe/compare/survey, every Edit slider, curves, colour grading, masking tools, crop/Upright, heal/clone, presets/profiles, versions/history, sync, export, menus, shortcuts | P1: lens-profile database, content-aware fill (patch synthesis), video playback/trim |
 | **RAW coverage** (formats people shoot) | ~50% | DNG (all kinds), CR2, ARW, NEF (uncompressed + Huffman lossless/lossy), uncompressed RAF/ORF, packed RW2, PEF; every container's embedded preview (incl. CR3) | **CR3** (every Canon since ~2018), compressed RAF/ORF, RW2 v4, Nikon lossy-after-split, Canon sRAW, HEIC/AVIF. Per-model verification is thin (~40 corpus files vs >1,000 models) |
-| **Colour & image quality** | ~55–65% | Pipeline is complete and fast; GPU path CPU-exact within 1/255 | **No camera colour calibration**: non-DNG raws use a neutral matrix, so colour is muted/inaccurate. No lens-profile database. No measured fidelity against Lightroom (tone, highlights, texture/clarity, NR, sharpening are tuned by eye) |
+| **Colour & image quality** | ~55–65% | Pipeline is complete and fast; GPU path CPU-exact within 1/255 | **No measured camera calibration database**: ARW has a guarded per-file embedded-JPEG colour estimate (docs/camera-preview-colour.md); other non-DNG raws and rejected estimates use a neutral matrix. Colour fidelity remains incomplete. No lens-profile database. No measured fidelity against Lightroom (tone, highlights, texture/clarity, NR, sharpening are tuned by eye) |
 | **AI & computational** | ~15–20% | Assisted culling (focus, bursts), auto tone, HDR/panorama merge; subject/sky/background masks as classical heuristics | Real segmentation masks (subject, sky, people, objects, landscape, depth), AI denoise, super resolution, lens blur, generative remove, faces/people, natural-language search. **Blocked on a model strategy** (licensable weights or our own training; pure-Rust inference is feasible) |
 | **Workflow & library** | ~85% (single machine) | Robust catalog (journal + snapshots, background compaction, crash-tested), 85k-photo libraries stay responsive, Local browsing with automatic cleanup, XMP interop, keywords, smart albums, Move import | Opening an 85k library takes 1.7–4.7 s; no cloud sync (out of scope), no tablet companion (#74, roadmap), shared albums, publish services, tethering |
 | **Classic modules** | ~30% | Geotagging from GPX track logs, soft proofing (partial), slideshow (basic) | **Map view, Book, Print, Slideshow module, Web, publish services**: ~40 tracker rows ⬜ |
 | **HDR & video** | 0% | | HDR edit/display/export; video play/trim/edit/export |
-| **Platform & robustness** | ~70% | macOS native; Windows/Linux builds; web via WASM; no-panic lints workspace-wide, `unsafe` confined to `crates/sysmem`; failed saves are reported; GPU errors fall back to CPU | Windows installer UI unverified on Windows (PR #79); GPU path proven only on Apple + user reports; no localisation; accessibility partial; headless UI tests time out under machine load |
+| **Platform & robustness** | ~70% | macOS native; Windows/Linux builds; web via WASM; no-panic lints workspace-wide, `unsafe` confined to `crates/sysmem`; failed saves are reported; GPU errors fall back to CPU | Windows installer UI unverified on Windows (PR #79); GPU path proven only on Apple + user reports; Japanese/English UI (see docs/localization-ja.md); remaining technical errors and other languages; accessibility partial; headless UI tests time out under machine load |
 
 ### By kind of user
 
 | User | Readiness | What blocks them |
 |---|---:|---|
 | JPEG / DNG shooter, single machine | ~85% | Fidelity polish, AI masks |
-| Nikon / Sony / older-Canon raw shooter | ~65% | Camera colour (muted colour on every photo) |
+| Nikon / Sony / older-Canon raw shooter | ~65% | Camera colour fidelity and coverage (ARW preview estimates are only a starting point) |
 | Canon CR3 / Fujifilm / Olympus shooter | ~35% | Their raws open as embedded previews only |
 | Lightroom Classic power user | ~45% | Print, Book, Map, publish, tethering |
 | Relies on AI (masks, denoise) | ~25% | No segmentation or AI denoise models |
@@ -46,7 +46,8 @@ duplicate Local entries #22, black GPU exports on an Intel iGPU #78).
 Priorities, in order. Each points at tracker rows in [`docs/parity.md`](docs/parity.md) → *Top gaps*.
 
 1. **Camera colour calibration of our own** (LR-PROF-CAMERACOLOR, P0): fit each camera to its own embedded JPEG, use
-   matrices the files carry themselves, then chart shots. Raises colour quality for every non-DNG raw at once.
+   matrices the files carry themselves, then chart shots. Sony ARW's file-local fit (matrix + tone curve from its own
+   JPEG) is the first step; generalise it to the other makes' raws (NEF, RW2, PEF, ORF…), then validate fidelity.
 2. **Raw formats, clean-room** (LR-IMP-FORMATS, P0): **CR3** first, then compressed RAF / ORF, RW2 v4, NEF
    lossy-after-split, sRAW. Decided 2026-10-05: write our own decoders from prose descriptions (never decoder source,
    no LGPL dependency); compressed NEF (#86) is the template.
@@ -81,12 +82,12 @@ hardening (#78), copyright metadata (#51), GPX geotagging (#60), import tag help
 | M8 | Heal / Remove | content-aware remove (PatchMatch), heal, clone, brush spots, visualize spots, red/pet eye | 6–10 | 🚧 (heal, clone, auto source, visualize spots, red/pet eye ✅; PatchMatch remove ⬜) |
 | M9 | Presets, profiles, versions, sync | preset browser + amount, create/import presets, profile browser, versions, history, copy/paste/sync settings | 5–8 | ✅ |
 | M10 | Export & share | export dialog (JPEG/PNG/TIFF/DNG/AVIF/JXL/original), sizing, sharpening, metadata, watermark, naming, batch jobs, XMP sidecars, HDR export | 6–10 | 🚧 (all formats incl. DNG/original, sizing, presets, background jobs ✅; JXL encode, HDR export ⬜) |
-| M11 | RAW II | CR3, RAF (X-Trans), ORF, RW2, PEF, SRW, 3FR, IIQ + long tail; camera calibration DB; HEIC/AVIF/JXL import | 20–35 | 🚧 (RAF uncompressed, RW2 packed, PEF, ORF uncompressed ✅; **camera colour calibration** ⬜ (top priority), CR3, compressed ORF/RAF ⬜) |
+| M11 | RAW II | CR3, RAF (X-Trans), ORF, RW2, PEF, SRW, 3FR, IIQ + long tail; camera calibration DB; HEIC/AVIF/JXL import | 20–35 | 🚧 (RAF uncompressed, RW2 packed, PEF, ORF uncompressed ✅; **camera colour calibration** 🚧 (guarded ARW preview fitting; measured database still missing), CR3, compressed ORF/RAF ⬜) |
 | M12 | AI & smart features | subject/sky/background/people/object masks, semantic search, faces/People (permissively licensed models, pure-Rust inference) | 20–40 | ⬜ |
 | M13 | Merge | HDR merge (deghost), panorama (projections, boundary warp, fill edges), HDR panorama | 10–15 | ✅ |
 | M14 | Video | import/playback/trim via FilmCraft crates, global edits + presets on video, video export | 6–10 | ⬜ |
 | M15 | Classic modules | Map, Book, Slideshow, Print, Web; smart collections, stacks, virtual copies, publish services, tethering | 25–40 | 🚧 (smart albums, stacks, virtual copies, compare/survey ✅; Map/Book/Slideshow/Print/Web ⬜) |
-| M16 | 1.0 polish | preferences, shortcut editor, accessibility, localization, packaging (dmg/msi/AppImage/web), hardening | 10–20 | 🚧 (settings, keyboard shortcuts sheet, packaging basics ✅; accessibility, localisation ⬜) |
+| M16 | 1.0 polish | preferences, shortcut editor, accessibility, localization, packaging (dmg/msi/AppImage/web), hardening | 10–20 | 🚧 (settings, keyboard shortcuts sheet, packaging basics ✅; Japanese/English localisation 🟡; accessibility and other locales ⬜) |
 
 ## Parity estimate (feature count updated 2026-10-05; effort estimate from 2026-10-02)
 
@@ -175,7 +176,7 @@ Not decoded yet — preview only (no permissively licensed description; black-bo
   from the same-colour pixel two to the left), the reconstruction rule for scales 2/3 is not established.
 - **Olympus compressed ORF**, **Fujifilm compressed RAF**, **Canon CR3/CRX** (M11.1), **Canon sRAW/mRAW**, lossy DNG.
 
-**Camera colour matrices:** non-DNG raws use the documented neutral fallback (camera RGB ≈ linear sRGB, flagged
+**Camera colour matrices:** ARW files can use guarded, separate chromaticity and tone estimates from their own embedded JPEG (see `docs/camera-preview-colour.md`); this is a per-file camera-look estimate with relative WB, not measured calibration or absolute-Kelvin WB. Other non-DNG raws and rejected fits use the documented neutral fallback (camera RGB ≈ linear sRGB, flagged
 `matrix_is_fallback`) with the file's as-shot white-balance multipliers. Clean sources to evaluate next: manufacturer
 matrices stored in the files themselves (Olympus ImageProcessing `ColorMatrix`, Pentax/Panasonic equivalents) and our
 own chart-based calibration (M11.4). Adobe matrices are never used.

apps/lightcraft-cli/src/main.rs

@@ -91,6 +91,17 @@ USAGE:
 #[global_allocator]
 static ALLOC: dhat::Alloc = dhat::Alloc;
 
+/// Why `--library DIR` can't be opened; for a library open in another program, how to work with
+/// that one instead (issue #99).
+fn library_error(dir: &str, e: lightcraft_engine::EngineError) -> String {
+    match e {
+        lightcraft_engine::EngineError::LibraryInUse(why) => format!(
+            "{dir}: {why}\nTo work with the library while the app has it open, start the app with `--control PORT` and use `lightcraft-cli mcp --connect 127.0.0.1:PORT`."
+        ),
+        e => format!("{dir}: {e}"),
+    }
+}
+
 fn main() -> ExitCode {
     // `--features dhat-heap`: count allocations; the profile is written when `_heap` drops
     // (LIGHTCRAFT_DHAT_FILE, default dhat-heap.json).
@@ -182,7 +193,7 @@ fn mcp(args: &[String]) -> Result<(), String> {
             let mut h = match &library {
                 Some(dir) => {
                     let mut h = Headless::default();
-                    let r = h.session.open_library(dir, demo).map_err(|e| e.to_string())?;
+                    let r = h.session.open_library(dir, demo).map_err(|e| library_error(dir, e))?;
                     eprintln!("lightcraft-cli mcp: opened library {dir} ({r:?})");
                     h
                 }
@@ -419,7 +430,7 @@ fn run(args: &[String]) -> Result<(), String> {
             let mut h = match &library {
                 Some(dir) => {
                     let mut h = Headless::default();
-                    h.session.open_library(dir, demo).map_err(|e| e.to_string())?;
+                    h.session.open_library(dir, demo).map_err(|e| library_error(dir, e))?;
                     h
                 }
                 None if demo => Headless::demo(),
@@ -586,7 +597,7 @@ fn snapshot(args: &[String]) -> Result<(), String> {
     let mut session = match &library {
         Some(dir) => {
             let mut s = Session::new().with_fs();
-            s.open_library(dir, false).map_err(|e| format!("{dir}: {e}"))?;
+            s.open_library(dir, false).map_err(|e| library_error(dir, e))?;
             s
         }
         None if files.is_empty() => Session::with_demo().with_fs(),

apps/lightcraft-cli/tests/cli.rs

@@ -260,3 +260,31 @@ fn devices_are_listed_and_imported_from() {
     let line: Value = serde_json::from_slice(o.stdout.split(|b| *b == b'\n').next().unwrap()).unwrap();
     assert_eq!(line["result"]["candidates"].as_array().map(Vec::len), Some(1), "{line}");
 }
+
+/// Issue #99: a library open in one process (here `mcp --library`) is refused by a second one,
+/// with who has it and how to drive the running app instead; free again once the first exits.
+#[test]
+fn a_library_open_in_another_process_is_refused() {
+    let lib = tmp("locked-lib");
+    let _ = std::fs::remove_dir_all(&lib);
+    let lib_s = lib.to_str().unwrap();
+    let mut holder =
+        Command::new(BIN).args(["mcp", "--library", lib_s]).stdin(Stdio::piped()).stdout(Stdio::null()).stderr(Stdio::piped()).spawn().unwrap();
+    let mut err = BufReader::new(holder.stderr.take().unwrap());
+    let mut line = String::new();
+    while !line.contains("opened library") {
+        line.clear();
+        assert!(err.read_line(&mut line).unwrap() > 0, "mcp exited before opening the library");
+    }
+    let (ok, _, stderr) = run_cli(&["--library", lib_s, "library.info"], None);
+    assert!(!ok);
+    assert!(stderr.contains("already open in lightcraft-cli") && stderr.contains(&format!("process {}", holder.id())), "{stderr}");
+    assert!(stderr.contains("mcp --connect"), "{stderr}");
+
+    drop(holder.stdin.take()); // EOF: the server exits and lets go of the library
+    assert!(holder.wait().unwrap().success());
+    let (ok, lines, stderr) = run_cli(&["--library", lib_s, "library.info"], None);
+    assert!(ok, "{stderr}");
+    assert_eq!(lines[0]["ok"], true);
+    let _ = std::fs::remove_dir_all(&lib);
+}

apps/lightcraft-web/Cargo.toml

@@ -21,6 +21,7 @@ lightcraft-preview = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 log = { workspace = true }
+crc32fast = { workspace = true }
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 eframe = { workspace = true, features = ["default_fonts", "glow"] }

apps/lightcraft-web/src/backend.rs

@@ -232,6 +232,18 @@ impl Backend {
         }
     }
 
+    /// Is there a file at `path`?
+    pub async fn exists(&self, path: &str) -> Result<bool, String> {
+        match self {
+            Backend::Opfs(root) => Ok(Self::opfs_file(root, path, false).await?.is_some()),
+            Backend::Idb(db) => {
+                let (_tx, store) = Self::idb_store(db, false)?;
+                let n = idb_req(&store.count_with_key(&path.into()).map_err(err)?).await?;
+                Ok(n.as_f64().is_some_and(|n| n > 0.0))
+            }
+        }
+    }
+
     pub async fn remove(&self, path: &str) -> Result<(), String> {
         match self {
             Backend::Opfs(root) => {
@@ -309,14 +321,25 @@ async fn dir_keys(dir: &FileSystemDirectoryHandle) -> Result<Vec<String>, String
     Ok(out)
 }
 
-/// Ask the browser not to evict our storage under pressure (best effort; fire and forget).
-pub fn request_persistence() {
-    if let Some(sm) = storage_manager()
-        && let Ok(p) = sm.persist()
-    {
-        wasm_bindgen_futures::spawn_local(async move {
-            let granted = JsFuture::from(p).await.ok().is_some_and(|v| v.is_truthy());
-            log::info!("lightcraft: persistent storage {}", if granted { "granted" } else { "not granted (best effort)" });
-        });
-    }
+/// Ask the browser not to evict our storage under pressure; `on_result(granted)` once known
+/// (`false` also when the browser has no storage manager).
+pub fn request_persistence(on_result: impl FnOnce(bool) + 'static) {
+    let Some(sm) = storage_manager() else {
+        on_result(false);
+        return;
+    };
+    wasm_bindgen_futures::spawn_local(async move {
+        // already persistent: nothing to ask
+        let already = match sm.persisted() {
+            Ok(p) => JsFuture::from(p).await.ok().is_some_and(|v| v.is_truthy()),
+            Err(_) => false,
+        };
+        let granted = already
+            || match sm.persist() {
+                Ok(p) => JsFuture::from(p).await.ok().is_some_and(|v| v.is_truthy()),
+                Err(_) => false,
+            };
+        log::info!("lightcraft: persistent storage {}", if granted { "granted" } else { "not granted" });
+        on_result(granted);
+    });
 }

apps/lightcraft-web/src/backup.rs

@@ -0,0 +1,306 @@
+//! Library backups for the browser build: a plain zip (entries stored, not compressed — photos
+//! don't shrink) of the library files and every stored original, built one entry at a time so
+//! only one file is in wasm memory at once, and read back the same way for a restore.
+//!
+//! Layout of a backup:
+//! - `library/catalog.snap`, `library/catalog.log`, `library/presets.json`, … (see
+//!   [`crate::files::LIBRARY_FILES`]);
+//! - `originals/<content hash>/<file name>`: each imported photo's original bytes, under its own
+//!   name so an unzipped backup is browsable;
+//! - `README.txt`.
+//!
+//! Restoring never deletes anything: the library files go to a new library folder in browser
+//! storage, originals that aren't stored yet are added (they're named by content, so existing
+//! ones are identical), and only then does a small pointer file ([`ACTIVE_LIBRARY`]) switch to
+//! the restored library. The library that was there before stays in storage.
+//!
+//! No zip64: a backup holds at most [`MAX_BYTES`] and 65 535 entries.
+
+/// Storage key of the file naming the library folder in use (absent: `library`).
+pub const ACTIVE_LIBRARY: &str = "active-library";
+
+/// The default library folder.
+pub const DEFAULT_LIBRARY_DIR: &str = "library";
+
+/// Largest backup (offsets are 32-bit without zip64).
+pub const MAX_BYTES: u64 = 0xFFFF_FFFF - (64 << 20);
+
+const LOCAL_SIG: u32 = 0x0403_4b50;
+const CENTRAL_SIG: u32 = 0x0201_4b50;
+const END_SIG: u32 = 0x0605_4b50;
+/// General-purpose flag bit 11: names are UTF-8.
+const UTF8: u16 = 0x0800;
+/// 1980-01-01 00:00 in MS-DOS format (date, time).
+const DOS_DATE: u16 = (1 << 5) | 1;
+
+/// The readme inside every backup.
+pub const README: &str = "LightCraft library backup (browser version)\n\n\
+library/      the catalog (catalog.snap + catalog.log), presets, view state and preferences\n\
+originals/    every imported photo, as originals/<content hash>/<file name>\n\n\
+Restore it in LightCraft for the web with File > Restore Library from Backup...\n\
+The photos in originals/ are the untouched files you imported; edits live in the catalog.\n";
+
+/// Is `name` a safe library folder name (`library` or `library-<letters, digits, ->`)?
+pub fn valid_library_dir(name: &str) -> bool {
+    name == DEFAULT_LIBRARY_DIR
+        || name.strip_prefix("library-").is_some_and(|s| !s.is_empty() && s.len() <= 64 && s.chars().all(|c| c.is_ascii_alphanumeric() || c == '-'))
+}
+
+/// Is `h` a plausible content hash (used as a storage key segment)?
+pub fn valid_hash(h: &str) -> bool {
+    !h.is_empty() && h.len() <= 128 && h.chars().all(|c| c.is_ascii_alphanumeric())
+}
+
+/// Zip entry name for an original.
+pub fn original_entry(hash: &str, file_name: &str) -> String {
+    let name: String = file_name.chars().map(|c| if c == '/' || c == '\\' || c.is_control() { '_' } else { c }).collect();
+    let name = if name.is_empty() || name == "." || name == ".." { "original".to_string() } else { name };
+    format!("originals/{hash}/{name}")
+}
+
+/// Where a backup entry goes when restoring into library folder `dir`: `Some(storage key)`, or
+/// `None` to skip it (README, thumbnails, anything unknown or unsafe).
+pub fn restore_key(entry: &str, dir: &str) -> Option<String> {
+    if let Some(name) = entry.strip_prefix("library/") {
+        return crate::files::LIBRARY_FILES.contains(&name).then(|| format!("{dir}/{name}"));
+    }
+    let rest = entry.strip_prefix("originals/")?;
+    let (hash, _) = rest.split_once('/').unwrap_or((rest, ""));
+    valid_hash(hash).then(|| format!("originals/{hash}"))
+}
+
+fn u16le(v: &mut Vec<u8>, x: u16) {
+    v.extend_from_slice(&x.to_le_bytes());
+}
+fn u32le(v: &mut Vec<u8>, x: u32) {
+    v.extend_from_slice(&x.to_le_bytes());
+}
+
+struct Central {
+    name: String,
+    crc: u32,
+    size: u32,
+    offset: u32,
+}
+
+/// Writes a stored (uncompressed) zip piece by piece: [`ZipWriter::entry`] returns the local
+/// header to emit before the entry's bytes, [`ZipWriter::finish`] the central directory.
+#[derive(Default)]
+pub struct ZipWriter {
+    entries: Vec<Central>,
+    offset: u64,
+}
+
+impl ZipWriter {
+    /// The local header for `name` holding `data` (emit it, then `data`).
+    pub fn entry(&mut self, name: &str, data: &[u8]) -> Result<Vec<u8>, String> {
+        let size = u32::try_from(data.len()).map_err(|_| format!("{name}: larger than 4 GB"))?;
+        let name_len = u16::try_from(name.len()).map_err(|_| format!("{name}: name too long"))?;
+        if self.entries.len() >= usize::from(u16::MAX) {
+            return Err("too many files for one backup".into());
+        }
+        let header_len = 30 + u64::from(name_len);
+        if self.offset + header_len + u64::from(size) > MAX_BYTES {
+            return Err("the library is too large for one backup file (4 GB)".into());
+        }
+        let offset = u32::try_from(self.offset).map_err(|_| "backup too large".to_string())?;
+        let crc = crc32fast::hash(data);
+        let mut h = Vec::with_capacity(header_len as usize);
+        u32le(&mut h, LOCAL_SIG);
+        u16le(&mut h, 20); // version needed
+        u16le(&mut h, UTF8);
+        u16le(&mut h, 0); // stored
+        u16le(&mut h, 0); // time
+        u16le(&mut h, DOS_DATE);
+        u32le(&mut h, crc);
+        u32le(&mut h, size);
+        u32le(&mut h, size);
+        u16le(&mut h, name_len);
+        u16le(&mut h, 0); // extra
+        h.extend_from_slice(name.as_bytes());
+        self.offset += header_len + u64::from(size);
+        self.entries.push(Central { name: name.to_string(), crc, size, offset });
+        Ok(h)
+    }
+
+    /// The central directory and end record (emit last).
+    pub fn finish(self) -> Result<Vec<u8>, String> {
+        let mut cd = Vec::new();
+        for e in &self.entries {
+            u32le(&mut cd, CENTRAL_SIG);
+            u16le(&mut cd, 20); // made by
+            u16le(&mut cd, 20); // needed
+            u16le(&mut cd, UTF8);
+            u16le(&mut cd, 0);
+            u16le(&mut cd, 0);
+            u16le(&mut cd, DOS_DATE);
+            u32le(&mut cd, e.crc);
+            u32le(&mut cd, e.size);
+            u32le(&mut cd, e.size);
+            u16le(&mut cd, e.name.len() as u16);
+            u16le(&mut cd, 0); // extra
+            u16le(&mut cd, 0); // comment
+            u16le(&mut cd, 0); // disk
+            u16le(&mut cd, 0); // internal attrs
+            u32le(&mut cd, 0); // external attrs
+            u32le(&mut cd, e.offset);
+            cd.extend_from_slice(e.name.as_bytes());
+        }
+        let cd_offset = u32::try_from(self.offset).map_err(|_| "backup too large".to_string())?;
+        let cd_size = u32::try_from(cd.len()).map_err(|_| "backup too large".to_string())?;
+        let n = self.entries.len() as u16;
+        let mut out = cd;
+        u32le(&mut out, END_SIG);
+        u16le(&mut out, 0);
+        u16le(&mut out, 0);
+        u16le(&mut out, n);
+        u16le(&mut out, n);
+        u32le(&mut out, cd_size);
+        u32le(&mut out, cd_offset);
+        u16le(&mut out, 0); // comment
+        Ok(out)
+    }
+}
+
+/// One entry of a zip's central directory.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct ZipEntry {
+    pub name: String,
+    pub crc: u32,
+    pub size: u64,
+    /// Offset of the entry's local header.
+    pub header: u64,
+    /// 0 = stored (the only method a restore reads).
+    pub method: u16,
+}
+
+fn rd16(b: &[u8], at: usize) -> Option<u16> {
+    Some(u16::from_le_bytes(b.get(at..at + 2)?.try_into().ok()?))
+}
+fn rd32(b: &[u8], at: usize) -> Option<u32> {
+    Some(u32::from_le_bytes(b.get(at..at + 4)?.try_into().ok()?))
+}
+
+/// How many bytes from the end of a zip to read to find its end record.
+pub fn tail_len(file_len: u64) -> u64 {
+    file_len.min(22 + 65_535)
+}
+
+/// The central directory's (offset, size) from the last [`tail_len`] bytes of a zip.
+pub fn find_central(tail: &[u8]) -> Result<(u64, u64), String> {
+    let at = (0..tail.len().saturating_sub(21)).rev().find(|&i| rd32(tail, i) == Some(END_SIG)).ok_or("not a zip file (no end record)")?;
+    let size = rd32(tail, at + 12).ok_or("truncated zip")?;
+    let offset = rd32(tail, at + 16).ok_or("truncated zip")?;
+    if size == u32::MAX || offset == u32::MAX {
+        return Err("zip64 backups are not supported".into());
+    }
+    Ok((u64::from(offset), u64::from(size)))
+}
+
+/// Parse a central directory.
+pub fn parse_central(cd: &[u8]) -> Result<Vec<ZipEntry>, String> {
+    let mut out = Vec::new();
+    let mut i = 0;
+    while i + 46 <= cd.len() {
+        if rd32(cd, i) != Some(CENTRAL_SIG) {
+            return Err("damaged zip directory".into());
+        }
+        let bad = || "damaged zip directory".to_string();
+        let method = rd16(cd, i + 10).ok_or_else(bad)?;
+        let crc = rd32(cd, i + 16).ok_or_else(bad)?;
+        let size = rd32(cd, i + 24).ok_or_else(bad)?;
+        let n = usize::from(rd16(cd, i + 28).ok_or_else(bad)?);
+        let extra = usize::from(rd16(cd, i + 30).ok_or_else(bad)?);
+        let comment = usize::from(rd16(cd, i + 32).ok_or_else(bad)?);
+        let header = rd32(cd, i + 42).ok_or_else(bad)?;
+        let name = cd.get(i + 46..i + 46 + n).ok_or_else(bad)?;
+        out.push(ZipEntry { name: String::from_utf8_lossy(name).into_owned(), crc, size: u64::from(size), header: u64::from(header), method });
+        i += 46 + n + extra + comment;
+    }
+    Ok(out)
+}
+
+/// Offset of an entry's data from its local header's first 30 bytes.
+pub fn data_offset(entry: &ZipEntry, local: &[u8]) -> Result<u64, String> {
+    if rd32(local, 0) != Some(LOCAL_SIG) {
+        return Err(format!("{}: damaged entry", entry.name));
+    }
+    let n = rd16(local, 26).ok_or("truncated entry")?;
+    let extra = rd16(local, 28).ok_or("truncated entry")?;
+    Ok(entry.header + 30 + u64::from(n) + u64::from(extra))
+}
+
+/// Check an entry's bytes.
+pub fn verify(entry: &ZipEntry, data: &[u8]) -> Result<(), String> {
+    if entry.method != 0 {
+        return Err(format!("{}: compressed entries are not supported (not a LightCraft backup?)", entry.name));
+    }
+    if data.len() as u64 != entry.size || crc32fast::hash(data) != entry.crc {
+        return Err(format!("{}: damaged (checksum mismatch)", entry.name));
+    }
+    Ok(())
+}
+
+/// A name for the restored library's folder.
+pub fn restored_dir_name(now_ms: f64) -> String {
+    format!("library-restored-{}", now_ms.max(0.0) as u64)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn build(files: &[(&str, &[u8])]) -> Vec<u8> {
+        let mut w = ZipWriter::default();
+        let mut out = Vec::new();
+        for (n, d) in files {
+            out.extend(w.entry(n, d).unwrap());
+            out.extend_from_slice(d);
+        }
+        out.extend(w.finish().unwrap());
+        out
+    }
+
+    #[test]
+    fn written_backups_read_back() {
+        let files: [(&str, &[u8]); 3] =
+            [("README.txt", README.as_bytes()), ("library/catalog.log", b"{\"seq\":1}\n"), ("originals/abc123/IMG 1.jpg", &[0, 1, 2, 3, 255])];
+        let zip = build(&files);
+        let tail = &zip[zip.len() - tail_len(zip.len() as u64) as usize..];
+        let (off, size) = find_central(tail).unwrap();
+        let entries = parse_central(&zip[off as usize..(off + size) as usize]).unwrap();
+        assert_eq!(entries.len(), 3);
+        for (e, (name, data)) in entries.iter().zip(files) {
+            assert_eq!(e.name, name);
+            let start = data_offset(e, &zip[e.header as usize..e.header as usize + 30]).unwrap() as usize;
+            let got = &zip[start..start + e.size as usize];
+            assert_eq!(got, data);
+            verify(e, got).unwrap();
+        }
+        // damage is caught
+        let e = &entries[2];
+        assert!(verify(e, &[0, 1, 2, 3, 254]).is_err());
+        assert!(find_central(b"not a zip at all, just some text").is_err());
+    }
+
+    #[test]
+    fn restore_keys_are_safe() {
+        assert_eq!(restore_key("library/catalog.snap", "library-restored-1").as_deref(), Some("library-restored-1/catalog.snap"));
+        assert_eq!(restore_key("library/../../x", "library-r"), None);
+        assert_eq!(restore_key("library/evil.bin", "library-r"), None);
+        assert_eq!(restore_key("originals/abc123/IMG.jpg", "d").as_deref(), Some("originals/abc123"));
+        assert_eq!(restore_key("originals/../library/catalog.log", "d"), None);
+        assert_eq!(restore_key("README.txt", "d"), None);
+        assert_eq!(restore_key("thumbs/x.jpg", "d"), None);
+        assert_eq!(original_entry("abc", "a/b\\c.jpg"), "originals/abc/a_b_c.jpg");
+        assert_eq!(original_entry("abc", ".."), "originals/abc/original");
+        assert!(valid_library_dir("library") && valid_library_dir("library-restored-17"));
+        assert!(!valid_library_dir("library-../x") && !valid_library_dir("originals") && !valid_library_dir("library-"));
+    }
+
+    #[test]
+    fn size_limits_are_errors_not_panics() {
+        let mut w = ZipWriter { offset: MAX_BYTES - 10, ..Default::default() };
+        assert!(w.entry("x", &[0; 64]).is_err());
+    }
+}

apps/lightcraft-web/src/files.rs

@@ -49,6 +49,8 @@ struct Mirror {
     files: BTreeMap<String, Vec<u8>>,
     /// Dirty files, least recently modified first.
     dirty: Vec<(String, Dirty)>,
+    /// Why the last flush to browser storage failed (quota, eviction…), until one succeeds.
+    error: Option<String>,
 }
 
 impl Mirror {
@@ -138,6 +140,18 @@ impl Files {
         }
     }
 
+    /// Record the outcome of a flush to browser storage: `Some(why)` when it failed, `None` once
+    /// one succeeds. While a flush is failing, the catalog [`Store`] refuses new writes, so the
+    /// engine keeps the changes queued and reports them unsaved (`library.info` → `unsavedOps`,
+    /// the top bar's warning) instead of pretending they were saved.
+    pub fn set_error(&self, e: Option<String>) {
+        self.lock().error = e;
+    }
+
+    pub fn error(&self) -> Option<String> {
+        self.lock().error.clone()
+    }
+
     /// A catalog [`Store`] over these files.
     pub fn store(&self) -> FilesStore {
         FilesStore(self.clone())
@@ -147,19 +161,32 @@ impl Files {
 /// [`Store`] implementation over [`Files`].
 pub struct FilesStore(Files);
 
+impl FilesStore {
+    /// Writes fail while browser storage does (see [`Files::set_error`]).
+    fn writable(&self) -> io::Result<()> {
+        match self.0.error() {
+            Some(e) => Err(io::Error::other(format!("browser storage: {e}"))),
+            None => Ok(()),
+        }
+    }
+}
+
 impl Store for FilesStore {
     fn read(&mut self, name: &str) -> io::Result<Option<Vec<u8>>> {
         Ok(self.0.get(name))
     }
     fn write_atomic(&mut self, name: &str, data: &[u8]) -> io::Result<()> {
+        self.writable()?;
         self.0.write(name, data);
         Ok(())
     }
     fn append(&mut self, name: &str, data: &[u8]) -> io::Result<()> {
+        self.writable()?;
         self.0.append(name, data);
         Ok(())
     }
     fn truncate(&mut self, name: &str, len: u64) -> io::Result<()> {
+        self.writable()?;
         self.0.truncate(name, len as usize);
         Ok(())
     }
@@ -224,6 +251,37 @@ mod tests {
         assert_eq!(names, ["catalog.snap", "catalog.log"]);
     }
 
+    /// A failing flush (quota exceeded, storage evicted) is not silent: commands report the change
+    /// as unsaved and the engine keeps it queued; once storage works again it is written.
+    #[test]
+    fn flush_failures_show_as_unsaved_and_are_retried() {
+        let mut disk = BTreeMap::new();
+        let files = Files::default();
+        let mut s = Session::new();
+        let stores = LibraryStores { dir: "browser".into(), catalog: Box::new(files.store()), files: Box::new(files.store()), on_disk: false };
+        s.open_library_in(stores, true).unwrap();
+        flush(&files, &mut disk);
+        files.set_error(Some("QuotaExceededError".into()));
+        let r = s.execute("photo.rate", &json!({"rating": 5}));
+        assert!(matches!(r, Err(lightcraft_engine::EngineError::NotSaved(_))), "{r:?}");
+        let (ops, why) = s.unsaved().unwrap();
+        assert!(ops > 0 && why.contains("QuotaExceeded"), "{why}");
+        files.set_error(None);
+        s.persist_if_dirty();
+        s.persist().unwrap();
+        assert!(s.unsaved().is_none(), "written once storage works again");
+        flush(&files, &mut disk);
+        let id = s.selection.active.unwrap();
+        let files2 = Files::default();
+        for (k, v) in &disk {
+            files2.preload(k, v.clone());
+        }
+        let mut s2 = Session::new();
+        let stores = LibraryStores { dir: "browser".into(), catalog: Box::new(files2.store()), files: Box::new(files2.store()), on_disk: false };
+        s2.open_library_in(stores, true).unwrap();
+        assert_eq!(s2.catalog.photo(id).unwrap().rating, 5, "the rating survived");
+    }
+
     #[test]
     fn library_survives_reload_through_flushes() {
         let mut disk = BTreeMap::new();

apps/lightcraft-web/src/lib.rs

@@ -16,6 +16,7 @@
 #![forbid(unsafe_code)]
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
 
+pub mod backup;
 pub mod bench;
 pub mod files;
 pub mod store;
@@ -24,6 +25,8 @@ pub mod wire;
 #[cfg(target_arch = "wasm32")]
 mod backend;
 #[cfg(target_arch = "wasm32")]
+mod safety;
+#[cfg(target_arch = "wasm32")]
 mod web;
 #[cfg(target_arch = "wasm32")]
 mod workers;

apps/lightcraft-web/src/safety.rs

@@ -0,0 +1,256 @@
+//! Keeping a library in the browser safe: notices the user must see (a failed save, storage the
+//! browser may evict, a file that couldn't be stored), one tab at a time per library, a message
+//! instead of a dead page after a panic, and backup / restore of the whole library
+//! ([`crate::backup`]).
+
+use std::cell::RefCell;
+use std::collections::HashMap;
+
+use js_sys::{Reflect, Uint8Array};
+use wasm_bindgen::JsCast;
+use wasm_bindgen::prelude::*;
+use wasm_bindgen_futures::JsFuture;
+
+use crate::backend::Backend;
+use crate::backup::{
+    ACTIVE_LIBRARY, README, ZipWriter, data_offset, find_central, original_entry, parse_central, restore_key, restored_dir_name, tail_len,
+    valid_hash, verify,
+};
+use crate::files::{Files, LIBRARY_FILES};
+use crate::store::storage_key;
+
+thread_local! {
+    /// Messages for the user, shown by the app on its next frame.
+    static NOTICES: RefCell<Vec<String>> = const { RefCell::new(Vec::new()) };
+}
+
+/// Queue a message for the user (shown for several seconds; also logged).
+pub fn notice(text: impl Into<String>) {
+    let text = text.into();
+    log::warn!("{text}");
+    NOTICES.with(|n| n.borrow_mut().push(text));
+    crate::web::request_repaint();
+}
+
+/// Messages queued since the last call.
+pub fn take_notices() -> Vec<String> {
+    NOTICES.with(|n| std::mem::take(&mut *n.borrow_mut()))
+}
+
+fn document() -> Option<web_sys::Document> {
+    web_sys::window()?.document()
+}
+
+/// Ask the user (the browser's own confirm box). `false` when it can't be shown.
+pub fn confirm(text: &str) -> bool {
+    web_sys::window().and_then(|w| w.confirm_with_message(text).ok()).unwrap_or(false)
+}
+
+/// Cover the page with a message (the app can't continue, or must not start).
+pub fn show_blocking(text: &str) {
+    let Some(doc) = document() else { return };
+    let el = match doc.get_element_by_id("lightcraft_blocking") {
+        Some(el) => el,
+        None => {
+            let Ok(el) = doc.create_element("div") else { return };
+            el.set_id("lightcraft_blocking");
+            let _ = el.set_attribute(
+                "style",
+                "position:fixed;inset:0;z-index:10;display:flex;align-items:center;justify-content:center;padding:32px;\
+                 background:#1c1c1c;color:#e0e0e0;font:15px/1.5 system-ui,-apple-system,'Segoe UI',sans-serif;text-align:center;white-space:pre-line",
+            );
+            if let Some(body) = doc.body() {
+                let _ = body.append_child(&el);
+            }
+            el
+        }
+    };
+    el.set_text_content(Some(text));
+    if let Some(loading) = doc.get_element_by_id("lightcraft_loading") {
+        loading.remove();
+    }
+}
+
+/// `panic = "abort"` on wasm: a panic ends the module. Say so on the page instead of leaving a
+/// frozen canvas, and say that the stored library is intact.
+pub fn install_panic_hook() {
+    std::panic::set_hook(Box::new(|info| {
+        let msg = match (info.payload().downcast_ref::<&str>(), info.payload().downcast_ref::<String>()) {
+            (Some(s), _) => (*s).to_string(),
+            (_, Some(s)) => s.clone(),
+            _ => "unknown error".into(),
+        };
+        let at = info.location().map(|l| format!(" at {}:{}", l.file(), l.line())).unwrap_or_default();
+        log::error!("LightCraft panicked{at}: {msg}");
+        show_blocking(&format!(
+            "LightCraft stopped after an internal error:\n{msg}\n\nThe library saved in this browser is kept. Reload the page to continue.\n\
+             If it happens again right away, a photo may be the cause: reload with ?workers=0 or report the error."
+        ));
+    }));
+}
+
+/// The name of the lock that keeps a library to one tab.
+const TAB_LOCK: &str = "lightcraft-library";
+
+/// Hold the library lock for as long as this page lives (Web Locks API). `Some(true)`: ours;
+/// `Some(false)`: another tab of this site has it; `None`: the browser can't tell (no Web Locks).
+pub async fn acquire_tab_lock() -> Option<bool> {
+    let nav = Reflect::get(&js_sys::global(), &"navigator".into()).ok()?;
+    let locks = Reflect::get(&nav, &"locks".into()).ok().filter(|l| !l.is_undefined() && !l.is_null())?;
+    let request: js_sys::Function = Reflect::get(&locks, &"request".into()).ok()?.dyn_into().ok()?;
+    let opts = js_sys::Object::new();
+    Reflect::set(&opts, &"ifAvailable".into(), &true.into()).ok()?;
+    let granted = js_sys::Promise::new(&mut |resolve, _reject| {
+        let cb = Closure::once_into_js(move |lock: JsValue| -> JsValue {
+            let ours = !lock.is_null() && !lock.is_undefined();
+            let _ = resolve.call1(&JsValue::NULL, &ours.into());
+            // keep the lock until the page goes away: a promise that never settles
+            if ours { js_sys::Promise::new(&mut |_, _| {}).into() } else { JsValue::NULL }
+        });
+        if let Err(e) = request.call3(&locks, &TAB_LOCK.into(), &opts, &cb) {
+            log::warn!("Web Locks request failed: {e:?}");
+        }
+    });
+    JsFuture::from(granted).await.ok().map(|v| v.is_truthy())
+}
+
+/// Offer a blob as a download named `name`.
+pub fn download_blob(name: &str, blob: &web_sys::Blob) -> Result<(), String> {
+    let e = |e: JsValue| format!("download failed: {e:?}");
+    let url = web_sys::Url::create_object_url_with_blob(blob).map_err(e)?;
+    let doc = document().ok_or("no document")?;
+    let a: web_sys::HtmlAnchorElement = doc.create_element("a").map_err(e)?.unchecked_into();
+    a.set_href(&url);
+    a.set_download(name);
+    a.click();
+    // revoke once the download has started
+    let revoke = Closure::once_into_js(move || {
+        let _ = web_sys::Url::revoke_object_url(&url);
+    });
+    if let Some(w) = web_sys::window() {
+        let _ = w.set_timeout_with_callback_and_timeout_and_arguments_0(revoke.unchecked_ref(), 60_000);
+    }
+    Ok(())
+}
+
+/// File ▸ Back Up Library…: a zip of the library files (as the app has them, saved or not) and
+/// every original in storage, built entry by entry into the browser's memory (outside the wasm
+/// heap) and downloaded. `names`: content hash → the photo's file name.
+pub async fn backup(files: Files, backend: Backend, names: HashMap<String, String>) -> Result<(usize, f64), String> {
+    let parts = js_sys::Array::new();
+    let mut zip = ZipWriter::default();
+    let mut bytes = 0f64;
+    let mut add = |zip: &mut ZipWriter, name: &str, data: &[u8]| -> Result<(), String> {
+        let header = zip.entry(name, data)?;
+        parts.push(&Uint8Array::from(&header[..]));
+        parts.push(&Uint8Array::from(data));
+        bytes += (header.len() + data.len()) as f64;
+        Ok(())
+    };
+    add(&mut zip, "README.txt", README.as_bytes())?;
+    for name in LIBRARY_FILES {
+        if let Some(d) = files.get(name) {
+            add(&mut zip, &format!("library/{name}"), &d)?;
+        }
+    }
+    let mut originals = 0;
+    for hash in backend.list("originals").await? {
+        if !valid_hash(&hash) {
+            continue;
+        }
+        match backend.read(&storage_key(&hash)).await {
+            Ok(Some(data)) => {
+                let name = names.get(&hash).map_or("original", String::as_str);
+                add(&mut zip, &original_entry(&hash, name), &data)?;
+                originals += 1;
+            }
+            Ok(None) => {}
+            Err(e) => return Err(format!("reading an original from browser storage: {e}")),
+        }
+    }
+    let tail = zip.finish()?;
+    parts.push(&Uint8Array::from(&tail[..]));
+    let opts = web_sys::BlobPropertyBag::new();
+    opts.set_type("application/zip");
+    let blob = web_sys::Blob::new_with_u8_array_sequence_and_options(&parts, &opts).map_err(|e| format!("{e:?}"))?;
+    let day: String = String::from(js_sys::Date::new_0().to_iso_string()).chars().take(10).collect();
+    download_blob(&format!("lightcraft-library-backup-{day}.zip"), &blob)?;
+    Ok((originals, bytes + tail.len() as f64))
+}
+
+/// Bytes `start..end` of a picked file.
+async fn read_range(file: &web_sys::File, start: u64, end: u64) -> Result<Vec<u8>, String> {
+    let blob = file.slice_with_f64_and_f64(start as f64, end as f64).map_err(|e| format!("{e:?}"))?;
+    let buf = JsFuture::from(blob.array_buffer()).await.map_err(|e| format!("{e:?}"))?;
+    Ok(Uint8Array::new(&buf).to_vec())
+}
+
+/// Restore a backup into a new library folder (nothing in storage is deleted or overwritten),
+/// then point [`ACTIVE_LIBRARY`] at it. Returns the folder's name; the caller reloads the page.
+pub async fn restore(file: web_sys::File, backend: Backend) -> Result<String, String> {
+    let len = file.size() as u64;
+    let tail = read_range(&file, len - tail_len(len), len).await?;
+    let (cd_offset, cd_size) = find_central(&tail)?;
+    let cd = read_range(&file, cd_offset, cd_offset + cd_size).await?;
+    let entries = parse_central(&cd)?;
+    if !entries.iter().any(|e| e.name == "library/catalog.snap" || e.name == "library/catalog.log") {
+        return Err("this isn't a LightCraft library backup (no library/catalog files)".into());
+    }
+    let dir = restored_dir_name(js_sys::Date::now());
+    let mut written = 0usize;
+    for e in &entries {
+        let Some(key) = restore_key(&e.name, &dir) else { continue };
+        // originals are named by their content: one already stored is the same file
+        if key.starts_with("originals/") && backend.exists(&key).await? {
+            continue;
+        }
+        let local = read_range(&file, e.header, e.header + 30).await?;
+        let start = data_offset(e, &local)?;
+        let data = read_range(&file, start, start + e.size).await?;
+        verify(e, &data)?;
+        backend.write(&key, &data).await.map_err(|err| format!("storing {}: {err}", e.name))?;
+        written += 1;
+    }
+    backend.write(ACTIVE_LIBRARY, dir.as_bytes()).await?;
+    log::info!("lightcraft: restored {written} files into {dir}");
+    Ok(dir)
+}
+
+/// File ▸ Restore Library from Backup…: confirm, pick the zip, restore, reload.
+pub fn pick_and_restore(backend: Backend, before_reload: impl FnOnce() + 'static) {
+    let ok = confirm(
+        "Restore a LightCraft library backup?\n\nThe backup becomes the library in this browser and the page reloads. \
+         The current library is not deleted: it stays in browser storage.",
+    );
+    if !ok {
+        return;
+    }
+    let Some(doc) = document() else { return };
+    let Ok(input) = doc.create_element("input").map(|e| e.unchecked_into::<web_sys::HtmlInputElement>()) else { return };
+    input.set_type("file");
+    input.set_accept(".zip,application/zip");
+    let inp = input.clone();
+    let mut before_reload = Some(before_reload);
+    let on_change = Closure::<dyn FnMut()>::new(move || {
+        let Some(file) = inp.files().and_then(|f| f.get(0)) else { return };
+        let backend = backend.clone();
+        let before = before_reload.take();
+        notice(format!("Restoring {}…", file.name()));
+        wasm_bindgen_futures::spawn_local(async move {
+            match restore(file, backend).await {
+                Ok(_) => {
+                    if let Some(f) = before {
+                        f();
+                    }
+                    if let Some(w) = web_sys::window() {
+                        let _ = w.location().reload();
+                    }
+                }
+                Err(e) => notice(format!("Restore failed: {e}. Nothing was changed: the current library is still in use.")),
+            }
+        });
+    });
+    input.set_onchange(Some(on_change.as_ref().unchecked_ref()));
+    on_change.forget();
+    input.click();
+}

apps/lightcraft-web/src/web.rs

@@ -15,16 +15,21 @@ use wasm_bindgen::JsCast;
 use wasm_bindgen::prelude::*;
 
 use crate::backend::Backend;
+use crate::backup::{ACTIVE_LIBRARY, DEFAULT_LIBRARY_DIR, valid_library_dir};
 use crate::bench::Bench;
 use crate::files::{Files, FlushOp, LIBRARY_FILES};
+use crate::safety::{self, notice};
 use crate::store::{Originals, content_hash, download_name, storage_key};
 use crate::wire::ThumbIndex;
 use crate::workers::{THUMB_INDEX, Workers};
 
 const ACCEPT: &str = ".jpg,.jpeg,.png,.tif,.tiff,.webp,.dng,.cr2,.nef,.arw,.psd,.jxl,.gif,.bmp";
 
-/// Where the library files live in browser storage.
-const LIBRARY_DIR: &str = "library";
+/// After a failed save, wait this long before trying again (ms).
+const SAVE_RETRY_MS: f64 = 2000.0;
+
+/// How long a notice stays on screen (s).
+const NOTICE_SECS: f64 = 8.0;
 
 /// How often view state, UI prefs and the thumbnail index are saved (ms).
 const SAVE_EVERY_MS: f64 = 1000.0;
@@ -45,8 +50,18 @@ fn set_status(text: &str) {
     }
 }
 
-fn library_key(name: &str) -> String {
-    format!("{LIBRARY_DIR}/{name}")
+/// Storage key of library file `name` in library folder `dir`.
+fn library_key(dir: &str, name: &str) -> String {
+    format!("{dir}/{name}")
+}
+
+/// Repaint the app (notices from async tasks).
+pub(crate) fn request_repaint() {
+    CTX.with(|c| {
+        if let Some(c) = c.borrow().as_ref() {
+            c.request_repaint();
+        }
+    });
 }
 
 /// URL options (`?bench&store=idb&workers=2&reset`).
@@ -86,8 +101,9 @@ async fn store_file(originals: Originals, backend: Option<Backend>, name: String
     if let Some(b) = &backend
         && let Err(e) = b.write(&storage_key(&hash), &bytes).await
     {
-        // still importable for this session; it won't survive a reload
-        log::error!("storing {name} in browser storage failed: {e}");
+        // a photo whose bytes aren't stored would be gone after a reload: don't add it
+        notice(format!("{name} was not added: browser storage refused it ({e}). Free up space or back up and clear old photos."));
+        return;
     }
     originals.added(&name, &hash, Arc::from(bytes));
     ctx.request_repaint();
@@ -148,8 +164,42 @@ fn download(path: &str, bytes: &[u8]) -> Result<(), String> {
     Ok(())
 }
 
-fn services(originals: Originals, backend: Option<Backend>, ctx: egui::Context) -> Services {
+fn services(originals: Originals, backend: Option<Backend>, files: Files, frozen: Rc<Cell<bool>>, ctx: egui::Context) -> Services {
+    let (backup_backend, backup_files) = (backend.clone(), files);
+    let restore_backend = backend.clone();
     Services {
+        backup_library: Some(Box::new(move |session: &mut Session| {
+            let Some(b) = backup_backend.clone() else { return Err("nothing is stored in this browser session (?store=memory)".into()) };
+            // the photos' own names for the originals in the zip
+            let names: std::collections::HashMap<String, String> = session
+                .catalog
+                .photos()
+                .filter_map(|p| match &p.source {
+                    Source::File { path } => crate::store::hash_of_path(path).map(|h| (h.to_string(), p.file_name.clone())),
+                    _ => None,
+                })
+                .collect();
+            let files = backup_files.clone();
+            notice("Backing up the library… (the download starts when it's ready)");
+            wasm_bindgen_futures::spawn_local(async move {
+                match safety::backup(files, b, names).await {
+                    Ok((n, bytes)) => notice(format!(
+                        "Library backed up: {n} original{} ({:.1} MB). Keep the file somewhere safe.",
+                        if n == 1 { "" } else { "s" },
+                        bytes / 1e6
+                    )),
+                    Err(e) => notice(format!("Backup failed: {e}")),
+                }
+            });
+            Ok(json!({"started": true}))
+        })),
+        restore_library: Some(Box::new(move |_session: &mut Session| {
+            let Some(b) = restore_backend.clone() else { return Err("nothing is stored in this browser session (?store=memory)".into()) };
+            let frozen = frozen.clone();
+            // once the backup is in place, stop saving the old library (the page reloads)
+            safety::pick_and_restore(b, move || frozen.set(true));
+            Ok(json!({"started": true}))
+        })),
         pick_files: Some(Box::new(move || {
             open_picker(originals.clone(), backend.clone(), ctx.clone());
             Vec::new() // files arrive asynchronously and are imported on a later frame
@@ -176,21 +226,29 @@ fn services(originals: Originals, backend: Option<Backend>, ctx: egui::Context)
     }
 }
 
-/// Write dirty library files to storage, in order, until none are left.
-async fn flush(files: Files, backend: Backend, flushing: Rc<Cell<bool>>) {
+/// Write dirty library files to storage, in order, until none are left. A failure (quota,
+/// storage cleared) is recorded in `files` — the catalog then reports changes as unsaved instead
+/// of accepting them silently — and retried after [`SAVE_RETRY_MS`].
+async fn flush(files: Files, backend: Backend, dir: String, flushing: Rc<Cell<bool>>, failed_at: Rc<Cell<f64>>) {
     'outer: loop {
         let ops = files.take_dirty();
         if ops.is_empty() {
+            if files.error().is_some() {
+                log::info!("lightcraft: saving works again");
+            }
+            files.set_error(None);
             break;
         }
         for (i, op) in ops.iter().enumerate() {
             let r = match op {
-                FlushOp::Write { name, data } => backend.write(&library_key(name), data).await,
-                FlushOp::Append { name, offset, data } => backend.write_at(&library_key(name), Some(*offset), data).await,
+                FlushOp::Write { name, data } => backend.write(&library_key(&dir, name), data).await,
+                FlushOp::Append { name, offset, data } => backend.write_at(&library_key(&dir, name), Some(*offset), data).await,
             };
             if let Err(e) = r {
                 log::error!("saving {} failed: {e}", op.name());
                 files.failed(&ops[i..]);
+                files.set_error(Some(e));
+                failed_at.set(perf_now());
                 break 'outer;
             }
         }
@@ -204,6 +262,8 @@ struct Boot {
     backend: Option<Backend>,
     files: Files,
     index: ThumbIndex,
+    /// The library folder in storage (`library`, or a restored backup's).
+    lib_dir: String,
 }
 
 async fn boot(opts: Options) -> Boot {
@@ -221,15 +281,32 @@ async fn boot(opts: Options) -> Boot {
     };
     let files = Files::default();
     let mut index = ThumbIndex::default();
+    let mut lib_dir = DEFAULT_LIBRARY_DIR.to_string();
     if let Some(b) = &backend {
         if opts.reset {
-            match b.clear().await {
-                Ok(()) => log::info!("lightcraft: storage cleared (?reset)"),
-                Err(e) => log::error!("clearing storage: {e}"),
+            // everything this site keeps in the browser, photos included: never without asking
+            let ok = safety::confirm(
+                "?reset deletes the LightCraft library stored in this browser, including every imported photo. \
+                 This can't be undone. Delete it?",
+            );
+            if ok {
+                match b.clear().await {
+                    Ok(()) => log::info!("lightcraft: storage cleared (?reset)"),
+                    Err(e) => log::error!("clearing storage: {e}"),
+                }
+            } else {
+                log::info!("lightcraft: ?reset declined; storage kept");
+            }
+        }
+        // a restored backup lives in its own folder (see `backup`)
+        if let Ok(Some(d)) = b.read(ACTIVE_LIBRARY).await {
+            let d = String::from_utf8_lossy(&d).trim().to_string();
+            if valid_library_dir(&d) {
+                lib_dir = d;
             }
         }
         for name in LIBRARY_FILES {
-            match b.read(&library_key(name)).await {
+            match b.read(&library_key(&lib_dir, name)).await {
                 Ok(Some(data)) => files.preload(name, data),
                 Ok(None) => {}
                 Err(e) => log::error!("reading {name}: {e}"),
@@ -238,7 +315,14 @@ async fn boot(opts: Options) -> Boot {
         if let Ok(Some(j)) = b.read(THUMB_INDEX).await {
             index = ThumbIndex::from_json(&j);
         }
-        crate::backend::request_persistence();
+        crate::backend::request_persistence(|granted| {
+            if !granted {
+                notice(
+                    "This browser may delete LightCraft's library when it runs short of space (persistent storage wasn't granted). \
+                     Keep your original photos elsewhere and use File ▸ Back Up Library… now and then.",
+                );
+            }
+        });
         // thumbnails stored without an index entry (index saved late, or lost): delete them
         let b2 = b.clone();
         let known: std::collections::HashSet<String> = b
@@ -266,7 +350,7 @@ async fn boot(opts: Options) -> Boot {
         index.len(),
         index.total() as f64 / 1e6
     );
-    Boot { opts, backend, files, index }
+    Boot { opts, backend, files, index, lib_dir }
 }
 
 struct WebApp {
@@ -276,6 +360,11 @@ struct WebApp {
     backend: Option<Backend>,
     workers: Option<Workers>,
     flushing: Rc<Cell<bool>>,
+    /// When the last save to storage failed (ms; 0 = never).
+    flush_failed_at: Rc<Cell<f64>>,
+    /// Saving stopped (a restored backup is about to replace this library: the page reloads).
+    frozen: Rc<Cell<bool>>,
+    lib_dir: String,
     bench: Option<Bench>,
     first_frame_logged: bool,
     last_save: f64,
@@ -284,17 +373,18 @@ struct WebApp {
 
 impl WebApp {
     fn new(cc: &eframe::CreationContext<'_>, boot: Boot) -> Self {
-        let Boot { opts, backend, files, index } = boot;
+        let Boot { opts, backend, files, index, lib_dir } = boot;
         let originals = Originals::default();
         let t = perf_now();
         let mut session = Session::new();
         originals.install(&mut session);
         let stores = LibraryStores {
-            dir: format!("browser:{}/{LIBRARY_DIR}", backend.as_ref().map_or("memory", |b| b.kind())).into(),
+            dir: format!("browser:{}/{lib_dir}", backend.as_ref().map_or("memory", |b| b.kind())).into(),
             catalog: Box::new(files.store()),
             files: Box::new(files.store()),
             on_disk: false,
         };
+        let mut problem = None;
         match session.open_library_in(stores, true).cloned() {
             Ok(r) => log::info!(
                 "lightcraft: library {} in {:.0} ms ({} photos; snapshot seq {}, {} ops replayed)",
@@ -305,19 +395,35 @@ impl WebApp {
                 r.replayed
             ),
             Err(e) => {
-                log::error!("opening the library failed: {e}; starting a temporary one");
-                session = Session::with_demo();
+                // never a silent demo session (issue #100): an empty one, and the window says why
+                log::error!("opening the library failed: {e}");
+                session = Session::new();
                 originals.install(&mut session);
+                problem = Some(lightcraft_ui_egui::panels::library_problem::LibraryProblem {
+                    can_retry: false,
+                    ..lightcraft_ui_egui::panels::library_problem::LibraryProblem::new(
+                        "the browser's storage for this page",
+                        format!("{e}. Reload the page to try again."),
+                    )
+                });
             }
         }
+        if backend.is_some() {
+            notice(
+                "LightCraft in the browser is experimental. Your library is kept in this browser's storage: keep your original photos \
+                 elsewhere and back up with File ▸ Back Up Library….",
+            );
+        }
         // previews are large (≤ 2560 px, f32): keep few in a 32-bit address space
         session.media.preview_capacity = 3;
-        let mut app = LightcraftApp::new(session, services(originals.clone(), backend.clone(), cc.egui_ctx.clone()));
+        let frozen = Rc::new(Cell::new(false));
+        let mut app = LightcraftApp::new(session, services(originals.clone(), backend.clone(), files.clone(), frozen.clone(), cc.egui_ctx.clone()));
         let ui_written = files.get("ui.json").unwrap_or_default();
         if let Ok(ui) = serde_json::from_slice::<UiState>(&ui_written) {
             app.ui = ui;
         }
         app.ui = app.ui.sanitized();
+        app.library_problem = problem;
         let n = opts.workers.unwrap_or_else(|| {
             let cores = window().map_or(1, |w| w.navigator().hardware_concurrency() as usize);
             cores.saturating_sub(1).clamp(1, 4)
@@ -337,6 +443,9 @@ impl WebApp {
             backend,
             workers,
             flushing: Rc::new(Cell::new(false)),
+            flush_failed_at: Rc::new(Cell::new(0.0)),
+            frozen,
+            lib_dir,
             bench: opts.bench.then(|| Bench::new(origin)),
             first_frame_logged: false,
             last_save: 0.0,
@@ -398,6 +507,9 @@ impl WebApp {
 
     /// Save view state, UI prefs and the thumbnail index now and then; flush dirty files.
     fn save(&mut self) {
+        if self.frozen.get() {
+            return;
+        }
         let now = perf_now();
         if now - self.last_save >= SAVE_EVERY_MS {
             self.last_save = now;
@@ -419,12 +531,16 @@ impl WebApp {
                 });
             }
         }
+        // after a failure, retry every couple of seconds rather than every frame
+        let backing_off = self.files.error().is_some() && now - self.flush_failed_at.get() < SAVE_RETRY_MS;
         if let Some(b) = &self.backend
             && self.files.is_dirty()
             && !self.flushing.get()
+            && !backing_off
         {
             self.flushing.set(true);
-            wasm_bindgen_futures::spawn_local(flush(self.files.clone(), b.clone(), self.flushing.clone()));
+            let (files, dir, flushing, failed_at) = (self.files.clone(), self.lib_dir.clone(), self.flushing.clone(), self.flush_failed_at.clone());
+            wasm_bindgen_futures::spawn_local(flush(files, b.clone(), dir, flushing, failed_at));
         }
     }
 }
@@ -454,8 +570,10 @@ impl WebApp {
         let (orig_n, orig_bytes) = self.originals.usage();
         json!({
             "storage": self.backend.as_ref().map_or("memory", |b| b.kind()),
+            "library": self.lib_dir,
             "dirty": self.files.is_dirty(),
             "flushing": self.flushing.get(),
+            "saveError": self.files.error(),
             "workers": {"alive": alive, "ready": ready, "remoteJobs": remote, "inlineJobs": inline},
             "originalsInMemory": orig_n,
             "originalBytesInMemory": orig_bytes,
@@ -480,6 +598,10 @@ impl WebApp {
 
 impl eframe::App for WebApp {
     fn logic(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        for text in safety::take_notices() {
+            let now = ctx.input(|i| i.time);
+            self.app.ui.toast = Some((text, now + NOTICE_SECS));
+        }
         self.run_inbox();
         self.import_dropped(ctx);
         self.load_originals(ctx);
@@ -517,9 +639,18 @@ impl eframe::App for WebApp {
 #[wasm_bindgen]
 pub fn start() {
     eframe::WebLogger::init(log::LevelFilter::Info).ok();
+    safety::install_panic_hook();
     log::info!("lightcraft: wasm instantiated at {:.0} ms", perf_now());
     let opts = Options::from_url();
     wasm_bindgen_futures::spawn_local(async move {
+        // one tab per library: two would each keep their own copy and overwrite each other's saves
+        if opts.store != "memory" && safety::acquire_tab_lock().await == Some(false) {
+            safety::show_blocking(
+                "LightCraft is already open in another tab or window of this browser.\n\n\
+                 Switch to that tab, or close it and reload this page. (Two tabs would overwrite each other's changes.)",
+            );
+            return;
+        }
         let Some(canvas) = window()
             .and_then(|w| w.document())
             .and_then(|d| d.get_element_by_id("lightcraft_canvas"))

apps/lightcraft-web/src/wire.rs

@@ -15,10 +15,9 @@ use std::sync::Arc;
 
 use lightcraft_engine::catalog::Source;
 use lightcraft_engine::develop::{DevelopSettings, EmbeddedLens};
-use lightcraft_engine::media::{MediaCache, RenderJob, SourceLevel, SourceRef};
+use lightcraft_engine::media::{DecodedSource, MediaCache, RenderJob, SourceLevel, SourceRef};
 use lightcraft_engine::pipeline::{Quality, RenderRequest, Rendered, SourceInfo, StageCache};
 use lightcraft_preview::Lru;
-use lightcraft_raster::Rgb32f;
 use serde::{Deserialize, Serialize};
 
 use crate::store::hash_of_path;
@@ -31,6 +30,8 @@ pub struct WireJob {
     /// Decode the source at most this long.
     pub max_edge: usize,
     pub raw: bool,
+    #[serde(default)]
+    pub relative_wb: bool,
     pub as_shot_temp: f64,
     pub as_shot_tint: f64,
     pub lens: Option<EmbeddedLens>,
@@ -55,7 +56,7 @@ impl WireJob {
     pub fn from_job(job: &RenderJob, thumb_cached: bool, view: &str) -> WireJob {
         let max_edge = match &job.source {
             SourceRef::Demo { max_edge, .. } | SourceRef::File { max_edge, .. } => *max_edge,
-            SourceRef::Loaded(img) => img.width.max(img.height),
+            SourceRef::Loaded(img) => img.image.width.max(img.image.height),
             SourceRef::Smart { .. } => 2560,
         };
         WireJob {
@@ -63,6 +64,7 @@ impl WireJob {
             origin: job.origin.clone(),
             max_edge,
             raw: job.info.raw,
+            relative_wb: job.info.relative_wb,
             as_shot_temp: job.info.as_shot_temp,
             as_shot_tint: job.info.as_shot_tint,
             lens: job.info.lens,
@@ -79,7 +81,14 @@ impl WireJob {
     }
 
     pub fn info(&self) -> SourceInfo {
-        SourceInfo { raw: self.raw, as_shot_temp: self.as_shot_temp, as_shot_tint: self.as_shot_tint, lens: self.lens }
+        SourceInfo {
+            raw: self.raw,
+            as_shot_temp: self.as_shot_temp,
+            as_shot_tint: self.as_shot_tint,
+            lens: self.lens,
+            relative_wb: self.relative_wb,
+            ..Default::default()
+        }
     }
 
     pub fn request(&self) -> RenderRequest {
@@ -119,7 +128,7 @@ const WORKER_SOURCE_BYTES: usize = 192 << 20;
 
 /// The synchronous part of a worker: decoded-source cache + rendering.
 pub struct WorkerCore {
-    sources: Lru<String, Arc<Rgb32f>>,
+    sources: Lru<String, DecodedSource>,
     media: MediaCache,
     stages: HashMap<String, Arc<StageCache>>,
 }
@@ -150,21 +159,25 @@ impl WorkerCore {
             Some(s) => s,
             None => {
                 let src = match (&job.origin, original) {
-                    (Source::File { .. }, Some(bytes)) => Arc::new(lightcraft_engine::files::load_bytes(bytes, job.max_edge)?.0),
+                    (Source::File { .. }, Some(bytes)) => {
+                        let (image, info) = lightcraft_engine::files::load_bytes(bytes, job.max_edge)?;
+                        DecodedSource::new(Arc::new(image), Some(info))
+                    }
                     (Source::File { path }, None) => return Err(format!("{path}: original not found in browser storage")),
-                    (origin @ Source::Demo { .. }, _) => self.media.origin_ref(origin, job.max_edge).load()?,
+                    (origin @ Source::Demo { .. }, _) => self.media.origin_ref(origin, job.max_edge).load_source()?,
                 };
-                let cost = src.width * src.height * 12 + 64;
+                let cost = src.image.width * src.image.height * 12 + 64;
                 self.sources.insert(key, src.clone(), cost);
                 src
             }
         };
+        let info = src.info_or(job.info());
         Ok(match &job.stages {
             Some(view) => {
                 let st = self.stages.entry(view.clone()).or_default().clone();
-                lightcraft_engine::pipeline::render_cached(&src, &job.info(), &job.settings, &job.request(), &st)
+                lightcraft_engine::pipeline::render_cached(&src.image, &info, &job.settings, &job.request(), &st)
             }
-            None => lightcraft_engine::pipeline::render(&src, &job.info(), &job.settings, &job.request()),
+            None => lightcraft_engine::pipeline::render(&src.image, &info, &job.settings, &job.request()),
         })
     }
 }
@@ -295,6 +308,7 @@ mod tests {
             origin,
             max_edge: 512,
             raw: false,
+            relative_wb: false,
             as_shot_temp: 6500.0,
             as_shot_tint: 0.0,
             lens: None,

apps/lightcraft/src/control_server.rs

@@ -1,14 +1,28 @@
 //! Loopback JSON-lines control server: one request per line, one reply per line.
 //! This is the transport the MCP server (`lightcraft-cli mcp --connect`) wraps.
+//!
+//! The server only ever reads requests: a line that is not a JSON object with a string `method`
+//! (an HTTP request line from a browser's cross-origin `fetch`, a stray `nc`, binary junk) gets
+//! one error reply and the connection is closed, so nothing after it is executed. Lines are
+//! bounded ([`MAX_LINE`]) and so is the number of open connections ([`MAX_CONNECTIONS`]); junk
+//! never reaches the UI thread. See `docs/control-protocol.md`.
 
-use std::io::{BufRead, BufReader, Write};
+use std::io::{BufRead, BufReader, Read, Write};
 use std::net::{TcpListener, TcpStream};
+use std::sync::Arc;
+use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::mpsc::{Receiver, Sender, channel};
 use std::time::Duration;
 
 use lightcraft_ui_egui::ControlRequest;
 use serde_json::{Value, json};
 
+/// Longest accepted request line (bytes, without the newline). Requests are small JSON objects;
+/// anything longer is refused and the connection closed.
+pub const MAX_LINE: usize = 4 * 1024 * 1024;
+/// Connections served at once; further ones get an error line and are closed.
+pub const MAX_CONNECTIONS: usize = 16;
+
 pub fn start(port: u16, ctx: egui::Context) -> Receiver<ControlRequest> {
     let (tx, rx) = channel::<ControlRequest>();
     let listener = match TcpListener::bind(("127.0.0.1", port)) {
@@ -19,44 +33,235 @@ pub fn start(port: u16, ctx: egui::Context) -> Receiver<ControlRequest> {
         }
     };
     eprintln!("lightcraft: control server listening on 127.0.0.1:{port}");
-    std::thread::spawn(move || {
-        for stream in listener.incoming().flatten() {
-            let tx = tx.clone();
-            let ctx = ctx.clone();
-            std::thread::spawn(move || serve(stream, tx, ctx));
-        }
-    });
+    std::thread::spawn(move || accept_loop(listener, tx, ctx));
     rx
 }
 
-fn serve(stream: TcpStream, tx: Sender<ControlRequest>, ctx: egui::Context) {
-    let Ok(read) = stream.try_clone() else { return };
-    let mut out = stream;
-    for line in BufReader::new(read).lines() {
-        let Ok(line) = line else { break };
-        if line.trim().is_empty() {
+fn accept_loop(listener: TcpListener, tx: Sender<ControlRequest>, ctx: egui::Context) {
+    let open = Arc::new(AtomicUsize::new(0));
+    for mut stream in listener.incoming().flatten() {
+        if open.fetch_add(1, Ordering::SeqCst) >= MAX_CONNECTIONS {
+            open.fetch_sub(1, Ordering::SeqCst);
+            let _ = writeln!(stream, "{}", json!({"ok": false, "error": "too many control connections"}));
             continue;
         }
-        let reply = match serde_json::from_str::<Value>(&line) {
-            Ok(msg) => {
-                let id = msg.get("id").cloned().unwrap_or(Value::Null);
-                let method = msg.get("method").and_then(Value::as_str).unwrap_or("").to_string();
-                let params = msg.get("params").cloned().unwrap_or(json!({}));
-                let (req, rrx) = ControlRequest::new(method, params);
-                if tx.send(req).is_err() {
-                    break;
-                }
-                ctx.request_repaint();
-                let mut r = rrx.recv_timeout(Duration::from_secs(60)).unwrap_or_else(|_| json!({"ok": false, "error": "timeout"}));
-                if let Some(o) = r.as_object_mut() {
-                    o.insert("id".into(), id);
+        let tx = tx.clone();
+        let ctx = ctx.clone();
+        let open = Arc::clone(&open);
+        std::thread::spawn(move || {
+            serve(stream, &tx, &ctx);
+            open.fetch_sub(1, Ordering::SeqCst);
+        });
+    }
+}
+
+fn serve(stream: TcpStream, tx: &Sender<ControlRequest>, ctx: &egui::Context) {
+    let Ok(read) = stream.try_clone() else { return };
+    serve_lines(read, stream, |method, params| {
+        let (req, rrx) = ControlRequest::new(method, params);
+        tx.send(req).ok()?;
+        ctx.request_repaint();
+        Some(rrx.recv_timeout(Duration::from_secs(60)).unwrap_or_else(|_| json!({"ok": false, "error": "timeout"})))
+    });
+}
+
+/// One parsed line.
+enum Line {
+    Request {
+        id: Value,
+        method: String,
+        params: Value,
+    },
+    Blank,
+    /// Not a request: reply with this error and close the connection.
+    Reject(String),
+}
+
+fn parse_line(bytes: &[u8]) -> Line {
+    let Ok(text) = std::str::from_utf8(bytes) else {
+        return Line::Reject("not a control request (invalid UTF-8); closing the connection".into());
+    };
+    let text = text.trim();
+    if text.is_empty() {
+        return Line::Blank;
+    }
+    let msg = match serde_json::from_str::<Value>(text) {
+        Ok(v) => v,
+        Err(e) => return Line::Reject(format!("bad JSON ({e}); expected one JSON request object per line; closing the connection")),
+    };
+    let Some(obj) = msg.as_object() else {
+        return Line::Reject("not a control request (expected a JSON object); closing the connection".into());
+    };
+    let Some(method) = obj.get("method").and_then(Value::as_str) else {
+        return Line::Reject("not a control request (missing string `method`); closing the connection".into());
+    };
+    Line::Request {
+        id: obj.get("id").cloned().unwrap_or(Value::Null),
+        method: method.to_string(),
+        params: obj.get("params").cloned().unwrap_or(json!({})),
+    }
+}
+
+/// Read one `\n`-terminated line of at most `max` bytes into `buf` (newline stripped).
+/// `Ok(false)` at end of stream; `Err` when the line is too long or the read fails.
+fn read_bounded_line(reader: &mut impl BufRead, buf: &mut Vec<u8>, max: usize) -> Result<bool, String> {
+    buf.clear();
+    // `take` bounds the bytes buffered for one line: a peer can't make us allocate more than `max`.
+    let limit = u64::try_from(max).unwrap_or(u64::MAX).saturating_add(1);
+    let n = reader.take(limit).read_until(b'\n', buf).map_err(|e| e.to_string())?;
+    if n == 0 {
+        return Ok(false);
+    }
+    if buf.last() == Some(&b'\n') {
+        buf.pop();
+        if buf.last() == Some(&b'\r') {
+            buf.pop();
+        }
+        return Ok(true);
+    }
+    if buf.len() > max {
+        return Err(format!("request line longer than {max} bytes; closing the connection"));
+    }
+    // Last line without a newline, then end of stream.
+    Ok(true)
+}
+
+/// Serve requests from `read`, answering on `out`, until the peer closes, sends something that is
+/// not a request, or `handle` returns `None` (app gone). `handle` gets `(method, params)` and
+/// returns the reply object (the request's `id` is added here).
+fn serve_lines<R: Read, W: Write>(read: R, mut out: W, mut handle: impl FnMut(String, Value) -> Option<Value>) {
+    let mut reader = BufReader::new(read);
+    let mut buf = Vec::new();
+    loop {
+        let reject = match read_bounded_line(&mut reader, &mut buf, MAX_LINE) {
+            Ok(false) => return,
+            Err(e) => e,
+            Ok(true) => match parse_line(&buf) {
+                Line::Blank => continue,
+                Line::Reject(e) => e,
+                Line::Request { id, method, params } => {
+                    let Some(mut r) = handle(method, params) else { return };
+                    if let Some(o) = r.as_object_mut() {
+                        o.insert("id".into(), id);
+                    }
+                    if writeln!(out, "{r}").and_then(|()| out.flush()).is_err() {
+                        return;
+                    }
+                    continue;
                 }
-                r
-            }
-            Err(e) => json!({"ok": false, "error": format!("bad JSON: {e}")}),
+            },
         };
-        if writeln!(out, "{reply}").is_err() {
-            break;
+        let _ = writeln!(out, "{}", json!({"ok": false, "error": reject})).and_then(|()| out.flush());
+        return;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn run(input: &[u8]) -> (Vec<Value>, Vec<String>) {
+        let mut out = Vec::new();
+        let mut calls = Vec::new();
+        serve_lines(input, &mut out, |m, _p| {
+            calls.push(m);
+            Some(json!({"ok": true, "result": null}))
+        });
+        let replies = String::from_utf8(out).unwrap().lines().map(|l| serde_json::from_str::<Value>(l).unwrap()).collect();
+        (replies, calls)
+    }
+
+    #[test]
+    fn requests_are_answered_in_order_with_ids() {
+        let (r, calls) = run(b"{\"id\":1,\"method\":\"a\"}\n\n{\"id\":2,\"method\":\"b\",\"params\":{}}\r\n{\"method\":\"c\"}");
+        assert_eq!(calls, ["a", "b", "c"]);
+        assert_eq!(r.len(), 3);
+        assert_eq!(r[0]["id"], 1);
+        assert_eq!(r[1]["id"], 2);
+        assert_eq!(r[2]["id"], Value::Null);
+    }
+
+    #[test]
+    fn http_request_closes_before_the_body_runs() {
+        // A browser's cross-origin `fetch` POST: the request line is rejected and the connection
+        // closed, so the JSON body is never executed.
+        let http = b"POST / HTTP/1.1\r\nHost: 127.0.0.1:7980\r\nContent-Type: text/plain\r\n\r\n\
+            {\"id\":1,\"method\":\"engine.execute\",\"params\":{\"command\":\"folder.move\"}}\n";
+        let (r, calls) = run(http);
+        assert!(calls.is_empty(), "nothing may run: {calls:?}");
+        assert_eq!(r.len(), 1);
+        assert_eq!(r[0]["ok"], false);
+        assert!(r[0]["error"].as_str().unwrap().contains("closing the connection"));
+    }
+
+    #[test]
+    fn non_request_json_closes_the_connection() {
+        for junk in [
+            &b"[1,2]\n{\"method\":\"a\"}\n"[..],
+            b"{\"id\":1}\n{\"method\":\"a\"}\n",
+            b"{\"method\":5}\n{\"method\":\"a\"}\n",
+            b"\xff\xfe\n{\"method\":\"a\"}\n",
+        ] {
+            let (r, calls) = run(junk);
+            assert!(calls.is_empty());
+            assert_eq!(r.len(), 1);
+            assert_eq!(r[0]["ok"], false);
         }
+    }
+
+    #[test]
+    fn a_request_before_junk_still_runs() {
+        let (r, calls) = run(b"{\"method\":\"a\"}\nGET / HTTP/1.1\n{\"method\":\"b\"}\n");
+        assert_eq!(calls, ["a"]);
+        assert_eq!(r.len(), 2);
+        assert_eq!(r[1]["ok"], false);
+    }
+
+    #[test]
+    fn overlong_line_is_refused_without_buffering_it_all() {
+        // An endless line without a newline: reading stops after MAX_LINE + 1 bytes.
+        let endless = std::io::repeat(b'x');
+        let mut out = Vec::new();
+        let mut ran = false;
+        serve_lines(endless, &mut out, |_, _| {
+            ran = true;
+            None
+        });
+        assert!(!ran);
+        let reply: Value = serde_json::from_slice(out.strip_suffix(b"\n").unwrap()).unwrap();
+        assert!(reply["error"].as_str().unwrap().contains("longer than"));
+    }
+
+    #[test]
+    fn line_at_the_limit_is_accepted() {
+        let mut buf = Vec::new();
+        let line = vec![b'a'; 10];
+        let mut input = line.clone();
+        input.push(b'\n');
+        assert_eq!(read_bounded_line(&mut &input[..], &mut buf, 10), Ok(true));
+        assert_eq!(buf, line);
+        assert!(read_bounded_line(&mut &[b'a'; 11][..], &mut buf, 10).is_err());
+    }
+
+    #[test]
+    fn tcp_connection_is_closed_after_junk() {
+        // End to end over a real loopback socket (the transport the app uses).
+        let listener = TcpListener::bind(("127.0.0.1", 0)).unwrap();
+        let addr = listener.local_addr().unwrap();
+        let server = std::thread::spawn(move || {
+            let (s, _) = listener.accept().unwrap();
+            let read = s.try_clone().unwrap();
+            serve_lines(read, s, |_, _| Some(json!({"ok": true})));
+        });
+        let mut c = TcpStream::connect(addr).unwrap();
+        c.set_read_timeout(Some(Duration::from_secs(10))).unwrap();
+        c.write_all(b"{\"id\":7,\"method\":\"x\"}\nhello\n{\"method\":\"y\"}\n").unwrap();
+        let mut text = String::new();
+        c.read_to_string(&mut text).unwrap(); // returns at EOF: the server closed the connection
+        server.join().unwrap();
+        let lines: Vec<&str> = text.lines().collect();
+        assert_eq!(lines.len(), 2, "{text}");
+        assert!(lines[0].contains("\"id\":7"));
+        assert!(lines[1].contains("closing the connection"));
     }
 }

apps/lightcraft/src/main.rs

@@ -7,7 +7,9 @@
 //! `~/Pictures/LightCraft Library`; a new library starts with the
 //! procedural demo photos unless `--no-demo` or files are given. Files and folders on the command
 //! line are imported (duplicates are skipped). `--memory` runs an in-memory session that writes
-//! nothing (demo photos unless files are given; used by the README showcase scripts).
+//! nothing (demo photos unless files are given; used by the README showcase scripts). A library
+//! that can't be opened is never replaced silently: the window says why and asks what to do
+//! (`lightcraft_ui_egui::panels::library_problem`).
 //!
 //! `--control <port>` (or `LIGHTCRAFT_CONTROL_PORT`) starts a localhost JSON-lines control server:
 //! `{"id":1,"method":"ui.inspect","params":{}}` → `{"id":1,"ok":true,"result":…}`.
@@ -26,6 +28,7 @@ mod control_server;
 mod native_menu;
 
 use lightcraft_engine::Session;
+use lightcraft_ui_egui::panels::library_problem::LibraryProblem;
 use lightcraft_ui_egui::{LightcraftApp, Services, UiState};
 
 /// Reverse-DNS app id: Wayland app id, `.desktop` file and hicolor icon name.
@@ -41,15 +44,16 @@ fn app_icon() -> egui::IconData {
     eframe::icon_data::from_png_bytes(png).unwrap_or_default()
 }
 
-struct App(LightcraftApp, #[cfg(target_os = "macos")] Option<native_menu::NativeMenu>);
+struct App(LightcraftApp, PrefsWriter, #[cfg(target_os = "macos")] Option<native_menu::NativeMenu>);
 
 impl eframe::App for App {
     fn logic(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
         #[cfg(target_os = "macos")]
-        if let Some(m) = self.1.as_mut() {
+        if let Some(m) = self.2.as_mut() {
             m.update(&mut self.0, ctx);
         }
         self.0.logic(ctx);
+        self.1.tick(&mut self.0, ctx);
     }
     fn raw_input_hook(&mut self, _ctx: &egui::Context, raw: &mut egui::RawInput) {
         self.0.raw_input_hook(raw);
@@ -58,7 +62,9 @@ impl eframe::App for App {
         self.0.ui(ui);
     }
     fn on_exit(&mut self) {
-        save_prefs(&self.0);
+        if let Err(e) = self.1.save(&self.0) {
+            eprintln!("lightcraft: {e}");
+        }
         if let Err(e) = self.0.session.close_library() {
             eprintln!("lightcraft: saving the library failed: {e}");
         }
@@ -78,30 +84,127 @@ fn config_dir() -> Option<std::path::PathBuf> {
     }
 }
 
-/// The saved UI state and app settings (`<config>/ui.json`), if any.
-fn load_prefs() -> Option<UiState> {
+/// The saved UI state and app settings (`<config>/ui.json`), if any, and a warning for the user
+/// when the file exists but can't be used (issue #103): a damaged file is kept as
+/// `ui.json.corrupt-<unix time>` first, so the next save can't lose the library location in it;
+/// one that can't be read at all is not written this session (`keep_file`).
+fn load_prefs() -> (Option<UiState>, Option<String>, bool) {
     if std::env::var_os("LIGHTCRAFT_NO_PREFS").is_some() {
-        return None;
+        return (None, None, false);
     }
-    let bytes = std::fs::read(config_dir()?.join("ui.json")).ok()?;
-    serde_json::from_slice::<UiState>(&bytes).ok().map(UiState::sanitized)
+    let Some(path) = config_dir().map(|d| d.join("ui.json")) else { return (None, None, false) };
+    load_prefs_at(&path)
 }
 
-fn save_prefs(app: &LightcraftApp) {
-    if std::env::var_os("LIGHTCRAFT_NO_PREFS").is_some() {
-        return;
+fn load_prefs_at(path: &std::path::Path) -> (Option<UiState>, Option<String>, bool) {
+    let bytes = match std::fs::read(path) {
+        Ok(b) => b,
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return (None, None, false),
+        Err(e) => {
+            let msg = format!("The app settings ({}) couldn't be read: {e}. Defaults are used, and the file isn't overwritten.", path.display());
+            return (None, Some(msg), true);
+        }
+    };
+    match serde_json::from_slice::<UiState>(&bytes) {
+        Ok(ui) => (Some(ui.sanitized()), None, false),
+        Err(e) => {
+            let secs = std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).map(|d| d.as_secs()).unwrap_or(0);
+            let keep = path.with_file_name(format!("ui.json.corrupt-{secs}"));
+            let kept = std::fs::rename(path, &keep);
+            let what = match &kept {
+                Ok(()) => format!("it was kept as {}", keep.display()),
+                Err(r) => format!("it couldn't be set aside ({r})"),
+            };
+            let msg = format!(
+                "The app settings ({}) are damaged ({e}); {what}. Defaults are used — reopen your library with Settings → Open Library… if it isn't shown.",
+                path.display()
+            );
+            (None, Some(msg), kept.is_err())
+        }
     }
-    if let Some(d) = config_dir() {
-        let _ = std::fs::create_dir_all(&d);
-        if let Ok(bytes) = serde_json::to_vec_pretty(&app.ui) {
-            let _ = std::fs::write(d.join("ui.json"), bytes);
+}
+
+/// Write `bytes` to `path` atomically: a temp file, fsynced, renamed over it (a crash or a full
+/// disk leaves the old file or the new one, never a truncated one).
+fn write_atomic(path: &std::path::Path, bytes: &[u8]) -> std::io::Result<()> {
+    use std::io::Write;
+    let tmp = path.with_extension("json.tmp");
+    let written = (|| {
+        let mut f = std::fs::File::create(&tmp)?;
+        f.write_all(bytes)?;
+        f.sync_all()
+    })();
+    if let Err(e) = written {
+        let _ = std::fs::remove_file(&tmp);
+        return Err(e);
+    }
+    std::fs::rename(&tmp, path)?;
+    if let Some(dir) = path.parent()
+        && let Ok(d) = std::fs::File::open(dir)
+    {
+        let _ = d.sync_all();
+    }
+    Ok(())
+}
+
+/// Saves `ui.json` (app settings, incl. the library to open at launch): as soon as the library
+/// changes, every few seconds when anything else changed, and at exit.
+#[derive(Default)]
+struct PrefsWriter {
+    written: Vec<u8>,
+    library: String,
+    checked: f64,
+    /// The last write failed (reported once until a write works).
+    failing: bool,
+    /// `ui.json` couldn't be read at launch: never overwrite it this session.
+    keep_file: bool,
+}
+
+impl PrefsWriter {
+    fn save(&mut self, app: &LightcraftApp) -> Result<(), String> {
+        if self.keep_file || std::env::var_os("LIGHTCRAFT_NO_PREFS").is_some() {
+            return Ok(());
+        }
+        let Some(d) = config_dir() else { return Ok(()) };
+        let bytes = serde_json::to_vec_pretty(&app.ui).map_err(|e| e.to_string())?;
+        if bytes == self.written {
+            return Ok(());
+        }
+        std::fs::create_dir_all(&d)
+            .and_then(|()| write_atomic(&d.join("ui.json"), &bytes))
+            .map_err(|e| format!("saving the app settings failed: {e}"))?;
+        self.written = bytes;
+        self.library = app.ui.settings.library_path.clone();
+        Ok(())
+    }
+
+    fn tick(&mut self, app: &mut LightcraftApp, ctx: &egui::Context) {
+        let now = ctx.input(|i| i.time);
+        let moved = app.ui.settings.library_path != self.library;
+        if !moved && now - self.checked < 3.0 {
+            return;
+        }
+        self.checked = now;
+        match self.save(app) {
+            Ok(()) => self.failing = false,
+            Err(e) => {
+                eprintln!("lightcraft: {e}");
+                if !self.failing {
+                    app.notices.push(format!("{e}. LightCraft keeps trying."));
+                }
+                self.failing = true;
+                // don't retry every frame
+                self.library = app.ui.settings.library_path.clone();
+            }
         }
     }
 }
 
 fn services() -> Services {
     Services {
-        pick_folder: Some(Box::new(|| rfd::FileDialog::new().set_title("Open Library").pick_folder().map(|p| p.to_string_lossy().to_string()))),
+        pick_folder: Some(Box::new(|| {
+            rfd::FileDialog::new().set_title(lightcraft_ui_egui::i18n::tr("Open Library")).pick_folder().map(|p| p.to_string_lossy().to_string())
+        })),
         open_with: Some(Box::new(|path: &str, app: &str| {
             // spawned, never waited for: the editor runs alongside
             let app = app.trim();
@@ -153,7 +256,7 @@ fn services() -> Services {
         pick_files: Some(Box::new(|| {
             rfd::FileDialog::new()
                 .add_filter(
-                    "Photos",
+                    lightcraft_ui_egui::i18n::tr("Photos"),
                     &[
                         "jpg", "jpeg", "png", "tif", "tiff", "webp", "dng", "cr2", "cr3", "nef", "nrw", "arw", "raf", "orf", "rw2", "pef", "psd",
                         "jxl", "gif", "bmp",
@@ -167,8 +270,11 @@ fn services() -> Services {
         })),
         pick_preset_files: Some(Box::new(|| {
             rfd::FileDialog::new()
-                .set_title("Import Presets")
-                .add_filter("Presets & Profiles", &["lcpreset", "xmp", "lrtemplate", "zip", "dng", "lmp", "mplumpack", "cube"])
+                .set_title(lightcraft_ui_egui::i18n::tr("Import Presets"))
+                .add_filter(
+                    lightcraft_ui_egui::i18n::tr("Presets & Profiles"),
+                    &["lcpreset", "xmp", "lrtemplate", "zip", "dng", "lmp", "mplumpack", "cube"],
+                )
                 .pick_files()
                 .unwrap_or_default()
                 .into_iter()
@@ -177,24 +283,24 @@ fn services() -> Services {
         })),
         pick_tracklog: Some(Box::new(|| {
             rfd::FileDialog::new()
-                .set_title("Auto-Tag from Tracklog")
-                .add_filter("GPS Track Log", &["gpx"])
+                .set_title(lightcraft_ui_egui::i18n::tr("Auto-Tag from Tracklog"))
+                .add_filter(lightcraft_ui_egui::i18n::tr("GPS Track Log"), &["gpx"])
                 .pick_file()
                 .map(|p| vec![p.to_string_lossy().to_string()])
                 .unwrap_or_default()
         })),
         save_preset_file: Some(Box::new(|name: &str| {
             rfd::FileDialog::new()
-                .set_title("Export Presets")
-                .add_filter("LightCraft Preset", &["lcpreset"])
+                .set_title(lightcraft_ui_egui::i18n::tr("Export Presets"))
+                .add_filter(lightcraft_ui_egui::i18n::tr("LightCraft Preset"), &["lcpreset"])
                 .set_file_name(name)
                 .save_file()
                 .map(|p| p.to_string_lossy().to_string())
         })),
         pick_curve_preset_files: Some(Box::new(|| {
             rfd::FileDialog::new()
-                .set_title("Import Point Curve Presets")
-                .add_filter("Point Curve Presets", &["lccurve", "json"])
+                .set_title(lightcraft_ui_egui::i18n::tr("Import Point Curve Presets"))
+                .add_filter(lightcraft_ui_egui::i18n::tr("Point Curve Presets"), &["lccurve", "json"])
                 .pick_files()
                 .unwrap_or_default()
                 .into_iter()
@@ -203,8 +309,8 @@ fn services() -> Services {
         })),
         save_curve_preset_file: Some(Box::new(|name: &str| {
             rfd::FileDialog::new()
-                .set_title("Export Point Curve Presets")
-                .add_filter("Point Curve Presets", &["lccurve"])
+                .set_title(lightcraft_ui_egui::i18n::tr("Export Point Curve Presets"))
+                .add_filter(lightcraft_ui_egui::i18n::tr("Point Curve Presets"), &["lccurve"])
                 .set_file_name(name)
                 .save_file()
                 .map(|p| p.to_string_lossy().to_string())
@@ -215,18 +321,25 @@ fn services() -> Services {
         png: Some(Box::new(|img: &lightcraft_raster::Rgba8| {
             lightcraft_codecs::encode_png(&lightcraft_codecs::EncodeImage::rgba8(img), &lightcraft_codecs::EncodeMeta::default()).unwrap_or_default()
         })),
+        // the library is a folder on disk: backed up with the user's other files
+        backup_library: None,
+        restore_library: None,
     }
 }
 
-/// The persistent library session (or an in-memory one with `--memory` / if the library can't open).
-fn open_session(in_memory: bool, dir: Option<std::path::PathBuf>, seed_demo: bool) -> Session {
-    let fallback = || if seed_demo { Session::with_demo() } else { Session::new() }.with_fs().with_system_clock();
+/// The persistent library session, or with `--memory` an in-memory one (demo photos).
+///
+/// If the library can't be opened the session is empty and in memory — never seeded with the
+/// demo photos, never written anywhere — and the problem is returned: the window then says so
+/// and offers Try Again / Choose Another Library… / Continue Without Saving / Quit (issue #100).
+fn open_session(in_memory: bool, dir: Option<std::path::PathBuf>, seed_demo: bool) -> (Session, Option<LibraryProblem>) {
     if in_memory {
-        return fallback();
+        return (if seed_demo { Session::with_demo() } else { Session::new() }.with_fs().with_system_clock(), None);
     }
+    let unopened = || Session::new().with_fs().with_system_clock();
     let Some(dir) = dir else {
-        eprintln!("lightcraft: no library location (set --library or LIGHTCRAFT_LIBRARY); running in memory");
-        return fallback();
+        eprintln!("lightcraft: no library location (set --library or LIGHTCRAFT_LIBRARY)");
+        return (unopened(), Some(LibraryProblem::new("", "There is no home folder to keep the library in. Choose a folder for it.")));
     };
     let t0 = std::time::Instant::now();
     let mut s = Session::new().with_fs().with_system_clock();
@@ -240,11 +353,11 @@ fn open_session(in_memory: bool, dir: Option<std::path::PathBuf>, seed_demo: boo
                 if torn > 0 { ", torn tail repaired" } else { "" },
                 t0.elapsed().as_secs_f64() * 1000.0
             );
-            s
+            (s, None)
         }
         Err(e) => {
-            eprintln!("lightcraft: can't open library {}: {e}; running in memory", dir.display());
-            fallback()
+            eprintln!("lightcraft: can't open library {}: {e}", dir.display());
+            (unopened(), Some(LibraryProblem::new(dir.to_string_lossy(), e.to_string())))
         }
     }
 }
@@ -293,7 +406,7 @@ fn main() -> eframe::Result {
             _ => files.push(a),
         }
     }
-    let prefs = load_prefs();
+    let (prefs, prefs_warning, keep_prefs_file) = load_prefs();
     // --library, else the library last opened from Settings, else the default location
     let library_dir = library_dir.or_else(|| {
         prefs
@@ -321,17 +434,30 @@ fn main() -> eframe::Result {
         "LightCraft",
         options,
         Box::new(move |cc| {
-            let session = open_session(in_memory, library_dir, seed_demo && files.is_empty());
+            let (session, problem) = open_session(in_memory, library_dir, seed_demo && files.is_empty());
             let mut app = LightcraftApp::new(session, services());
             if let Some(ui) = prefs {
                 app.ui = ui;
             }
+            lightcraft_ui_egui::i18n::set_language(app.ui.language);
             app.integrated_titlebar = cfg!(target_os = "macos");
+            app.notices.extend(prefs_warning);
+            // what's on disk now: only changes are written
+            let writer = PrefsWriter {
+                written: serde_json::to_vec_pretty(&app.ui).unwrap_or_default(),
+                library: app.ui.settings.library_path.clone(),
+                keep_file: keep_prefs_file,
+                ..Default::default()
+            };
             if let Some(port) = control_port {
                 let rx = control_server::start(port, cc.egui_ctx.clone());
                 app = app.with_control(rx);
             }
-            if !files.is_empty() {
+            if let Some(mut p) = problem {
+                // imported once the user has chosen where (into the library, or the temporary session)
+                p.pending_import = files;
+                app.library_problem = Some(p);
+            } else if !files.is_empty() {
                 let _ = app.run("library.import", serde_json::json!({"paths": files}));
                 app.ui.view = lightcraft_ui_egui::state::ViewMode::PhotoGrid;
             }
@@ -341,9 +467,61 @@ fn main() -> eframe::Result {
             let menu = (std::env::var_os("LIGHTCRAFT_NO_NATIVE_MENU").is_none()).then(|| native_menu::NativeMenu::install(&mut app, &cc.egui_ctx));
             Ok(Box::new(App(
                 app,
+                writer,
                 #[cfg(target_os = "macos")]
                 menu,
             )))
         }),
     )
 }
+
+#[cfg(test)]
+#[allow(clippy::unwrap_used)]
+mod tests {
+    use super::*;
+
+    fn dir(tag: &str) -> std::path::PathBuf {
+        let d = std::env::temp_dir().join(format!("lc-app-prefs-{tag}-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&d);
+        std::fs::create_dir_all(&d).unwrap();
+        d
+    }
+
+    /// Issue #103: a damaged ui.json (which holds the library location) is kept aside and
+    /// reported, not silently replaced by the defaults.
+    #[test]
+    fn damaged_ui_json_is_kept_and_reported() {
+        let d = dir("damaged");
+        let path = d.join("ui.json");
+        std::fs::write(&path, br#"{"settings": {"library_path": "/Volumes/Photos/Lib"#).unwrap();
+        let (ui, warning, keep) = load_prefs_at(&path);
+        assert!(ui.is_none() && !keep);
+        let warning = warning.unwrap();
+        assert!(warning.contains("damaged") && warning.contains("ui.json.corrupt-"), "{warning}");
+        assert!(!path.exists());
+        let kept: Vec<_> = std::fs::read_dir(&d).unwrap().map(|e| e.unwrap().file_name().to_string_lossy().to_string()).collect();
+        assert!(kept.len() == 1 && kept[0].starts_with("ui.json.corrupt-"), "{kept:?}");
+        // a missing file is just "no settings yet"
+        assert_eq!(load_prefs_at(&path).1, None);
+        let _ = std::fs::remove_dir_all(&d);
+    }
+
+    #[test]
+    fn ui_json_is_written_atomically() {
+        let d = dir("atomic");
+        let path = d.join("ui.json");
+        std::fs::write(&path, b"old").unwrap();
+        write_atomic(&path, b"{\"new\": true}").unwrap();
+        assert_eq!(std::fs::read(&path).unwrap(), b"{\"new\": true}");
+        assert!(!d.join("ui.json.tmp").exists());
+        // a failed write leaves the old file
+        let missing = d.join("gone").join("ui.json");
+        assert!(write_atomic(&missing, b"x").is_err());
+        assert_eq!(std::fs::read(&path).unwrap(), b"{\"new\": true}");
+        let ui = UiState::default();
+        write_atomic(&path, &serde_json::to_vec_pretty(&ui).unwrap()).unwrap();
+        let (loaded, warning, _) = load_prefs_at(&path);
+        assert!(loaded.is_some() && warning.is_none());
+        let _ = std::fs::remove_dir_all(&d);
+    }
+}

apps/lightcraft/src/native_menu.rs

@@ -148,7 +148,7 @@ fn yields_to_text(sc: &str) -> bool {
 
 /// `&` marks a mnemonic in muda labels.
 fn label_text(s: &str) -> String {
-    s.replace('&', "&&")
+    lightcraft_ui_egui::i18n::tr(s).replace('&', "&&")
 }
 
 fn structure_of(bar: &[(String, Vec<MenuNode>)]) -> String {
@@ -171,7 +171,7 @@ fn structure_of(bar: &[(String, Vec<MenuNode>)]) -> String {
             out.push(';');
         }
     }
-    let mut s = String::new();
+    let mut s = format!("{};", lightcraft_ui_egui::i18n::is_japanese());
     for (t, items) in bar {
         s.push_str(t);
         walk(items, &mut s);
@@ -210,30 +210,30 @@ impl NativeMenu {
 
         // the application menu
         let app_menu = Submenu::new("LightCraft", true);
-        let about = MenuItem::with_id("app.about", "About LightCraft", true, None);
-        let settings = MenuItem::with_id(SETTINGS, app.ui.language.tr("Settings…"), true, accelerator(SETTINGS_KEY));
-        let quit = MenuItem::with_id(QUIT, "Quit LightCraft", true, accelerator("Cmd+Q"));
+        let about = MenuItem::with_id("app.about", lightcraft_ui_egui::i18n::tr("About LightCraft"), true, None);
+        let settings = MenuItem::with_id(SETTINGS, lightcraft_ui_egui::i18n::tr("Settings…"), true, accelerator(SETTINGS_KEY));
+        let quit = MenuItem::with_id(QUIT, lightcraft_ui_egui::i18n::tr("Quit LightCraft"), true, accelerator("Cmd+Q"));
         let _ = app_menu.append_items(&[
             &about,
             &PredefinedMenuItem::separator(),
             &settings,
             &PredefinedMenuItem::separator(),
-            &PredefinedMenuItem::services(None),
+            &PredefinedMenuItem::services(Some(lightcraft_ui_egui::i18n::tr("Services"))),
             &PredefinedMenuItem::separator(),
-            &PredefinedMenuItem::hide(Some("Hide LightCraft")),
-            &PredefinedMenuItem::hide_others(None),
-            &PredefinedMenuItem::show_all(None),
+            &PredefinedMenuItem::hide(Some(lightcraft_ui_egui::i18n::tr("Hide LightCraft"))),
+            &PredefinedMenuItem::hide_others(Some(lightcraft_ui_egui::i18n::tr("Hide Others"))),
+            &PredefinedMenuItem::show_all(Some(lightcraft_ui_egui::i18n::tr("Show All"))),
             &PredefinedMenuItem::separator(),
             &quit,
         ]);
         let _ = self.menu.append(&app_menu);
 
         for (title, nodes) in &bar {
-            let sub = Submenu::new(title, true);
-            if title == app.ui.language.tr("Window") {
+            let sub = Submenu::new(label_text(title), true);
+            if title == "Window" {
                 let _ = sub.append_items(&[
-                    &PredefinedMenuItem::minimize(None),
-                    &PredefinedMenuItem::maximize(Some("Zoom")),
+                    &PredefinedMenuItem::minimize(Some(lightcraft_ui_egui::i18n::tr("Minimize"))),
+                    &PredefinedMenuItem::maximize(Some(lightcraft_ui_egui::i18n::tr("Zoom"))),
                     &PredefinedMenuItem::separator(),
                 ]);
             }
@@ -245,15 +245,21 @@ impl NativeMenu {
                 .collect();
             let nodes = tidy_separators(nodes);
             self.append_nodes(&sub, &nodes);
-            if title == app.ui.language.tr("File") {
+            if title == "File" {
                 // ⌘W, the system's own item
-                let _ = sub.append_items(&[&PredefinedMenuItem::separator(), &PredefinedMenuItem::close_window(None)]);
+                let _ = sub.append_items(&[
+                    &PredefinedMenuItem::separator(),
+                    &PredefinedMenuItem::close_window(Some(lightcraft_ui_egui::i18n::tr("Close Window"))),
+                ]);
             }
-            if title == app.ui.language.tr("Window") {
-                let _ = sub.append_items(&[&PredefinedMenuItem::separator(), &PredefinedMenuItem::bring_all_to_front(None)]);
+            if title == "Window" {
+                let _ = sub.append_items(&[
+                    &PredefinedMenuItem::separator(),
+                    &PredefinedMenuItem::bring_all_to_front(Some(lightcraft_ui_egui::i18n::tr("Bring All to Front"))),
+                ]);
                 sub.set_as_windows_menu_for_nsapp();
             }
-            if title == app.ui.language.tr("Help") {
+            if title == "Help" {
                 sub.set_as_help_menu_for_nsapp();
             }
             let _ = self.menu.append(&sub);
@@ -282,12 +288,23 @@ impl NativeMenu {
                     let accel = shortcut.as_deref().filter(|s| !CONTEXTUAL.contains(s)).and_then(accelerator);
                     let handle = match checked {
                         Some(c) => {
-                            let it = CheckMenuItem::with_id(key.clone(), label_text(label), *enabled, *c, accel);
+                            let it = CheckMenuItem::with_id(
+                                key.clone(),
+                                lightcraft_ui_egui::menubar::display_item_label(id, params, label).replace('&', "&&"),
+                                *enabled,
+                                *c,
+                                accel,
+                            );
                             let _ = sub.append(&it);
                             Handle::Check(it)
                         }
                         None => {
-                            let it = MenuItem::with_id(key.clone(), label_text(label), *enabled, accel);
+                            let it = MenuItem::with_id(
+                                key.clone(),
+                                lightcraft_ui_egui::menubar::display_item_label(id, params, label).replace('&', "&&"),
+                                *enabled,
+                                accel,
+                            );
                             let _ = sub.append(&it);
                             Handle::Plain(it)
                         }
@@ -325,6 +342,7 @@ impl NativeMenu {
     /// Per frame: run chosen items, then sync labels / enabled / checked and the text-focus
     /// accelerators with the app state.
     pub fn update(&mut self, app: &mut LightcraftApp, ctx: &egui::Context) {
+        lightcraft_ui_egui::i18n::set_language(app.ui.language);
         while let Ok(key) = self.rx.try_recv() {
             if key == QUIT {
                 ctx.send_viewport_cmd(egui::ViewportCommand::Close);
@@ -352,8 +370,8 @@ impl NativeMenu {
                         let Some(it) = items.get_mut(&MenuNode::key(id, params)) else { continue };
                         if it.label != *label {
                             match &it.handle {
-                                Handle::Plain(h) => h.set_text(label_text(label)),
-                                Handle::Check(h) => h.set_text(label_text(label)),
+                                Handle::Plain(h) => h.set_text(lightcraft_ui_egui::menubar::display_item_label(id, params, label).replace('&', "&&")),
+                                Handle::Check(h) => h.set_text(lightcraft_ui_egui::menubar::display_item_label(id, params, label).replace('&', "&&")),
                             }
                             it.label = label.clone();
                         }

assets/ATTRIBUTION.md

@@ -21,6 +21,8 @@ covers a whole directory), or if a licence file referenced in the Licence column
 | `docs/images/*.jpg` (UI) | LightCraft application screenshots | LightCraft contributors | original work (captured with `docs/showcase/`) | MIT OR Apache-2.0 | 2026-09-30 | n/a |
 | `docs/brand/` (artcraft-logo and artcraft-mark, SVG and PNG) | ArtCraft wordmark and mark | ArtCraft Team | original work (https://getartcraft.com/) | ArtCraft trademark, see `docs/brand/LICENSE-brand.txt` (not open source) | 2026-10-01 | none |
 
+| `assets/fonts/BIZUDPGothic-*.ttf` | BIZ UDPGothic (Regular, Bold) | Morisawa / BIZ UDGothic Project Authors | https://github.com/googlefonts/morisawa-biz-ud-gothic/tree/18934af56b9c003ca58c54bffbf226848cb11032 | SIL Open Font License 1.1 (`assets/fonts/OFL-BIZUDGothic.txt`) | 2026-10-05 | none |
+
 Notes
 - Fonts authored or published by Adobe (Source Sans/Serif/Code, Source Han, …) are not used, even though some are
   OFL-licensed: the asset rule excludes anything from Adobe. Source Sans 3 was removed on 2026-09-30 and replaced by Inter.

assets/fonts/OFL-BIZUDGothic.txt

@@ -0,0 +1,93 @@
+Copyright 2022 The BIZ UDGothic Project Authors (https://github.com/googlefonts/morisawa-biz-ud-mincho)
+
+This Font Software is licensed under the SIL Open Font License, Version 1.1.
+This license is copied below, and is also available with a FAQ at:
+https://scripts.sil.org/OFL
+
+
+-----------------------------------------------------------
+SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
+-----------------------------------------------------------
+
+PREAMBLE
+The goals of the Open Font License (OFL) are to stimulate worldwide
+development of collaborative font projects, to support the font creation
+efforts of academic and linguistic communities, and to provide a free and
+open framework in which fonts may be shared and improved in partnership
+with others.
+
+The OFL allows the licensed fonts to be used, studied, modified and
+redistributed freely as long as they are not sold by themselves. The
+fonts, including any derivative works, can be bundled, embedded, 
+redistributed and/or sold with any software provided that any reserved
+names are not used by derivative works. The fonts and derivatives,
+however, cannot be released under any other type of license. The
+requirement for fonts to remain under this license does not apply
+to any document created using the fonts or their derivatives.
+
+DEFINITIONS
+"Font Software" refers to the set of files released by the Copyright
+Holder(s) under this license and clearly marked as such. This may
+include source files, build scripts and documentation.
+
+"Reserved Font Name" refers to any names specified as such after the
+copyright statement(s).
+
+"Original Version" refers to the collection of Font Software components as
+distributed by the Copyright Holder(s).
+
+"Modified Version" refers to any derivative made by adding to, deleting,
+or substituting -- in part or in whole -- any of the components of the
+Original Version, by changing formats or by porting the Font Software to a
+new environment.
+
+"Author" refers to any designer, engineer, programmer, technical
+writer or other person who contributed to the Font Software.
+
+PERMISSION & CONDITIONS
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of the Font Software, to use, study, copy, merge, embed, modify,
+redistribute, and sell modified and unmodified copies of the Font
+Software, subject to the following conditions:
+
+1) Neither the Font Software nor any of its individual components,
+in Original or Modified Versions, may be sold by itself.
+
+2) Original or Modified Versions of the Font Software may be bundled,
+redistributed and/or sold with any software, provided that each copy
+contains the above copyright notice and this license. These can be
+included either as stand-alone text files, human-readable headers or
+in the appropriate machine-readable metadata fields within text or
+binary files as long as those fields can be easily viewed by the user.
+
+3) No Modified Version of the Font Software may use the Reserved Font
+Name(s) unless explicit written permission is granted by the corresponding
+Copyright Holder. This restriction only applies to the primary font name as
+presented to the users.
+
+4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
+Software shall not be used to promote, endorse or advertise any
+Modified Version, except to acknowledge the contribution(s) of the
+Copyright Holder(s) and the Author(s) or with their explicit written
+permission.
+
+5) The Font Software, modified or unmodified, in part or in whole,
+must be distributed entirely under this license, and must not be
+distributed under any other license. The requirement for fonts to
+remain under this license does not apply to any document created
+using the Font Software.
+
+TERMINATION
+This license becomes null and void if any of the above conditions are
+not met.
+
+DISCLAIMER
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
+OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE
+COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
+DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM
+OTHER DEALINGS IN THE FONT SOFTWARE.

crates/catalog/src/journal.rs

@@ -1,8 +1,9 @@
 //! Crash-safe catalog persistence: an append-only op log plus periodic snapshots.
 //!
 //! Files (in a [`Store`]):
-//! - `catalog.snap` — `{"format":"lightcraft-catalog","version":1,"seq":N,"catalog":{…}}`, the
-//!   state after op `N`; replaced atomically (temp + fsync + rename).
+//! - `catalog.snap` — `{"format":"lightcraft-catalog","version":V,"seq":N,"catalog":{…}}`, the
+//!   state after op `N` in catalog format `V` ([`VERSION`]); replaced atomically (temp + fsync +
+//!   rename).
 //! - `catalog.log` — JSON lines, one per op applied after the snapshot:
 //!   `{"seq":N,"crc":C,"op":{…}}` where `C` is the CRC-32 of the op's JSON text. Appends are
 //!   fsynced before [`Journal::append`] returns.
@@ -10,6 +11,12 @@
 //! Loading = snapshot + replay of the records with `seq > snapshot seq`. Recovery rules:
 //! - a **torn final record** (crash mid-append: truncated line or bad CRC at the end) is dropped
 //!   and the file is cut back to the last good record, so later appends start on a clean line;
+//! - a **failed append** (disk full, a dropped network share) may leave part of its batch in the
+//!   file: [`Journal::append`] cuts the log back to the last whole record before returning the
+//!   error (or, if that fails too, before the next append), so the retry — the same ops with the
+//!   same `seq`s — starts on a clean line. Logs written by builds without that cut-back hold the
+//!   fragment glued to the first retried record on one line; the loader recognises the whole,
+//!   CRC-valid record at the end of such a line and skips only the fragment;
 //! - records already covered by the snapshot (crash between writing the snapshot and resetting
 //!   the log) are skipped;
 //! - a bad record **followed by good ones** is real damage: replay stops there, the log is kept
@@ -27,6 +34,32 @@
 //!
 //! At most one snapshot is in flight; a synchronous [`Journal::snapshot`] and dropping the journal
 //! first wait for it, so an older snapshot can never replace a newer one.
+//!
+//! # Format versions
+//!
+//! The snapshot's `version` is the catalog format, and it covers the log beside it: the log has
+//! no header of its own, and is only ever appended to under a snapshot of this build's format.
+//!
+//! | Version | Written by | Adds |
+//! |---|---|---|
+//! | (none) | early builds: a log without a snapshot | |
+//! | 1 | up to v0.2.0 | |
+//! | 2 | after v0.2.0 | `Op::SetBrowsed`, `Catalog.browsed`, `Photo.local_baseline` |
+//!
+//! Rules:
+//! - **Bump [`VERSION`]** (and add a row above) in the change that adds an [`Op`] variant or a
+//!   serialized field to the catalog, a photo, an album, a stack or develop settings that an older
+//!   build would misread or silently drop. New fields must deserialize from older data
+//!   (`#[serde(default)]`), so newer builds keep reading every older format.
+//! - **Opening an older format upgrades it**: right after loading, [`Journal::open`] writes a
+//!   snapshot in this build's format (also for a new library), before anything is appended — so a
+//!   library is never a mix, and older builds refuse it from then on instead of reading part of it.
+//!   [`LoadReport::upgraded_from`] says when that happened.
+//! - **A newer format is refused, untouched**: a snapshot whose `version` is above [`VERSION`],
+//!   or a log record whose CRC matches (so it is exactly what was written) but whose op doesn't
+//!   parse, fails [`Journal::open`] with [`CatalogError::Newer`] before any file is modified — it
+//!   is never mistaken for a torn tail or damage. (Builds up to v0.2.0 refuse a v2 snapshot with
+//!   "unsupported format".)
 
 use crate::store::Store;
 use crate::{Catalog, CatalogError, Op, Result};
@@ -34,7 +67,9 @@ use crate::{Catalog, CatalogError, Op, Result};
 pub const SNAPSHOT: &str = "catalog.snap";
 pub const LOG: &str = "catalog.log";
 const FORMAT: &str = "lightcraft-catalog";
-const VERSION: u32 = 1;
+/// The catalog format this build writes (and the newest it reads). See the module docs →
+/// *Format versions*; bump it whenever an [`Op`] variant or a serialized field is added.
+pub const VERSION: u32 = 2;
 
 /// When [`Journal::wants_snapshot`] says it's time to compact the log.
 #[derive(Clone, Copy, Debug)]
@@ -62,10 +97,16 @@ pub struct LoadReport {
     pub failed: usize,
     /// Bytes of a torn final record that were dropped.
     pub torn_bytes: u64,
+    /// Partial records left mid-log by a failed append that was retried (written by builds that
+    /// didn't cut the log back after a failed write): skipped, the retried records were replayed.
+    pub torn_fragments: usize,
     /// The damaged log was preserved under this name.
     pub damaged: Option<String>,
     /// No catalog files existed (a new library).
     pub created: bool,
+    /// The library was in an older catalog format (`0` = before format versions: a log without a
+    /// snapshot) and was rewritten in this version's format ([`VERSION`]).
+    pub upgraded_from: Option<u32>,
 }
 
 /// Where persistence time goes (reported by `library.info` → `persistence`; printed to stderr
@@ -140,6 +181,9 @@ pub struct Journal {
     pending: Option<Pending>,
     /// After a failed background snapshot: don't retry before the log has this many records.
     retry_at_records: u64,
+    /// A failed append may have left part of its records after `log_bytes`, and cutting them off
+    /// failed too: the next append cuts the log back to `log_bytes` first.
+    tail_dirty: bool,
 }
 
 /// A background snapshot in flight.
@@ -168,18 +212,58 @@ pub fn encode_record(seq: u64, op: &Op) -> String {
     format!("{{\"seq\":{seq},\"crc\":{crc},\"op\":{body}}}")
 }
 
-/// Parse one log line (without the newline). `None` if it's malformed or the CRC doesn't match.
+/// Parse one log line (without the newline). `None` if it's malformed, the CRC doesn't match, or
+/// the op is one this version doesn't know (see [`Journal::open`]).
 pub fn decode_record(line: &str) -> Option<(u64, Op)> {
-    let rest = line.strip_prefix("{\"seq\":")?;
-    let (seq, rest) = rest.split_once(",\"crc\":")?;
-    let (crc, rest) = rest.split_once(",\"op\":")?;
-    let body = rest.strip_suffix('}')?;
-    let seq: u64 = seq.parse().ok()?;
-    let crc: u32 = crc.parse().ok()?;
-    if crc32fast::hash(body.as_bytes()) != crc {
-        return None;
+    match decode_line(line) {
+        Line::Record(seq, op) => Some((seq, op)),
+        Line::Newer(_) | Line::Bad => None,
     }
-    serde_json::from_str(body).ok().map(|op| (seq, op))
+}
+
+/// One log line, decoded.
+enum Line {
+    Record(u64, Op),
+    /// The CRC matches — the line is exactly what was written — but the op doesn't parse: it
+    /// was written by a newer LightCraft (an op or field this version doesn't know), not damaged.
+    Newer(u64),
+    /// Malformed or a CRC mismatch: torn or damaged.
+    Bad,
+}
+
+fn decode_line(line: &str) -> Line {
+    let parts = || {
+        let rest = line.strip_prefix("{\"seq\":")?;
+        let (seq, rest) = rest.split_once(",\"crc\":")?;
+        let (crc, rest) = rest.split_once(",\"op\":")?;
+        let body = rest.strip_suffix('}')?;
+        Some((seq.parse::<u64>().ok()?, crc.parse::<u32>().ok()?, body))
+    };
+    let Some((seq, crc, body)) = parts() else { return Line::Bad };
+    if crc32fast::hash(body.as_bytes()) != crc {
+        return Line::Bad;
+    }
+    match serde_json::from_str(body) {
+        Ok(op) => Line::Record(seq, op),
+        Err(_) => Line::Newer(seq),
+    }
+}
+
+/// The error for a library written by a newer LightCraft.
+fn newer(what: String) -> CatalogError {
+    CatalogError::Newer(format!("{what}; this version reads catalog format v{VERSION} and older"))
+}
+
+/// A line that doesn't decode but ends with a whole record: a fragment of a failed append followed
+/// by the record that retried it (the retry re-encodes the same ops with the same `seq`s). Returns
+/// the fragment's length and the record, if that record continues the log (`seq <= last + 1`).
+/// The record's CRC must match, so damage is never mistaken for it.
+fn resync(line: &[u8], last: u64) -> Option<(usize, (u64, Op))> {
+    const START: &[u8] = b"{\"seq\":";
+    (1..line.len().saturating_sub(START.len() - 1)).filter(|&i| line[i..].starts_with(START)).find_map(|i| {
+        let rec = std::str::from_utf8(&line[i..]).ok().map(|l| l.trim_end_matches('\r')).and_then(decode_record)?;
+        (rec.0 <= last + 1).then_some((i, rec))
+    })
 }
 
 /// Write `catalog.snap` for the state after op `seq`, streaming the JSON into the store (no
@@ -205,10 +289,16 @@ fn write_snapshot(store: &mut dyn Store, seq: u64, catalog: &Catalog) -> std::io
     Ok(SnapshotTiming { serialize_ms, write_sync_ms: (ms_since(t0) - serialize_ms).max(0.0), bytes, ..Default::default() })
 }
 
+/// Just the identification of `catalog.snap` (read before the catalog itself).
 #[derive(serde::Deserialize)]
-struct SnapFile {
+struct SnapHeader {
     format: String,
     version: u32,
+}
+
+/// The whole `catalog.snap` (after [`SnapHeader`] was checked; `format` and `version` are ignored).
+#[derive(serde::Deserialize)]
+struct SnapFile {
     seq: u64,
     catalog: Catalog,
 }
@@ -221,15 +311,20 @@ impl Journal {
         let snap = store.read(SNAPSHOT).map_err(io)?;
         let log = store.read(LOG).map_err(io)?;
         report.created = snap.is_none() && log.is_none();
-        let (mut catalog, snapshot_seq) = match snap {
+        let (mut catalog, snapshot_seq, snapshot_version) = match snap {
             Some(bytes) => {
-                let s: SnapFile = serde_json::from_slice(&bytes).map_err(|e| CatalogError::Corrupt(format!("{SNAPSHOT}: {e}")))?;
-                if s.format != FORMAT || s.version > VERSION {
-                    return Err(CatalogError::Corrupt(format!("{SNAPSHOT}: unsupported format {} v{}", s.format, s.version)));
+                // the header first: a newer snapshot may not parse as this version's catalog
+                let h: SnapHeader = serde_json::from_slice(&bytes).map_err(|e| CatalogError::Corrupt(format!("{SNAPSHOT}: {e}")))?;
+                if h.format != FORMAT {
+                    return Err(CatalogError::Corrupt(format!("{SNAPSHOT}: not a LightCraft catalog (format {:?})", h.format)));
                 }
-                (s.catalog, s.seq)
+                if h.version > VERSION {
+                    return Err(newer(format!("{SNAPSHOT} is catalog format v{}", h.version)));
+                }
+                let s: SnapFile = serde_json::from_slice(&bytes).map_err(|e| CatalogError::Corrupt(format!("{SNAPSHOT}: {e}")))?;
+                (s.catalog, s.seq, Some(h.version))
             }
-            None => (Catalog::new(), 0),
+            None => (Catalog::new(), 0, None),
         };
         report.snapshot_seq = snapshot_seq;
         let mut j = Journal {
@@ -242,6 +337,7 @@ impl Journal {
             stats: PersistStats::default(),
             pending: None,
             retry_at_records: 0,
+            tail_dirty: false,
         };
         let log = log.unwrap_or_default();
 
@@ -261,7 +357,22 @@ impl Journal {
                 good_end = next;
                 continue;
             }
-            match line.and_then(decode_record) {
+            let mut record = line.and_then(decode_record);
+            if record.is_none()
+                && let Some((at, r)) = resync(&log[pos..line_end], j.seq)
+            {
+                // the torn start of a failed append, then the retried records (older builds
+                // appended them right after the fragment)
+                log::warn!("catalog log: skipped a partial record ({at} bytes) left by a failed write");
+                report.torn_fragments += 1;
+                record = Some(r);
+            }
+            if record.is_none()
+                && let Some(Line::Newer(seq)) = line.map(decode_line)
+            {
+                return Err(newer(format!("{LOG} record {seq} holds a change this version doesn't know")));
+            }
+            match record {
                 Some((seq, op)) if seq <= j.seq => {
                     // already in the snapshot
                     let _ = op;
@@ -277,7 +388,15 @@ impl Journal {
                 }
                 _ => {
                     // bad record (or a gap): torn tail if nothing good follows, else damage
-                    let rest_has_good = log[next..].split(|b| *b == b'\n').any(|l| std::str::from_utf8(l).ok().and_then(decode_record).is_some());
+                    let mut rest_has_good = false;
+                    for l in log[next..].split(|b| *b == b'\n') {
+                        match std::str::from_utf8(l).map(|l| decode_line(l.trim_end_matches('\r'))) {
+                            Ok(Line::Record(..)) => rest_has_good = true,
+                            // refused before anything is modified
+                            Ok(Line::Newer(seq)) => return Err(newer(format!("{LOG} record {seq} holds a change this version doesn't know"))),
+                            Ok(Line::Bad) | Err(_) => {}
+                        }
+                    }
                     if rest_has_good {
                         damaged_at = Some(pos);
                     }
@@ -301,10 +420,34 @@ impl Journal {
                 report.torn_bytes = (log.len() - good_end) as u64;
                 log::warn!("catalog log: dropped a torn final record ({} bytes)", report.torn_bytes);
                 j.store.truncate(LOG, good_end as u64).map_err(io)?;
+                j.log_bytes = good_end as u64;
             } else if needs_newline {
                 j.store.append(LOG, b"\n").map_err(io)?;
+                j.log_bytes = good_end as u64 + 1;
+            } else {
+                j.log_bytes = good_end as u64;
+            }
+        }
+        // Bring an older (or new, or snapshot-less) library to this version's format before
+        // anything is appended: a snapshot in this format makes older builds refuse the library
+        // instead of misreading ops or dropping fields they don't know.
+        if report.created {
+            // tiny: written directly, not counted as a compaction
+            let empty = format!("{{\"format\":\"{FORMAT}\",\"version\":{VERSION},\"seq\":0,\"catalog\":{}}}\n", catalog.to_snapshot());
+            if let Err(e) = j.store.write_atomic(SNAPSHOT, empty.as_bytes()) {
+                log::warn!("catalog: can't write the new library's snapshot: {e}");
+            }
+        } else if report.damaged.is_none() && snapshot_version != Some(VERSION) {
+            report.upgraded_from = Some(snapshot_version.unwrap_or(0));
+            match j.snapshot(&catalog) {
+                Ok(()) => {
+                    if let Some(v) = report.upgraded_from {
+                        log::info!("catalog: upgraded from format v{v} to v{VERSION}");
+                    }
+                }
+                // nothing lost: the old files are intact and still load; retried on next open
+                Err(e) => log::warn!("catalog: can't write the format v{VERSION} snapshot: {e}"),
             }
-            j.log_bytes = good_end as u64;
         }
         catalog.revision = 0;
         Ok((j, catalog, report))
@@ -323,7 +466,20 @@ impl Journal {
             buf.push_str(&encode_record(seq, op));
             buf.push('\n');
         }
-        self.store.append(LOG, buf.as_bytes()).map_err(io)?;
+        if self.tail_dirty {
+            self.store.truncate(LOG, self.log_bytes).map_err(io)?;
+            self.tail_dirty = false;
+        }
+        if let Err(e) = self.store.append(LOG, buf.as_bytes()) {
+            // Part of the batch may be in the file. Cut it back to the last whole record, so the
+            // retry (same seqs) starts on a clean line instead of after a fragment that would
+            // read back as damage.
+            if let Err(t) = self.store.truncate(LOG, self.log_bytes) {
+                log::error!("catalog: can't cut the log back after a failed append: {t}");
+                self.tail_dirty = true;
+            }
+            return Err(io(e));
+        }
         if let Some(p) = self.pending.as_mut() {
             p.tail.extend_from_slice(buf.as_bytes());
             p.tail_records += ops.len() as u64;
@@ -343,12 +499,22 @@ impl Journal {
 
     /// Write a snapshot of `catalog` (which must reflect every appended op) and reset the log.
     pub fn snapshot(&mut self, catalog: &Catalog) -> Result<()> {
+        self.snapshot_with_unlogged(catalog, 0)
+    }
+
+    /// [`Journal::snapshot`] of a catalog that also reflects `unlogged` ops applied after the
+    /// last appended one but never written to the log (their append failed). The snapshot counts
+    /// them (it holds the state after op `seq + unlogged`), so they are saved and must not be
+    /// appended afterwards. Once the snapshot is durable [`Journal::seq`] includes them, even if
+    /// resetting the log then fails (the error is still returned).
+    pub fn snapshot_with_unlogged(&mut self, catalog: &Catalog, unlogged: u64) -> Result<()> {
         // never two snapshot writers; the one in flight is older, so it must land first
         if let Err(e) = self.wait() {
             log::warn!("catalog: background snapshot failed ({e}); writing one now");
         }
         let t0 = web_time::Instant::now();
-        let mut timing = match write_snapshot(self.store.as_mut(), self.seq, catalog) {
+        let seq = self.seq + unlogged;
+        let mut timing = match write_snapshot(self.store.as_mut(), seq, catalog) {
             Ok(t) => t,
             Err(e) => {
                 // nothing lost (the log is whole); don't retry on every append
@@ -357,6 +523,9 @@ impl Journal {
                 return Err(io(e));
             }
         };
+        // the snapshot is durable: it holds every op up to `seq`
+        self.seq = seq;
+        self.snapshot_seq = seq;
         let t2 = web_time::Instant::now();
         // A crash here leaves old records in the log; they are skipped by seq on load.
         self.store.write_atomic(LOG, b"").map_err(io)?;
@@ -365,10 +534,10 @@ impl Journal {
         timing.blocking_ms = timing.total_ms;
         timing.records = self.log_records;
         self.record_snapshot(timing);
-        self.snapshot_seq = self.seq;
         self.log_records = 0;
         self.log_bytes = 0;
         self.retry_at_records = 0;
+        self.tail_dirty = false;
         Ok(())
     }
 
@@ -459,6 +628,7 @@ impl Journal {
         self.log_records = p.tail_records;
         self.log_bytes = p.tail.len() as u64;
         self.retry_at_records = 0;
+        self.tail_dirty = false;
         Ok(())
     }
 

crates/catalog/src/lib.rs

@@ -5,6 +5,11 @@
 //!   snapshot — crash-safe and diff-friendly (see [`journal`]);
 //! - **undo/redo**: the engine keeps inverse ops;
 //! - **determinism**: replaying the log reproduces the state exactly (property-tested).
+//!
+//! **Catalog format version** ([`journal::VERSION`], see [`journal`] → *Format versions*): adding
+//! an [`Op`] variant or a serialized field means bumping it. Newer builds read every older format
+//! (and upgrade it on open); older builds refuse a newer library with [`CatalogError::Newer`]
+//! instead of reading part of it.
 #![forbid(unsafe_code)]
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
 
@@ -12,6 +17,7 @@ pub mod dates;
 pub mod journal;
 pub mod keywords;
 pub mod local;
+pub mod lock;
 pub mod model;
 pub mod query;
 pub mod rules;
@@ -27,6 +33,7 @@ pub use journal::{Journal, LoadReport, PersistStats, SnapshotPolicy, SnapshotTim
 pub use keywords::KeywordNode;
 use lightcraft_develop::DevelopSettings;
 pub use local::{DEFAULT_FORGET_DAYS, ForgetPlan, folder_of};
+pub use lock::{LibraryLock, LockError, LockOwner};
 pub use model::*;
 pub use query::{DateGroup, Filter, RatingOp, Sort, SortKey};
 pub use rules::{Match, Rule, RuleSet};
@@ -47,6 +54,10 @@ pub enum CatalogError {
     Corrupt(String),
     #[error("catalog storage: {0}")]
     Io(String),
+    /// The library was written by a newer LightCraft (a newer catalog format, or a change this
+    /// version doesn't know). Nothing was read into the session and nothing was modified.
+    #[error("this library was written by a newer version of LightCraft ({0}); update LightCraft to open it. The library was left unchanged.")]
+    Newer(String),
 }
 
 pub type Result<T> = std::result::Result<T, CatalogError>;
@@ -644,6 +655,12 @@ mod tests;
 #[cfg(test)]
 mod tests_background;
 #[cfg(test)]
+mod tests_format_version;
+#[cfg(test)]
 mod tests_journal;
 #[cfg(test)]
 mod tests_local;
+#[cfg(test)]
+mod tests_lock;
+#[cfg(test)]
+mod tests_torn_append;

crates/catalog/src/lock.rs

@@ -0,0 +1,140 @@
+//! One process per library: an exclusive OS lock on `<library>/catalog.lock`, held for as long as
+//! the library is open (issue #99).
+//!
+//! Two processes on the same library (the app and `lightcraft-cli --library`, two app instances,
+//! two computers on a shared folder) would each keep their own catalog and `seq` counter, and
+//! whichever wrote the last snapshot would silently drop the other's edits. So opening a library
+//! takes the lock first, and a second opener gets [`LockError::InUse`] instead.
+//!
+//! - The lock is the OS's (`flock` on Unix, `LockFileEx` on Windows, via [`std::fs::File::try_lock`]):
+//!   it is released when the [`LibraryLock`] is dropped and, after a crash or a kill, by the OS when
+//!   the process ends. A `catalog.lock` file left behind is therefore never "stale": only a lock
+//!   that's actually held refuses the open.
+//! - Who holds it (process id, computer, program, version) is written to `catalog.lock.owner`, for
+//!   the error message. It's a separate file because a Windows lock also blocks reading the
+//!   locked file. It's only a hint: it may be missing or left over from a crash.
+//! - File systems without lock support (some network shares): the library opens unlocked, with a
+//!   warning — refusing it would lock the user out of their own library. Locks over SMB/NFS are
+//!   advisory and depend on the server; the owner file is then the only hint.
+//! - Browser storage (OPFS) has no file locks: see the web host for its own guard.
+
+use std::fs::{File, OpenOptions, TryLockError};
+use std::io;
+use std::path::{Path, PathBuf};
+
+/// The lock file in the library directory.
+pub const LOCK: &str = "catalog.lock";
+/// Who holds the lock (JSON, see [`LockOwner`]).
+pub const OWNER: &str = "catalog.lock.owner";
+
+/// Who has the library open (as written in [`OWNER`]).
+#[derive(Clone, Debug, Default, PartialEq, serde::Serialize, serde::Deserialize)]
+#[serde(default)]
+pub struct LockOwner {
+    pub pid: u32,
+    /// Computer name, if known.
+    pub host: String,
+    /// The program (`LightCraft`, `lightcraft-cli`…) and its version.
+    pub program: String,
+    pub version: String,
+    /// When it opened the library (seconds since 1970).
+    pub since: u64,
+}
+
+impl LockOwner {
+    /// This process, as `program`.
+    pub fn this_process(program: &str) -> LockOwner {
+        LockOwner {
+            pid: std::process::id(),
+            host: host_name(),
+            program: program.to_string(),
+            version: env!("CARGO_PKG_VERSION").to_string(),
+            since: web_time::SystemTime::now().duration_since(web_time::UNIX_EPOCH).map(|d| d.as_secs()).unwrap_or(0),
+        }
+    }
+
+    /// "LightCraft 0.3.0 (process 123 on studio-mac)".
+    pub fn describe(&self) -> String {
+        let program = if self.program.is_empty() { "another LightCraft" } else { self.program.as_str() };
+        let version = if self.version.is_empty() { String::new() } else { format!(" {}", self.version) };
+        let host = if self.host.is_empty() {
+            String::new()
+        } else if self.host == host_name() {
+            " on this computer".to_string()
+        } else {
+            format!(" on {}", self.host)
+        };
+        format!("{program}{version} (process {}{host})", self.pid)
+    }
+}
+
+/// The computer's name, best effort (empty if unknown).
+fn host_name() -> String {
+    let env = ["COMPUTERNAME", "HOSTNAME"].iter().find_map(|k| std::env::var(k).ok().filter(|h| !h.trim().is_empty()));
+    env.or_else(|| std::fs::read_to_string("/etc/hostname").ok()).map(|h| h.trim().to_string()).filter(|h| !h.is_empty()).unwrap_or_default()
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum LockError {
+    /// Another process has the library open.
+    #[error("This library is already open in {}. Close it there first.", .0.as_ref().map(LockOwner::describe).unwrap_or_else(|| "another LightCraft program".into()))]
+    InUse(Option<LockOwner>),
+}
+
+/// The exclusive lock on a library directory; released on drop (and by the OS if the process
+/// dies).
+#[derive(Debug)]
+pub struct LibraryLock {
+    dir: PathBuf,
+    /// `None` when the file system can't lock (the library is open unlocked).
+    _file: Option<File>,
+    held: bool,
+}
+
+impl LibraryLock {
+    /// Lock `dir` (which must exist) for this process. Fails only when another process holds it.
+    pub fn acquire(dir: &Path, program: &str) -> Result<LibraryLock, LockError> {
+        let unlocked = |why: io::Error| {
+            log::warn!("library {}: can't lock {LOCK} ({why}); opening it without protection against a second program", dir.display());
+            LibraryLock { dir: dir.to_path_buf(), _file: None, held: false }
+        };
+        let file = match OpenOptions::new().read(true).write(true).create(true).truncate(false).open(dir.join(LOCK)) {
+            Ok(f) => f,
+            Err(e) => return Ok(unlocked(e)),
+        };
+        match file.try_lock() {
+            Ok(()) => {}
+            Err(TryLockError::WouldBlock) => {
+                let owner = std::fs::read(dir.join(OWNER)).ok().and_then(|b| serde_json::from_slice::<LockOwner>(&b).ok());
+                return Err(LockError::InUse(owner));
+            }
+            Err(TryLockError::Error(e)) => return Ok(unlocked(e)),
+        }
+        let owner = LockOwner::this_process(program);
+        if let Ok(json) = serde_json::to_vec_pretty(&owner)
+            && let Err(e) = std::fs::write(dir.join(OWNER), json)
+        {
+            log::warn!("library {}: can't write {OWNER}: {e}", dir.display());
+        }
+        Ok(LibraryLock { dir: dir.to_path_buf(), _file: Some(file), held: true })
+    }
+
+    /// The OS lock is held (`false`: the file system can't lock; opened unprotected).
+    pub fn held(&self) -> bool {
+        self.held
+    }
+
+    pub fn dir(&self) -> &Path {
+        &self.dir
+    }
+}
+
+impl Drop for LibraryLock {
+    /// Remove the owner note while still holding the lock (so it can't delete the next holder's),
+    /// then the file handle closes and the OS releases the lock.
+    fn drop(&mut self) {
+        if self.held {
+            let _ = std::fs::remove_file(self.dir.join(OWNER));
+        }
+    }
+}

crates/catalog/src/model.rs

@@ -331,6 +331,11 @@ impl Photo {
     pub fn develops_raw(&self) -> bool {
         self.kind == MediaKind::Raw && self.preview_only.is_none()
     }
+    /// The current ARW reader has vendor WB multipliers but no measured camera illuminant.
+    /// Use adjustments relative to the camera's as-shot look, as for rendered photographs.
+    pub fn relative_wb(&self) -> bool {
+        self.develops_raw() && self.format.eq_ignore_ascii_case("ARW")
+    }
     /// The develop settings import gave this photo: [`Photo::camera_defaults`], or the user's
     /// default preset applied on top of them ([`Photo::import_look`]).
     pub fn import_defaults(&self) -> DevelopSettings {
@@ -342,7 +347,8 @@ impl Photo {
     /// The built-in defaults for this photo, before any user default preset: raws start from
     /// their as-shot white balance; embedded lens corrections on when the file has them.
     pub fn camera_defaults(&self) -> DevelopSettings {
-        let mut d = match self.as_shot_wb {
+        let wb = if self.relative_wb() { Some((6500.0, 0.0)) } else { self.as_shot_wb };
+        let mut d = match wb {
             Some((t, tint)) => DevelopSettings::for_raw(t, tint),
             None => DevelopSettings::default(),
         };

crates/catalog/src/store.rs

@@ -28,9 +28,12 @@ pub trait Store: Send {
         self.write_atomic(name, &buf)?;
         Ok(buf.len() as u64)
     }
-    /// Append and make durable (fsync) before returning.
+    /// Append and make durable (fsync) before returning. On an error, part of `data` may have
+    /// been written (a full disk, a dropped network share): the journal cuts the file back to its
+    /// previous length with [`Store::truncate`] before appending again.
     fn append(&mut self, name: &str, data: &[u8]) -> io::Result<()>;
-    /// Cut a file to `len` bytes (drop a torn tail before appending again).
+    /// Cut a file to `len` bytes (drop a torn tail before appending again). A missing file is
+    /// left missing.
     fn truncate(&mut self, name: &str, len: u64) -> io::Result<()>;
     /// Human-readable location (diagnostics).
     fn describe(&self) -> String;
@@ -132,15 +135,26 @@ impl Store for FsStore {
             self.appender = Some((name.to_string(), f));
         }
         let Some((_, f)) = self.appender.as_mut() else { return Err(io::Error::other("appender not open")) };
-        f.write_all(data)?;
-        f.sync_data()
+        let written = f.write_all(data).and_then(|()| f.sync_data());
+        if written.is_err() {
+            // The handle may be dead (a network share that reconnected, a removed volume): the next
+            // attempt reopens the file. Part of `data` may be in the file; the caller cuts it back
+            // ([`Store::truncate`]) before appending again.
+            self.appender = None;
+        }
+        written
     }
 
     fn truncate(&mut self, name: &str, len: u64) -> io::Result<()> {
         if self.appender.as_ref().is_some_and(|(n, _)| n == name) {
             self.appender = None;
         }
-        let f = std::fs::OpenOptions::new().write(true).open(self.path(name))?;
+        let f = match std::fs::OpenOptions::new().write(true).open(self.path(name)) {
+            Ok(f) => f,
+            // nothing to cut (an append that failed before creating the file)
+            Err(e) if e.kind() == io::ErrorKind::NotFound => return Ok(()),
+            Err(e) => return Err(e),
+        };
         f.set_len(len)?;
         f.sync_all()
     }

crates/catalog/src/tests_background.rs

@@ -180,7 +180,8 @@ fn failed_background_snapshot_loses_nothing_and_retries_later() {
     wait_written(&j);
     assert!(j.poll().is_err());
     assert_eq!((j.snapshot_seq(), j.stats().failed_snapshots), (0, 1));
-    assert!(g.files.get(SNAPSHOT).is_none());
+    // still the (empty) snapshot written when the library was created
+    assert_eq!(g.snapshot_seq_on_disk(), Some(0));
     assert_recovers(&g, &live);
     // no retry storm: the next attempt waits for another `max_records` records
     assert!(!j.wants_snapshot());

crates/catalog/src/tests_format_version.rs

@@ -0,0 +1,186 @@
+//! Issue #102: catalog format versions. Older formats load and are upgraded; a newer format is
+//! refused with a clear error and left untouched (never read in part, truncated or set aside).
+
+use crate::journal::{LOG, SNAPSHOT, VERSION, encode_record};
+use crate::*;
+
+fn photo(c: &mut Catalog) -> Op {
+    let id = c.alloc_photo_id();
+    Op::AddPhoto { photo: Box::new(Photo::new(id, Source::File { path: format!("/p/{}.jpg", id.0) }, "p.jpg", "JPEG", 4, 3, "2026-01-01")) }
+}
+
+/// A catalog with two photos and the log line for a third op on top of it.
+fn legacy_parts() -> (Catalog, String, Catalog) {
+    let mut c = Catalog::new();
+    for _ in 0..2 {
+        let op = photo(&mut c);
+        c.apply(op).unwrap();
+    }
+    let base = c.clone();
+    let id = c.photos().next().unwrap().id;
+    let op = Op::SetRating { id, rating: 4 };
+    c.apply(op.clone()).unwrap();
+    (base, format!("{}\n", encode_record(3, &op)), c)
+}
+
+fn snapshot_version(m: &MemStore) -> u64 {
+    let v: serde_json::Value = serde_json::from_slice(&m.get(SNAPSHOT).unwrap()).unwrap();
+    v["version"].as_u64().unwrap()
+}
+
+#[test]
+fn v1_library_loads_and_is_upgraded() {
+    let (base, log, full) = legacy_parts();
+    let m = MemStore::new();
+    m.set(SNAPSHOT, format!("{{\"format\":\"lightcraft-catalog\",\"version\":1,\"seq\":2,\"catalog\":{}}}\n", base.to_snapshot()).into_bytes());
+    m.set(LOG, log.into_bytes());
+    let (mut j, c, r) = Journal::open(Box::new(m.clone())).unwrap();
+    assert_eq!(c.to_snapshot(), full.to_snapshot());
+    assert_eq!((r.replayed, r.upgraded_from), (1, Some(1)));
+    // rewritten in this format before anything is appended
+    assert_eq!(snapshot_version(&m), u64::from(VERSION));
+    assert!(m.get(LOG).unwrap().is_empty());
+    assert_eq!(j.seq(), 3);
+    j.append(&[Op::SetLabelName { label: ColorLabel::ALL[0], name: Some("x".into()) }]).unwrap();
+    drop(j);
+    let (_, _, r) = Journal::open(Box::new(m)).unwrap();
+    assert_eq!((r.replayed, r.upgraded_from), (1, None));
+}
+
+#[test]
+fn versionless_log_only_library_is_upgraded() {
+    let mut c = Catalog::new();
+    let op = photo(&mut c);
+    c.apply(op.clone()).unwrap();
+    let m = MemStore::new();
+    m.set(LOG, format!("{}\n", encode_record(1, &op)).into_bytes());
+    let (_, loaded, r) = Journal::open(Box::new(m.clone())).unwrap();
+    assert_eq!(loaded.to_snapshot(), c.to_snapshot());
+    assert_eq!(r.upgraded_from, Some(0));
+    assert_eq!(snapshot_version(&m), u64::from(VERSION));
+}
+
+/// A new library gets a snapshot in this format at once, so an older build never sees a bare log
+/// it would read in part.
+#[test]
+fn new_library_is_written_in_this_format() {
+    let m = MemStore::new();
+    let (_, _, r) = Journal::open(Box::new(m.clone())).unwrap();
+    assert!(r.created);
+    assert_eq!(r.upgraded_from, None);
+    assert_eq!(snapshot_version(&m), u64::from(VERSION));
+}
+
+fn assert_refused_untouched(m: &MemStore) {
+    let before = m.files.lock().unwrap().clone();
+    let e = Journal::open(Box::new(m.clone())).err().expect("refused");
+    assert!(matches!(e, CatalogError::Newer(_)), "{e:?}");
+    let msg = e.to_string();
+    assert!(msg.contains("newer version of LightCraft") && msg.contains("left unchanged"), "{msg}");
+    assert_eq!(*m.files.lock().unwrap(), before, "nothing modified, nothing renamed");
+}
+
+#[test]
+fn newer_snapshot_is_refused_untouched() {
+    let (base, log, _) = legacy_parts();
+    let m = MemStore::new();
+    m.set(
+        SNAPSHOT,
+        format!("{{\"format\":\"lightcraft-catalog\",\"version\":{},\"seq\":2,\"catalog\":{}}}\n", VERSION + 1, base.to_snapshot()).into_bytes(),
+    );
+    m.set(LOG, log.into_bytes());
+    assert_refused_untouched(&m);
+    // even when its catalog doesn't parse as this version's
+    let m = MemStore::new();
+    m.set(
+        SNAPSHOT,
+        format!("{{\"format\":\"lightcraft-catalog\",\"version\":{},\"seq\":2,\"catalog\":{{\"photos\":7}}}}\n", VERSION + 1).into_bytes(),
+    );
+    assert_refused_untouched(&m);
+    let e = Journal::open(Box::new(m)).err().unwrap().to_string();
+    assert!(e.contains(&format!("v{}", VERSION + 1)), "{e}");
+}
+
+/// A log record with a valid CRC whose op this version doesn't know: refused, not taken for a
+/// torn tail (truncated) or damage (renamed) — wherever it is in the log.
+#[test]
+fn unknown_op_in_the_log_is_refused_untouched() {
+    let (base, log, _) = legacy_parts();
+    let future = |seq: u64| {
+        let body = r#"{"op":"fromTheFuture","id":1,"what":"something new"}"#;
+        format!("{{\"seq\":{seq},\"crc\":{},\"op\":{body}}}\n", crc32fast::hash(body.as_bytes()))
+    };
+    let snap = format!("{{\"format\":\"lightcraft-catalog\",\"version\":{VERSION},\"seq\":2,\"catalog\":{}}}\n", base.to_snapshot());
+    let id = base.photos().next().unwrap().id;
+    let after = format!("{}\n", encode_record(5, &Op::SetRating { id, rating: 1 }));
+    for log in [format!("{log}{}", future(4)), format!("{log}{}{after}", future(4)), format!("{}{log}", future(3))] {
+        let m = MemStore::new();
+        m.set(SNAPSHOT, snap.clone().into_bytes());
+        m.set(LOG, log.into_bytes());
+        assert_refused_untouched(&m);
+    }
+    // a known op with a field of an unknown shape is "newer" too
+    let body = r#"{"op":"setRating","id":1,"rating":"five stars"}"#;
+    let m = MemStore::new();
+    m.set(SNAPSHOT, snap.into_bytes());
+    m.set(LOG, format!("{log}{{\"seq\":4,\"crc\":{},\"op\":{body}}}\n", crc32fast::hash(body.as_bytes())).into_bytes());
+    assert_refused_untouched(&m);
+}
+
+/// A CRC mismatch is still damage / a torn tail (not "newer").
+#[test]
+fn bad_crc_is_still_a_torn_tail() {
+    let (base, log, _) = legacy_parts();
+    let m = MemStore::new();
+    m.set(
+        SNAPSHOT,
+        format!("{{\"format\":\"lightcraft-catalog\",\"version\":{VERSION},\"seq\":2,\"catalog\":{}}}\n", base.to_snapshot()).into_bytes(),
+    );
+    let body = r#"{"op":"fromTheFuture"}"#;
+    m.set(LOG, format!("{log}{{\"seq\":4,\"crc\":1,\"op\":{body}}}\n").into_bytes());
+    let (_, _, r) = Journal::open(Box::new(m)).unwrap();
+    assert!(r.torn_bytes > 0 && r.damaged.is_none(), "{r:?}");
+}
+
+/// Guard for the version rule (see `journal` → *Format versions*): adding an [`Op`] variant breaks
+/// this match. When it does, bump `journal::VERSION`, add a row to the format table, and add the
+/// variant here under the new version.
+#[test]
+fn op_variants_are_versioned() {
+    fn since(op: &Op) -> u32 {
+        match op {
+            Op::AddPhoto { .. }
+            | Op::RemovePhoto { .. }
+            | Op::SetRating { .. }
+            | Op::SetFlag { .. }
+            | Op::SetLabel { .. }
+            | Op::SetDevelop { .. }
+            | Op::SetMeta { .. }
+            | Op::SetDeleted { .. }
+            | Op::SetLocal { .. }
+            | Op::SetVersions { .. }
+            | Op::SetHistory { .. }
+            | Op::PushHistory { .. }
+            | Op::AddAlbum { .. }
+            | Op::RemoveAlbum { .. }
+            | Op::RenameAlbum { .. }
+            | Op::MoveAlbum { .. }
+            | Op::SetAlbumPhotos { .. }
+            | Op::SetAlbumCover { .. }
+            | Op::SetAlbumRules { .. }
+            | Op::AddStack { .. }
+            | Op::RemoveStack { .. }
+            | Op::SetStack { .. }
+            | Op::SetCaptured { .. }
+            | Op::SetAnalysis { .. }
+            | Op::SetFile { .. }
+            | Op::Relink { .. }
+            | Op::SetContent { .. }
+            | Op::SetLabelName { .. }
+            | Op::Batch { .. } => 1,
+            Op::SetBrowsed { .. } => 2,
+        }
+    }
+    let newest = since(&Op::SetBrowsed { folder: String::new(), at: None });
+    assert_eq!(newest, VERSION, "the newest op's version must be the current format version");
+}

crates/catalog/src/tests_journal.rs

@@ -283,7 +283,12 @@ fn streamed_snapshot_keeps_the_on_disk_format() {
     let (mut j, c, _) = open(&m);
     assert_eq!(c.to_snapshot(), full.to_snapshot());
     j.snapshot(&c).unwrap();
-    let legacy = format!("{{\"format\":\"lightcraft-catalog\",\"version\":1,\"seq\":{},\"catalog\":{}}}\n", j.seq(), c.to_snapshot());
+    let legacy = format!(
+        "{{\"format\":\"lightcraft-catalog\",\"version\":{},\"seq\":{},\"catalog\":{}}}\n",
+        crate::journal::VERSION,
+        j.seq(),
+        c.to_snapshot()
+    );
     assert_eq!(String::from_utf8(m.get(SNAPSHOT).unwrap()).unwrap(), legacy);
     assert_eq!(j.stats().last_snapshot.bytes, legacy.len() as u64);
 

crates/catalog/src/tests_lock.rs

@@ -0,0 +1,93 @@
+//! Issue #99: one process per library.
+
+use std::path::PathBuf;
+
+use crate::lock::{LOCK, OWNER};
+use crate::*;
+
+fn temp_dir(tag: &str) -> PathBuf {
+    let d = std::env::temp_dir().join(format!("lc-lock-{tag}-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&d);
+    std::fs::create_dir_all(&d).unwrap();
+    d
+}
+
+#[test]
+fn second_opener_is_refused_until_the_first_lets_go() {
+    let dir = temp_dir("twice");
+    let first = LibraryLock::acquire(&dir, "LightCraft").unwrap();
+    assert!(first.held());
+    let owner: LockOwner = serde_json::from_slice(&std::fs::read(dir.join(OWNER)).unwrap()).unwrap();
+    assert_eq!((owner.pid, owner.program.as_str()), (std::process::id(), "LightCraft"));
+
+    let e = LibraryLock::acquire(&dir, "lightcraft-cli").unwrap_err();
+    let LockError::InUse(Some(who)) = &e else { panic!("{e:?}") };
+    assert_eq!(who.pid, std::process::id());
+    let msg = e.to_string();
+    assert!(msg.contains("already open in LightCraft") && msg.contains(&format!("process {}", std::process::id())), "{msg}");
+
+    drop(first);
+    assert!(!dir.join(OWNER).exists(), "the owner note goes with the lock");
+    assert!(dir.join(LOCK).exists(), "the lock file itself may stay: only a held lock refuses");
+    let again = LibraryLock::acquire(&dir, "lightcraft-cli").unwrap();
+    assert!(again.held());
+    drop(again);
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
+/// Files left behind by a crash (lock file + owner note) don't lock anyone out.
+#[test]
+fn leftover_lock_files_are_not_a_lock() {
+    let dir = temp_dir("stale");
+    std::fs::write(dir.join(LOCK), b"").unwrap();
+    std::fs::write(dir.join(OWNER), br#"{"pid":999999,"host":"elsewhere","program":"LightCraft","version":"0.2.0","since":1}"#).unwrap();
+    let l = LibraryLock::acquire(&dir, "LightCraft").unwrap();
+    assert!(l.held());
+    let owner: LockOwner = serde_json::from_slice(&std::fs::read(dir.join(OWNER)).unwrap()).unwrap();
+    assert_eq!(owner.pid, std::process::id(), "the note now names this process");
+    drop(l);
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
+/// Another process holds the lock; when it is killed (a crash), the OS releases it.
+#[test]
+fn lock_held_by_another_process_is_released_when_it_dies() {
+    let dir = temp_dir("child");
+    let exe = std::env::current_exe().unwrap();
+    let mut child = std::process::Command::new(exe)
+        .args(["--exact", "tests_lock::lock_holder_child", "--ignored", "--test-threads=1"])
+        .env("LC_LOCK_CHILD_DIR", &dir)
+        .stdout(std::process::Stdio::null())
+        .stderr(std::process::Stdio::null())
+        .spawn()
+        .unwrap();
+    let deadline = std::time::Instant::now() + std::time::Duration::from_secs(60);
+    while !dir.join("child-locked").exists() {
+        assert!(child.try_wait().unwrap().is_none(), "child exited before locking");
+        assert!(std::time::Instant::now() < deadline, "child never locked");
+        std::thread::sleep(std::time::Duration::from_millis(20));
+    }
+    let e = LibraryLock::acquire(&dir, "LightCraft").unwrap_err();
+    let LockError::InUse(Some(who)) = &e else { panic!("{e:?}") };
+    assert_eq!(who.pid, child.id());
+    assert!(e.to_string().contains("on this computer") || who.host.is_empty(), "{e}");
+
+    child.kill().unwrap(); // SIGKILL: no clean-up runs, like a crash
+    child.wait().unwrap();
+    assert!(dir.join(OWNER).exists(), "the crashed holder's note is left behind");
+    let l = LibraryLock::acquire(&dir, "LightCraft").expect("the OS released the dead process's lock");
+    assert!(l.held());
+    drop(l);
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
+/// Run by [`lock_held_by_another_process_is_released_when_it_dies`] in a child process: take the
+/// lock, say so, and wait to be killed.
+#[test]
+#[ignore = "helper process for lock_held_by_another_process_is_released_when_it_dies"]
+fn lock_holder_child() {
+    let Some(dir) = std::env::var_os("LC_LOCK_CHILD_DIR") else { return };
+    let _l = LibraryLock::acquire(std::path::Path::new(&dir), "lightcraft-cli").unwrap();
+    std::fs::write(std::path::Path::new(&dir).join("child-locked"), b"").unwrap();
+    std::thread::sleep(std::time::Duration::from_secs(120));
+}

crates/catalog/src/tests_torn_append.rs

@@ -0,0 +1,223 @@
+//! Issue #101: an append that fails part-way (disk full, a dropped network share) and is then
+//! retried must not read back as log damage, and must lose nothing.
+
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::{Arc, Mutex};
+
+use crate::journal::LOG;
+use crate::*;
+
+/// A store whose next append writes only a prefix of its data, then fails.
+#[derive(Clone, Default)]
+struct Torn {
+    files: MemStore,
+    /// The next append writes this many bytes, then returns an error.
+    torn_at: Arc<Mutex<Option<usize>>>,
+    /// `truncate` fails (the cut-back after a failed append can't be done right away).
+    truncate_fails: Arc<AtomicBool>,
+}
+
+impl Torn {
+    fn tear_next_append(&self, bytes: usize) {
+        *self.torn_at.lock().unwrap() = Some(bytes);
+    }
+}
+
+impl Store for Torn {
+    fn read(&mut self, name: &str) -> std::io::Result<Option<Vec<u8>>> {
+        self.files.read(name)
+    }
+    fn write_atomic(&mut self, name: &str, data: &[u8]) -> std::io::Result<()> {
+        self.files.write_atomic(name, data)
+    }
+    fn append(&mut self, name: &str, data: &[u8]) -> std::io::Result<()> {
+        if let Some(n) = self.torn_at.lock().unwrap().take() {
+            self.files.append(name, &data[..n.min(data.len())])?;
+            return Err(std::io::Error::other("disk full"));
+        }
+        self.files.append(name, data)
+    }
+    fn truncate(&mut self, name: &str, len: u64) -> std::io::Result<()> {
+        if self.truncate_fails.load(Ordering::SeqCst) {
+            return Err(std::io::Error::other("share unavailable"));
+        }
+        self.files.truncate(name, len)
+    }
+    fn describe(&self) -> String {
+        "torn".into()
+    }
+}
+
+fn add_photo(c: &mut Catalog) -> Op {
+    let id = c.alloc_photo_id();
+    Op::AddPhoto { photo: Box::new(Photo::new(id, Source::File { path: format!("/p/{}.jpg", id.0) }, "p.jpg", "JPEG", 4, 3, "2026-01-01")) }
+}
+
+/// Apply `ops` to the live catalog (like a command) and return them for the journal.
+fn apply(c: &mut Catalog, ops: Vec<Op>) -> Vec<Op> {
+    for op in &ops {
+        c.apply(op.clone()).unwrap();
+    }
+    ops
+}
+
+/// Every tear position of a batch, then the retry (same ops, same seqs, like the engine's queue)
+/// and more appends: reloading replays everything, reports no damage and no torn bytes.
+#[test]
+fn partial_append_then_retry_loads_cleanly() {
+    let probe = MemStore::new();
+    let (mut j, mut c, _) = Journal::open(Box::new(probe.clone())).unwrap();
+    let add = add_photo(&mut c);
+    let first = apply(&mut c, vec![add]);
+    j.append(&first).unwrap();
+    let id = c.photos().next().unwrap().id;
+    let batch = apply(&mut c, vec![Op::SetRating { id, rating: 3 }, Op::SetFlag { id, flag: Flag::Pick }, Op::SetRating { id, rating: 4 }]);
+    let before = probe.get(LOG).unwrap().len();
+    j.append(&batch).unwrap();
+    let batch_len = probe.get(LOG).unwrap().len() - before;
+
+    for tear in 1..batch_len {
+        let t = Torn::default();
+        let (mut j, mut c, _) = Journal::open(Box::new(t.clone())).unwrap();
+        let add = add_photo(&mut c);
+        let first = apply(&mut c, vec![add]);
+        j.append(&first).unwrap();
+        let good_len = t.files.get(LOG).unwrap().len();
+        let batch = apply(&mut c, vec![Op::SetRating { id, rating: 3 }, Op::SetFlag { id, flag: Flag::Pick }, Op::SetRating { id, rating: 4 }]);
+        t.tear_next_append(tear);
+        assert!(j.append(&batch).is_err(), "tear at {tear}");
+        // cut back to the last whole record
+        assert_eq!(t.files.get(LOG).unwrap().len(), good_len, "tear at {tear}");
+        j.append(&batch).unwrap();
+        let more = apply(&mut c, vec![Op::SetLabel { id, label: Some(ColorLabel::ALL[0]) }]);
+        j.append(&more).unwrap();
+        drop(j);
+
+        let (_, loaded, r) = Journal::open(Box::new(t.clone())).unwrap();
+        assert!(r.damaged.is_none(), "tear at {tear}: {r:?}");
+        assert_eq!((r.torn_bytes, r.torn_fragments, r.replayed), (0, 0, 5), "tear at {tear}");
+        assert_eq!(loaded.to_snapshot(), c.to_snapshot(), "tear at {tear}");
+    }
+}
+
+/// When cutting back fails too (the share is gone), the next append cuts back first; until that
+/// works nothing more is appended after the fragment.
+#[test]
+fn failed_cut_back_is_done_before_the_next_append() {
+    let t = Torn::default();
+    let (mut j, mut c, _) = Journal::open(Box::new(t.clone())).unwrap();
+    let add = add_photo(&mut c);
+    let first = apply(&mut c, vec![add]);
+    j.append(&first).unwrap();
+    let good_len = t.files.get(LOG).unwrap().len();
+    let id = c.photos().next().unwrap().id;
+    let batch = apply(&mut c, vec![Op::SetRating { id, rating: 2 }, Op::SetRating { id, rating: 5 }]);
+    t.truncate_fails.store(true, Ordering::SeqCst);
+    t.tear_next_append(30);
+    assert!(j.append(&batch).is_err());
+    assert_eq!(t.files.get(LOG).unwrap().len(), good_len + 30, "the fragment is still there");
+    // still unreachable: the retry fails without writing anything after the fragment
+    assert!(j.append(&batch).is_err());
+    assert_eq!(t.files.get(LOG).unwrap().len(), good_len + 30);
+    t.truncate_fails.store(false, Ordering::SeqCst);
+    j.append(&batch).unwrap();
+    drop(j);
+    let (_, loaded, r) = Journal::open(Box::new(t.clone())).unwrap();
+    assert!(r.damaged.is_none(), "{r:?}");
+    assert_eq!(r.replayed, 3);
+    assert_eq!(loaded.to_snapshot(), c.to_snapshot());
+}
+
+/// Logs written before the fix: the fragment of the failed append is glued to the first retried
+/// record on one line, followed by the rest of the retry. They load in full (the fragment is
+/// skipped), instead of stopping at the fragment and setting the later records aside as damage.
+#[test]
+fn legacy_fragment_glued_to_the_retry_is_skipped() {
+    let m = MemStore::new();
+    let (mut j, mut c, _) = Journal::open(Box::new(m.clone())).unwrap();
+    let add = add_photo(&mut c);
+    let first = apply(&mut c, vec![add]);
+    j.append(&first).unwrap();
+    let good = m.get(LOG).unwrap();
+    let id = c.photos().next().unwrap().id;
+    let batch = apply(
+        &mut c,
+        vec![
+            Op::SetRating { id, rating: 3 },
+            Op::SetFlag { id, flag: Flag::Pick },
+            Op::SetLabelName { label: ColorLabel::ALL[1], name: Some("Größe ✓".into()) },
+        ],
+    );
+    j.append(&batch).unwrap();
+    let full = m.get(LOG).unwrap();
+    let batch_bytes = &full[good.len()..];
+    let later = apply(&mut c, vec![Op::SetRating { id, rating: 1 }]);
+    j.append(&later).unwrap();
+    let later_bytes = m.get(LOG).unwrap()[full.len()..].to_vec();
+    drop(j);
+
+    // every tear (inside the first record, after it, inside a multi-byte character…)
+    for tear in 1..batch_bytes.len() {
+        if batch_bytes[tear - 1] == b'\n' {
+            continue; // a tear on a record boundary leaves no fragment
+        }
+        let mut log = good.clone();
+        log.extend_from_slice(&batch_bytes[..tear]);
+        log.extend_from_slice(batch_bytes);
+        log.extend_from_slice(&later_bytes);
+        let t = MemStore::new();
+        t.set(LOG, log);
+        let (_, loaded, r) = Journal::open(Box::new(t)).unwrap();
+        assert!(r.damaged.is_none(), "tear at {tear}: {r:?}");
+        assert_eq!(r.torn_fragments, 1, "tear at {tear}");
+        assert_eq!(loaded.to_snapshot(), c.to_snapshot(), "tear at {tear}");
+    }
+
+    // a damaged record whose tail happens to be a whole record from the future is still damage
+    let mut log = good.clone();
+    log.extend_from_slice(b"garbage");
+    log.extend_from_slice(&later_bytes);
+    log.extend_from_slice(&later_bytes);
+    let t = MemStore::new();
+    t.set(LOG, log);
+    let (_, _, r) = Journal::open(Box::new(t)).unwrap();
+    assert!(r.damaged.is_some(), "{r:?}");
+}
+
+/// A snapshot can absorb ops whose append failed: it records them as saved (`seq` moves past
+/// them), and appending after it continues from there.
+#[test]
+fn snapshot_with_unlogged_ops_saves_them() {
+    let t = Torn::default();
+    let (mut j, mut c, _) = Journal::open(Box::new(t.clone())).unwrap();
+    let add = add_photo(&mut c);
+    let first = apply(&mut c, vec![add]);
+    j.append(&first).unwrap();
+    let id = c.photos().next().unwrap().id;
+    let queued = apply(&mut c, vec![Op::SetRating { id, rating: 2 }, Op::SetFlag { id, flag: Flag::Reject }]);
+    t.tear_next_append(10);
+    assert!(j.append(&queued).is_err());
+    j.snapshot_with_unlogged(&c, queued.len() as u64).unwrap();
+    assert_eq!(j.seq(), 3);
+    let after = apply(&mut c, vec![Op::SetRating { id, rating: 5 }]);
+    j.append(&after).unwrap();
+    drop(j);
+    let (j, loaded, r) = Journal::open(Box::new(t.clone())).unwrap();
+    assert_eq!((r.snapshot_seq, r.replayed), (3, 1));
+    assert_eq!(j.seq(), 4);
+    assert_eq!(loaded.to_snapshot(), c.to_snapshot());
+}
+
+/// `FsStore::truncate` on a file that was never created (an append that failed first) is a no-op.
+#[test]
+fn fs_store_truncates_a_missing_file_quietly() {
+    let dir = std::env::temp_dir().join(format!("lc-torn-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    let mut s = FsStore::open(&dir).unwrap();
+    s.truncate(LOG, 0).unwrap();
+    assert!(!dir.join(LOG).exists());
+    s.append(LOG, b"abc\n").unwrap();
+    s.truncate(LOG, 0).unwrap();
+    assert_eq!(std::fs::read(dir.join(LOG)).unwrap(), b"");
+    let _ = std::fs::remove_dir_all(&dir);
+}

crates/engine/src/availability.rs

@@ -0,0 +1,215 @@
+//! Is a file there? — answered without blocking the caller.
+//!
+//! On a sleeping NAS, a dropped share or a USB drive spinning up, one `stat` can take as long as
+//! the OS or SMB timeout. The UI asks about files every frame (grid cells, the Info panel, the
+//! Missing Photos view), so in the app the answers come from a cache that a worker thread fills
+//! ([`Availability::run_in_background`]): an unknown file is reported as `None` ("assume it is
+//! there"; the render worker finds out if it isn't), known answers are rechecked after
+//! [`RECHECK`]. Everywhere else (CLI, MCP, tests) the default is synchronous: every question is a
+//! fresh check, as before.
+
+use std::collections::{HashMap, HashSet, VecDeque};
+use std::sync::{Arc, Mutex, MutexGuard, PoisonError};
+use std::time::Duration;
+
+/// Checks whether a path exists (injectable: tests use a slow one).
+pub type ExistsProbe = Arc<dyn Fn(&str) -> bool + Send + Sync>;
+/// Called (from the worker) when an answer changed, e.g. to repaint the UI.
+pub type Waker = Arc<dyn Fn() + Send + Sync>;
+
+/// How long a cached answer is used before it is checked again (it is still returned meanwhile).
+pub const RECHECK: Duration = Duration::from_secs(15);
+
+fn fs_exists(path: &str) -> bool {
+    // the browser build has no file system: its originals are always "there"
+    cfg!(target_arch = "wasm32") || std::path::Path::new(path).exists()
+}
+
+#[derive(Default)]
+struct State {
+    /// path → (exists, when checked)
+    known: HashMap<String, (bool, std::time::Instant)>,
+    queue: VecDeque<String>,
+    queued: HashSet<String>,
+    worker: bool,
+    /// Bumped whenever an answer changes (callers recompute what depends on it).
+    generation: u64,
+}
+
+fn lock(m: &Mutex<State>) -> MutexGuard<'_, State> {
+    m.lock().unwrap_or_else(PoisonError::into_inner)
+}
+
+/// File availability, synchronous or cached + background-checked. Cloning shares the cache.
+#[derive(Clone)]
+pub struct Availability {
+    probe: ExistsProbe,
+    background: Option<Waker>,
+    state: Arc<Mutex<State>>,
+}
+
+impl Default for Availability {
+    fn default() -> Self {
+        Self { probe: Arc::new(fs_exists), background: None, state: Arc::default() }
+    }
+}
+
+impl std::fmt::Debug for Availability {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Availability").field("background", &self.background.is_some()).finish()
+    }
+}
+
+impl Availability {
+    /// Replace the existence check (tests: a slow or counting probe). Forgets cached answers.
+    pub fn set_probe(&mut self, probe: ExistsProbe) {
+        self.probe = probe;
+        let mut st = lock(&self.state);
+        st.known.clear();
+        st.generation += 1;
+    }
+
+    /// Answer from the cache and check on a worker thread from now on; `wake` runs when an
+    /// answer changed. No effect in the browser build (no threads, no file system).
+    pub fn run_in_background(&mut self, wake: Waker) {
+        if cfg!(target_arch = "wasm32") {
+            return;
+        }
+        self.background = Some(wake);
+    }
+
+    /// The existence check itself (blocking: for worker threads, e.g. the Rename preview's).
+    pub fn probe(&self) -> ExistsProbe {
+        self.probe.clone()
+    }
+
+    pub fn is_background(&self) -> bool {
+        self.background.is_some()
+    }
+
+    /// Does `path` exist? Synchronous mode: checked now. Background mode: the cached answer
+    /// (`None` while unknown); unknown or stale answers are queued for the worker.
+    pub fn exists(&self, path: &str) -> Option<bool> {
+        let Some(wake) = &self.background else {
+            return Some((self.probe)(path));
+        };
+        let mut st = lock(&self.state);
+        let now = std::time::Instant::now();
+        let cached = st.known.get(path).copied();
+        if cached.is_none_or(|(_, at)| now.saturating_duration_since(at) >= RECHECK) && !st.queued.contains(path) {
+            st.queued.insert(path.to_string());
+            st.queue.push_back(path.to_string());
+            if !st.worker {
+                st.worker = true;
+                drop(st);
+                self.spawn_worker(wake.clone());
+                return cached.map(|c| c.0);
+            }
+        }
+        cached.map(|c| c.0)
+    }
+
+    /// Known to be missing (unknown counts as present).
+    pub fn is_offline(&self, path: &str) -> bool {
+        self.exists(path) == Some(false)
+    }
+
+    /// Changes whenever a cached answer changes.
+    pub fn generation(&self) -> u64 {
+        lock(&self.state).generation
+    }
+
+    /// Paths waiting for the worker.
+    pub fn pending(&self) -> usize {
+        lock(&self.state).queue.len()
+    }
+
+    fn spawn_worker(&self, wake: Waker) {
+        let (state, probe) = (self.state.clone(), self.probe.clone());
+        let started = std::thread::Builder::new().name("lc-availability".into()).spawn(move || {
+            loop {
+                let path = {
+                    let mut st = lock(&state);
+                    let Some(p) = st.queue.pop_front() else {
+                        st.worker = false;
+                        return;
+                    };
+                    p
+                };
+                let ok = probe(&path);
+                let changed = {
+                    let mut st = lock(&state);
+                    st.queued.remove(&path);
+                    let prev = st.known.insert(path, (ok, std::time::Instant::now()));
+                    let changed = prev.map(|p| p.0) != Some(ok);
+                    if changed {
+                        st.generation += 1;
+                    }
+                    changed
+                };
+                if changed {
+                    wake();
+                }
+            }
+        });
+        if started.is_err() {
+            // try again on the next question
+            lock(&self.state).worker = false;
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::sync::atomic::{AtomicUsize, Ordering};
+
+    #[test]
+    fn synchronous_by_default() {
+        let mut a = Availability::default();
+        let n = Arc::new(AtomicUsize::new(0));
+        let c = n.clone();
+        a.set_probe(Arc::new(move |p| {
+            c.fetch_add(1, Ordering::SeqCst);
+            p == "here"
+        }));
+        assert_eq!(a.exists("here"), Some(true));
+        assert_eq!(a.exists("gone"), Some(false));
+        assert_eq!(a.exists("gone"), Some(false));
+        assert_eq!(n.load(Ordering::SeqCst), 3, "every question is a fresh check");
+    }
+
+    #[test]
+    fn background_answers_from_the_cache_without_blocking() {
+        let mut a = Availability::default();
+        let caller = std::thread::current().id();
+        let on_caller = Arc::new(AtomicUsize::new(0));
+        let c = on_caller.clone();
+        a.set_probe(Arc::new(move |p| {
+            if std::thread::current().id() == caller {
+                c.fetch_add(1, Ordering::SeqCst);
+            }
+            std::thread::sleep(Duration::from_millis(200)); // a sleeping NAS
+            p == "here"
+        }));
+        let woke = Arc::new(AtomicUsize::new(0));
+        let w = woke.clone();
+        a.run_in_background(Arc::new(move || {
+            w.fetch_add(1, Ordering::SeqCst);
+        }));
+        let t0 = std::time::Instant::now();
+        assert_eq!(a.exists("here"), None, "unknown at first");
+        assert_eq!(a.exists("gone"), None);
+        assert!(t0.elapsed() < Duration::from_millis(150), "the caller never waits for the probe");
+        let deadline = std::time::Instant::now() + Duration::from_secs(20);
+        while (a.exists("here").is_none() || a.exists("gone").is_none()) && std::time::Instant::now() < deadline {
+            std::thread::sleep(Duration::from_millis(10));
+        }
+        assert_eq!(a.exists("here"), Some(true));
+        assert_eq!(a.exists("gone"), Some(false));
+        assert!(a.is_offline("gone") && !a.is_offline("here") && !a.is_offline("unknown"));
+        assert_eq!(on_caller.load(Ordering::SeqCst), 0, "never probed on the calling thread");
+        assert!(woke.load(Ordering::SeqCst) >= 2);
+        assert!(a.generation() >= 2);
+    }
+}

crates/engine/src/camera_preview.rs

@@ -0,0 +1,272 @@
+//! Estimate an ARW starting look from its own JPEG. Colour and luminance are fitted separately;
+//! the JPEG supplies correspondences only, never output pixels or a replacement for RAW editing.
+use lightcraft_color::{Mat3, luminance_2020};
+use lightcraft_pipeline::tone::{CameraTone, ToneMap};
+use lightcraft_raster::{
+    Rgb32f,
+    resample::{Filter, fit},
+};
+use lightcraft_raw::{RawImage, color::CameraTransform};
+
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct CameraLook {
+    pub matrix: Mat3,
+    pub tone: CameraTone,
+}
+
+pub(crate) fn fit_preview(raw: &RawImage, bytes: &[u8], transform: &CameraTransform) -> Option<CameraLook> {
+    if !transform.matrix_is_fallback || raw.format != lightcraft_raw::RawFormat::Arw {
+        return None;
+    }
+    let jpeg = lightcraft_raw::embedded_preview(bytes)?;
+    let decoded = lightcraft_codecs::decode(&jpeg, lightcraft_codecs::DecodeOptions { max_size: Some((384, 384)), max_pixels: 64_000_000 }).ok()?;
+    let reference = decoded.to_working();
+    let crop = raw.crop.clipped(raw.active_area.width, raw.active_area.height);
+    if crop.width == 0 || crop.height == 0 || reference.width == 0 || reference.height == 0 {
+        return None;
+    }
+    let aspect = crop.width as f64 / crop.height as f64;
+    if (reference.width as f64 / reference.height as f64 / aspect - 1.0).abs() > 0.02 {
+        return None;
+    }
+    // Fixed, bounded proxy: the selected look cannot depend on thumbnail/export resolution.
+    let k = (crop.width.max(crop.height).div_ceil(384).max(2)).div_ceil(2) * 2;
+    let sensor = raw.develop_binned(k, 0.99).ok()??;
+    let mut sensor = fit(&sensor, 96, 96, Filter::Box);
+    let reference = fit(&reference, sensor.width, sensor.height, Filter::Box);
+    let gain = 2f32.powf(transform.baseline_exposure as f32);
+    sensor.map_in_place(|p| transform.matrix.apply_f32(std::array::from_fn(|i| p[i] * transform.wb[i] * gain)));
+    let look = fit_pairs(&sensor, &reference)?;
+    if lightcraft_pipeline::profiling() {
+        eprintln!("[profile] ARW camera look: {:?}, {:?}", look.matrix.0, look.tone);
+    }
+    Some(look)
+}
+
+/// A fit must cut the held-out squared error to below this share of the fallback's.
+const MIN_IMPROVEMENT: f64 = 0.7;
+/// ...and stay within this per-channel RMS of the camera JPEG (linear display values). On public
+/// raw.pixls.us samples (eight Sony bodies) good fits that still beat the fallback 1.5–3× landed
+/// at 0.065–0.093 (camera local tone, vignetting and lens processing that a global matrix + curve
+/// cannot follow): visibly better renders that 0.055 rejected.
+const MAX_HOLDOUT_RMS: f64 = 0.10;
+
+fn luma(p: [f64; 3]) -> f64 {
+    p[0] * 0.2627 + p[1] * 0.6780 + p[2] * 0.0593
+}
+
+fn displayed(scene: [f64; 3], tone: &ToneMap) -> [f64; 3] {
+    let scene = scene.map(|v| v.max(0.0));
+    let y = luma(scene);
+    if y <= 0.0 {
+        return [0.0; 3];
+    }
+    scene.map(|v| v * f64::from(tone.apply(y as f32)) / y)
+}
+
+fn fit_pairs(sensor: &Rgb32f, reference: &Rgb32f) -> Option<CameraLook> {
+    if (sensor.width, sensor.height) != (reference.width, reference.height) || sensor.data.len() != reference.data.len() {
+        return None;
+    }
+    let mut pairs = Vec::new();
+    let mut colour = 0;
+    for (input, output) in sensor.data.iter().zip(&reference.data) {
+        let y = luminance_2020(*output);
+        if !input.iter().all(|v| v.is_finite() && *v > 0.001 && *v < 1.5)
+            || !output.iter().all(|v| v.is_finite() && *v > 0.004 && *v < 0.98)
+            || !(0.015..0.85).contains(&y)
+        {
+            continue;
+        }
+        let min = output.iter().copied().fold(f32::INFINITY, f32::min);
+        let max = output.iter().copied().fold(0.0, f32::max);
+        colour += usize::from(max - min > 0.05);
+        pairs.push((input.map(f64::from), output.map(f64::from)));
+    }
+    if pairs.len() < 256 || colour < pairs.len() / 20 {
+        return None;
+    }
+    let mut gram = [[0.0; 3]; 3];
+    let mut cross = [[0.0; 3]; 3];
+    for (i, (x, y)) in pairs.iter().enumerate() {
+        if i % 3 == 0 {
+            continue;
+        }
+        let (lx, ly) = (luma(*x), luma(*y));
+        for row in 0..3 {
+            for col in 0..3 {
+                // Normalising by luminance prevents a camera S-curve from corrupting colour.
+                gram[row][col] += x[row] * x[col] / (lx * lx);
+                cross[row][col] += y[row] * x[col] / (ly * lx);
+            }
+        }
+    }
+    let trace: f64 = (0..3).map(|i| gram[i][i]).sum();
+    let inverse = Mat3(gram).inverse()?;
+    let condition = trace * (0..3).map(|i| inverse.0[i][i].abs()).sum::<f64>();
+    if trace <= 0.0 || !condition.is_finite() || condition > 1e6 {
+        return None;
+    }
+    let regularization = trace * 1e-4;
+    for i in 0..3 {
+        gram[i][i] += regularization;
+        cross[i][i] += regularization;
+    }
+    let matrix = Mat3(cross).mul(&Mat3(gram).inverse()?);
+    if !matrix.0.iter().flatten().all(|v| v.is_finite() && v.abs() < 8.0) {
+        return None;
+    }
+    let tone_pairs: Vec<_> =
+        pairs.iter().enumerate().filter(|(i, _)| i % 3 != 0).map(|(_, (x, y))| (luma(matrix.apply(*x).map(|v| v.max(0.0))), luma(*y))).collect();
+    let curve = fit_tone(tone_pairs)?;
+    let tone = ToneMap::camera(&curve, 0.0, 0.0, 0.0);
+    let original_tone = ToneMap::new(0.0, 0.0, 0.0);
+    let mut before = 0.0;
+    let mut after = 0.0;
+    let mut samples = 0;
+    for (i, (x, target)) in pairs.iter().enumerate() {
+        if i % 3 != 0 {
+            continue;
+        }
+        let corrected = displayed(matrix.apply(*x), &tone);
+        let original = displayed(*x, &original_tone);
+        for c in 0..3 {
+            before += (original[c] - target[c]).powi(2);
+            after += (corrected[c] - target[c]).powi(2);
+            samples += 1;
+        }
+    }
+    if lightcraft_pipeline::profiling() {
+        eprintln!("[profile] ARW holdout RMS {:.5} -> {:.5} ({samples} channels)", (before / samples as f64).sqrt(), (after / samples as f64).sqrt());
+    }
+    if !after.is_finite() || samples == 0 || after >= before * MIN_IMPROVEMENT || after / samples as f64 > MAX_HOLDOUT_RMS.powi(2) {
+        return None;
+    }
+    Some(CameraLook { matrix, tone: curve })
+}
+
+fn median(values: &mut [f64]) -> Option<f64> {
+    values.sort_by(f64::total_cmp);
+    values.get(values.len() / 2).copied()
+}
+
+fn fit_tone(mut pairs: Vec<(f64, f64)>) -> Option<CameraTone> {
+    if pairs.len() < 128 || !pairs.iter().all(|(x, y)| x.is_finite() && *x > 0.0 && y.is_finite()) {
+        return None;
+    }
+    pairs.sort_by(|a, b| a.0.total_cmp(&b.0));
+    let mut knots = [[0.0; 2]; 32];
+    for (i, knot) in knots.iter_mut().enumerate() {
+        let bin = pairs.get(i * pairs.len() / 32..(i + 1) * pairs.len() / 32)?;
+        let mut xs: Vec<_> = bin.iter().map(|p| p.0).collect();
+        let mut ys: Vec<_> = bin.iter().map(|p| p.1).collect();
+        *knot = [median(&mut xs)? as f32, median(&mut ys)? as f32];
+    }
+    if knots[31][0] < knots[0][0] * 1.5 {
+        return None;
+    }
+    // Pool adjacent violating bins (isotonic regression): no reversals or arbitrary polynomial.
+    let mut blocks: Vec<(f32, usize)> = Vec::new();
+    for knot in knots {
+        blocks.push((knot[1], 1));
+        while blocks.len() >= 2 {
+            let (a, an) = *blocks.get(blocks.len() - 2)?;
+            let (b, bn) = *blocks.last()?;
+            if a <= b {
+                break;
+            }
+            blocks.truncate(blocks.len() - 2);
+            blocks.push(((a * an as f32 + b * bn as f32) / (an + bn) as f32, an + bn));
+        }
+    }
+    let mut i = 0;
+    for (y, n) in blocks {
+        for knot in knots.get_mut(i..i + n)? {
+            knot[1] = y;
+        }
+        i += n;
+    }
+    CameraTone::new(knots)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn separates_nonlinear_tone_from_colour_and_keeps_sensor_headroom() {
+        let known = Mat3([[1.8, -0.4, -0.1], [-0.2, 1.5, -0.1], [-0.05, -0.3, 1.7]]);
+        let mut sensor = Rgb32f::new(64, 64);
+        let mut reference = sensor.clone();
+        for (i, (src, dst)) in sensor.data.iter_mut().zip(&mut reference.data).enumerate() {
+            let ev = 0.05 + (i % 31) as f32 * 0.017;
+            *src = [ev * (0.8 + (i % 11) as f32 * 0.025), ev, ev * (0.8 + (i % 17) as f32 * 0.014)];
+            let p = known.apply_f32(*src);
+            let y = luminance_2020(p);
+            *dst = p.map(|v| v * (1.0 - (-2.5 * y).exp()) / y);
+        }
+        let original = sensor.clone();
+        let fit = fit_pairs(&sensor, &reference).unwrap();
+        assert_eq!(sensor.data, original.data);
+        let tone = ToneMap::camera(&fit.tone, 0.0, 0.0, 0.0);
+        let error: f64 = sensor
+            .data
+            .iter()
+            .zip(&reference.data)
+            .map(|(x, y)| {
+                let p = displayed(fit.matrix.apply(x.map(f64::from)), &tone);
+                (0..3).map(|c| (p[c] - f64::from(y[c])).powi(2)).sum::<f64>() / 3.0
+            })
+            .sum::<f64>()
+            / sensor.data.len() as f64;
+        assert!(error.sqrt() < 0.025, "{error}");
+        // The colour transform is homogeneous; tone mapping happens only after exposure.
+        let p = fit.matrix.apply([2.0, 2.0, 2.0]);
+        assert!(luma(p) > 1.0);
+        assert!(tone.apply(0.2) < tone.apply(0.4));
+    }
+    #[test]
+    fn accepts_a_much_better_fit_despite_local_camera_processing() {
+        // The camera JPEG departs from any global matrix + curve (local tone, vignetting): ±0.12
+        // per-pixel deviations, ~0.07 RMS. The fit is still far closer than the fallback.
+        let known = Mat3([[1.8, -0.4, -0.1], [-0.2, 1.5, -0.1], [-0.05, -0.3, 1.7]]);
+        let mut sensor = Rgb32f::new(64, 64);
+        let mut reference = sensor.clone();
+        let mut seed = 0x2545_f491_u32;
+        for (i, (src, dst)) in sensor.data.iter_mut().zip(&mut reference.data).enumerate() {
+            let ev = 0.05 + (i % 31) as f32 * 0.017;
+            *src = [ev * (0.8 + (i % 11) as f32 * 0.025), ev, ev * (0.8 + (i % 17) as f32 * 0.014)];
+            let p = known.apply_f32(*src);
+            let y = luminance_2020(p);
+            *dst = p.map(|v| {
+                seed ^= seed << 13;
+                seed ^= seed >> 17;
+                seed ^= seed << 5;
+                let noise = (seed % 2001) as f32 / 1000.0 - 1.0;
+                (v * (1.0 - (-2.5 * y).exp()) / y + 0.12 * noise).clamp(0.005, 0.97)
+            });
+        }
+        assert!(fit_pairs(&sensor, &reference).is_some());
+    }
+
+    #[test]
+    fn rejects_monochrome_invalid_and_unrelated_previews() {
+        let mut sensor = Rgb32f::new(32, 32);
+        let mut reference = sensor.clone();
+        for (i, p) in sensor.data.iter_mut().enumerate() {
+            *p = [0.1 + (i % 13) as f32 * 0.02, 0.15, 0.1];
+        }
+        reference.data.fill([0.2; 3]);
+        assert!(fit_pairs(&sensor, &reference).is_none());
+        reference.data.fill([f32::NAN; 3]);
+        assert!(fit_pairs(&sensor, &reference).is_none());
+        for (i, (src, dst)) in sensor.data.iter_mut().zip(&mut reference.data).enumerate() {
+            *src = [0.04 + (i % 11) as f32 * 0.02, 0.05 + (i % 17) as f32 * 0.01, 0.03 + (i % 23) as f32 * 0.01];
+            *dst = [0.05 + (i % 7) as f32 * 0.07, 0.05 + (i % 19) as f32 * 0.02, 0.05 + (i % 29) as f32 * 0.01];
+        }
+        assert!(fit_pairs(&sensor, &reference).is_none());
+        sensor.data.fill([0.1, 0.15, 0.12]);
+        assert!(fit_pairs(&sensor, &reference).is_none());
+        reference.data.truncate(8);
+        assert!(fit_pairs(&sensor, &reference).is_none());
+    }
+}

crates/engine/src/cmd/browse.rs

@@ -166,7 +166,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Rename Folder",
             [],
             None,
-            "{path, name} — rename a folder on disk (its files and sidecars go along) and relink the photos in it; not an undo step → {path, relinked}",
+            "{path, name} — rename a folder on disk (its files and sidecars go along) and relink the photos in it; one undo step (undo renames it back, refused if the old name is taken) → {path, relinked}",
             always,
             |s, p| {
                 let from = str_param(p, "path").ok_or_else(|| bad("folder.rename", "missing path"))?.trim_end_matches(['/', '\\']).to_string();
@@ -184,7 +184,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Move Folder",
             [],
             None,
-            "{path, into: destination folder} — move a folder on disk into another and relink the photos in it; not an undo step → {path, relinked}",
+            "{path, into: destination folder} — move a folder on disk into another and relink the photos in it; one undo step (undo moves it back, refused if the old place is taken) → {path, relinked}",
             always,
             |s, p| {
                 let from = str_param(p, "path").ok_or_else(|| bad("folder.move", "missing path"))?.trim_end_matches(['/', '\\']).to_string();
@@ -217,58 +217,85 @@ pub fn specs() -> Vec<CommandSpec> {
     ]
 }
 
-/// Rename or move a folder on disk (everything in it goes along, sidecars included) and relink
-/// the photos inside. Like a rename in the file manager it is not an undo step: undoing would
-/// point the photos back at a folder that no longer exists.
-pub(crate) fn move_folder(s: &mut crate::Session, from: &str, to: &str) -> std::result::Result<usize, String> {
-    use std::path::Path;
+/// Rename `from` to `to` on disk (a folder; everything in it goes along). Never overwrites:
+/// refused when `to` exists (a case-only rename on a case-insensitive file system goes through
+/// a temporary name). Missing parents of `to` are created.
+pub(crate) fn rename_folder_on_disk(from: &str, to: &str) -> std::result::Result<(), String> {
     let (src, dst) = (Path::new(from), Path::new(to));
     if !src.is_dir() {
-        return Err(format!("{from} is not a folder"));
+        return Err(format!("{from} is not a folder (moved or deleted?)"));
     }
-    if dst.exists() {
+    let case_only = from != to && from.to_lowercase() == to.to_lowercase();
+    if dst.exists() && !case_only {
         return Err(format!("{to} already exists"));
     }
     if dst.starts_with(src) {
         return Err("a folder can't move into itself".into());
     }
-    if s.library.as_ref().is_some_and(|l| l.dir.starts_with(src) || src.starts_with(&l.dir)) {
-        return Err("the library's own folders can't be moved here".into());
-    }
     if let Some(parent) = dst.parent() {
         std::fs::create_dir_all(parent).map_err(|e| format!("{}: {e}", parent.display()))?;
     }
-    std::fs::rename(src, dst).map_err(|e| format!("{from} → {to}: {e}"))?;
-    let mut n = 0;
-    let ops: Vec<lightcraft_catalog::Op> = s
+    if case_only {
+        let tmp = src.with_file_name(format!(".lc-rename-{}", std::process::id()));
+        if tmp.exists() {
+            return Err(format!("{} already exists", tmp.display()));
+        }
+        std::fs::rename(src, &tmp).map_err(|e| format!("{from} → {to}: {e}"))?;
+        return std::fs::rename(&tmp, dst).map_err(|e| {
+            let _ = std::fs::rename(&tmp, src);
+            format!("{from} → {to}: {e}")
+        });
+    }
+    std::fs::rename(src, dst).map_err(|e| format!("{from} → {to}: {e}"))
+}
+
+/// After a folder moved from `from` to `to`: a browsed folder at or below it follows.
+pub(crate) fn follow_folder(s: &mut Session, from: &str, to: &str) {
+    if let Some(b) = &mut s.browse
+        && let Ok(rel) = Path::new(&b.path).strip_prefix(from)
+    {
+        b.path = Path::new(to).join(rel).to_string_lossy().to_string();
+        let f = b.path.clone();
+        s.filter.folder = Some(f);
+    }
+}
+
+/// Rename or move a folder on disk (everything in it goes along, sidecars included) and relink
+/// the photos inside, as one undo step: undo renames the folder back and restores the photos'
+/// paths, redo repeats the move — each refused (and reported) when the destination is taken.
+pub(crate) fn move_folder(s: &mut Session, from: &str, to: &str) -> std::result::Result<usize, String> {
+    let (src, dst) = (Path::new(from), Path::new(to));
+    if !src.is_dir() {
+        return Err(format!("{from} is not a folder"));
+    }
+    if s.library.as_ref().is_some_and(|l| l.dir.starts_with(src) || src.starts_with(&l.dir)) {
+        return Err("the library's own folders can't be moved here".into());
+    }
+    rename_folder_on_disk(from, to)?;
+    let ops: Vec<Op> = s
         .catalog
         .photos()
         .filter_map(|p| match &p.source {
             lightcraft_catalog::Source::File { path } => Path::new(path).strip_prefix(src).ok().map(|rel| (p.id, p.file_name.clone(), dst.join(rel))),
             _ => None,
         })
-        .map(|(id, file_name, np)| {
-            n += 1;
-            lightcraft_catalog::Op::Relink {
-                id,
-                file_name,
-                source: lightcraft_catalog::Source::File { path: np.to_string_lossy().to_string() },
-                format: None,
-            }
+        .map(|(id, file_name, np)| Op::Relink {
+            id,
+            file_name,
+            source: lightcraft_catalog::Source::File { path: np.to_string_lossy().to_string() },
+            format: None,
         })
         .collect();
-    for op in ops {
-        if s.catalog.apply(op.clone()).is_ok() {
-            s.pending_log.push(op);
-        }
-    }
-    // a browsed folder at or below it follows
-    if let Some(b) = &mut s.browse
-        && let Ok(rel) = Path::new(&b.path).strip_prefix(src)
-    {
-        b.path = dst.join(rel).to_string_lossy().to_string();
-        let f = b.path.clone();
-        s.filter.folder = Some(f);
+    let n = ops.len();
+    let name = Path::new(to).file_name().map(|n| n.to_string_lossy().to_string()).unwrap_or_default();
+    let renamed = src.parent() == dst.parent();
+    let label = if renamed { format!("Rename Folder to “{name}”") } else { format!("Move Folder “{name}”") };
+    let folder = crate::FolderMove { from: to.to_string(), to: from.to_string() };
+    if let Err(e) = s.commit_with_folder(&label, Op::Batch { ops }, folder) {
+        // the catalog didn't take it: put the folder back where the photos still point
+        let back = rename_folder_on_disk(to, from).err().map(|b| format!("; moving it back failed too: {b}")).unwrap_or_default();
+        return Err(format!("{e}{back}"));
     }
+    follow_folder(s, from, to);
     Ok(n)
 }

crates/engine/src/cmd/color.rs

@@ -26,7 +26,7 @@ const PROBE_EDGE: usize = 384;
 pub(crate) fn probe(s: &mut Session, c: &str, x: f64, y: f64, neutral: impl FnOnce(&mut DevelopSettings)) -> Result<[f32; 3]> {
     let id = s.active().ok_or_else(|| bad(c, "no active photo"))?;
     let src = s.source_now(id, SourceLevel::Thumb).map_err(|e| bad(c, e))?;
-    let info = s.catalog.photo(id).map(|p| crate::media::source_info(p)).unwrap_or_default();
+    let info = s.source_info(id);
     let mut d = (*s.develop_of(id).unwrap_or_default()).clone();
     neutral(&mut d);
     let req = lightcraft_pipeline::RenderRequest::fit(PROBE_EDGE, PROBE_EDGE);

crates/engine/src/cmd/convert.rs

@@ -10,24 +10,28 @@ use serde_json::{Value, json};
 use super::{CommandSpec, bad, cmd, has_active, has_selection};
 use crate::{Result, Session};
 
-/// A free `<stem>.dng` (then `<stem>-2.dng`…) next to `path`.
-fn dng_path(path: &str) -> String {
+/// `<stem>.dng`, then `<stem>-2.dng`, `<stem>-3.dng`… next to `path`.
+fn dng_names(path: &str) -> impl Iterator<Item = std::path::PathBuf> {
     let p = Path::new(path);
-    let dir = p.parent().unwrap_or(Path::new(""));
+    let dir = p.parent().unwrap_or(Path::new("")).to_path_buf();
     let stem = p.file_stem().map(|s| s.to_string_lossy().to_string()).unwrap_or_else(|| "photo".into());
-    let mut out = dir.join(format!("{stem}.dng"));
-    let mut n = 2;
-    while out.exists() {
-        out = dir.join(format!("{stem}-{n}.dng"));
-        n += 1;
-    }
-    out.to_string_lossy().to_string()
+    (1u64..).map(move |n| if n == 1 { dir.join(format!("{stem}.dng")) } else { dir.join(format!("{stem}-{n}.dng")) })
 }
 
-/// Write the DNG for raw file `path` (develop settings in `packet`); returns the new path.
-/// An empty `packet` writes no XMP.
+/// Write the DNG for raw file `path` (develop settings in `packet`) next to it under a free name;
+/// returns the new path. An empty `packet` writes no XMP.
+///
+/// The DNG is checked before anyone relies on it (Convert to DNG relinks the photo to it, Copy as
+/// DNG deletes the raw copy): the encoded file must decode to the same raw data, and it is
+/// written to a temp file, synced, read back identical and only then given its name — never
+/// replacing an existing file. On any failure no DNG is left behind and the raw stays in use.
 pub(crate) fn write_dng_for(s: &Session, path: &str, packet: String) -> std::result::Result<String, String> {
-    let bytes = match &s.media.file_bytes {
+    write_dng_with(s.media.file_bytes.as_ref(), path, packet)
+}
+
+/// [`write_dng_for`] without the session (imports convert on a worker thread).
+pub(crate) fn write_dng_with(file_bytes: Option<&crate::merge::ByteReader>, path: &str, packet: String) -> std::result::Result<String, String> {
+    let bytes = match file_bytes {
         Some(r) => r(path)?,
         None => std::fs::read(path).map_err(|e| format!("{path}: {e}"))?,
     };
@@ -35,9 +39,21 @@ pub(crate) fn write_dng_for(s: &Session, path: &str, packet: String) -> std::res
     drop(bytes);
     let dng = lightcraft_raw::write_dng(&raw, &lightcraft_raw::DngWriteOptions { xmp: (!packet.is_empty()).then_some(packet), ..Default::default() })
         .map_err(|e| e.to_string())?;
-    let out = dng_path(path);
-    std::fs::write(&out, dng).map_err(|e| format!("{out}: {e}"))?;
-    Ok(out)
+    let back = lightcraft_raw::decode(&dng).map_err(|e| format!("{path}: the DNG written for it doesn't decode ({e}); the raw is kept"))?;
+    let same = match (&back.data, &raw.data) {
+        (lightcraft_raw::RawData::U16(a), lightcraft_raw::RawData::U16(b)) => a == b,
+        (lightcraft_raw::RawData::F32(a), lightcraft_raw::RawData::F32(b)) => {
+            a.len() == b.len() && a.iter().zip(b).all(|(x, y)| x.to_bits() == y.to_bits())
+        }
+        _ => false,
+    };
+    if (back.width, back.height, back.cpp) != (raw.width, raw.height, raw.cpp) || !same {
+        return Err(format!("{path}: the DNG written for it doesn't hold the same raw data; the raw is kept"));
+    }
+    drop((raw, back));
+    let out = lightcraft_catalog::safe_file::write_new_unique(&mut dng_names(path), &dng)
+        .map_err(|e| format!("{path}: could not write its DNG ({e}); the raw is kept"))?;
+    Ok(out.to_string_lossy().to_string())
 }
 
 fn convert(s: &mut Session, p: &Value) -> Result<Value> {

crates/engine/src/cmd/develop.rs

@@ -98,7 +98,11 @@ pub fn specs() -> Vec<CommandSpec> {
                     }
                 }
                 let label = if vals.len() == 1 { controls::find(&vals[0].0).map(|c| c.label).unwrap_or("Edit").to_string() } else { "Edit".into() };
-                let apply = |d: &mut DevelopSettings| {
+                let apply = |d: &mut DevelopSettings, info: &lightcraft_pipeline::SourceInfo| {
+                    if d.wb.mode == WbMode::AsShot && vals.iter().any(|(k, _)| k == "wb.temp" || k == "wb.tint") {
+                        d.wb.temp = info.as_shot_temp;
+                        d.wb.tint = info.as_shot_tint;
+                    }
                     for (k, v) in &vals {
                         controls::set(d, k, *v);
                         if k == "wb.temp" || k == "wb.tint" {
@@ -113,15 +117,18 @@ pub fn specs() -> Vec<CommandSpec> {
                         .filter_map(|id| s.develop_of(*id).map(|d| (*id, d)))
                         .filter_map(|(id, d)| {
                             let mut d = (*d).clone();
-                            apply(&mut d);
+                            let info = s.source_info(id);
+                            apply(&mut d, &info);
                             s.develop_op(id, d, &label)
                         })
                         .collect();
                     s.commit(&label, Op::Batch { ops })?;
                     return ok();
                 }
+                let id = active(s, "develop.set")?;
+                let info = s.source_info(id);
                 edit(s, "develop.set", &label, |d| {
-                    apply(d);
+                    apply(d, &info);
                     Ok(())
                 })
             }
@@ -130,7 +137,15 @@ pub fn specs() -> Vec<CommandSpec> {
             let c = str_param(p, "control").ok_or_else(|| bad("develop.adjust", "missing control"))?.to_string();
             let spec = controls::find(&c).ok_or_else(|| bad("develop.adjust", "unknown control"))?;
             let delta = f64_req(p, "delta", "develop.adjust")?;
+            let info = s.source_info(active(s, "develop.adjust")?);
             edit(s, "develop.adjust", spec.label, |d| {
+                if c == "wb.temp" || c == "wb.tint" {
+                    if d.wb.mode == WbMode::AsShot {
+                        d.wb.temp = info.as_shot_temp;
+                        d.wb.tint = info.as_shot_tint;
+                    }
+                    d.wb.mode = WbMode::Custom;
+                }
                 let v = controls::get(d, &c).unwrap_or(spec.default);
                 controls::set(d, &c, v + delta);
                 Ok(())
@@ -149,12 +164,18 @@ pub fn specs() -> Vec<CommandSpec> {
             let ops = ids
                 .iter()
                 .filter_map(|id| s.develop_of(*id).map(|d| (*id, d)))
-                .filter_map(|(id, d)| {
+                .filter_map(|(id, _d)| {
                     // back to the photo's import defaults when a default preset gave it its look
                     let look = s.catalog.photo(id).and_then(|p| p.import_look.clone());
                     let fresh = match look {
                         Some(l) => (*l).clone(),
-                        None => DevelopSettings { wb: lightcraft_develop::WhiteBalance { mode: WbMode::AsShot, ..d.wb }, ..Default::default() },
+                        None => {
+                            let info = s.source_info(id);
+                            DevelopSettings {
+                                wb: lightcraft_develop::WhiteBalance { mode: WbMode::AsShot, temp: info.as_shot_temp, tint: info.as_shot_tint },
+                                ..Default::default()
+                            }
+                        }
                     };
                     s.develop_op(id, fresh, "Reset")
                 })
@@ -203,7 +224,7 @@ pub fn specs() -> Vec<CommandSpec> {
             |s, _| {
                 let id = active(s, "develop.autoBwMix")?;
                 let src = s.source_now(id, SourceLevel::Thumb).map_err(|e| bad("develop.autoBwMix", e))?;
-                let info = s.catalog.photo(id).map(|p| crate::media::source_info(p)).unwrap_or_default();
+                let info = s.source_info(id);
                 let d = s.develop_of(id).unwrap_or_default();
                 let m = lightcraft_pipeline::auto::auto_bw_mix(&src, &info, &d);
                 edit(s, "develop.autoBwMix", "Auto B&W Mix", |d| {
@@ -218,7 +239,7 @@ pub fn specs() -> Vec<CommandSpec> {
         cmd!("develop.auto", "Auto Settings", ["Photo"], Some("Shift+A"), "{}", has_active, |s, _| {
             let id = active(s, "develop.auto")?;
             let src = s.source_now(id, SourceLevel::Thumb).map_err(|e| bad("develop.auto", e))?;
-            let info = s.catalog.photo(id).map(|p| crate::media::source_info(p)).unwrap_or_default();
+            let info = s.source_info(id);
             let d = s.develop_of(id).unwrap_or_default();
             let a = lightcraft_pipeline::auto::auto_tone(&src, &info, &d);
             edit(s, "develop.auto", "Auto", |d| {
@@ -245,7 +266,7 @@ pub fn specs() -> Vec<CommandSpec> {
                 let mode: WbMode =
                     serde_json::from_value(p.get("mode").cloned().unwrap_or(json!("custom"))).map_err(|e| bad("develop.wb", e.to_string()))?;
                 let id = active(s, "develop.wb")?;
-                let info = s.catalog.photo(id).map(|p| crate::media::source_info(p)).unwrap_or_default();
+                let info = s.source_info(id);
                 let (mut t, mut tint) = match mode {
                     WbMode::AsShot => (info.as_shot_temp, info.as_shot_tint),
                     WbMode::Auto => {
@@ -256,7 +277,7 @@ pub fn specs() -> Vec<CommandSpec> {
                         .preset()
                         .map(|(t, ti)| {
                             // presets are relative to daylight for rendered files
-                            if info.raw { (t, ti) } else { (6500.0 * t / 5500.0, ti) }
+                            if info.raw && !info.relative_wb { (t, ti) } else { (6500.0 * t / 5500.0, ti) }
                         })
                         .unwrap_or((info.as_shot_temp, info.as_shot_tint)),
                 };
@@ -277,7 +298,7 @@ pub fn specs() -> Vec<CommandSpec> {
             let (x, y) = (f64_req(p, "x", "develop.wbPick")?, f64_req(p, "y", "develop.wbPick")?);
             let id = active(s, "develop.wbPick")?;
             let src = s.source_now(id, SourceLevel::Thumb).map_err(|e| bad("develop.wbPick", e))?;
-            let info = s.catalog.photo(id).map(|p| crate::media::source_info(p)).unwrap_or_default();
+            let info = s.source_info(id);
             let d = s.develop_of(id).unwrap_or_default();
             // Sample a small neighbourhood in the oriented source.
             let o = src.oriented(d.orientation);
@@ -405,7 +426,7 @@ pub fn specs() -> Vec<CommandSpec> {
             |s, _| {
                 let id = active(s, "crop.autoStraighten")?;
                 let src = s.source_now(id, SourceLevel::Preview).map_err(|e| bad("crop.autoStraighten", e))?;
-                let info = s.catalog.photo(id).map(|p| crate::media::source_info(p)).unwrap_or_default();
+                let info = s.source_info(id);
                 let d = s.develop_of(id).unwrap_or_default();
                 let Some(level) = lightcraft_pipeline::upright::level_degrees(&src, &info, &d) else {
                     return Ok(json!({"changed": false, "reason": "no dominant horizontal or vertical lines"}));
@@ -501,7 +522,7 @@ pub fn specs() -> Vec<CommandSpec> {
                     Upright::Off | Upright::Guided => None,
                     m => {
                         let src = s.source_now(id, SourceLevel::Preview).map_err(|e| bad("geometry.upright", e))?;
-                        let info = s.catalog.photo(id).map(|p| crate::media::source_info(p)).unwrap_or_default();
+                        let info = s.source_info(id);
                         Some(lightcraft_pipeline::upright::auto_transform(&src, &info, &d, m))
                     }
                 };
@@ -657,6 +678,11 @@ pub fn specs() -> Vec<CommandSpec> {
                     .filter_map(|id| s.develop_of(id).map(|d| (id, d)))
                     .filter_map(|(id, d)| {
                         let mut nd = (*d).clone();
+                        if nd.wb.mode == WbMode::AsShot && (ctl == "wb.temp" || ctl == "wb.tint") {
+                            let info = s.source_info(id);
+                            nd.wb.temp = info.as_shot_temp;
+                            nd.wb.tint = info.as_shot_tint;
+                        }
                         let v = controls::get(&nd, &ctl).unwrap_or(spec.default);
                         controls::set(&mut nd, &ctl, v + delta);
                         if ctl == "wb.temp" || ctl == "wb.tint" {

crates/engine/src/cmd/library.rs

@@ -7,6 +7,105 @@ use serde_json::{Value, json};
 use super::{CommandSpec, always, bad, bool_or, cmd, has_active, has_selection, ok, str_param};
 use crate::{LibrarySource, Result, Selection, Session};
 
+/// The auto-import folder's visible files with their sizes (the file-system half of
+/// `library.autoImportScan`; the app lists on a worker thread and passes `listing`).
+pub fn list_auto_import_folder(folder: &str) -> std::result::Result<Vec<(String, u64)>, String> {
+    let rd = std::fs::read_dir(folder).map_err(|e| format!("{folder}: {e}"))?;
+    Ok(rd
+        .flatten()
+        .filter(|e| !e.file_name().to_string_lossy().starts_with('.'))
+        .filter_map(|e| {
+            let m = std::fs::metadata(e.path()).ok()?;
+            m.is_file().then(|| (e.path().to_string_lossy().to_string(), m.len()))
+        })
+        .collect())
+}
+
+/// `library.import`'s params, checked (no file-system calls).
+pub struct ImportRequest {
+    pub paths: Vec<String>,
+    pub opts: crate::import::ImportOptions,
+    pub album: Option<u64>,
+    pub album_name: Option<String>,
+}
+
+/// Parse and check `library.import`'s params (the app's import task runs the import itself, on a
+/// worker thread, with the same options).
+pub fn import_params(s: &Session, p: &Value) -> Result<ImportRequest> {
+    let paths = strs(p, "paths");
+    let mode = match str_param(p, "mode").unwrap_or("add") {
+        "add" => crate::import::ImportMode::Add,
+        "copy" => crate::import::ImportMode::Copy,
+        "move" => crate::import::ImportMode::Move,
+        other => return Err(bad("library.import", format!("unknown mode `{other}` (add|copy|move)"))),
+    };
+    let preset = match str_param(p, "preset").filter(|x| !x.is_empty()) {
+        Some(id) => Some(s.presets.iter().find(|x| x.id == id).cloned().ok_or_else(|| bad("library.import", format!("unknown preset `{id}`")))?),
+        None => None,
+    };
+    let album = p.get("album").and_then(Value::as_u64);
+    if let Some(a) = album
+        && s.catalog.album(AlbumId(a)).is_none_or(|al| al.folder || al.is_smart())
+    {
+        return Err(bad("library.import", "album must be a regular album"));
+    }
+    let organize = match str_param(p, "organize") {
+        Some(o) => crate::import::Organize::parse(o).ok_or_else(|| {
+            bad("library.import", format!("unknown organize `{o}` (date|month|flat, or a folder template like {{date:%Y}}/{{date:%Y%m%d}})"))
+        })?,
+        None => Default::default(),
+    };
+    if let crate::import::Organize::Template(t) = &organize
+        && let Some(e) = crate::rename::folder_template_error(t)
+    {
+        return Err(bad("library.import", e));
+    }
+    let metadata_preset = str_param(p, "metadataPreset").map(str::trim).filter(|n| !n.is_empty()).map(str::to_string);
+    if let Some(n) = &metadata_preset
+        && !s.metadata_presets.iter().any(|m| m.name.eq_ignore_ascii_case(n))
+    {
+        return Err(bad("library.import", format!("unknown metadata preset `{n}`")));
+    }
+    let opts = crate::import::ImportOptions {
+        mode,
+        preset,
+        keywords: strs(p, "keywords"),
+        destination: str_param(p, "destination").map(str::to_string),
+        organize,
+        rename: str_param(p, "rename").map(str::to_string),
+        rename_start: p.get("renameStart").and_then(Value::as_u64).unwrap_or(1) as usize,
+        metadata_preset,
+        convert_dng: bool_or(p, "dng", false),
+        local: bool_or(p, "local", false),
+    };
+    let album_name = str_param(p, "albumName").map(str::trim).filter(|n| !n.is_empty()).map(str::to_string);
+    Ok(ImportRequest { paths, opts, album, album_name })
+}
+
+/// After a batch of an import was committed: the album (a new one named `album_name` when there
+/// is no `album` and something was imported) gets the photos. Returns the report as JSON (with
+/// `album`).
+pub fn import_batch_done(s: &mut Session, report: crate::import::ImportReport, mut album: Option<u64>, album_name: Option<&str>) -> Result<Value> {
+    let mut report = serde_json::to_value(report).unwrap_or_default();
+    let imported: Vec<u64> = report["imported"].as_array().map(|a| a.iter().filter_map(Value::as_u64).collect()).unwrap_or_default();
+    if album.is_none()
+        && let Some(name) = album_name
+        && !imported.is_empty()
+    {
+        let r = s.execute("album.create", &json!({"name": name}))?;
+        album = r["id"].as_u64();
+    }
+    if let Some(a) = album
+        && !imported.is_empty()
+    {
+        // (album.addPhotos wants a selection: the new photos are about to be it)
+        s.selection = Selection::single(PhotoId(imported[0]));
+        s.execute("album.addPhotos", &json!({"id": a, "ids": imported}))?;
+        report["album"] = json!(a);
+    }
+    Ok(report)
+}
+
 fn album_param(p: &Value, key: &str, c: &str) -> Result<AlbumId> {
     p.get(key).and_then(Value::as_u64).map(AlbumId).ok_or_else(|| bad(c, format!("missing album `{key}`")))
 }
@@ -657,9 +756,9 @@ pub fn specs() -> Vec<CommandSpec> {
             "Auto Import Now",
             [],
             None,
-            "{} — add the watched folder's new photos (files the library doesn't have yet; partial / still-copying files wait for the next scan) → {imported, folder}",
+            "{listing?: [[path, size]] (the folder as listed by the caller, e.g. on a worker thread), start?: bool (false: return the `library.import` params as `import` instead of importing)} — add the watched folder's new photos (files the library doesn't have yet; partial / still-copying files wait for the next scan) → {imported, folder, import?}",
             always,
-            |s, _| {
+            |s, p| {
                 let Some(folder) = s.import_defaults.auto_folder.clone() else { return Ok(json!({"imported": [], "folder": null})) };
                 // only files that stopped growing: a file still being written is left for later
                 let known: std::collections::HashSet<String> = s
@@ -670,18 +769,20 @@ pub fn specs() -> Vec<CommandSpec> {
                         _ => None,
                     })
                     .collect();
+                // the folder's files and sizes: listed here, or already listed on a worker thread (the app)
+                let listing: Vec<(String, u64)> = match p.get("listing").and_then(Value::as_array) {
+                    Some(l) => l.iter().filter_map(|e| Some((e.get(0)?.as_str()?.to_string(), e.get(1)?.as_u64()?))).collect(),
+                    None => list_auto_import_folder(&folder).map_err(|e| bad("library.autoImportScan", e))?,
+                };
                 let mut fresh = Vec::new();
-                for e in std::fs::read_dir(&folder).map_err(|e| bad("library.autoImportScan", format!("{folder}: {e}")))?.flatten() {
-                    let path = e.path();
-                    let ps = path.to_string_lossy().to_string();
-                    if !path.is_file() || known.contains(&ps) || path.file_name().is_some_and(|n| n.to_string_lossy().starts_with('.')) {
+                for (ps, size) in listing {
+                    if known.contains(&ps) {
                         continue;
                     }
                     // each file is tried once (a non-photo isn't retried every scan)
                     if s.auto_import_seen.get(&ps) == Some(&u64::MAX) {
                         continue;
                     }
-                    let size = e.metadata().map(|m| m.len()).unwrap_or(0);
                     let seen = s.auto_import_seen.insert(ps.clone(), size);
                     if size > 0 && seen == Some(size) {
                         fresh.push(ps);
@@ -701,6 +802,10 @@ pub fn specs() -> Vec<CommandSpec> {
                 for f in &fresh {
                     s.auto_import_seen.insert(f.clone(), u64::MAX);
                 }
+                if p.get("start").and_then(Value::as_bool) == Some(false) {
+                    // the caller imports them (the app: on a worker thread)
+                    return Ok(json!({"imported": [], "folder": folder, "import": params}));
+                }
                 let sel = s.selection.clone();
                 let r = s.execute("library.import", &params)?;
                 // arriving photos don't take over the selection
@@ -751,79 +856,15 @@ pub fn specs() -> Vec<CommandSpec> {
             "{paths: [file or folder (recursive)], mode?: add|copy|move (add = reference the files in place; copy = into the library's Originals/YYYY/YYYY-MM-DD/; move = as copy, then each original and its XMP sidecars are removed from the source — only after the copy is verified (a hard link on the same volume, else copied, synced and compared byte for byte) and its catalog record is saved; failed, duplicate and unchecked files keep their sources; a taken name gets -1, -2…; undo removes the photos from the library but leaves the files at the destination), destination?: folder for copies / moves, organize?: date (YYYY/YYYY-MM-DD) | month (YYYY/YYYY-MM) | flat | a folder template, e.g. `{date:%Y}/{date:%Y%m%d}` → 2026/20260114 (the template's `/` make the folders, each level expanded with the rename tokens and made a safe folder name: never outside the destination; must be relative, no `..`; a level with missing metadata is `unknown`) — dated by capture time, else the import time, rename?: file-name template for copies, original extension added (tokens: {name} {num} {seq} {seq:N} {date} {date:%Y%m%d} {folder} {camera} {lens} {iso} {rating} {title} {creator} {ext}; photo.renameTokens explains each; blank = keep names), renameStart?: 1, metadataPreset?: name, dng?: bool (copy raws as DNG; copy only), local?: bool (browsing: the photos stay out of the library, like library.browse; not with move), album?: albumId, albumName?: new album, preset?: presetId, keywords?: [..]} → {imported, duplicates, failed, moved?: [{from, to, sidecars?}], kept?: [{path, reason}] (move: sources left in place and why), album?}",
             always,
             |s, p| {
-                let paths = strs(p, "paths");
-                if paths.is_empty() {
+                let req = import_params(s, p)?;
+                if req.paths.is_empty() {
                     return Err(bad("library.import", "no paths"));
                 }
-                let mode = match str_param(p, "mode").unwrap_or("add") {
-                    "add" => crate::import::ImportMode::Add,
-                    "copy" => crate::import::ImportMode::Copy,
-                    "move" => crate::import::ImportMode::Move,
-                    other => return Err(bad("library.import", format!("unknown mode `{other}` (add|copy|move)"))),
-                };
-                let preset = match str_param(p, "preset").filter(|x| !x.is_empty()) {
-                    Some(id) => {
-                        Some(s.presets.iter().find(|x| x.id == id).cloned().ok_or_else(|| bad("library.import", format!("unknown preset `{id}`")))?)
-                    }
-                    None => None,
-                };
-                let mut album = p.get("album").and_then(Value::as_u64);
-                if let Some(a) = album
-                    && s.catalog.album(AlbumId(a)).is_none_or(|al| al.folder || al.is_smart())
-                {
-                    return Err(bad("library.import", "album must be a regular album"));
-                }
-                let organize = match str_param(p, "organize") {
-                    Some(o) => crate::import::Organize::parse(o).ok_or_else(|| {
-                        bad(
-                            "library.import",
-                            format!("unknown organize `{o}` (date|month|flat, or a folder template like {{date:%Y}}/{{date:%Y%m%d}})"),
-                        )
-                    })?,
-                    None => Default::default(),
-                };
-                if let crate::import::Organize::Template(t) = &organize
-                    && let Some(e) = crate::rename::folder_template_error(t)
-                {
-                    return Err(bad("library.import", e));
-                }
-                let metadata_preset = str_param(p, "metadataPreset").map(str::trim).filter(|n| !n.is_empty()).map(str::to_string);
-                if let Some(n) = &metadata_preset
-                    && !s.metadata_presets.iter().any(|m| m.name.eq_ignore_ascii_case(n))
-                {
-                    return Err(bad("library.import", format!("unknown metadata preset `{n}`")));
-                }
-                let opts = crate::import::ImportOptions {
-                    mode,
-                    preset,
-                    keywords: strs(p, "keywords"),
-                    destination: str_param(p, "destination").map(str::to_string),
-                    organize,
-                    rename: str_param(p, "rename").map(str::to_string),
-                    rename_start: p.get("renameStart").and_then(Value::as_u64).unwrap_or(1) as usize,
-                    metadata_preset,
-                    convert_dng: super::bool_or(p, "dng", false),
-                    local: super::bool_or(p, "local", false),
-                };
                 let undo0 = s.undo.len();
-                let mut report = serde_json::to_value(crate::import::import_with(s, &paths, &opts)?).unwrap_or_default();
-                let imported: Vec<u64> = report["imported"].as_array().map(|a| a.iter().filter_map(Value::as_u64).collect()).unwrap_or_default();
-                if album.is_none()
-                    && let Some(name) = str_param(p, "albumName").map(str::trim).filter(|n| !n.is_empty())
-                    && !imported.is_empty()
-                {
-                    let r = s.execute("album.create", &json!({"name": name}))?;
-                    album = r["id"].as_u64();
-                }
-                if let Some(a) = album
-                    && !imported.is_empty()
-                {
-                    // (album.addPhotos wants a selection: the new photos are about to be it)
-                    s.selection = Selection::single(PhotoId(imported[0]));
-                    s.execute("album.addPhotos", &json!({"id": a, "ids": imported}))?;
-                    report["album"] = json!(a);
-                }
+                let report = crate::import::import_with(s, &req.paths, &req.opts)?;
+                let report = import_batch_done(s, report, req.album, req.album_name.as_deref())?;
                 // one undo step for the whole import
+                let imported: Vec<u64> = report["imported"].as_array().map(|a| a.iter().filter_map(Value::as_u64).collect()).unwrap_or_default();
                 let n = s.undo.len().saturating_sub(undo0);
                 s.merge_undo(n, &format!("Add {} Photo{}", imported.len(), if imported.len() == 1 { "" } else { "s" }));
                 if let Some(f) = imported.first() {
@@ -867,6 +908,8 @@ pub fn specs() -> Vec<CommandSpec> {
                 "logRecords": j.log_records(),
                 "logBytes": j.log_bytes(),
                 "lastError": lib.last_error,
+                // settings files that were unreadable or damaged at open (kept, defaults used)
+                "settingsWarnings": lib.settings_warnings,
                 // changes applied in memory whose write failed (retried by every save)
                 "unsavedOps": s.unsaved().map_or(0, |u| u.0),
                 "unsavedError": s.unsaved().map(|u| u.1),

crates/engine/src/cmd/masks.rs

@@ -185,7 +185,7 @@ pub fn specs() -> Vec<CommandSpec> {
                 let add = p.get("add").and_then(Value::as_bool).unwrap_or(false);
                 let id = s.active().ok_or_else(|| bad(c, "no active photo"))?;
                 let src = s.source_now(id, crate::media::SourceLevel::Thumb).map_err(|e| bad(c, e))?;
-                let info = s.catalog.photo(id).map(|p| crate::media::source_info(p)).unwrap_or_default();
+                let info = s.source_info(id);
                 let d = s.develop_of(id).unwrap_or_default();
                 let req = lightcraft_pipeline::RenderRequest::fit(384, 384);
                 let lab = lightcraft_pipeline::color_range_sample(&src, &info, &d, &req, lightcraft_geom::Point::new(x, y))
@@ -646,7 +646,7 @@ fn spots_edit(s: &mut Session, c: &str, label: &str, f: impl FnOnce(&mut Vec<Spo
 /// An automatic source for `spot` on photo `id` (a small proxy of the photo, framed by `d`).
 fn pick_source(s: &mut Session, id: crate::PhotoId, d: &lightcraft_develop::DevelopSettings, spot: &Spot, avoid: Option<Point>) -> Option<Point> {
     let src = s.source_now(id, crate::media::SourceLevel::Thumb).ok()?;
-    let info = crate::media::source_info(s.catalog.photo(id)?);
+    let info = s.source_info(id);
     lightcraft_pipeline::spots::pick_source(&src, &info, d, spot, avoid)
 }
 

crates/engine/src/cmd/missing.rs

@@ -1,8 +1,9 @@
 //! Missing originals: photos whose file is no longer where the library expects it (moved,
 //! renamed, on an unplugged drive), and relinking them — one at a time (`photo.relink`) or by
-//! searching a folder for files with the same name and size (`library.findMissing`).
+//! searching a folder for files with the same name and size, or the same content
+//! (`library.findMissing`).
 
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::path::Path;
 
 use lightcraft_catalog::{Catalog, Op, Photo, PhotoId, Source};
@@ -44,9 +45,10 @@ pub fn missing(s: &Session) -> Vec<(PhotoId, String)> {
 }
 
 /// Whether photo `id` is in scope and its file is gone (the Missing Photos view checks only
-/// the photos its query already narrowed to).
-pub fn is_missing(cat: &Catalog, id: PhotoId) -> bool {
-    !cfg!(target_arch = "wasm32") && cat.photo(id).and_then(|p| checked_path(p)).is_some_and(|f| !Path::new(f).exists())
+/// the photos its query already narrowed to). In the app `avail` answers from its cache (files
+/// not checked yet count as present until the background check finds them gone).
+pub fn is_missing(cat: &Catalog, avail: &crate::availability::Availability, id: PhotoId) -> bool {
+    !cfg!(target_arch = "wasm32") && cat.photo(id).and_then(|p| checked_path(p)).is_some_and(|f| avail.is_offline(f))
 }
 
 fn relink_op(id: PhotoId, path: &str) -> Op {
@@ -83,48 +85,255 @@ fn relink(s: &mut Session, p: &Value) -> Result<Value> {
     Ok(json!({"id": id.0, "path": abs}))
 }
 
-/// Search `folder` (recursively) for each missing photo's file name — and its size when the
-/// library knows it — and relink every match in one undoable step.
-fn find_missing(s: &mut Session, p: &Value) -> Result<Value> {
-    const C: &str = "library.findMissing";
-    let folder = str_param(p, "folder").ok_or_else(|| bad(C, "missing `folder`"))?;
+/// The stored content hash of a photo, without the `:dupN` suffix duplicates get.
+fn stored_hash(p: &Photo) -> Option<&str> {
+    p.content_hash.as_deref().map(|h| h.split(':').next().unwrap_or(h)).filter(|h| !h.is_empty())
+}
+
+/// The content hash of the file at `path` (as import computes it), if it can be read.
+fn file_hash(path: &str) -> Option<String> {
+    std::fs::read(path).ok().map(|b| lightcraft_preview::hash_bytes(&b).to_string())
+}
+
+/// An in-scope photo ([`checked_path`]) as Find Missing Photos sees it: its file, the size and
+/// content hash the library knows (0 / `None` = unknown).
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct FindCandidate {
+    pub id: PhotoId,
+    pub path: String,
+    pub size: u64,
+    pub hash: Option<String>,
+}
+
+/// Every in-scope photo, for [`plan_find_missing`]: the missing ones are looked for, and no
+/// photo's file is used for another. No file-system calls, so the app takes this snapshot on the
+/// UI thread and plans on a worker without holding the session.
+pub fn find_candidates(cat: &Catalog) -> Vec<FindCandidate> {
+    cat.photos()
+        .filter_map(|p| {
+            checked_path(p).map(|f| FindCandidate { id: p.id, path: f.to_string(), size: p.file_size, hash: stored_hash(p).map(str::to_string) })
+        })
+        .collect()
+}
+
+/// How a missing photo's file was recognised.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum MatchBy {
+    /// Same name and size (and content, when the library knows its hash).
+    Name,
+    /// Renamed: same size and content hash.
+    Content,
+}
+
+impl MatchBy {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            MatchBy::Name => "name",
+            MatchBy::Content => "content",
+        }
+    }
+}
+
+/// A missing photo and the file found for it.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct FoundFile {
+    pub id: PhotoId,
+    pub from: String,
+    pub to: String,
+    pub by: MatchBy,
+}
+
+/// A missing photo with several look-alike files (same name and size, no hash to tell them
+/// apart): skipped, never guessed.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct AmbiguousFile {
+    pub id: PhotoId,
+    pub from: String,
+    pub candidates: Vec<String>,
+}
+
+/// What Find Missing Photos found ([`plan_find_missing`]), before relinking.
+#[derive(Clone, Debug, Default, PartialEq, Eq)]
+pub struct FindPlan {
+    pub found: Vec<FoundFile>,
+    /// In-scope photos that stay missing (the ambiguous ones included).
+    pub missing: usize,
+    pub ambiguous: Vec<AmbiguousFile>,
+}
+
+impl FindPlan {
+    /// `{found: [{id, from, to, by}], missing, ambiguous: [{id, from, candidates}]}` — the
+    /// command's result, and what `library.findMissing {found, …}` takes back.
+    pub fn to_json(&self) -> Value {
+        let found: Vec<Value> = self.found.iter().map(|f| json!({"id": f.id.0, "from": f.from, "to": f.to, "by": f.by.as_str()})).collect();
+        let ambiguous: Vec<Value> = self.ambiguous.iter().map(|a| json!({"id": a.id.0, "from": a.from, "candidates": a.candidates})).collect();
+        json!({"found": found, "missing": self.missing, "ambiguous": ambiguous})
+    }
+
+    /// The inverse of [`FindPlan::to_json`] (entries it can't read are dropped).
+    pub fn from_json(v: &Value) -> FindPlan {
+        let list = |k: &str| v.get(k).and_then(Value::as_array).cloned().unwrap_or_default();
+        let found = list("found")
+            .iter()
+            .filter_map(|f| {
+                let by = if f.get("by").and_then(Value::as_str) == Some("content") { MatchBy::Content } else { MatchBy::Name };
+                Some(FoundFile {
+                    id: PhotoId(f.get("id")?.as_u64()?),
+                    from: str_param(f, "from")?.to_string(),
+                    to: str_param(f, "to")?.to_string(),
+                    by,
+                })
+            })
+            .collect();
+        let ambiguous = list("ambiguous")
+            .iter()
+            .filter_map(|a| {
+                let candidates = a.get("candidates")?.as_array()?.iter().filter_map(|c| c.as_str().map(str::to_string)).collect();
+                Some(AmbiguousFile { id: PhotoId(a.get("id")?.as_u64()?), from: str_param(a, "from")?.to_string(), candidates })
+            })
+            .collect();
+        let missing = v.get("missing").and_then(Value::as_u64).map_or(0, |n| usize::try_from(n).unwrap_or(usize::MAX));
+        FindPlan { found, missing, ambiguous }
+    }
+}
+
+/// The file-system half of Find Missing Photos: which `candidates` are gone, and which file in
+/// `folder` (recursively) is each one's. Touches only the disk — never the session — so the app
+/// runs it on a worker thread (walking a big folder on a network share and hashing look-alikes
+/// takes a while) and relinks the result with `library.findMissing {found, missing, ambiguous}`.
+///
+/// Matching, per photo:
+/// 1. a file with the same name (any letter case), the same size and the same content hash;
+/// 2. renamed: a file of the same size with the same content hash (only same-size files are
+///    read, so this stays cheap);
+/// 3. without a hash to confirm (or the file was edited in place): the one file with the same
+///    name and size. Several such files are ambiguous: the photo is skipped and reported in
+///    `ambiguous`, never guessed (two cameras' `IMG_0001.CR3` of one size are different photos).
+///
+/// Files that are already some photo's original, or that another photo was just matched with,
+/// are not used.
+pub fn plan_find_missing(candidates: &[FindCandidate], folder: &str) -> std::result::Result<FindPlan, String> {
     if !Path::new(folder).is_dir() {
-        return Err(bad(C, format!("{folder}: not a folder")));
+        return Err(format!("{folder}: not a folder"));
     }
-    let lost = missing(s);
+    if cfg!(target_arch = "wasm32") {
+        return Ok(FindPlan::default());
+    }
+    let lost: Vec<&FindCandidate> = candidates.iter().filter(|c| !Path::new(&c.path).exists()).collect();
     if lost.is_empty() {
-        return Ok(json!({"found": [], "missing": 0}));
+        return Ok(FindPlan::default());
     }
-    // file name (lower case) → candidate paths
+    let in_use: HashSet<&str> = candidates.iter().map(|c| c.path.as_str()).collect();
+    // file name (lower case) → candidate paths; size → paths (filled lazily)
     let mut by_name: HashMap<String, Vec<String>> = HashMap::new();
-    for f in crate::import::expand(&[folder.to_string()], None) {
-        if let Some(n) = Path::new(&f).file_name() {
-            by_name.entry(n.to_string_lossy().to_lowercase()).or_default().push(f);
+    let files: Vec<String> = crate::import::expand(&[folder.to_string()], None).into_iter().filter(|f| !in_use.contains(f.as_str())).collect();
+    for f in &files {
+        if let Some(n) = Path::new(f).file_name() {
+            by_name.entry(n.to_string_lossy().to_lowercase()).or_default().push(f.clone());
         }
     }
-    let mut ops = Vec::new();
-    let mut found = Vec::new();
-    for (id, old) in &lost {
-        let name = Path::new(old).file_name().map(|n| n.to_string_lossy().to_lowercase()).unwrap_or_default();
-        let size = s.catalog.photo(*id).map(|p| p.file_size).unwrap_or(0);
-        let hit = by_name.get(&name).and_then(|c| {
-            c.iter().find(|f| size == 0 || std::fs::metadata(f).is_ok_and(|m| m.len() == size)).or_else(|| (c.len() == 1 && size == 0).then(|| &c[0]))
-        });
-        if let Some(path) = hit {
-            ops.push(relink_op(*id, path));
-            found.push(json!({"id": id.0, "from": old, "to": path}));
+    let mut by_size: Option<HashMap<u64, Vec<String>>> = None;
+    let mut hashes: HashMap<String, Option<String>> = HashMap::new();
+    let mut hash_of = |f: &str| hashes.entry(f.to_string()).or_insert_with(|| file_hash(f)).clone();
+    let size_of = |f: &str| std::fs::metadata(f).map(|m| m.len()).ok();
+    let mut used: HashSet<String> = HashSet::new();
+    let mut plan = FindPlan::default();
+    for c in &lost {
+        let name = Path::new(&c.path).file_name().map(|n| n.to_string_lossy().to_lowercase()).unwrap_or_default();
+        let size = c.size;
+        let hash = c.hash.as_deref();
+        let named: Vec<&String> = by_name
+            .get(&name)
+            .map(|v| v.iter().filter(|f| !used.contains(*f) && (size == 0 || size_of(f) == Some(size))).collect())
+            .unwrap_or_default();
+        // 1. same name and size, confirmed by the content hash
+        let mut hit: Option<(String, MatchBy)> =
+            hash.and_then(|h| named.iter().find(|f| hash_of(f).as_deref() == Some(h))).map(|f| (f.to_string(), MatchBy::Name));
+        // 2. renamed: same size and content
+        if hit.is_none()
+            && let Some(h) = hash
+            && size > 0
+        {
+            let sizes = by_size.get_or_insert_with(|| {
+                let mut m: HashMap<u64, Vec<String>> = HashMap::new();
+                for f in &files {
+                    if let Some(n) = size_of(f) {
+                        m.entry(n).or_default().push(f.clone());
+                    }
+                }
+                m
+            });
+            hit = sizes
+                .get(&size)
+                .and_then(|v| v.iter().find(|f| !used.contains(*f) && hash_of(f).as_deref() == Some(h)))
+                .map(|f| (f.clone(), MatchBy::Content));
         }
-    }
-    let still = lost.len() - found.len();
-    if !ops.is_empty() {
-        s.commit("Find Missing Photos", Op::Batch { ops })?;
-        for f in &found {
-            if let Some(id) = f["id"].as_u64() {
-                s.media.forget(PhotoId(id));
+        // 3. same name and size only (no hash, or the file was edited in place): one candidate
+        //    is taken, several are ambiguous and skipped rather than guessed
+        if hit.is_none() {
+            match named.as_slice() {
+                [one] => hit = Some(((*one).clone(), MatchBy::Name)),
+                [] => {}
+                _ => {
+                    plan.ambiguous.push(AmbiguousFile { id: c.id, from: c.path.clone(), candidates: named.iter().map(|f| (*f).clone()).collect() });
+                    continue;
+                }
             }
         }
+        let Some((path, by)) = hit else { continue };
+        used.insert(path.clone());
+        plan.found.push(FoundFile { id: c.id, from: c.path.clone(), to: path, by });
     }
-    Ok(json!({"found": found, "missing": still}))
+    plan.missing = lost.len() - plan.found.len();
+    Ok(plan)
+}
+
+/// Relink what [`plan_find_missing`] found, in one undoable step, re-checked against the
+/// catalog as it is now (the search may have run on a worker while the library changed): a
+/// photo that no longer points at the path it was missing from (relinked, removed) is left
+/// alone, and a file that is now some photo's original — or that the plan names twice — is not
+/// used (that photo stays missing). `missing` is the plan's count, corrected for what changed
+/// among the photos the plan names.
+fn commit_find(s: &mut Session, plan: FindPlan) -> Result<Value> {
+    let still_at = |cat: &Catalog, id: PhotoId, from: &str| cat.photo(id).and_then(|p| checked_path(p)) == Some(from);
+    let mut in_use: HashSet<String> = candidates(&s.catalog).into_iter().collect();
+    let mut found = Vec::new();
+    let mut missing = plan.missing;
+    for f in plan.found {
+        if !still_at(&s.catalog, f.id, &f.from) {
+            continue;
+        }
+        if in_use.contains(&f.to) {
+            missing += 1;
+            continue;
+        }
+        in_use.insert(f.to.clone());
+        found.push(f);
+    }
+    let planned = plan.ambiguous.len();
+    let ambiguous: Vec<AmbiguousFile> = plan.ambiguous.into_iter().filter(|a| still_at(&s.catalog, a.id, &a.from)).collect();
+    // ambiguous photos relinked meanwhile aren't missing any more
+    missing = missing.saturating_sub(planned - ambiguous.len());
+    if !found.is_empty() {
+        s.commit("Find Missing Photos", Op::Batch { ops: found.iter().map(|f| relink_op(f.id, &f.to)).collect() })?;
+        for f in &found {
+            s.media.forget(f.id);
+        }
+    }
+    Ok(FindPlan { found, missing, ambiguous }.to_json())
+}
+
+/// Search `folder` (recursively) for each missing photo's file ([`plan_find_missing`]) and
+/// relink every match in one undoable step. With `found` instead (what a search on a worker
+/// thread returned, as `{found, missing, ambiguous}`), only the relinking is done.
+fn find_missing(s: &mut Session, p: &Value) -> Result<Value> {
+    const C: &str = "library.findMissing";
+    if p.get("found").is_some_and(Value::is_array) {
+        return commit_find(s, FindPlan::from_json(p));
+    }
+    let folder = str_param(p, "folder").ok_or_else(|| bad(C, "missing `folder`"))?;
+    let plan = plan_find_missing(&find_candidates(&s.catalog), folder).map_err(|e| bad(C, e))?;
+    commit_find(s, plan)
 }
 
 pub fn specs() -> Vec<CommandSpec> {
@@ -146,7 +355,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Find Missing Photos",
             [],
             None,
-            "{folder} — relink every missing photo whose file (same name and size) is somewhere in the folder → {found: [{id, from, to}], missing}",
+            "{folder} — relink every missing photo whose file is somewhere in the folder: same name and size (and content, when the library knows its hash), or — renamed — same size and content; or {found, missing, ambiguous} — relink what a search already found (the app searches on a worker thread; photos relinked meanwhile and files now in use are skipped) → {found: [{id, from, to, by: name|content}], missing, ambiguous: [{id, from, candidates}] (several same-name candidates and no hash to tell them apart: skipped)}",
             always,
             find_missing
         ),

crates/engine/src/cmd/mod.rs

@@ -5,7 +5,7 @@
 //! `edit.*` (undo/redo), and queries (`catalog.query`, `photo.inspect`, `develop.get`…).
 
 mod before;
-mod browse;
+pub(crate) mod browse;
 mod color;
 pub(crate) mod convert;
 mod cull;
@@ -15,7 +15,7 @@ mod edit;
 mod export;
 pub mod filters;
 pub mod keywords;
-mod library;
+pub mod library;
 pub mod lut_profiles;
 pub mod manage;
 mod masks;

crates/engine/src/cmd/previews.rs

@@ -23,6 +23,12 @@ pub struct PreviewBuild {
     pub failed: AtomicUsize,
     pub cancel: AtomicBool,
     pub finished: AtomicBool,
+    /// Damaged smart previews rebuilt (Build Smart Previews only).
+    pub repaired: AtomicUsize,
+    /// What is built ("" = previews; "smart previews" — Build Smart Previews runs the same way).
+    pub what: &'static str,
+    /// Why the whole build failed (e.g. the smart previews folder isn't there).
+    pub error: std::sync::Mutex<Option<String>>,
 }
 
 impl PreviewBuild {
@@ -33,8 +39,15 @@ impl PreviewBuild {
             "failed": self.failed.load(Ordering::Relaxed),
             "running": !self.finished.load(Ordering::Relaxed),
             "cancelled": self.cancel.load(Ordering::Relaxed),
+            "what": if self.what.is_empty() { "previews" } else { self.what },
+            "repaired": self.repaired.load(Ordering::Relaxed),
+            "error": self.error(),
         })
     }
+
+    pub fn error(&self) -> Option<String> {
+        self.error.lock().unwrap_or_else(std::sync::PoisonError::into_inner).clone()
+    }
 }
 
 /// The jobs that build `id`'s previews: the largest grid thumbnail, then the view render at
@@ -94,49 +107,134 @@ fn build(s: &mut Session, p: &Value) -> Result<Value> {
     Ok(state.json())
 }
 
+/// One photo's smart preview to build or discard: (photo, its file in the smart previews folder,
+/// how to load the original at preview size).
+#[cfg(not(target_arch = "wasm32"))]
+type SmartJob = (lightcraft_catalog::PhotoId, std::path::PathBuf, Option<crate::media::SourceRef>);
+
+/// What Build / Discard Smart Previews did.
+#[cfg(not(target_arch = "wasm32"))]
+#[derive(Default)]
+struct SmartCounts {
+    /// Proxies there now (complete ones kept, missing or damaged ones written).
+    built: usize,
+    /// Of those, damaged ones (cut short by a crash or a full drive) that were rebuilt.
+    repaired: usize,
+    removed: usize,
+    /// `[[id, why]]`
+    failed: Vec<Value>,
+}
+
+/// The file-system half of Build / Discard Smart Previews (runs on a worker thread in the app).
+/// `custom`: the folder was chosen (on another drive, perhaps): it must be there, it is never
+/// recreated. With `state`, progress and cancel.
+#[cfg(not(target_arch = "wasm32"))]
+fn smart_run(
+    dir: &std::path::Path,
+    custom: bool,
+    discard: bool,
+    jobs: Vec<SmartJob>,
+    state: Option<&PreviewBuild>,
+) -> std::result::Result<SmartCounts, String> {
+    let mut n = SmartCounts::default();
+    if !discard {
+        // a chosen folder on another drive must be there: never recreate it on this one
+        if custom {
+            crate::smart::check_writable(dir)?;
+        } else {
+            std::fs::create_dir_all(dir).map_err(|e| format!("{}: {e}", dir.display()))?;
+        }
+    }
+    for (id, path, source) in jobs {
+        if state.is_some_and(|st| st.cancel.load(Ordering::Relaxed)) {
+            break;
+        }
+        if discard {
+            if std::fs::remove_file(&path).is_ok() {
+                n.removed += 1;
+            }
+        } else {
+            // a complete proxy is kept; a missing or damaged one (cut short by a crash or a full
+            // drive) is (re)built
+            let damaged = path.exists();
+            if damaged && crate::smart::is_valid(&path) {
+                n.built += 1;
+            } else {
+                // atomic: a failed write leaves no partial proxy that would pass for a built one
+                let r = source
+                    .ok_or_else(|| "nothing to build from".to_string())
+                    .and_then(|s| s.load_source())
+                    .and_then(|src| crate::smart::encode(&src.image, src.info_or(Default::default()).camera_tone.as_ref()))
+                    .and_then(|b| lightcraft_catalog::safe_file::write_atomic(&path, &b).map_err(|e| format!("{}: {e}", path.display())));
+                match r {
+                    Ok(()) => {
+                        n.built += 1;
+                        if damaged {
+                            n.repaired += 1;
+                            if let Some(st) = state {
+                                st.repaired.fetch_add(1, Ordering::Relaxed);
+                            }
+                        }
+                    }
+                    Err(e) => {
+                        n.failed.push(json!([id.0, e]));
+                        if let Some(st) = state {
+                            st.failed.fetch_add(1, Ordering::Relaxed);
+                        }
+                    }
+                }
+            }
+        }
+        if let Some(st) = state {
+            st.done.fetch_add(1, Ordering::Relaxed);
+        }
+    }
+    Ok(n)
+}
+
 /// Smart previews: build (from the original, at preview size) or discard the proxies that keep
-/// photos editable while their originals are offline.
+/// photos editable while their originals are offline. With `background` (the app) the files are
+/// read and written on a worker thread; progress like Build Previews (`library.previewProgress`).
 #[cfg(not(target_arch = "wasm32"))]
 fn smart(s: &mut Session, p: &Value) -> Result<Value> {
     const C: &str = "library.smartPreviews";
     let dir = s.media.smart_dir.clone().ok_or_else(|| bad(C, "smart previews need a library on disk"))?;
     let discard = p.get("discard").and_then(Value::as_bool).unwrap_or(false);
-    let ids = if p.get("ids").is_some() || !s.selection.ids.is_empty() { s.targets(p) } else { s.visible_cloned() };
-    let (mut built, mut removed, mut failed) = (0usize, 0usize, Vec::new());
-    if !discard {
-        // a chosen folder on another drive must be there: never recreate it on this one
-        if s.smart_previews_dir.is_some() {
-            crate::smart::check_writable(&dir).map_err(|e| bad(C, e))?;
-        } else {
-            std::fs::create_dir_all(&dir).map_err(|e| bad(C, format!("{}: {e}", dir.display())))?;
-        }
+    let background = p.get("background").and_then(Value::as_bool).unwrap_or(false);
+    if background && s.preview_build.as_ref().is_some_and(|b| !b.finished.load(Ordering::Relaxed)) {
+        return Err(bad(C, "a preview build is already running"));
     }
+    let ids = if p.get("ids").is_some() || !s.selection.ids.is_empty() { s.targets(p) } else { s.visible_cloned() };
+    let mut jobs: Vec<SmartJob> = Vec::new();
     for id in ids {
         let Some(ph) = s.catalog.photo(id).cloned() else { continue };
         if !matches!(ph.source, lightcraft_catalog::Source::File { .. }) {
             continue;
         }
         let path = dir.join(crate::smart::file_name(&ph));
-        if discard {
-            if std::fs::remove_file(&path).is_ok() {
-                removed += 1;
-            }
-            continue;
-        }
-        if path.exists() {
-            built += 1;
-            continue;
-        }
-        let r = s
-            .source_now(id, crate::media::SourceLevel::Preview)
-            .and_then(|src| crate::smart::encode(&src))
-            .and_then(|b| std::fs::write(&path, b).map_err(|e| e.to_string()));
-        match r {
-            Ok(()) => built += 1,
-            Err(e) => failed.push(json!([id.0, e])),
-        }
+        let source = (!discard).then(|| s.media.source_ref(&ph, crate::media::SourceLevel::Preview));
+        jobs.push((id, path, source));
     }
-    Ok(json!({"built": built, "removed": removed, "failed": failed}))
+    let custom = s.smart_previews_dir.is_some();
+    if background {
+        let what = if discard { "discarding smart previews" } else { "smart previews" };
+        let state = Arc::new(PreviewBuild { total: jobs.len(), what, ..Default::default() });
+        s.preview_build = Some(state.clone());
+        let st = state.clone();
+        std::thread::Builder::new()
+            .name("lc-smart-previews".into())
+            .spawn(move || {
+                if let Err(e) = smart_run(&dir, custom, discard, jobs, Some(&st)) {
+                    log::warn!("{C}: {e}");
+                    *st.error.lock().unwrap_or_else(std::sync::PoisonError::into_inner) = Some(e);
+                }
+                st.finished.store(true, Ordering::Relaxed);
+            })
+            .map_err(|e| bad(C, format!("could not start: {e}")))?;
+        return Ok(state.json());
+    }
+    let r = smart_run(&dir, custom, discard, jobs, None).map_err(|e| bad(C, e))?;
+    Ok(json!({"built": r.built, "repaired": r.repaired, "removed": r.removed, "failed": r.failed}))
 }
 
 /// The smart previews folder: where it is, whether it is custom, what it holds, whether it can be
@@ -205,7 +303,7 @@ fn smart_location(s: &mut Session, p: &Value) -> Result<Value> {
 /// Whether photo `id` has a smart preview.
 pub fn has_smart_preview(s: &Session, id: lightcraft_catalog::PhotoId) -> bool {
     match (&s.media.smart_dir, s.catalog.photo(id)) {
-        (Some(dir), Some(p)) => dir.join(crate::smart::file_name(p)).exists(),
+        (Some(dir), Some(p)) => crate::smart::is_valid(&dir.join(crate::smart::file_name(p))),
         _ => false,
     }
 }
@@ -218,7 +316,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Build Smart Previews",
             [],
             None,
-            "{ids?, discard?: bool} — build (or discard) the smart previews of the selected photos (else all in view): compact proxies in the library that keep photos editable and exportable (at proxy size) while their originals are offline → {built, removed, failed}",
+            "{ids?, discard?: bool, background?: bool} — build (or discard) the smart previews of the selected photos (else all in view): compact proxies in the library that keep photos editable and exportable (at proxy size) while their originals are offline; a damaged proxy (cut short) is rebuilt → {built, repaired, removed, failed}; with background (the app's menu) the files are read and written on a worker thread → {total, done, failed, repaired, running, what} like library.buildPreviews (progress: library.previewProgress, stop: library.cancelPreviews)",
             always,
             smart
         ),
@@ -249,7 +347,7 @@ pub fn specs() -> Vec<CommandSpec> {
             always,
             build
         ),
-        cmd!(query "library.previewProgress", "Preview Build Progress", [], None, "{} → {total, done, failed, running, cancelled} | null", always, |s, _| {
+        cmd!(query "library.previewProgress", "Preview Build Progress", [], None, "{} → {total, done, failed, repaired, running, cancelled, what, error} | null", always, |s, _| {
             Ok(s.preview_build.as_ref().map_or(Value::Null, |b| b.json()))
         }),
         cmd!("library.cancelPreviews", "Cancel Preview Build", [], None, "{}", always, |s, _| {

crates/engine/src/cmd/query.rs

@@ -113,7 +113,7 @@ pub fn specs() -> Vec<CommandSpec> {
                 .map(|r| json!({"group": r.group, "tag": r.tag, "name": r.name, "value": r.value}))
                 .collect();
             // XMP: the sidecar if there is one, else the file's own packet
-            let packet = crate::sidecar::read_packet(path, ph.kind, s.xmp.naming).map(|(x, _)| x).or_else(|| lightcraft_meta::embedded(&bytes).xmp);
+            let packet = crate::sidecar::read_packet(path, ph.kind, s.sidecar_naming(ph.id)).map(|(x, _)| x).or_else(|| lightcraft_meta::embedded(&bytes).xmp);
             let xmp: Vec<Value> = packet
                 .and_then(|x| lightcraft_meta::parse_xmp(&x).ok())
                 .map(|d| d.properties.into_iter().filter(|(k, _)| !k.starts_with("lc:")).map(|(k, v)| json!({"name": k, "value": v.join("; ")})).collect())

crates/engine/src/cmd/xmp.rs

@@ -9,14 +9,26 @@ use crate::{Result, Session};
 
 fn save(s: &mut Session, p: &Value) -> Result<Value> {
     let mut written = Vec::new();
+    let mut merged = Vec::new();
+    let mut backups = Vec::new();
     let mut failed = Vec::new();
+    let owners = crate::sidecar::StemOwners::of(&s.catalog);
     for id in s.targets(p) {
-        match s.save_sidecar(id) {
-            Ok(path) => written.push(path.display().to_string()),
+        match s.save_sidecar_with(id, &owners) {
+            Ok(r) => {
+                let path = r.path.display().to_string();
+                if r.merged {
+                    merged.push(path.clone());
+                }
+                if let Some(b) = r.backup {
+                    backups.push(json!({"path": path, "backup": b.display().to_string()}));
+                }
+                written.push(path);
+            }
             Err(e) => failed.push(json!({"id": id.0, "error": e.to_string()})),
         }
     }
-    Ok(json!({"written": written, "failed": failed}))
+    Ok(json!({"written": written, "merged": merged, "backups": backups, "failed": failed}))
 }
 
 fn read(s: &mut Session, p: &Value) -> Result<Value> {
@@ -63,7 +75,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Save Metadata to File",
             ["Photo"],
             Some("Cmd+S"),
-            "{ids?} — writes each photo's XMP sidecar (metadata + develop settings) next to the original → {written: [path], failed}",
+            "{ids?} — writes each photo's XMP sidecar (metadata + develop settings) next to the original, merged into an existing one (other apps' data kept; an unreadable one is backed up first) → {written: [path], merged: [path], backups: [{path, backup}], failed}",
             has_selection,
             save
         ),

crates/engine/src/files.rs

@@ -131,7 +131,9 @@ pub fn probe_bytes(name: &str, bytes: &[u8]) -> Result<ProbeInfo, String> {
             std::mem::swap(&mut w, &mut h);
         }
         let (t, tint) = xy_to_temp_tint(lightcraft_raw::color::as_shot_white_xy_of(&raw));
-        let as_shot_wb = Some((t.round(), tint.round()));
+        // Vendor RGB multipliers do not identify an absolute illuminant without camera calibration.
+        let relative = raw.format == lightcraft_raw::RawFormat::Arw && !lightcraft_raw::color::has_matrix(&raw.color);
+        let as_shot_wb = Some(if relative { (6500.0, 0.0) } else { (t.round(), tint.round()) });
         let embedded_lens = embedded_lens(&raw);
         return Ok(ProbeInfo {
             embedded_lens,
@@ -221,6 +223,9 @@ fn load_bytes_now(bytes: std::borrow::Cow<'_, [u8]>, max_edge: usize) -> Result<
             }
             Err(e) => return Err(e.to_string()),
         };
+        let xy = lightcraft_raw::color::as_shot_white_xy(&raw);
+        let t = lightcraft_raw::color::camera_transform(&raw, xy);
+        let camera_look = crate::camera_preview::fit_preview(&raw, &bytes, &t);
         drop(bytes);
         // Embedded lens corrections are applied by the pipeline ("Enable Profile Corrections"), not baked in.
         let lens = embedded_lens(&raw.info());
@@ -242,12 +247,10 @@ fn load_bytes_now(bytes: std::borrow::Cow<'_, [u8]>, max_edge: usize) -> Result<
         // the samples aren't needed any more (the colour model below reads only the tags)
         raw.data = lightcraft_raw::RawData::U16(Vec::new());
         let mut stages = vec![("develop", t0.elapsed())];
-        let xy = lightcraft_raw::color::as_shot_white_xy(&raw);
-        let t = lightcraft_raw::color::camera_transform(&raw, xy);
         stages.push(("transform", t0.elapsed()));
         lightcraft_raw::highlight::reconstruct(&mut img, t.wb, HIGHLIGHT_CLIP);
         stages.push(("highlights", t0.elapsed()));
-        let m = t.matrix.to_f32();
+        let m = camera_look.map(|p| p.matrix.mul(&t.matrix)).unwrap_or(t.matrix).to_f32();
         let gain = 2f32.powf(t.baseline_exposure as f32);
         let wb = t.wb;
         img.map_in_place(|p| {
@@ -276,7 +279,12 @@ fn load_bytes_now(bytes: std::borrow::Cow<'_, [u8]>, max_edge: usize) -> Result<
             eprintln!("[profile] raw source {}×{} (max {max_edge}, ms after decode): {}", img.width, img.height, parts.join(", "));
         }
         let (temp, tint) = xy_to_temp_tint(xy);
-        return Ok((img, SourceInfo { raw: true, as_shot_temp: temp.round(), as_shot_tint: tint.round(), lens }));
+        let relative = raw.format == lightcraft_raw::RawFormat::Arw && t.matrix_is_fallback;
+        let (temp, tint) = if relative { (6500.0, 0.0) } else { (temp.round(), tint.round()) };
+        return Ok((
+            img,
+            SourceInfo { raw: true, as_shot_temp: temp, as_shot_tint: tint, lens, relative_wb: relative, camera_tone: camera_look.map(|p| p.tone) },
+        ));
     }
     let d = lightcraft_codecs::decode(&bytes, lightcraft_codecs::DecodeOptions::fit(max_edge as u32, max_edge as u32)).map_err(|e| e.to_string())?;
     drop(bytes);

crates/engine/src/import.rs

@@ -374,25 +374,14 @@ fn probe_all(probe: Option<&crate::media::FileProbe>, paths: &[String], progress
 }
 
 /// Copy `src` into `root`/`folders` as `name` (default: its own name), made unique with -1, -2…;
-/// returns the new path.
+/// returns the new path. The copy is verified ([`crate::import_move::copy_new`]: a new file,
+/// synced and compared byte for byte); a bad one is removed and the photo reported as failed.
 fn copy_into(root: &Path, src: &str, folders: &[String], name: Option<&str>) -> Result<String, String> {
     let dir = folders.iter().fold(root.to_path_buf(), |d, f| d.join(f));
-    std::fs::create_dir_all(&dir).map_err(|e| format!("{}: {e}", dir.display()))?;
     let name = name
         .map(str::to_string)
         .unwrap_or_else(|| Path::new(src).file_name().map(|n| n.to_string_lossy().to_string()).unwrap_or_else(|| "photo".into()));
-    let (stem, ext) = match name.rsplit_once('.') {
-        Some((s, e)) => (s.to_string(), format!(".{e}")),
-        None => (name.clone(), String::new()),
-    };
-    let mut dst = dir.join(&name);
-    let mut i = 1;
-    while dst.exists() {
-        dst = dir.join(format!("{stem}-{i}{ext}"));
-        i += 1;
-    }
-    std::fs::copy(src, &dst).map_err(|e| format!("copy {src}: {e}"))?;
-    Ok(dst.to_string_lossy().to_string())
+    crate::import_move::copy_new(Path::new(src), &dir, &name).map(|p| p.to_string_lossy().to_string())
 }
 
 /// What a [`scan`] needs from the session, so it can run on another thread (a folder on a network
@@ -528,205 +517,392 @@ pub fn import(s: &mut Session, paths: &[String], mode: ImportMode) -> crate::Res
 }
 
 /// Import files/folders with options (preset, keywords). See the module docs.
+///
+/// The file-system half ([`ImportJob::prepare`]: expanding folders, probing, reading sidecars,
+/// copying / placing files) and the catalog half ([`commit_prepared`]) are separate so the app can
+/// run the first on a worker thread; here both run in turn.
 pub fn import_with(s: &mut Session, paths: &[String], opts: &ImportOptions) -> crate::Result<ImportReport> {
-    let mode = opts.mode;
-    // Only a library on disk has an `Originals/` folder. The browser build keeps the bytes of every
-    // added file in its own storage already, so "copy" there means "add".
-    let transfer = matches!(mode, ImportMode::Copy | ImportMode::Move);
-    let mode = if transfer && s.library.as_ref().is_some_and(|l| !l.on_disk) { ImportMode::Add } else { mode };
-    if mode == ImportMode::Move && opts.local {
-        return Err(crate::EngineError::Other("browsing a folder never moves its files".into()));
-    }
-    let lib_dir = s.library.as_ref().filter(|l| l.on_disk).map(|l| l.dir.clone());
-    // where copies go: the chosen folder, else the library's Originals/
-    let copy_root = opts
-        .destination
-        .as_deref()
-        .filter(|d| !d.trim().is_empty())
-        .map(std::path::PathBuf::from)
-        .or_else(|| lib_dir.as_ref().map(|l| l.join("Originals")));
-    if matches!(mode, ImportMode::Copy | ImportMode::Move) && copy_root.is_none() {
-        return Err(crate::EngineError::Other("copying or moving needs a destination folder or an open library".into()));
-    }
-    let mut seq = opts.rename_start.max(1);
-    let files = expand(paths, lib_dir.as_deref());
-    let mut report = ImportReport { scanned: files.len(), ..Default::default() };
+    let mut job = ImportJob::new(s, opts.clone())?;
+    let prepared = job.prepare(paths, &std::sync::atomic::AtomicBool::new(false));
+    // probes a scan left for files not imported now stay for a later import
+    s.import_probes.extend(std::mem::take(&mut job.cache));
+    commit_prepared(s, &job.opts, &job.now, prepared)
+}
 
-    // existing paths and content hashes
-    let mut by_path: HashMap<&str, PhotoId> = HashMap::new();
-    let mut by_hash: HashMap<String, PhotoId> = HashMap::new();
-    for p in s.catalog.photos() {
-        if let Source::File { path } = &p.source {
-            by_path.insert(path.as_str(), p.id);
-        }
-        if let Some(h) = &p.content_hash {
-            by_hash.insert(h.clone(), p.id);
-        }
-    }
-    let mut todo = Vec::new();
-    // a file that was only browsed (Local) joins the library when it is imported for real
-    let mut promote = Vec::new();
-    for f in files {
-        match by_path.get(f.as_str()) {
-            Some(id) if !opts.local && s.catalog.photo(*id).is_some_and(|p| p.local) => {
-                promote.push(Op::SetLocal { id: *id, local: false });
-                report.imported.push(id.0);
+/// Everything the file-system half of an import needs, detached from the session so it can run
+/// on another thread (a network share or a card can take minutes). Built by [`ImportJob::new`];
+/// [`ImportJob::prepare`] may be called for several batches in turn (renamed copies keep counting,
+/// duplicates are found across batches); each batch is then [`commit_prepared`] on the session.
+pub struct ImportJob {
+    pub opts: ImportOptions,
+    /// The mode in effect (Copy / Move become Add in a library without its own folder).
+    mode: ImportMode,
+    lib_dir: Option<PathBuf>,
+    copy_root: Option<PathBuf>,
+    /// path → (photo, a Local browse record?)
+    by_path: HashMap<String, (PhotoId, bool)>,
+    /// content hash → the photo that has it (`None`: a file earlier in this import)
+    by_hash: HashMap<String, Option<PhotoId>>,
+    probe: Option<crate::media::FileProbe>,
+    file_bytes: Option<crate::merge::ByteReader>,
+    /// Probes from a preceding scan (not read again).
+    cache: HashMap<String, ProbeInfo>,
+    naming: crate::sidecar::SidecarNaming,
+    now: String,
+    seq: usize,
+    /// Files found so far (folders expanded) and handled so far, for progress.
+    pub total: std::sync::Arc<std::sync::atomic::AtomicUsize>,
+    pub done: std::sync::Arc<std::sync::atomic::AtomicUsize>,
+}
+
+/// The outcome of [`ImportJob::prepare`] for one batch, in file order.
+#[derive(Debug, Default)]
+pub struct Prepared {
+    pub scanned: usize,
+    items: Vec<PreparedItem>,
+}
+
+#[derive(Debug)]
+enum PreparedItem {
+    /// A Local (browsed) record imported for real.
+    Promote(PhotoId),
+    Duplicate {
+        path: String,
+        existing: Option<PhotoId>,
+        reason: &'static str,
+        hash: Option<String>,
+    },
+    Failed(String, String),
+    Kept(Kept),
+    Ready(Box<ReadyFile>),
+}
+
+#[derive(Debug)]
+struct ReadyFile {
+    path: String,
+    stored: String,
+    info: ProbeInfo,
+    sidecar: Option<crate::sidecar::SidecarData>,
+    placed: Option<crate::import_move::Placed>,
+}
+
+impl Prepared {
+    /// Undo what the batch did on disk that only a commit would make permanent: files placed by a
+    /// Move (their sources were never touched). Copies stay, like copies of a failed commit.
+    pub fn rollback(&self) {
+        for it in &self.items {
+            if let PreparedItem::Ready(r) = it
+                && let Some(pl) = &r.placed
+            {
+                crate::import_move::rollback(pl);
             }
-            Some(id) => report.duplicates.push(Duplicate { path: f, existing: Some(id.0), reason: "path" }),
-            None => todo.push(f),
         }
     }
 
-    // files a preceding scan already probed are not read again (a network share is slow to read)
-    let cached: Vec<Option<ProbeInfo>> = todo.iter().map(|f| s.import_probes.remove(f)).collect();
-    let missing: Vec<String> = todo.iter().zip(&cached).filter(|(_, c)| c.is_none()).map(|(f, _)| f.clone()).collect();
-    let mut fresh = probe_all(s.media.file_probe.as_ref(), &missing, &ScanProgress::default()).into_iter();
-    let probed: Vec<Result<ProbeInfo, String>> =
-        cached.into_iter().map(|c| c.map(Ok).unwrap_or_else(|| fresh.next().unwrap_or_else(|| Err("not probed".into())))).collect();
-    crate::memory::release();
-    let now = (s.clock)();
-    let mut ops = promote;
-    // Move: placed at the destination, sources untouched until the records are committed
-    let mut placed: Vec<crate::import_move::Placed> = Vec::new();
-    for (path, info) in todo.into_iter().zip(probed) {
-        let info = match info {
-            Ok(i) => i,
-            Err(e) => {
-                log::warn!("import {path}: {e}");
-                report.failed.push((path, e));
+    /// Entries in the batch (after expanding folders).
+    pub fn len(&self) -> usize {
+        self.items.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.items.is_empty()
+    }
+}
+
+impl ImportJob {
+    /// Snapshot what an import with `opts` needs from the session (no file-system calls). Takes
+    /// the probes a preceding scan left ([`Session::import_probes`]).
+    pub fn new(s: &mut Session, opts: ImportOptions) -> crate::Result<Self> {
+        let mode = opts.mode;
+        // Only a library on disk has an `Originals/` folder. The browser build keeps the bytes of
+        // every added file in its own storage already, so "copy" there means "add".
+        let transfer = matches!(mode, ImportMode::Copy | ImportMode::Move);
+        let mode = if transfer && s.library.as_ref().is_some_and(|l| !l.on_disk) { ImportMode::Add } else { mode };
+        if mode == ImportMode::Move && opts.local {
+            return Err(crate::EngineError::Other("browsing a folder never moves its files".into()));
+        }
+        let lib_dir = s.library.as_ref().filter(|l| l.on_disk).map(|l| l.dir.clone());
+        // where copies go: the chosen folder, else the library's Originals/
+        let copy_root = opts
+            .destination
+            .as_deref()
+            .filter(|d| !d.trim().is_empty())
+            .map(std::path::PathBuf::from)
+            .or_else(|| lib_dir.as_ref().map(|l| l.join("Originals")));
+        if matches!(mode, ImportMode::Copy | ImportMode::Move) && copy_root.is_none() {
+            return Err(crate::EngineError::Other("copying or moving needs a destination folder or an open library".into()));
+        }
+        let mut by_path = HashMap::new();
+        let mut by_hash = HashMap::new();
+        for p in s.catalog.photos() {
+            if let Source::File { path } = &p.source {
+                by_path.insert(path.clone(), (p.id, p.local));
+            }
+            if let Some(h) = &p.content_hash {
+                by_hash.insert(h.clone(), Some(p.id));
+            }
+        }
+        Ok(ImportJob {
+            seq: opts.rename_start.max(1),
+            opts,
+            mode,
+            lib_dir,
+            copy_root,
+            by_path,
+            by_hash,
+            probe: s.media.file_probe.clone(),
+            file_bytes: s.media.file_bytes.clone(),
+            cache: std::mem::take(&mut s.import_probes),
+            naming: s.xmp.naming,
+            now: (s.clock)(),
+            total: Default::default(),
+            done: Default::default(),
+        })
+    }
+
+    /// The file-system half of importing `paths`: expand folders, skip known paths, probe, skip
+    /// duplicates by content, read sidecars, copy or place (Move) the files. Nothing in the
+    /// catalog changes. Stops before the next file once `cancel` is set.
+    pub fn prepare(&mut self, paths: &[String], cancel: &std::sync::atomic::AtomicBool) -> Prepared {
+        let files = self.expand(paths);
+        self.prepare_files(files, cancel)
+    }
+
+    /// Expand `paths` (folders recursively, the library's own folder skipped) into the files an
+    /// import would handle; counted in [`ImportJob::total`].
+    pub fn expand(&self, paths: &[String]) -> Vec<String> {
+        let files = expand(paths, self.lib_dir.as_deref());
+        self.total.fetch_add(files.len(), std::sync::atomic::Ordering::Relaxed);
+        files
+    }
+
+    /// When the import started ([`Session::clock`]), for [`commit_prepared`].
+    pub fn now(&self) -> &str {
+        &self.now
+    }
+
+    /// [`ImportJob::prepare`] for files [`ImportJob::expand`] returned.
+    pub fn prepare_files(&mut self, files: Vec<String>, cancel: &std::sync::atomic::AtomicBool) -> Prepared {
+        use std::sync::atomic::Ordering::Relaxed;
+        let opts = self.opts.clone();
+        let mode = self.mode;
+        let mut out = Prepared { scanned: files.len(), items: Vec::new() };
+        let mut todo = Vec::new();
+        for f in files {
+            match self.by_path.get(f.as_str()).copied() {
+                Some((id, true)) if !opts.local => {
+                    // a file that was only browsed (Local) joins the library when it is imported for real
+                    self.by_path.insert(f, (id, false));
+                    out.items.push(PreparedItem::Promote(id));
+                    self.done.fetch_add(1, Relaxed);
+                }
+                Some((id, _)) => {
+                    out.items.push(PreparedItem::Duplicate { path: f, existing: Some(id), reason: "path", hash: None });
+                    self.done.fetch_add(1, Relaxed);
+                }
+                None => todo.push(f),
+            }
+        }
+
+        // files a preceding scan already probed are not read again (a network share is slow to read)
+        let cached: Vec<Option<ProbeInfo>> = todo.iter().map(|f| self.cache.remove(f)).collect();
+        let missing: Vec<String> = todo.iter().zip(&cached).filter(|(_, c)| c.is_none()).map(|(f, _)| f.clone()).collect();
+        let progress = ScanProgress::default();
+        let mut fresh = probe_all(self.probe.as_ref(), &missing, &progress).into_iter();
+        let probed: Vec<Result<ProbeInfo, String>> =
+            cached.into_iter().map(|c| c.map(Ok).unwrap_or_else(|| fresh.next().unwrap_or_else(|| Err("not probed".into())))).collect();
+        crate::memory::release();
+        for (path, info) in todo.into_iter().zip(probed) {
+            if cancel.load(Relaxed) {
+                break;
+            }
+            self.done.fetch_add(1, Relaxed);
+            let mut info = match info {
+                Ok(i) => i,
+                Err(e) => {
+                    log::warn!("import {path}: {e}");
+                    out.items.push(PreparedItem::Failed(path, e));
+                    continue;
+                }
+            };
+            if let Some(h) = &info.content_hash
+                && !opts.local
+                && let Some(existing) = self.by_hash.get(h)
+            {
+                out.items.push(PreparedItem::Duplicate { path, existing: *existing, reason: "content", hash: Some(h.clone()) });
                 continue;
             }
-        };
-        if let Some(h) = &info.content_hash
-            && !opts.local
-            && let Some(id) = by_hash.get(h)
-        {
-            report.duplicates.push(Duplicate { path, existing: Some(id.0), reason: "content" });
-            continue;
-        }
-        // the XMP sidecar (or a raw's embedded XMP), read before copying: its capture time files
-        // and names the copy when the file itself has none
-        let raw = info.kind == MediaKind::Raw;
-        let packet = crate::sidecar::find_sidecar(&path, s.xmp.naming)
-            .and_then(|f| std::fs::read_to_string(f).ok())
-            .or_else(|| info.xmp.clone().filter(|_| raw));
-        let sidecar = packet.and_then(|x| match crate::sidecar::parse_sidecar(&x, raw).map(|sc| sc.resolve_label(&s.catalog)) {
-            Ok(sc) => (sc != crate::sidecar::SidecarData::default()).then_some(sc),
-            Err(e) => {
-                log::warn!("import {path}: XMP: {e}");
-                None
+            // the XMP sidecar (or a raw's embedded XMP), read before copying: its capture time files
+            // and names the copy when the file itself has none
+            let raw = info.kind == MediaKind::Raw;
+            let packet = crate::sidecar::find_sidecar(&path, self.naming)
+                .and_then(|f| std::fs::read_to_string(f).ok())
+                .or_else(|| info.xmp.clone().filter(|_| raw));
+            let sidecar = packet.and_then(|x| match crate::sidecar::parse_sidecar(&x, raw) {
+                Ok(sc) => Some(sc),
+                Err(e) => {
+                    log::warn!("import {path}: XMP: {e}");
+                    None
+                }
+            });
+            if info.captured.is_none() {
+                info.captured = sidecar.as_ref().and_then(|sc| sc.captured.clone());
             }
-        });
-        let mut info = info;
-        if info.captured.is_none() {
-            info.captured = sidecar.as_ref().and_then(|sc| sc.captured.clone());
-        }
-        let stored = match (mode, &copy_root) {
-            (ImportMode::Copy | ImportMode::Move, Some(root))
-                if !crate::import_move::inside(Path::new(&path), root)
-                    && !lib_dir.as_ref().is_some_and(|l| crate::import_move::inside(Path::new(&path), l)) =>
+            let mut placed = None;
+            let stored = match (mode, &self.copy_root) {
+                (ImportMode::Copy | ImportMode::Move, Some(root))
+                    if !crate::import_move::inside(Path::new(&path), root)
+                        && !self.lib_dir.as_ref().is_some_and(|l| crate::import_move::inside(Path::new(&path), l)) =>
+                {
+                    // the templates see the photo as it will be catalogued (undated: the import time)
+                    let own = Path::new(&path).file_name().map(|n| n.to_string_lossy().to_string()).unwrap_or_default();
+                    let mut q = Photo::new(PhotoId(0), Source::File { path: path.clone() }, &own, &info.format, 0, 0, &self.now);
+                    q.captured = info.captured.clone();
+                    q.meta = info.meta.clone();
+                    let name = opts.rename.as_deref().filter(|t| !t.trim().is_empty()).map(|t| {
+                        let n = crate::rename::expand(t, &q, self.seq);
+                        self.seq += 1;
+                        n
+                    });
+                    let folders = opts.organize.folders(&q);
+                    if mode == ImportMode::Move && !crate::import_move::is_symlink(Path::new(&path)) {
+                        let dir = folders.iter().fold(root.to_path_buf(), |d, f| d.join(f));
+                        let name = name.unwrap_or(own);
+                        match crate::import_move::place(Path::new(&path), &dir, &name) {
+                            Ok(pl) => {
+                                let dst = pl.dst.to_string_lossy().to_string();
+                                placed = Some(pl);
+                                dst
+                            }
+                            Err(e) => {
+                                out.items.push(PreparedItem::Failed(path, e));
+                                continue;
+                            }
+                        }
+                    } else {
+                        if mode == ImportMode::Move {
+                            let reason = "a symbolic link: the file it points to was copied, the link and its target stay";
+                            out.items.push(PreparedItem::Kept(Kept { path: path.clone(), reason: reason.into() }));
+                        }
+                        match copy_into(root, &path, &folders, name.as_deref()) {
+                            Ok(p) => p,
+                            Err(e) => {
+                                out.items.push(PreparedItem::Failed(path, e));
+                                continue;
+                            }
+                        }
+                    }
+                }
+                (ImportMode::Move, _) => {
+                    let reason = "already inside the destination or the library: added where it is";
+                    out.items.push(PreparedItem::Kept(Kept { path: path.clone(), reason: reason.into() }));
+                    path.clone()
+                }
+                _ => path.clone(),
+            };
+            if let Some(h) = &info.content_hash {
+                self.by_hash.insert(h.clone(), None);
+            }
+            // Copy as DNG: the copied raw becomes a DNG (the copy is ours to replace)
+            let mut stored = stored;
+            if opts.convert_dng
+                && mode == ImportMode::Copy
+                && stored != path
+                && info.kind == MediaKind::Raw
+                && !info.format.eq_ignore_ascii_case("DNG")
             {
-                // the templates see the photo as it will be catalogued (undated: the import time)
-                let own = Path::new(&path).file_name().map(|n| n.to_string_lossy().to_string()).unwrap_or_default();
-                let mut q = Photo::new(PhotoId(0), Source::File { path: path.clone() }, &own, &info.format, 0, 0, &now);
-                q.captured = info.captured.clone();
-                q.meta = info.meta.clone();
-                let name = opts.rename.as_deref().filter(|t| !t.trim().is_empty()).map(|t| {
-                    let n = crate::rename::expand(t, &q, seq);
-                    seq += 1;
-                    n
+                match crate::cmd::convert::write_dng_with(self.file_bytes.as_ref(), &stored, String::new()) {
+                    Ok(dng) => {
+                        let _ = std::fs::remove_file(&stored);
+                        stored = dng;
+                        info.format = "DNG".into();
+                    }
+                    Err(e) => log::warn!("import {path}: copy as DNG: {e}"),
+                }
+            }
+            out.items.push(PreparedItem::Ready(Box::new(ReadyFile { path, stored, info, sidecar, placed })));
+        }
+        out
+    }
+}
+
+/// The catalog half of an import: add the photos [`ImportJob::prepare`] readied (one undoable op;
+/// a Move's sources are removed once it is saved). On a failed commit a Move's placed files are
+/// taken back.
+pub fn commit_prepared(s: &mut Session, opts: &ImportOptions, now: &str, prepared: Prepared) -> crate::Result<ImportReport> {
+    let now = now.to_string();
+    let mut report = ImportReport { scanned: prepared.scanned, ..Default::default() };
+    let mut ops = Vec::new();
+    // Move: placed at the destination, sources untouched until the records are committed
+    let mut placed: Vec<crate::import_move::Placed> = Vec::new();
+    // photos added by this batch, by content (a duplicate of a file earlier in the import names it)
+    let mut new_hash: HashMap<String, PhotoId> = HashMap::new();
+    for it in prepared.items {
+        match it {
+            PreparedItem::Promote(id) => {
+                if s.catalog.photo(id).is_some_and(|p| p.local) {
+                    ops.push(Op::SetLocal { id, local: false });
+                }
+                report.imported.push(id.0);
+            }
+            PreparedItem::Duplicate { path, existing, reason, hash } => {
+                let existing = existing.or_else(|| {
+                    let h = hash?;
+                    new_hash.get(&h).copied().or_else(|| s.catalog.photos().find(|p| p.content_hash.as_deref() == Some(h.as_str())).map(|p| p.id))
                 });
-                let folders = opts.organize.folders(&q);
-                if mode == ImportMode::Move && !crate::import_move::is_symlink(Path::new(&path)) {
-                    let dir = folders.iter().fold(root.to_path_buf(), |d, f| d.join(f));
-                    let name = name.unwrap_or(own);
-                    match crate::import_move::place(Path::new(&path), &dir, &name) {
-                        Ok(pl) => {
-                            let dst = pl.dst.to_string_lossy().to_string();
-                            placed.push(pl);
-                            dst
-                        }
-                        Err(e) => {
-                            report.failed.push((path, e));
-                            continue;
-                        }
-                    }
-                } else {
-                    if mode == ImportMode::Move {
-                        let reason = "a symbolic link: the file it points to was copied, the link and its target stay";
-                        report.kept.push(Kept { path: path.clone(), reason: reason.into() });
-                    }
-                    match copy_into(root, &path, &folders, name.as_deref()) {
-                        Ok(p) => p,
-                        Err(e) => {
-                            report.failed.push((path, e));
-                            continue;
-                        }
+                report.duplicates.push(Duplicate { path, existing: existing.map(|i| i.0), reason });
+            }
+            PreparedItem::Failed(path, e) => report.failed.push((path, e)),
+            PreparedItem::Kept(k) => report.kept.push(k),
+            PreparedItem::Ready(r) => {
+                let ReadyFile { path, stored, info, sidecar, placed: pl } = *r;
+                placed.extend(pl);
+                let id = s.catalog.alloc_photo_id();
+                if let Some(h) = &info.content_hash {
+                    new_hash.insert(h.clone(), id);
+                }
+                let sidecar = sidecar.map(|sc| sc.resolve_label(&s.catalog)).filter(|sc| *sc != crate::sidecar::SidecarData::default());
+                // a copy is catalogued under its new name
+                let name = Path::new(&stored).file_name().map(|n| n.to_string_lossy().to_string()).unwrap_or_else(|| path.clone());
+                let mut p = Photo::new(id, Source::File { path: stored }, &name, &info.format, info.width, info.height, &now);
+                p.kind = info.kind;
+                p.file_size = info.file_size;
+                p.captured = info.captured;
+                p.meta = info.meta;
+                p.as_shot_wb = info.as_shot_wb;
+                p.content_hash = info.content_hash;
+                p.embedded_lens = info.embedded_lens;
+                p.preview_only = info.preview_only.clone();
+                apply_import_defaults(s, &mut p);
+                if let Some(sc) = &sidecar {
+                    crate::sidecar::merge_into(&mut p, sc, &now);
+                    report.sidecars += 1;
+                }
+                if let Some(mp) = opts.metadata_preset.as_ref().and_then(|n| s.metadata_presets.iter().find(|m| m.name.eq_ignore_ascii_case(n))) {
+                    crate::cmd::metadata::apply_to(&mut p.meta, &mp.fields);
+                }
+                for k in &opts.keywords {
+                    let k = lightcraft_catalog::keywords::clean(k);
+                    if !k.is_empty() && !p.meta.keywords.iter().any(|x| x.eq_ignore_ascii_case(&k)) {
+                        p.meta.keywords.push(k);
                     }
                 }
-            }
-            (ImportMode::Move, _) => {
-                let reason = "already inside the destination or the library: added where it is";
-                report.kept.push(Kept { path: path.clone(), reason: reason.into() });
-                path.clone()
-            }
-            _ => path.clone(),
-        };
-        let id = s.catalog.alloc_photo_id();
-        if let Some(h) = &info.content_hash {
-            by_hash.insert(h.clone(), id);
-        }
-        // Copy as DNG: the copied raw becomes a DNG (the copy is ours to replace)
-        let mut stored = stored;
-        if opts.convert_dng && mode == ImportMode::Copy && stored != path && info.kind == MediaKind::Raw && !info.format.eq_ignore_ascii_case("DNG") {
-            match crate::cmd::convert::write_dng_for(s, &stored, String::new()) {
-                Ok(dng) => {
-                    let _ = std::fs::remove_file(&stored);
-                    stored = dng;
-                    info.format = "DNG".into();
+                if let Some(preset) = &opts.preset {
+                    let d = std::sync::Arc::new(preset.apply(&p.develop, 1.0));
+                    let label = format!("Preset: {}", preset.name);
+                    p.develop = d.clone();
+                    p.edited = Some(now.clone());
+                    p.history.push(lightcraft_catalog::HistoryStep { label, settings: d });
                 }
-                Err(e) => log::warn!("import {path}: copy as DNG: {e}"),
+                report.imported.push(id.0);
+                p.local = opts.local;
+                if opts.local {
+                    // the state as browsed: a later change keeps the record from being forgotten
+                    p.set_local_baseline();
+                }
+                ops.push(Op::AddPhoto { photo: Box::new(p) });
             }
         }
-        // a copy is catalogued under its new name
-        let name = Path::new(&stored).file_name().map(|n| n.to_string_lossy().to_string()).unwrap_or_else(|| path.clone());
-        let mut p = Photo::new(id, Source::File { path: stored }, &name, &info.format, info.width, info.height, &now);
-        p.kind = info.kind;
-        p.file_size = info.file_size;
-        p.captured = info.captured;
-        p.meta = info.meta;
-        p.as_shot_wb = info.as_shot_wb;
-        p.content_hash = info.content_hash;
-        p.embedded_lens = info.embedded_lens;
-        p.preview_only = info.preview_only.clone();
-        apply_import_defaults(s, &mut p);
-        if let Some(sc) = &sidecar {
-            crate::sidecar::merge_into(&mut p, sc, &now);
-            report.sidecars += 1;
-        }
-        if let Some(mp) = opts.metadata_preset.as_ref().and_then(|n| s.metadata_presets.iter().find(|m| m.name.eq_ignore_ascii_case(n))) {
-            crate::cmd::metadata::apply_to(&mut p.meta, &mp.fields);
-        }
-        for k in &opts.keywords {
-            let k = lightcraft_catalog::keywords::clean(k);
-            if !k.is_empty() && !p.meta.keywords.iter().any(|x| x.eq_ignore_ascii_case(&k)) {
-                p.meta.keywords.push(k);
-            }
-        }
-        if let Some(preset) = &opts.preset {
-            let d = std::sync::Arc::new(preset.apply(&p.develop, 1.0));
-            let label = format!("Preset: {}", preset.name);
-            p.develop = d.clone();
-            p.edited = Some(now.clone());
-            p.history.push(lightcraft_catalog::HistoryStep { label, settings: d });
-        }
-        report.imported.push(id.0);
-        p.local = opts.local;
-        if opts.local {
-            // the state as browsed: a later change keeps the record from being forgotten
-            p.set_local_baseline();
-        }
-        ops.push(Op::AddPhoto { photo: Box::new(p) });
     }
     let log0 = s.pending_log.len();
     if !ops.is_empty()

crates/engine/src/import_move.rs

@@ -169,6 +169,27 @@ pub(crate) fn place(src: &Path, dir: &Path, name: &str) -> Result<Placed, String
     Ok(placed)
 }
 
+/// Import → **Copy**: copy `src` into `dir` as `name` (-1, -2… when taken) with the same checks as
+/// a move's copy — a new file (never overwriting one, even one that appears meanwhile), synced to
+/// disk and compared byte for byte with the source; a bad copy is removed and reported, so a card
+/// is never wiped on the strength of it. Returns the new path.
+pub(crate) fn copy_new(src: &Path, dir: &Path, name: &str) -> Result<PathBuf, String> {
+    fs::create_dir_all(dir).map_err(|e| format!("{}: {e}", dir.display()))?;
+    let (stem, ext) = match name.rsplit_once('.') {
+        Some((s, e)) if !s.is_empty() => (s.to_string(), format!(".{e}")),
+        _ => (name.to_string(), String::new()),
+    };
+    for i in 0..100_000u32 {
+        let d = if i == 0 { dir.join(name) } else { dir.join(format!("{stem}-{i}{ext}")) };
+        match copy_verified(src, &d) {
+            Ok(()) => return Ok(d),
+            Err(e) if e.kind() == io::ErrorKind::AlreadyExists => continue,
+            Err(e) => return Err(format!("copy {}: {e} (nothing was imported from it; the original is untouched)", src.display())),
+        }
+    }
+    Err(format!("copy {}: no free name in {}", src.display(), dir.display()))
+}
+
 /// Undo a [`place`]: remove what it created at the destination (the sources were never touched).
 pub(crate) fn rollback(p: &Placed) {
     for sc in p.sidecars.iter().filter(|s| s.created) {
@@ -213,7 +234,7 @@ pub(crate) fn finish(p: &Placed) -> Result<Vec<(String, String)>, String> {
 }
 
 /// A photo (by extension) still beside a stem-named sidecar, sharing its stem.
-fn sibling_photo(sidecar: &Path) -> Option<String> {
+pub(crate) fn sibling_photo(sidecar: &Path) -> Option<String> {
     let dir = sidecar.parent()?;
     let stem = sidecar.file_stem()?.to_string_lossy().to_string();
     fs::read_dir(dir).ok()?.flatten().map(|e| e.path()).find_map(|f| {

crates/engine/src/lib.rs

@@ -10,6 +10,8 @@
 //! run them off the UI thread.
 #![forbid(unsafe_code)]
 
+pub mod availability;
+mod camera_preview;
 pub mod cmd;
 pub mod crs;
 pub mod crs_masks;
@@ -57,6 +59,9 @@ pub enum EngineError {
     /// be written. They stay queued and are written by the next successful save.
     #[error("saved in memory but not written to disk: {0}; LightCraft will retry")]
     NotSaved(String),
+    /// Another process (the app, `lightcraft-cli`, another computer) has the library open.
+    #[error("{0}")]
+    LibraryInUse(String),
     #[error("{0}")]
     Other(String),
 }
@@ -68,6 +73,22 @@ pub type Result<T> = std::result::Result<T, EngineError>;
 pub struct UndoEntry {
     pub label: String,
     pub op: Op,
+    /// A folder to rename on disk (`from` → `to`) before `op` is applied: Rename / Move Folder
+    /// (whose `op` relinks the photos inside). Never overwrites; refused when `to` exists.
+    pub folder: Option<FolderMove>,
+}
+
+/// A folder renamed or moved on disk as part of an undo step.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct FolderMove {
+    pub from: String,
+    pub to: String,
+}
+
+impl FolderMove {
+    fn reversed(&self) -> Self {
+        Self { from: self.to.clone(), to: self.from.clone() }
+    }
 }
 
 /// An in-progress slider drag / brush stroke: one undo step when it ends.
@@ -253,11 +274,22 @@ impl Session {
         (spec.enabled)(self).map_err(|why| EngineError::Disabled(id.to_string(), why))?;
         let empty = Value::Object(Default::default());
         let params = if params.is_null() { &empty } else { params };
+        self.run_command(id, spec.journal.then_some(params), |s| (spec.run)(s, params))
+    }
+
+    /// Run `f` as command `id` with what [`Session::execute`] does around every command: the
+    /// panic guard, auto versions, XMP sidecar auto-write and the durable save (a failed save is
+    /// `NotSaved`). Not journaled. The app's import task commits its batches this way.
+    pub fn execute_fn(&mut self, id: &str, f: impl FnOnce(&mut Session) -> Result<Value>) -> Result<Value> {
+        self.run_command(id, None, f)
+    }
+
+    fn run_command(&mut self, id: &str, journal: Option<&Value>, f: impl FnOnce(&mut Session) -> Result<Value>) -> Result<Value> {
         let log_start = self.pending_log.len();
         let was_active = self.active();
         self.depth += 1;
         // last-resort guard: a panic in a command is that command's error, not a crash
-        let r = guard::catch(&format!("`{id}`"), || (spec.run)(self, params)).unwrap_or_else(|e| Err(EngineError::Other(e)));
+        let r = guard::catch(&format!("`{id}`"), || f(self)).unwrap_or_else(|e| Err(EngineError::Other(e)));
         self.depth -= 1;
         if self.depth == 0 && was_active.is_some() && self.active() != was_active {
             self.previous_active = was_active;
@@ -265,7 +297,10 @@ impl Session {
                 self.auto_version(left);
             }
         }
-        if r.is_ok() && spec.journal && self.depth == 0 {
+        if r.is_ok()
+            && let Some(params) = journal
+            && self.depth == 0
+        {
             self.journal.push((id.to_string(), params.clone()));
             if self.journal.len() > 10_000 {
                 self.journal.drain(..1000);
@@ -302,7 +337,7 @@ impl Session {
         let fwd = op.clone();
         let inv = self.catalog.apply(op)?;
         self.pending_log.push(fwd);
-        self.undo.push(UndoEntry { label: label.to_string(), op: inv });
+        self.undo.push(UndoEntry { label: label.to_string(), op: inv, folder: None });
         if self.undo.len() > 1000 {
             self.undo.remove(0);
         }
@@ -310,6 +345,16 @@ impl Session {
         Ok(())
     }
 
+    /// [`Session::commit`] for an op that goes with a folder already renamed on disk; the undo
+    /// step renames it back (`folder` is the undo direction: current place → old place).
+    pub(crate) fn commit_with_folder(&mut self, label: &str, op: Op, folder: FolderMove) -> Result<()> {
+        self.commit(label, op)?;
+        if let Some(e) = self.undo.last_mut() {
+            e.folder = Some(folder);
+        }
+        Ok(())
+    }
+
     /// Leaving photo `id` after editing it: keep its settings as an automatic version (when they
     /// differ from its latest version; at most [`AUTO_VERSIONS`] auto versions, oldest dropped).
     /// Saved with the library but not an undo step.
@@ -340,9 +385,13 @@ impl Session {
         if n < 2 || n > self.undo.len() {
             return;
         }
+        // a step that moves a folder on disk stays on its own
+        if self.undo[self.undo.len() - n..].iter().any(|e| e.folder.is_some()) {
+            return;
+        }
         let tail = self.undo.split_off(self.undo.len() - n);
         let ops = tail.into_iter().rev().map(|e| e.op).collect();
-        self.undo.push(UndoEntry { label: label.to_string(), op: Op::Batch { ops } });
+        self.undo.push(UndoEntry { label: label.to_string(), op: Op::Batch { ops }, folder: None });
     }
 
     /// Apply without recording undo (interactive previews).
@@ -353,7 +402,7 @@ impl Session {
 
     pub fn undo_step(&mut self) -> Result<String> {
         let e = self.undo.pop().ok_or_else(|| EngineError::Other("nothing to undo".into()))?;
-        let redo = match self.apply_with_files(&e.op) {
+        let redo = match self.apply_with_files(&e.op, e.folder.as_ref()) {
             Ok(r) => r,
             Err(err) => {
                 self.undo.push(e);
@@ -361,13 +410,13 @@ impl Session {
             }
         };
         self.pending_log.push(e.op);
-        self.redo.push(UndoEntry { label: e.label.clone(), op: redo });
+        self.redo.push(UndoEntry { label: e.label.clone(), op: redo, folder: e.folder.as_ref().map(FolderMove::reversed) });
         Ok(e.label)
     }
 
     pub fn redo_step(&mut self) -> Result<String> {
         let e = self.redo.pop().ok_or_else(|| EngineError::Other("nothing to redo".into()))?;
-        let undo = match self.apply_with_files(&e.op) {
+        let undo = match self.apply_with_files(&e.op, e.folder.as_ref()) {
             Ok(r) => r,
             Err(err) => {
                 self.redo.push(e);
@@ -375,19 +424,44 @@ impl Session {
             }
         };
         self.pending_log.push(e.op);
-        self.undo.push(UndoEntry { label: e.label.clone(), op: undo });
+        self.undo.push(UndoEntry { label: e.label.clone(), op: undo, folder: e.folder.as_ref().map(FolderMove::reversed) });
         Ok(e.label)
     }
 
-    /// Apply an undo/redo op, first moving the files its renames imply (all or nothing).
-    fn apply_with_files(&mut self, op: &Op) -> Result<Op> {
+    /// Apply an undo/redo op, first renaming the step's folder and moving the files its renames
+    /// imply (all or nothing). Files that can't be moved back after a failure are reported and the
+    /// library follows them (a logged change outside the undo history), so none goes missing; the
+    /// folder is only moved back when no file was left behind at its new path.
+    fn apply_with_files(&mut self, op: &Op, folder: Option<&FolderMove>) -> Result<Op> {
+        let fs = rename::RealFs;
+        if let Some(f) = folder {
+            cmd::browse::rename_folder_on_disk(&f.from, &f.to).map_err(|e| EngineError::Other(format!("can't move the folder back: {e}")))?;
+        }
+        let undo_folder = || {
+            if let Some(f) = folder {
+                let _ = cmd::browse::rename_folder_on_disk(&f.to, &f.from);
+            }
+        };
         let moves = self.file_moves(op);
-        Session::move_files(&moves)?;
+        if let Err(e) = rename::move_all(&fs, &moves) {
+            if e.stuck.is_empty() {
+                undo_folder();
+            }
+            return Err(EngineError::Other(format!("can't move the files back: {}", self.follow_stuck(op, e, false))));
+        }
         match self.catalog.apply(op.clone()) {
-            Ok(inv) => Ok(inv),
+            Ok(inv) => {
+                if let Some(f) = folder {
+                    cmd::browse::follow_folder(self, &f.from, &f.to);
+                }
+                Ok(inv)
+            }
             Err(e) => {
                 let back: Vec<(String, String)> = moves.iter().rev().map(|(a, b)| (b.clone(), a.clone())).collect();
-                let _ = Session::move_files(&back);
+                if let Err(be) = rename::move_all(&fs, &back) {
+                    return Err(EngineError::Other(format!("{e}; the files could not all be moved back: {}", be.message)));
+                }
+                undo_folder();
                 Err(e.into())
             }
         }
@@ -502,7 +576,11 @@ impl Session {
 
     /// Photos shown in the grid/filmstrip for the current source, filter and sort.
     pub fn visible(&mut self) -> &[PhotoId] {
-        let key = (self.catalog.revision, format!("{:?}|{:?}|{:?}|{:?}", self.source, self.filter, self.sort, self.browse));
+        let mut key = (self.catalog.revision, format!("{:?}|{:?}|{:?}|{:?}", self.source, self.filter, self.sort, self.browse));
+        if self.source == LibrarySource::Missing && self.media.availability.is_background() {
+            // the view fills in as the background checks find files gone
+            key.1.push_str(&format!("|{}", self.media.availability.generation()));
+        }
         if self.visible_key.as_ref() != Some(&key) {
             // "in the last N days" rules count back from the session's clock
             lightcraft_catalog::rules::set_now(Some((self.clock)()));
@@ -537,8 +615,8 @@ impl Session {
             }
             if self.source == LibrarySource::Missing {
                 // only the photos the query kept (library photos, not Local browse records) are checked
-                let cat = &self.catalog;
-                visible.retain(|id| cmd::missing::is_missing(cat, *id));
+                let (cat, avail) = (&self.catalog, &self.media.availability);
+                visible.retain(|id| cmd::missing::is_missing(cat, avail, *id));
             }
             if self.source != LibrarySource::RecentlyDeleted {
                 visible = self.catalog.arrange_stacks(&visible);
@@ -635,6 +713,8 @@ mod tests_persist;
 #[cfg(test)]
 mod tests_prefs;
 #[cfg(test)]
+mod tests_settings_files;
+#[cfg(test)]
 mod tests_spots;
 #[cfg(test)]
 mod tests_xmp;

crates/engine/src/library.rs

@@ -23,7 +23,7 @@
 
 use std::path::{Path, PathBuf};
 
-use lightcraft_catalog::{FsStore, Journal, LoadReport, Store};
+use lightcraft_catalog::{FsStore, Journal, LibraryLock, LoadReport, Store};
 use lightcraft_develop::Preset;
 use serde::{Deserialize, Serialize};
 
@@ -64,6 +64,15 @@ pub struct Library {
     pub forgot_local: Option<lightcraft_catalog::ForgetPlan>,
     presets_written: String,
     view_written: Vec<u8>,
+    /// Settings files that were unreadable or damaged when the library opened (`library.info` →
+    /// `settingsWarnings`; shown by the UI once, see [`Session::take_library_warnings`]).
+    pub settings_warnings: Vec<String>,
+    warnings_reported: usize,
+    /// Settings files that couldn't be read or set aside: never overwritten this session.
+    blocked: Vec<&'static str>,
+    /// Keeps other processes out of this library while it's open (last: released after the
+    /// journal's background snapshot has landed).
+    lock: Option<LibraryLock>,
 }
 
 /// Where a library's files live (see [`Session::open_library_in`]).
@@ -171,23 +180,112 @@ fn poll_compaction(lib: &mut Library) {
 /// How long the frame loop waits before retrying a failed append (commands retry at once).
 const RETRY_BACKOFF: std::time::Duration = std::time::Duration::from_secs(2);
 
-fn read_json<T: serde::de::DeserializeOwned>(store: &mut dyn Store, name: &str) -> Option<T> {
-    store.read(name).ok().flatten().and_then(|b| serde_json::from_slice(&b).ok())
+/// `a` and `b` name the same directory.
+fn same_dir(a: &Path, b: &Path) -> bool {
+    match (std::fs::canonicalize(a), std::fs::canonicalize(b)) {
+        (Ok(a), Ok(b)) => a == b,
+        _ => a == b,
+    }
+}
+
+/// This program, for the lock owner note ("LightCraft", "lightcraft-cli").
+fn program_name() -> String {
+    let exe = std::env::current_exe().ok().and_then(|p| p.file_stem().map(|s| s.to_string_lossy().to_string()));
+    match exe.as_deref() {
+        Some("lightcraft") | None => "LightCraft".into(),
+        Some(other) => other.to_string(),
+    }
+}
+
+/// Problems reading the settings files (`presets.json`, `prefs.json`, `view.json`) when the library
+/// opened (issue #103). A missing file is not a problem (defaults). A file that doesn't parse is
+/// kept as `<name>.corrupt-<unix time>` before the defaults are used (so the next save can't
+/// lose it); a file that can't be read at all (locked by another program, I/O error) is never
+/// written this session, so its content survives until the library is opened again.
+#[derive(Default)]
+struct SettingsLoad {
+    warnings: Vec<String>,
+    /// Files not to overwrite this session.
+    blocked: Vec<&'static str>,
+}
+
+impl SettingsLoad {
+    fn read<T: serde::de::DeserializeOwned>(&mut self, store: &mut dyn Store, name: &'static str) -> Option<T> {
+        let bytes = match store.read(name) {
+            Ok(b) => b?,
+            Err(e) => {
+                log::error!("library: {name}: {e}");
+                self.blocked.push(name);
+                self.warnings.push(format!(
+                    "{name} couldn't be read ({e}). LightCraft uses the defaults for now and won't overwrite the file; reopen the library to try again."
+                ));
+                return None;
+            }
+        };
+        let err = match serde_json::from_slice(&bytes) {
+            Ok(v) => return Some(v),
+            Err(e) => e,
+        };
+        let secs = web_time::SystemTime::now().duration_since(web_time::UNIX_EPOCH).map(|d| d.as_secs()).unwrap_or(0);
+        let keep = format!("{name}.corrupt-{secs}");
+        log::error!("library: {name} is damaged: {err}");
+        match store.write_atomic(&keep, &bytes) {
+            Ok(()) => self.warnings.push(format!("{name} is damaged ({err}). It was kept as {keep}, and the defaults are used.")),
+            Err(w) => {
+                self.blocked.push(name);
+                self.warnings.push(format!(
+                    "{name} is damaged ({err}) and couldn't be set aside ({w}). LightCraft uses the defaults and won't overwrite the file."
+                ));
+            }
+        }
+        None
+    }
 }
 
 impl Session {
     /// Open (or create) the library at `dir` into this session, replacing its catalog. With
     /// `seed_demo`, a newly created library starts with the procedural demo photos.
+    ///
+    /// The library is locked for this session ([`lightcraft_catalog::lock`]): if another process
+    /// has it open, this fails with [`EngineError::LibraryInUse`] and nothing is read or changed.
+    /// Reopening the library this session already has open keeps its lock.
     pub fn open_library(&mut self, dir: impl AsRef<Path>, seed_demo: bool) -> Result<&LoadReport> {
         let dir = dir.as_ref().to_path_buf();
         let open = || FsStore::open(&dir).map_err(|e| EngineError::Other(format!("can't open library {}: {e}", dir.display())));
         let stores = LibraryStores { catalog: Box::new(open()?), files: Box::new(open()?), on_disk: true, dir: dir.clone() };
-        self.open_library_in(stores, seed_demo)
+        // the library open in this session (same directory): hand its lock over
+        let reused = self.library.as_mut().filter(|l| same_dir(&l.dir, &dir)).and_then(|l| l.lock.take());
+        let reusing = reused.is_some();
+        let mut lock = match reused {
+            Some(l) => Some(l),
+            None => Some(LibraryLock::acquire(&dir, &program_name()).map_err(|e| EngineError::LibraryInUse(e.to_string()))?),
+        };
+        if let Err(e) = self.open_stores(stores, seed_demo, &mut lock) {
+            if reusing && let Some(lib) = self.library.as_mut() {
+                lib.lock = lock.take();
+            }
+            return Err(e);
+        }
+        self.loaded_report()
     }
 
     /// Open (or create) a library whose files live in `stores` (e.g. browser storage), replacing
-    /// this session's catalog.
+    /// this session's catalog. Not locked: the host guards against a second opener (see
+    /// [`Session::open_library`] for directories).
     pub fn open_library_in(&mut self, stores: LibraryStores, seed_demo: bool) -> Result<&LoadReport> {
+        self.open_stores(stores, seed_demo, &mut None)?;
+        self.loaded_report()
+    }
+
+    fn loaded_report(&self) -> Result<&LoadReport> {
+        match &self.library {
+            Some(lib) => Ok(&lib.report),
+            None => Err(EngineError::Other("library closed while opening".into())),
+        }
+    }
+
+    /// Open `stores`; the new library takes `lock` once nothing can fail any more.
+    fn open_stores(&mut self, stores: LibraryStores, seed_demo: bool, lock: &mut Option<LibraryLock>) -> Result<()> {
         let LibraryStores { dir, catalog, mut files, on_disk } = stores;
         self.media.smart_dir = on_disk.then(|| crate::smart::dir(&dir));
         // the current library may be these same files: let its background snapshot land first
@@ -208,8 +306,9 @@ impl Session {
             crate::demo::load(self);
             journal.snapshot(&self.catalog)?;
         }
+        let mut settings = SettingsLoad::default();
         // presets
-        if let Some(f) = read_json::<PresetsFile>(files.as_mut(), "presets.json") {
+        if let Some(f) = settings.read::<PresetsFile>(files.as_mut(), "presets.json") {
             for p in &mut self.presets {
                 p.favorite = p.builtin && f.favorites.contains(&p.id) || (!p.builtin && p.favorite);
             }
@@ -223,7 +322,7 @@ impl Session {
             self.profile_recent = f.profile_recent.into_iter().filter(known).take(crate::presets::RECENT_PROFILES).collect();
         }
         // preferences
-        let prefs = read_json::<PrefsFile>(files.as_mut(), "prefs.json").unwrap_or_default();
+        let prefs = settings.read::<PrefsFile>(files.as_mut(), "prefs.json").unwrap_or_default();
         self.xmp = prefs.xmp;
         self.last_export = prefs.last_export;
         self.export_presets = prefs.export_presets;
@@ -244,7 +343,7 @@ impl Session {
             self.media.smart_dir = Some(d.clone());
         }
         // view state
-        if let Some(v) = read_json::<ViewFile>(files.as_mut(), "view.json") {
+        if let Some(v) = settings.read::<ViewFile>(files.as_mut(), "view.json") {
             self.source = v.source;
             self.browse = v.browse;
             self.filter = v.filter;
@@ -277,6 +376,10 @@ impl Session {
             forgot_local: None,
             presets_written,
             view_written,
+            settings_warnings: settings.warnings,
+            warnings_reported: 0,
+            blocked: settings.blocked,
+            lock: lock.take(),
         });
         // forget untouched Local records of folders not browsed for a while (journaled at once)
         if self.forget_local_days > 0 {
@@ -290,10 +393,7 @@ impl Session {
                 lib.forgot_local = Some(plan);
             }
         }
-        match &self.library {
-            Some(lib) => Ok(&lib.report),
-            None => Err(EngineError::Other("library closed while opening".into())),
-        }
+        Ok(())
     }
 
     /// Write pending ops to the log (fsynced), compact when due, and save changed presets.
@@ -332,7 +432,7 @@ impl Session {
         }
         let presets = presets_json(self);
         let Some(lib) = self.library.as_mut() else { return Ok(()) };
-        if presets != lib.presets_written {
+        if presets != lib.presets_written && !lib.blocked.contains(&"presets.json") {
             if let Err(e) = lib.files.write_atomic("presets.json", presets.as_bytes()) {
                 log::error!("library: presets: {e}");
             } else {
@@ -362,16 +462,35 @@ impl Session {
     }
 
     /// Flush everything and write a snapshot (on quit). Ends an open interaction first.
+    ///
+    /// The snapshot is written even when appending the queued ops fails: it is a fresh file
+    /// holding everything in memory, so it saves those ops too (the log handle may be the only
+    /// thing that's broken). Fails only if nothing could be saved; the ops then stay queued.
     pub fn close_library(&mut self) -> Result<()> {
         if self.library.is_none() {
             return Ok(());
         }
         let _ = self.end_interaction();
-        self.persist()?;
+        let persisted = self.persist();
         self.save_view();
+        let unlogged = if persisted.is_err() { self.pending_log.len() as u64 } else { 0 };
         let Some(lib) = self.library.as_mut() else { return Ok(()) };
-        lib.journal.snapshot(&self.catalog)?;
-        Ok(())
+        let before = lib.journal.seq();
+        let snapshot = lib.journal.snapshot_with_unlogged(&self.catalog, unlogged);
+        if unlogged > 0 && lib.journal.seq() == before + unlogged {
+            // the snapshot holds the queued ops: they are saved, never append them again
+            log::info!("library: {unlogged} queued change(s) saved in the closing snapshot");
+            self.pending_log.clear();
+            lib.unsaved_error = None;
+            lib.retry_at = None;
+            lib.last_error = None;
+        }
+        match (persisted, snapshot) {
+            (_, Ok(())) => Ok(()),
+            // neither the log nor the snapshot took the queued ops
+            (Err(EngineError::NotSaved(e)), Err(s)) if lib.journal.seq() == before => Err(EngineError::NotSaved(format!("{e}; snapshot: {s}"))),
+            (_, Err(s)) => Err(s.into()),
+        }
     }
 
     fn view_json(&self) -> Vec<u8> {
@@ -394,7 +513,7 @@ impl Session {
         }
         let v = self.view_json();
         let Some(lib) = self.library.as_mut() else { return };
-        if v != lib.view_written {
+        if v != lib.view_written && !lib.blocked.contains(&"view.json") {
             match lib.files.write_atomic("view.json", &v) {
                 Ok(()) => lib.view_written = v,
                 Err(e) => log::error!("library: view: {e}"),
@@ -423,9 +542,22 @@ impl Session {
         })
         .unwrap_or_default();
         let Some(lib) = self.library.as_mut() else { return Ok(()) };
+        if lib.blocked.contains(&"prefs.json") {
+            return Err(EngineError::Other(
+                "prefs: prefs.json couldn't be read when the library opened, so it isn't overwritten; reopen the library to save preferences".into(),
+            ));
+        }
         lib.files.write_atomic("prefs.json", &v).map_err(|e| EngineError::Other(format!("prefs: {e}")))
     }
 
+    /// Settings-file warnings of the open library not handed out yet (the UI shows each once).
+    pub fn take_library_warnings(&mut self) -> Vec<String> {
+        let Some(lib) = self.library.as_mut() else { return vec![] };
+        let new = lib.settings_warnings[lib.warnings_reported..].to_vec();
+        lib.warnings_reported = lib.settings_warnings.len();
+        new
+    }
+
     /// The thumbnail disk cache budget in bytes ([`Session::cache_mb`], else the default).
     pub fn cache_bytes(&self) -> u64 {
         if self.cache_mb == 0 { crate::media::DISK_CACHE_BYTES } else { u64::from(self.cache_mb) << 20 }

crates/engine/src/media.rs

@@ -26,7 +26,7 @@ use lightcraft_raster::{Histogram, Rgb32f, Rgba8};
 use serde::{Deserialize, Serialize};
 
 /// Bump when the pipeline's output changes, to invalidate cached thumbnails.
-pub const RENDER_CACHE_VERSION: u64 = 4;
+pub const RENDER_CACHE_VERSION: u64 = 6;
 
 /// Thumbnails render at one of these long edges (so window/cell size changes reuse the cache).
 pub const THUMB_SIZES: [usize; 4] = [128, 256, 384, 512];
@@ -71,9 +71,31 @@ pub type FileLoader = Arc<dyn Fn(&str, usize) -> Result<(Rgb32f, SourceInfo), St
 /// `max_edge` (set by the app). `None`: no usable preview.
 pub type PreviewLoader = Arc<dyn Fn(&str, usize) -> Option<Rgba8> + Send + Sync>;
 
+/// Pixels and the source interpretation learned while decoding; they must be cached together.
+#[derive(Clone)]
+pub struct DecodedSource {
+    pub image: Arc<Rgb32f>,
+    pub info: Option<SourceInfo>,
+    /// A smart preview's stored camera tone curve: the one decoder fact its pixels need that the
+    /// catalog's header facts lack (used when `info` is `None`).
+    pub camera_tone: Option<lightcraft_pipeline::tone::CameraTone>,
+}
+
+impl DecodedSource {
+    pub fn new(image: Arc<Rgb32f>, info: Option<SourceInfo>) -> Self {
+        DecodedSource { image, info, camera_tone: None }
+    }
+
+    /// What to render these pixels against: the decoder's facts, else `header` (the catalog's)
+    /// with any stored camera tone curve.
+    pub fn info_or(&self, header: SourceInfo) -> SourceInfo {
+        self.info.unwrap_or(SourceInfo { camera_tone: self.camera_tone.or(header.camera_tone), ..header })
+    }
+}
+
 #[derive(Clone)]
 pub enum SourceRef {
-    Loaded(Arc<Rgb32f>),
+    Loaded(Box<DecodedSource>),
     Demo {
         scene: Box<lightcraft_scenes::Scene>,
         max_edge: usize,
@@ -82,6 +104,9 @@ pub enum SourceRef {
         path: String,
         max_edge: usize,
         loader: Option<FileLoader>,
+        /// The photo's smart preview, used when the original can't be read (offline drive). The
+        /// UI thread never checks whether the original is there; the render worker finds out.
+        fallback: Option<std::path::PathBuf>,
     },
     /// A smart preview standing in for a missing original.
     Smart {
@@ -91,28 +116,41 @@ pub enum SourceRef {
 
 impl SourceRef {
     pub fn load(&self) -> Result<Arc<Rgb32f>, String> {
-        match self {
-            SourceRef::Loaded(a) => Ok(a.clone()),
-            SourceRef::Demo { scene, max_edge } => Ok(Arc::new(scene.render_fit(*max_edge))),
-            SourceRef::File { path, max_edge, loader } => match loader {
-                Some(l) => l(path, *max_edge).map(|(img, _)| Arc::new(img)),
-                None => Err(format!("no decoder available for {path}")),
-            },
+        self.load_source().map(|s| s.image)
+    }
+
+    pub fn load_source(&self) -> Result<DecodedSource, String> {
+        let image = match self {
+            SourceRef::Loaded(a) => return Ok((**a).clone()),
+            SourceRef::Demo { scene, max_edge } => Arc::new(scene.render_fit(*max_edge)),
+            SourceRef::File { path, max_edge, loader, fallback } => {
+                let r = match loader {
+                    Some(l) => l(path, *max_edge).map(|(image, info)| DecodedSource::new(Arc::new(image), Some(info))),
+                    None => Err(format!("no decoder available for {path}")),
+                };
+                // An offline original renders from its smart preview (no decoder facts: header ones).
+                return match (r, fallback) {
+                    #[cfg(not(target_arch = "wasm32"))]
+                    (Err(e), Some(sp)) if crate::smart::is_valid(sp) => crate::smart::load(sp).map_err(|e2| format!("{e}; smart preview: {e2}")),
+                    (r, _) => r,
+                };
+            }
             #[cfg(not(target_arch = "wasm32"))]
-            SourceRef::Smart { path } => crate::smart::load(path),
+            SourceRef::Smart { path } => return crate::smart::load(path),
             #[cfg(target_arch = "wasm32")]
-            SourceRef::Smart { .. } => Err("smart previews are not available here".into()),
-        }
+            SourceRef::Smart { .. } => return Err("smart previews are not available here".into()),
+        };
+        Ok(DecodedSource::new(image, None))
     }
 }
 
 pub struct MediaCache {
     /// Decoded thumbnail-level sources (LRU by bytes).
-    thumbs: Lru<PhotoId, Arc<Rgb32f>>,
+    thumbs: Lru<PhotoId, DecodedSource>,
     /// Decoded preview-level sources with their last use ([`lightcraft_preview::next_tick`]).
-    previews: Vec<(PhotoId, Arc<Rgb32f>, u64)>,
+    previews: Vec<(PhotoId, DecodedSource, u64)>,
     /// The last full-resolution original (exports; one at a time: ~300 MB at 24 MP).
-    full: Option<(PhotoId, Arc<Rgb32f>, u64)>,
+    full: Option<(PhotoId, DecodedSource, u64)>,
     /// How many previews to keep (LRU).
     pub preview_capacity: usize,
     /// Bytes all decoded sources and rendered previews in memory may take together (the cache
@@ -125,6 +163,9 @@ pub struct MediaCache {
     pub file_bytes: Option<crate::merge::ByteReader>,
     /// The library's smart previews folder (originals offline: render from the proxy).
     pub smart_dir: Option<std::path::PathBuf>,
+    /// Whether originals (and smart previews) are on disk: cached and checked off the UI thread
+    /// in the app (see [`crate::availability`]).
+    pub availability: crate::availability::Availability,
     scenes: Vec<lightcraft_scenes::Scene>,
     /// Rendered thumbnails (memory, plus disk once a library is attached).
     pub rendered: Arc<PreviewCache>,
@@ -144,6 +185,7 @@ impl Default for MediaCache {
             preview_loader: None,
             file_bytes: None,
             smart_dir: None,
+            availability: Default::default(),
             scenes: Vec::new(),
             rendered: Arc::new(PreviewCache::memory(rendered_budget(budget))),
         }
@@ -156,7 +198,7 @@ fn rendered_budget(share: usize) -> usize {
 }
 
 fn source_bytes(img: &Rgb32f) -> usize {
-    img.data.len() * 12 + 64
+    img.data.len() * 12 + 64 + std::mem::size_of::<SourceInfo>()
 }
 
 impl MediaCache {
@@ -207,8 +249,8 @@ impl MediaCache {
             let Some((tick, which)) = candidates.into_iter().flatten().min() else { break };
             let freed = match which {
                 0 => self.thumbs.pop_oldest(),
-                1 => self.previews.iter().position(|e| e.2 == tick).map(|i| source_bytes(&self.previews.remove(i).1)),
-                2 => self.full.take().map(|e| source_bytes(&e.1)),
+                1 => self.previews.iter().position(|e| e.2 == tick).map(|i| source_bytes(&self.previews.remove(i).1.image)),
+                2 => self.full.take().map(|e| source_bytes(&e.1.image)),
                 _ => self.rendered.evict_oldest(),
             };
             match freed {
@@ -219,6 +261,10 @@ impl MediaCache {
     }
 
     pub fn get(&mut self, id: PhotoId, level: SourceLevel) -> Option<Arc<Rgb32f>> {
+        self.get_source(id, level).map(|s| s.image)
+    }
+
+    fn get_source(&mut self, id: PhotoId, level: SourceLevel) -> Option<DecodedSource> {
         match level {
             SourceLevel::Thumb => self.thumbs.get(&id).cloned(),
             SourceLevel::Preview => self.previews.iter_mut().find(|e| e.0 == id).map(|e| {
@@ -232,11 +278,31 @@ impl MediaCache {
         }
     }
 
+    /// The facts of photo `id`'s cached sources: the decoder's when one has them, else `header`
+    /// (with a smart preview's stored camera tone curve).
+    fn source_facts(&self, id: PhotoId, header: SourceInfo) -> SourceInfo {
+        let cached = || {
+            self.thumbs
+                .peek(&id)
+                .into_iter()
+                .chain(self.previews.iter().filter(|e| e.0 == id).map(|e| &e.1))
+                .chain(self.full.iter().filter(|e| e.0 == id).map(|e| &e.1))
+        };
+        match cached().find(|s| s.info.is_some()).or_else(|| cached().next()) {
+            Some(s) => s.info_or(header),
+            None => header,
+        }
+    }
+
     pub fn insert(&mut self, id: PhotoId, level: SourceLevel, img: Arc<Rgb32f>) {
+        self.insert_source(id, level, DecodedSource::new(img, None));
+    }
+
+    fn insert_source(&mut self, id: PhotoId, level: SourceLevel, img: DecodedSource) {
         let tick = lightcraft_preview::next_tick();
         match level {
             SourceLevel::Thumb => {
-                let cost = source_bytes(&img);
+                let cost = source_bytes(&img.image);
                 self.thumbs.insert(id, img, cost);
             }
             SourceLevel::Preview => {
@@ -270,29 +336,36 @@ impl MediaCache {
     /// Decoded sources held: (thumbnail level, preview level, full size).
     pub fn usage(&self) -> (crate::memory::Usage, crate::memory::Usage, crate::memory::Usage) {
         use crate::memory::Usage;
-        let previews = Usage::new(self.previews.len(), self.previews.iter().map(|e| source_bytes(&e.1)).sum());
-        let full = self.full.as_ref().map(|e| Usage::new(1, source_bytes(&e.1))).unwrap_or_default();
+        let previews = Usage::new(self.previews.len(), self.previews.iter().map(|e| source_bytes(&e.1.image)).sum());
+        let full = self.full.as_ref().map(|e| Usage::new(1, source_bytes(&e.1.image))).unwrap_or_default();
         (Usage::new(self.thumbs.len(), self.thumbs.cost()), previews, full)
     }
 
     pub fn source_ref(&mut self, p: &Photo, level: SourceLevel) -> SourceRef {
-        if let Some(a) = self.get(p.id, level) {
-            return SourceRef::Loaded(a);
+        if let Some(a) = self.get_source(p.id, level) {
+            return SourceRef::Loaded(Box::new(a));
         }
         // Procedural scenes have a nominal size: "full" is that size, not unbounded.
         let max_edge = level.max_edge().min(match (&p.source, level) {
             (Source::Demo { .. }, SourceLevel::Full) => p.width.max(p.height).max(1) as usize,
             _ => usize::MAX,
         });
-        // the original is offline: its smart preview, when there is one
+        // the original is offline: its smart preview, when there is one. Only cached answers are
+        // used here (no file-system call on the UI thread in the app); an original not known to
+        // be offline is tried first and its smart preview is the render worker's fallback.
         #[cfg(not(target_arch = "wasm32"))]
-        if let (Source::File { path }, Some(dir)) = (&p.source, &self.smart_dir)
-            && !std::path::Path::new(path).exists()
-        {
+        if let (Source::File { path }, Some(dir)) = (&p.source, &self.smart_dir) {
             let sp = dir.join(crate::smart::file_name(p));
-            if sp.exists() {
+            // (a proxy cut short fails to load, like the offline original; the worker's fallback
+            // in `SourceRef::load` only uses a proxy that passes `smart::is_valid`)
+            if self.availability.is_offline(path) && self.availability.exists(&sp.to_string_lossy()) == Some(true) {
                 return SourceRef::Smart { path: sp };
             }
+            let mut r = self.origin_ref(&p.source, max_edge);
+            if let SourceRef::File { fallback, .. } = &mut r {
+                *fallback = Some(sp);
+            }
+            return r;
         }
         self.origin_ref(&p.source, max_edge)
     }
@@ -307,10 +380,10 @@ impl MediaCache {
                 }
                 match self.scenes.iter().find(|s| s.id == *scene) {
                     Some(s) => SourceRef::Demo { scene: Box::new(s.clone()), max_edge },
-                    None => SourceRef::File { path: format!("demo:{scene}"), max_edge, loader: None },
+                    None => SourceRef::File { path: format!("demo:{scene}"), max_edge, loader: None, fallback: None },
                 }
             }
-            Source::File { path } => SourceRef::File { path: path.clone(), max_edge, loader: self.file_loader.clone() },
+            Source::File { path } => SourceRef::File { path: path.clone(), max_edge, loader: self.file_loader.clone(), fallback: None },
         }
     }
 }
@@ -344,7 +417,7 @@ pub struct RenderResult {
     pub key: u64,
     pub rendered: Result<Rendered, String>,
     /// A source that was loaded by this job (to be inserted into the cache).
-    pub loaded: Option<Arc<Rgb32f>>,
+    pub loaded: Option<DecodedSource>,
     /// Set for a [`QuickJob`]'s stand-in: where the image came from.
     pub quick: Option<QuickSource>,
 }
@@ -410,12 +483,14 @@ impl RenderJob {
             };
         }
         let was_loaded = matches!(self.source, SourceRef::Loaded(_));
-        match self.source.load() {
-            Ok(src) => {
+        match self.source.load_source() {
+            Ok(source) => {
+                let src = &source.image;
+                let info = source.info_or(self.info);
                 // Thumbnails (many small jobs side by side) stay on the CPU; views and exports use
                 // the GPU when there is one.
                 let gpu = self.cache.is_none();
-                let rendered = develop(&src, &self.info, &self.settings, &self.request, self.stages.as_deref(), gpu);
+                let rendered = develop(src, &info, &self.settings, &self.request, self.stages.as_deref(), gpu);
                 if let Some((cache, key)) = &self.cache {
                     cache.put(*key, Arc::new(rendered.image.clone()));
                 }
@@ -429,7 +504,7 @@ impl RenderJob {
                     level: self.level,
                     key: self.key,
                     rendered: Ok(rendered),
-                    loaded: (!was_loaded).then_some(src),
+                    loaded: (!was_loaded).then_some(source),
                     quick: None,
                 }
             }
@@ -521,11 +596,16 @@ pub fn content_key(p: &Photo) -> String {
 pub fn source_info(p: &Photo) -> SourceInfo {
     // Procedural demo scenes are scene-referred HDR (like raw files): use the filmic tone map.
     if matches!(p.source, Source::Demo { .. }) {
-        return SourceInfo { raw: true, as_shot_temp: 6500.0, as_shot_tint: 0.0, lens: None };
+        return SourceInfo { raw: true, ..Default::default() };
     }
     // A raw shown from its embedded preview is a rendered (display-referred) JPEG: relative white
     // balance and the display tone curve, like any other rendered file.
-    if p.develops_raw() { SourceInfo { raw: true, as_shot_temp: 5500.0, as_shot_tint: 0.0, lens: p.embedded_lens } } else { SourceInfo::default() }
+    if p.develops_raw() {
+        let (temp, tint) = if p.relative_wb() { (6500.0, 0.0) } else { p.as_shot_wb.unwrap_or((5500.0, 0.0)) };
+        SourceInfo { raw: true, as_shot_temp: temp, as_shot_tint: tint, lens: p.embedded_lens, relative_wb: p.relative_wb(), ..Default::default() }
+    } else {
+        SourceInfo::default()
+    }
 }
 
 impl crate::Session {
@@ -680,7 +760,7 @@ impl crate::Session {
     /// Accept a finished job's loaded source into the cache.
     pub fn accept(&mut self, r: &RenderResult) {
         if let Some(src) = &r.loaded {
-            self.media.insert(r.photo, r.level, src.clone());
+            self.media.insert_source(r.photo, r.level, src.clone());
         }
     }
 
@@ -723,12 +803,19 @@ impl crate::Session {
         Ok(job)
     }
 
+    /// Prefer decoder facts to header-only metadata for pixel-statistics commands.
+    pub fn source_info(&self, id: PhotoId) -> SourceInfo {
+        let header = self.catalog.photo(id).map(|p| source_info(p)).unwrap_or_default();
+        self.media.source_facts(id, header)
+    }
+
     /// The source proxy for pixel-statistics commands (auto tone/WB), loading synchronously.
     pub fn source_now(&mut self, id: PhotoId, level: SourceLevel) -> Result<Arc<Rgb32f>, String> {
         let p = self.catalog.photo(id).ok_or("no such photo")?.clone();
-        let r = self.media.source_ref(&p, level).load()?;
-        self.media.insert(id, level, r.clone());
-        Ok(r)
+        let r = self.media.source_ref(&p, level).load_source()?;
+        let image = r.image.clone();
+        self.media.insert_source(id, level, r);
+        Ok(image)
     }
 }
 
@@ -760,6 +847,42 @@ pub type FileProbe = Arc<dyn Fn(&str) -> Result<ProbeInfo, String> + Send + Sync
 mod tests {
     use super::*;
 
+    #[test]
+    fn decoder_info_survives_render_jobs_cache_and_eviction() {
+        let tone = lightcraft_pipeline::tone::CameraTone::new(std::array::from_fn(|i| {
+            let x = 0.01 * (i + 1) as f32;
+            [x, (x * 2.0).min(0.9)]
+        }))
+        .unwrap();
+        let info = SourceInfo { raw: true, relative_wb: true, camera_tone: Some(tone), ..Default::default() };
+        let mut s = crate::Session::with_demo();
+        let id = s.active().unwrap();
+        let mut job = s.render_job(id, 64, 64, false, true).unwrap();
+        job.source = SourceRef::File {
+            path: "synthetic.arw".into(),
+            max_edge: 64,
+            loader: Some(Arc::new(move |_, _| {
+                let mut image = Rgb32f::new(64, 64);
+                image.data.fill([0.1; 3]);
+                Ok((image, info))
+            })),
+            fallback: None,
+        };
+        job.info = SourceInfo::default(); // Header facts cannot override decoder facts.
+        job.settings = Arc::new(DevelopSettings::default());
+        let r = job.clone().run();
+        assert_eq!(r.loaded.as_ref().unwrap().info, Some(info));
+        let expected = lightcraft_pipeline::render(&r.loaded.as_ref().unwrap().image, &info, &job.settings, &job.request);
+        assert_eq!(r.rendered.as_ref().unwrap().image.data, expected.image.data);
+        s.accept(&r);
+        job.source = s.media.source_ref(s.catalog.photo(id).unwrap(), job.level);
+        let again = job.run();
+        assert!(again.loaded.is_none());
+        assert_eq!(r.rendered.unwrap().image.data, again.rendered.unwrap().image.data);
+        s.media.forget(id);
+        assert!(s.media.get_source(id, r.level).is_none());
+    }
+
     #[test]
     fn budget_evicts_least_recently_used_across_caches() {
         let img = |w: usize| Arc::new(Rgb32f::new(w, w));

crates/engine/src/merge.rs

@@ -304,15 +304,13 @@ fn apply_auto(s: &mut DevelopSettings, src: &Rgb32f, info: &SourceInfo) {
     s.color.saturation = a.saturation;
 }
 
-/// A free file name `dir/<stem>-<suffix>.dng` (`-2`, `-3`… when taken).
-fn output_path(first: &str, suffix: &str) -> String {
+/// `dir/<stem>-<suffix>.dng`, then `-2`, `-3`… (the candidates for a merge's output).
+fn output_names(first: &str, suffix: &str) -> impl Iterator<Item = std::path::PathBuf> {
     let p = std::path::Path::new(first);
     let dir = p.parent().map(|d| d.to_path_buf()).unwrap_or_default();
     let stem = p.file_stem().map(|s| s.to_string_lossy().to_string()).unwrap_or_else(|| "Merge".into());
-    let cand = |k: u64| dir.join(if k == 1 { format!("{stem}-{suffix}.dng") } else { format!("{stem}-{suffix}-{k}.dng") });
-    // (`u64::MAX` taken names can't exist; the last candidate is the fallback)
-    let free = (1..u64::MAX).map(cand).find(|c| !c.exists()).unwrap_or_else(|| cand(u64::MAX));
-    free.to_string_lossy().to_string()
+    let suffix = suffix.to_string();
+    (1u64..).map(move |k| dir.join(if k == 1 { format!("{stem}-{suffix}.dng") } else { format!("{stem}-{suffix}-{k}.dng") }))
 }
 
 /// Parse `merge.*` command parameters into a kind and finishing options.
@@ -367,8 +365,11 @@ impl Session {
     /// apply Auto Settings / the auto crop. Returns `{id, path, …info}`.
     pub fn finish_merge(&mut self, job: &MergeJob, out: MergeOutput) -> Result<Value> {
         let first = &job.sources.first().ok_or_else(|| EngineError::Other("nothing merged".into()))?.1;
-        let path = output_path(first, job.kind.suffix());
-        std::fs::write(&path, &out.dng).map_err(|e| EngineError::Other(format!("{path}: {e}")))?;
+        // a new file under a free name (never replacing one), complete and synced before it appears
+        let path = lightcraft_catalog::safe_file::write_new_unique(&mut output_names(first, job.kind.suffix()), &out.dng)
+            .map_err(|e| EngineError::Other(format!("could not write the merged DNG next to {first}: {e}")))?
+            .to_string_lossy()
+            .to_string();
         let report = crate::import::import(self, std::slice::from_ref(&path), crate::import::ImportMode::Add)?;
         let id = report
             .imported

crates/engine/src/rename.rs

@@ -11,7 +11,11 @@
 //!
 //! Safety:
 //! - a target that exists on disk, or that another photo in the batch gets, receives a `-1`, `-2`…
-//!   suffix — no file is ever overwritten;
+//!   suffix — no file is ever overwritten. Whether an existing target is the photo itself (a
+//!   change of letter case on a case-insensitive volume) is decided by file identity, not by
+//!   comparing names, so on a case-sensitive volume `img_1.jpg` next to `IMG_1.JPG` is a collision
+//!   (issue #95); moves never replace a file even if one appears after the check (hard link +
+//!   unlink where the volume supports it);
 //! - the moves happen before the catalog changes; if one fails, the ones already done are moved
 //!   back and nothing is committed;
 //! - the catalog op ([`Op::SetFile`]) is undoable: undo/redo move the files back and forth (see
@@ -297,139 +301,352 @@ fn sidecars(path: &str) -> Vec<(PathBuf, SidecarNaming, bool)> {
     v
 }
 
-/// Move `from` to `to` (never over an existing file) together with its sidecars. On error nothing
-/// is left moved.
-pub fn move_file(from: &str, to: &str) -> std::result::Result<(), String> {
+/// The file-system primitives renaming uses. [`RealFs`] is the disk; tests substitute a model of
+/// a case-insensitive or case-sensitive volume (and inject failures).
+pub(crate) trait MoveFs {
+    /// Something (file, folder, link) answers to `p`.
+    fn exists(&self, p: &Path) -> bool;
+    fn is_file(&self, p: &Path) -> bool;
+    /// `a` and `b` name the same file (e.g. `IMG.JPG` and `img.jpg` on a case-insensitive
+    /// volume). Decided by file identity, never by comparing names: on a case-sensitive volume
+    /// they are two different photos. When in doubt: `false`.
+    fn same_file(&self, a: &Path, b: &Path) -> bool;
+    /// Rename `a` to `b`, failing (never replacing) when `b` exists.
+    fn rename_no_replace(&self, a: &Path, b: &Path) -> std::io::Result<()>;
+    /// Copy `a` to a new file `b` (an independent copy, never a link), failing when `b` exists.
+    fn copy_no_replace(&self, a: &Path, b: &Path) -> std::io::Result<()>;
+    fn remove_file(&self, p: &Path) -> std::io::Result<()>;
+    /// Another photo file beside the stem-named sidecar `sidecar` that shares its stem (e.g.
+    /// `IMG_1.JPG` for `IMG_1.xmp`), which still uses that sidecar.
+    fn stem_sibling(&self, sidecar: &Path) -> Option<String>;
+}
+
+/// The real file system.
+pub(crate) struct RealFs;
+
+impl MoveFs for RealFs {
+    fn exists(&self, p: &Path) -> bool {
+        std::fs::symlink_metadata(p).is_ok()
+    }
+
+    fn is_file(&self, p: &Path) -> bool {
+        p.is_file()
+    }
+
+    fn same_file(&self, a: &Path, b: &Path) -> bool {
+        if a == b {
+            return true;
+        }
+        let (Ok(ma), Ok(mb)) = (std::fs::metadata(a), std::fs::metadata(b)) else { return false };
+        #[cfg(unix)]
+        {
+            use std::os::unix::fs::MetadataExt;
+            ma.dev() == mb.dev() && ma.ino() == mb.ino()
+        }
+        #[cfg(not(unix))]
+        {
+            // no stable file id in std here: `b` is `a` under another spelling when they look
+            // alike and the folder has no entry spelled exactly like `b` (on a case-sensitive
+            // folder holding both `IMG.JPG` and `img.jpg`, both entries are listed)
+            let (Some(dir), Some(name)) = (b.parent(), b.file_name()) else { return false };
+            if a.parent() != Some(dir) || ma.len() != mb.len() || ma.modified().ok() != mb.modified().ok() {
+                return false;
+            }
+            let Ok(entries) = std::fs::read_dir(dir) else { return false };
+            !entries.flatten().any(|e| e.file_name() == name)
+        }
+    }
+
+    fn rename_no_replace(&self, a: &Path, b: &Path) -> std::io::Result<()> {
+        if self.exists(b) {
+            return Err(std::io::Error::new(std::io::ErrorKind::AlreadyExists, format!("{} already exists", b.display())));
+        }
+        // A hard link fails when `b` exists — even if it appeared since the check above — so
+        // nothing is ever replaced. Volumes without hard links (FAT, some network shares) fall back
+        // to a plain rename after the check.
+        match std::fs::hard_link(a, b) {
+            Ok(()) => std::fs::remove_file(a).inspect_err(|_| {
+                // both names are the same file: dropping the new one loses nothing
+                let _ = std::fs::remove_file(b);
+            }),
+            Err(e) if e.kind() == std::io::ErrorKind::AlreadyExists => Err(e),
+            Err(_) => std::fs::rename(a, b),
+        }
+    }
+
+    fn copy_no_replace(&self, a: &Path, b: &Path) -> std::io::Result<()> {
+        use std::io::Write;
+        let bytes = std::fs::read(a)?;
+        let mut f = std::fs::OpenOptions::new().write(true).create_new(true).open(b)?;
+        f.write_all(&bytes).and_then(|_| f.sync_all()).inspect_err(|_| {
+            let _ = std::fs::remove_file(b);
+        })
+    }
+
+    fn remove_file(&self, p: &Path) -> std::io::Result<()> {
+        std::fs::remove_file(p)
+    }
+
+    fn stem_sibling(&self, sidecar: &Path) -> Option<String> {
+        crate::import_move::sibling_photo(sidecar)
+    }
+}
+
+/// `from` → `to` differs only in letter case and `to` is that very file (a case-insensitive
+/// volume): the rename must go through a temporary name.
+fn is_respelling(fs: &dyn MoveFs, from: &Path, to: &Path) -> bool {
+    from != to && from.to_string_lossy().to_lowercase() == to.to_string_lossy().to_lowercase() && fs.exists(to) && fs.same_file(from, to)
+}
+
+/// Rename `a` to `b` without ever replacing a file; a change of letter case only goes through a
+/// unique temporary name so case-insensitive volumes see a real change.
+fn move_one(fs: &dyn MoveFs, a: &Path, b: &Path) -> std::io::Result<()> {
+    if !is_respelling(fs, a, b) {
+        return fs.rename_no_replace(a, b);
+    }
+    let tmp = (0..1000u32)
+        .map(|k| a.with_file_name(format!(".lc-rename-{}-{k}", std::process::id())))
+        .find(|t| !fs.exists(t))
+        .ok_or_else(|| std::io::Error::other("no free temporary name"))?;
+    fs.rename_no_replace(a, &tmp)?;
+    fs.rename_no_replace(&tmp, b).map_err(|e| match fs.rename_no_replace(&tmp, a) {
+        Ok(()) => e,
+        Err(e2) => std::io::Error::other(format!("{e}; it could not be given its old name back either ({e2}): it is now {}", tmp.display())),
+    })
+}
+
+/// Why [`move_file`] failed, and what it left behind.
+#[derive(Clone, Debug, PartialEq)]
+pub struct MoveError {
+    /// What went wrong, including every step that could not be undone and where that file is now.
+    pub message: String,
+    /// The file itself ended up at the new path: it moved, a sidecar didn't, and moving the file
+    /// back failed too. Its sidecars that did move stay with it.
+    pub moved: bool,
+}
+
+impl std::fmt::Display for MoveError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(&self.message)
+    }
+}
+
+/// Move `from` to `to` (never over an existing file) together with its sidecars. On error the
+/// moves are undone; whatever can't be undone is named in the error (see [`MoveError`]).
+pub fn move_file(from: &str, to: &str) -> std::result::Result<(), MoveError> {
+    move_file_with(&RealFs, from, to)
+}
+
+/// [`move_file`] on the file system `fs`.
+pub(crate) fn move_file_with(fs: &dyn MoveFs, from: &str, to: &str) -> std::result::Result<(), MoveError> {
     if from == to {
         return Ok(());
     }
+    let fail = |message: String| MoveError { message, moved: false };
     let (f, t) = (Path::new(from), Path::new(to));
-    // a case-only change on a case-insensitive file system "exists" already: that is this file
-    let case_only = from.to_lowercase() == to.to_lowercase();
-    if t.exists() && !case_only {
-        return Err(format!("{to} already exists"));
+    // `to` may be this very file spelled differently (case-insensitive volume); any other file
+    // there — e.g. `img.jpg` next to `IMG.JPG` on a case-sensitive volume — is never replaced
+    if fs.exists(t) && !is_respelling(fs, f, t) {
+        return Err(fail(format!("{to} already exists")));
     }
-    let mut done: Vec<(PathBuf, PathBuf)> = Vec::new();
-    let mv = |a: &Path, b: &Path| -> std::io::Result<()> {
-        if case_only {
-            // via a temporary name, so case-insensitive file systems see a real change
-            let tmp = a.with_file_name(format!(".lc-rename-{}", std::process::id()));
-            std::fs::rename(a, &tmp)?;
-            std::fs::rename(&tmp, b).inspect_err(|_| {
-                let _ = std::fs::rename(&tmp, a);
-            })
-        } else {
-            std::fs::rename(a, b)
-        }
-    };
-    mv(f, t).map_err(|e| format!("rename {from}: {e}"))?;
-    done.push((f.to_path_buf(), t.to_path_buf()));
+    move_one(fs, f, t).map_err(|e| fail(format!("rename {from}: {e}")))?;
+    // sidecars moved (or copied: `true`)
+    let mut done: Vec<(PathBuf, PathBuf, bool)> = Vec::new();
     for (sc, naming, upper) in sidecars(from) {
-        if !sc.is_file() {
+        if !fs.is_file(&sc) {
             continue;
         }
         let mut dst = crate::sidecar::sidecar_path(to, naming);
         if upper {
             dst = dst.with_extension("XMP");
         }
-        if dst.exists() && !case_only {
+        // a stem sidecar another file still uses (`IMG_1.xmp` of `IMG_1.CR3` and `IMG_1.JPG`)
+        // is copied, not taken away from it (issue #92)
+        let shared = naming == SidecarNaming::Stem && fs.stem_sibling(&sc).is_some();
+        if fs.exists(&dst) && (shared || !is_respelling(fs, &sc, &dst)) {
             continue; // never overwrite: the old sidecar stays where it was
         }
-        if let Err(e) = mv(&sc, &dst) {
-            for (a, b) in done.iter().rev() {
-                let _ = std::fs::rename(b, a);
+        let r = if shared { fs.copy_no_replace(&sc, &dst) } else { move_one(fs, &sc, &dst) };
+        if let Err(e) = r {
+            let mut message = format!("rename {}: {e}", sc.display());
+            // the file first: if it can't go back, the sidecars that moved stay with it
+            if let Err(e) = move_one(fs, t, f) {
+                message.push_str(&format!("; {from} could not be moved back ({e}): it is now {to}"));
+                if !done.is_empty() {
+                    let names: Vec<String> = done.iter().map(|(_, b, _)| b.display().to_string()).collect();
+                    message.push_str(&format!(" with its sidecar {}", names.join(", ")));
+                }
+                return Err(MoveError { message, moved: true });
             }
-            return Err(format!("rename {}: {e}", sc.display()));
+            for (a, b, copied) in done.iter().rev() {
+                if *copied {
+                    // the original is still there: the copy just goes (a leftover copy loses nothing)
+                    let _ = fs.remove_file(b);
+                } else if let Err(e) = move_one(fs, b, a) {
+                    message.push_str(&format!("; sidecar {} could not be moved back ({e}): it is now {}", a.display(), b.display()));
+                }
+            }
+            return Err(fail(message));
         }
-        done.push((sc, dst));
+        done.push((sc, dst, shared));
     }
     Ok(())
 }
 
+/// What a failed batch of moves ([`move_all`]) left behind.
+#[derive(Debug)]
+pub(crate) struct BatchMoveError {
+    /// The first failure and every move that could not be undone.
+    pub message: String,
+    /// Moves that stayed done, (from, to): those files are at `to` now.
+    pub stuck: Vec<(String, String)>,
+}
+
+/// Move the files `moves` names, all or nothing: after a failure the earlier moves are undone.
+/// Moves that can't be undone (e.g. the network share went away) are reported, not ignored.
+pub(crate) fn move_all(fs: &dyn MoveFs, moves: &[(String, String)]) -> std::result::Result<(), BatchMoveError> {
+    let mut done: Vec<&(String, String)> = Vec::new();
+    for m in moves {
+        let Err(e) = move_file_with(fs, &m.0, &m.1) else {
+            done.push(m);
+            continue;
+        };
+        let mut message = e.message;
+        let mut stuck = Vec::new();
+        if e.moved {
+            stuck.push(m.clone());
+        }
+        for d in done.iter().rev() {
+            if let Err(e) = move_file_with(fs, &d.1, &d.0) {
+                message.push_str(&format!("; {} could not be moved back to {}: {}", d.1, d.0, e.message));
+                if !e.moved {
+                    stuck.push((*d).clone());
+                }
+            }
+        }
+        return Err(BatchMoveError { message, stuck });
+    }
+    Ok(())
+}
+
+/// The `SetFile` ops in `op` (nested batches included) that point a photo at one of `to`.
+fn set_file_ops_to(op: &Op, to: &HashSet<&str>, out: &mut Vec<Op>) {
+    match op {
+        Op::Batch { ops } => ops.iter().for_each(|o| set_file_ops_to(o, to, out)),
+        Op::SetFile { source: Source::File { path }, .. } if to.contains(path.as_str()) => out.push(op.clone()),
+        _ => {}
+    }
+}
+
+/// The photos among `ids` a rename handles, in order: photos sharing one file (virtual copies)
+/// rename once. No file-system calls.
+pub fn rename_photos(cat: &lightcraft_catalog::Catalog, ids: &[PhotoId]) -> Vec<std::sync::Arc<Photo>> {
+    let mut seen_paths: HashSet<String> = HashSet::new();
+    ids.iter()
+        .filter_map(|id| cat.photo(*id))
+        .filter(|p| match &p.source {
+            Source::File { path } => seen_paths.insert(path.clone()),
+            _ => true,
+        })
+        .cloned()
+        .collect()
+}
+
+/// [`Session::plan_rename`] for [`rename_photos`], with the "is this name taken on disk?" check
+/// supplied: the Rename dialog plans its preview on a worker thread (a check can block on a slow
+/// drive). Whether a case-only change names this very file is decided on the disk.
+pub fn plan_rename_photos(photos: &[std::sync::Arc<Photo>], template: &str, start: usize, exists: &dyn Fn(&str) -> bool) -> Vec<RenamePlan> {
+    plan_rename_core(photos, template, start, &|p| exists(&p.to_string_lossy()), &|a, b| RealFs.same_file(a, b))
+}
+
+/// Plan renaming `photos`: `exists` says whether something answers to a path, `same_file` whether
+/// two spellings name one file (see [`MoveFs`]).
+fn plan_rename_core(
+    photos: &[std::sync::Arc<Photo>],
+    template: &str,
+    start: usize,
+    exists: &dyn Fn(&Path) -> bool,
+    same_file: &dyn Fn(&Path, &Path) -> bool,
+) -> Vec<RenamePlan> {
+    let mut taken: HashSet<String> = HashSet::new(); // lower-case target paths/names claimed in this batch
+    let mut out = Vec::new();
+    for (seq, p) in (start..).zip(photos) {
+        let want = expand(template, p, seq);
+        let (stem, ext) = split_ext(&want);
+        let (stem, ext) = (stem.to_string(), ext.to_string());
+        let candidate = |k: usize| {
+            if k == 0 {
+                want.clone()
+            } else if ext.is_empty() {
+                format!("{stem}-{k}")
+            } else {
+                format!("{stem}-{k}.{ext}")
+            }
+        };
+        let (to, to_path) = match &p.source {
+            Source::File { path } => {
+                let dir = Path::new(path).parent().map(Path::to_path_buf).unwrap_or_default();
+                let mut k = 0;
+                loop {
+                    let name = candidate(k);
+                    let tp = dir.join(&name).to_string_lossy().to_string();
+                    let key = tp.to_lowercase();
+                    // this very file, maybe spelled differently (case-insensitive volume)? By
+                    // identity: on a case-sensitive volume `img_1.jpg` may be another photo
+                    let (from, to) = (Path::new(path), Path::new(&tp));
+                    let same = tp == *path || (from != to && key == path.to_lowercase() && exists(to) && same_file(from, to));
+                    // free: not claimed in this batch and not on disk (unless it is this very file).
+                    // A file this batch moves away still counts as taken: simple and safe.
+                    if !taken.contains(&key) && (same || !exists(to)) {
+                        taken.insert(key);
+                        break (name, Some(tp));
+                    }
+                    k += 1;
+                }
+            }
+            Source::Demo { .. } => {
+                let mut k = 0;
+                loop {
+                    let name = candidate(k);
+                    if taken.insert(format!("demo:{}", name.to_lowercase())) {
+                        break (name, None);
+                    }
+                    k += 1;
+                }
+            }
+        };
+        let from_path = match &p.source {
+            Source::File { path } => Some(path.clone()),
+            _ => None,
+        };
+        out.push(RenamePlan { id: p.id.0, from: p.file_name.clone(), to, from_path, to_path });
+    }
+    out
+}
+
 impl Session {
     /// Plan renaming `ids` with `template` (sequence numbers from `start`), resolving collisions.
     pub fn plan_rename(&self, ids: &[PhotoId], template: &str, start: usize) -> Vec<RenamePlan> {
-        // photos sharing one file (virtual copies) rename once
-        let mut seen_paths: HashSet<String> = HashSet::new();
-        let mut taken: HashSet<String> = HashSet::new(); // lower-case target paths/names claimed in this batch
-        let mut out = Vec::new();
-        let mut seq = start;
-        for id in ids {
-            let Some(p) = self.catalog.photo(*id) else { continue };
-            if let Source::File { path } = &p.source
-                && !seen_paths.insert(path.clone())
-            {
-                continue;
-            }
-            let want = expand(template, p, seq);
-            seq += 1;
-            let (stem, ext) = split_ext(&want);
-            let (stem, ext) = (stem.to_string(), ext.to_string());
-            let candidate = |k: usize| {
-                if k == 0 {
-                    want.clone()
-                } else if ext.is_empty() {
-                    format!("{stem}-{k}")
-                } else {
-                    format!("{stem}-{k}.{ext}")
-                }
-            };
-            let (to, to_path) = match &p.source {
-                Source::File { path } => {
-                    let dir = Path::new(path).parent().map(Path::to_path_buf).unwrap_or_default();
-                    let mut k = 0;
-                    loop {
-                        let name = candidate(k);
-                        let tp = dir.join(&name).to_string_lossy().to_string();
-                        let key = tp.to_lowercase();
-                        let same = key == path.to_lowercase();
-                        // free: not claimed in this batch and not on disk (unless it is this very file).
-                        // A file this batch moves away still counts as taken: simple and safe.
-                        let on_disk = Path::new(&tp).exists() && !same;
-                        if !taken.contains(&key) && !on_disk {
-                            taken.insert(key);
-                            break (name, Some(tp));
-                        }
-                        k += 1;
-                    }
-                }
-                Source::Demo { .. } => {
-                    let mut k = 0;
-                    loop {
-                        let name = candidate(k);
-                        if taken.insert(format!("demo:{}", name.to_lowercase())) {
-                            break (name, None);
-                        }
-                        k += 1;
-                    }
-                }
-            };
-            let from_path = match &p.source {
-                Source::File { path } => Some(path.clone()),
-                _ => None,
-            };
-            out.push(RenamePlan { id: id.0, from: p.file_name.clone(), to, from_path, to_path });
-        }
-        out
+        self.plan_rename_with(&RealFs, ids, template, start)
+    }
+
+    /// [`Session::plan_rename`] on the file system `fs`.
+    pub(crate) fn plan_rename_with(&self, fs: &dyn MoveFs, ids: &[PhotoId], template: &str, start: usize) -> Vec<RenamePlan> {
+        plan_rename_core(&rename_photos(&self.catalog, ids), template, start, &|p| fs.exists(p), &|a, b| fs.same_file(a, b))
     }
 
     /// Carry out `plans`: move the files (rolled back on failure), then commit one undoable op
     /// that updates the photos (and their virtual copies).
+    ///
+    /// When a failure can't be fully rolled back, the files that kept their new names are
+    /// committed as a smaller undoable rename, so the library points at them (nothing goes
+    /// missing), and the error lists them (old → new).
     pub fn apply_rename(&mut self, plans: &[RenamePlan]) -> Result<usize> {
-        let mut moved: Vec<(String, String)> = Vec::new();
-        for pl in plans {
-            if let (Some(a), Some(b)) = (&pl.from_path, &pl.to_path)
-                && a != b
-            {
-                if let Err(e) = move_file(a, b) {
-                    for (a, b) in moved.iter().rev() {
-                        let _ = move_file(b, a);
-                    }
-                    return Err(EngineError::Other(e));
-                }
-                moved.push((a.clone(), b.clone()));
-            }
-        }
+        self.apply_rename_with(&RealFs, plans)
+    }
+
+    /// [`Session::apply_rename`] on the file system `fs`.
+    pub(crate) fn apply_rename_with(&mut self, fs: &dyn MoveFs, plans: &[RenamePlan]) -> Result<usize> {
         let mut ops = Vec::new();
         let by_path: HashMap<&str, &RenamePlan> = plans.iter().filter_map(|p| p.from_path.as_deref().map(|f| (f, p))).collect();
         for p in self.catalog.photos() {
@@ -447,17 +664,66 @@ impl Session {
             }
         }
         let n = ops.len();
+        let op = Op::Batch { ops };
+        let moves: Vec<(String, String)> = plans
+            .iter()
+            .filter_map(|pl| match (&pl.from_path, &pl.to_path) {
+                (Some(a), Some(b)) if a != b => Some((a.clone(), b.clone())),
+                _ => None,
+            })
+            .collect();
+        if let Err(e) = move_all(fs, &moves) {
+            return Err(EngineError::Other(self.follow_stuck(&op, e, true)));
+        }
         if n > 0
-            && let Err(e) = self.commit(&format!("Rename {n} Photo{}", if n == 1 { "" } else { "s" }), Op::Batch { ops })
+            && let Err(err) = self.commit(&format!("Rename {n} Photo{}", if n == 1 { "" } else { "s" }), op)
         {
-            for (a, b) in moved.iter().rev() {
-                let _ = move_file(b, a);
+            let back: Vec<(String, String)> = moves.iter().rev().map(|(a, b)| (b.clone(), a.clone())).collect();
+            if let Err(e) = move_all(fs, &back) {
+                return Err(EngineError::Other(format!("{err}; the renamed files could not all be moved back: {}", e.message)));
             }
-            return Err(e);
+            return Err(err);
         }
         Ok(n)
     }
 
+    /// After a failed batch of moves for `op`: point the photos whose files stayed moved at
+    /// their new paths (an undoable "partly" rename when `undoable`, otherwise a plain logged
+    /// change), so the library matches the disk. Returns the message for the user.
+    pub(crate) fn follow_stuck(&mut self, op: &Op, e: BatchMoveError, undoable: bool) -> String {
+        let mut msg = e.message;
+        if e.stuck.is_empty() {
+            return msg;
+        }
+        let to: HashSet<&str> = e.stuck.iter().map(|m| m.1.as_str()).collect();
+        let mut keep = Vec::new();
+        set_file_ops_to(op, &to, &mut keep);
+        let list: Vec<String> = e.stuck.iter().map(|(a, b)| format!("{a} → {b}")).collect();
+        let n = e.stuck.len();
+        let s = if n == 1 { "" } else { "s" };
+        let fix = Op::Batch { ops: keep };
+        let applied = if undoable {
+            self.commit(&format!("Rename {n} Photo{s} (partly)"), fix)
+        } else {
+            match self.catalog.apply(fix.clone()) {
+                Ok(_) => {
+                    self.pending_log.push(fix);
+                    Ok(())
+                }
+                Err(e) => Err(e.into()),
+            }
+        };
+        match applied {
+            Ok(()) => msg
+                .push_str(&format!(". {n} file{s} could not be moved back and kept the new name; the library now points there: {}", list.join(", "))),
+            Err(err) => msg.push_str(&format!(
+                ". {n} file{s} could not be moved back and the library could not follow ({err}); relink with Find Missing Photos: {}",
+                list.join(", ")
+            )),
+        }
+        msg
+    }
+
     /// File moves an undo/redo op implies: `SetFile` ops whose source path differs from the photo's
     /// current one.
     pub(crate) fn file_moves(&self, op: &Op) -> Vec<(String, String)> {
@@ -479,26 +745,240 @@ impl Session {
         rec(self, op, &mut v);
         v
     }
-
-    /// Move the files `moves` names; all or nothing.
-    pub(crate) fn move_files(moves: &[(String, String)]) -> Result<()> {
-        let mut done: Vec<&(String, String)> = Vec::new();
-        for m in moves {
-            if let Err(e) = move_file(&m.0, &m.1) {
-                for (a, b) in done.iter().rev().map(|m| (&m.0, &m.1)) {
-                    let _ = move_file(b, a);
-                }
-                return Err(EngineError::Other(format!("can't undo the rename: {e}")));
-            }
-            done.push(m);
-        }
-        Ok(())
-    }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::cell::RefCell;
+
+    /// A model volume: files by path with contents; case-insensitive (default APFS/NTFS) or
+    /// case-sensitive (Linux, case-sensitive APFS). `fail` makes renames from a matching source fail.
+    pub(crate) struct FakeFs {
+        pub ci: bool,
+        pub files: RefCell<Vec<(String, Vec<u8>)>>,
+        pub fail: RefCell<Vec<String>>,
+    }
+
+    impl FakeFs {
+        pub fn new(ci: bool, files: &[(&str, &str)]) -> FakeFs {
+            FakeFs {
+                ci,
+                files: RefCell::new(files.iter().map(|(p, c)| (p.to_string(), c.as_bytes().to_vec())).collect()),
+                fail: RefCell::new(Vec::new()),
+            }
+        }
+        fn idx(&self, p: &Path) -> Option<usize> {
+            let p = p.to_string_lossy();
+            self.files.borrow().iter().position(|(f, _)| if self.ci { f.to_lowercase() == p.to_lowercase() } else { *f == p })
+        }
+        /// The listing: (exact path, contents), sorted.
+        pub fn listing(&self) -> Vec<(String, String)> {
+            let mut v: Vec<_> = self.files.borrow().iter().map(|(p, c)| (p.clone(), String::from_utf8_lossy(c).to_string())).collect();
+            v.sort();
+            v
+        }
+    }
+
+    impl MoveFs for FakeFs {
+        fn exists(&self, p: &Path) -> bool {
+            self.idx(p).is_some()
+        }
+        fn is_file(&self, p: &Path) -> bool {
+            self.exists(p)
+        }
+        fn same_file(&self, a: &Path, b: &Path) -> bool {
+            self.idx(a).is_some() && self.idx(a) == self.idx(b)
+        }
+        fn rename_no_replace(&self, a: &Path, b: &Path) -> std::io::Result<()> {
+            if self.fail.borrow().iter().any(|f| a.to_string_lossy().contains(f.as_str())) {
+                return Err(std::io::Error::other("injected failure"));
+            }
+            if self.exists(b) {
+                return Err(std::io::Error::new(std::io::ErrorKind::AlreadyExists, "exists"));
+            }
+            let i = self.idx(a).ok_or_else(|| std::io::Error::new(std::io::ErrorKind::NotFound, "no such file"))?;
+            self.files.borrow_mut()[i].0 = b.to_string_lossy().to_string();
+            Ok(())
+        }
+        fn copy_no_replace(&self, a: &Path, b: &Path) -> std::io::Result<()> {
+            if self.exists(b) {
+                return Err(std::io::Error::new(std::io::ErrorKind::AlreadyExists, "exists"));
+            }
+            let i = self.idx(a).ok_or_else(|| std::io::Error::new(std::io::ErrorKind::NotFound, "no such file"))?;
+            let c = self.files.borrow()[i].1.clone();
+            self.files.borrow_mut().push((b.to_string_lossy().to_string(), c));
+            Ok(())
+        }
+        fn remove_file(&self, p: &Path) -> std::io::Result<()> {
+            let i = self.idx(p).ok_or_else(|| std::io::Error::new(std::io::ErrorKind::NotFound, "no such file"))?;
+            self.files.borrow_mut().remove(i);
+            Ok(())
+        }
+        fn stem_sibling(&self, sidecar: &Path) -> Option<String> {
+            let stem = sidecar.with_extension("").to_string_lossy().to_string();
+            self.files.borrow().iter().map(|(f, _)| f.clone()).find(|f| {
+                let p = Path::new(f);
+                p.with_extension("").to_string_lossy() == stem && !p.extension().is_some_and(|e| e.eq_ignore_ascii_case("xmp"))
+            })
+        }
+    }
+
+    fn file_photo(id: u64, path: &str) -> Photo {
+        let name = Path::new(path).file_name().map(|n| n.to_string_lossy().to_string()).unwrap_or_default();
+        Photo::new(PhotoId(id), Source::File { path: path.into() }, &name, "JPG", 1, 1, "2026-01-01T00:00:00")
+    }
+
+    /// Issue #95: a case-only rename is a real change on a case-insensitive volume and never
+    /// replaces a different file that differs only by case on a case-sensitive one.
+    #[test]
+    fn case_only_renames_never_replace_another_file() {
+        // case-sensitive: IMG_1.JPG and img_1.JPG are two photos
+        let fs = FakeFs::new(false, &[("/p/IMG_1.JPG", "first"), ("/p/img_1.JPG", "second"), ("/p/IMG_1.xmp", "sc1"), ("/p/img_1.xmp", "sc2")]);
+        assert!(move_file_with(&fs, "/p/IMG_1.JPG", "/p/img_1.JPG").unwrap_err().message.contains("already exists"));
+        assert_eq!(fs.listing().len(), 4);
+        assert!(fs.listing().contains(&("/p/img_1.JPG".into(), "second".into())));
+        // the planner picks a free name instead
+        let mut s = Session::new();
+        s.catalog.apply(Op::AddPhoto { photo: Box::new(file_photo(1, "/p/IMG_1.JPG")) }).unwrap();
+        let plans = s.plan_rename_with(&fs, &[PhotoId(1)], "img_1", 1);
+        assert_eq!(plans[0].to, "img_1-1.JPG");
+        move_file_with(&fs, "/p/IMG_1.JPG", plans[0].to_path.as_deref().unwrap()).unwrap();
+        assert_eq!(
+            fs.listing(),
+            vec![
+                ("/p/img_1-1.JPG".into(), "first".into()),
+                ("/p/img_1-1.xmp".into(), "sc1".into()),
+                ("/p/img_1.JPG".into(), "second".into()),
+                ("/p/img_1.xmp".into(), "sc2".into())
+            ]
+        );
+        // case-sensitive, target free: a plain rename
+        let fs = FakeFs::new(false, &[("/p/IMG_2.JPG", "x")]);
+        move_file_with(&fs, "/p/IMG_2.JPG", "/p/img_2.JPG").unwrap();
+        assert_eq!(fs.listing(), vec![("/p/img_2.JPG".into(), "x".into())]);
+
+        // case-insensitive: the "existing" target is the photo itself → renamed via a temp name
+        let fs = FakeFs::new(true, &[("/p/IMG_1.JPG", "first"), ("/p/IMG_1.xmp", "sc1")]);
+        let mut s = Session::new();
+        s.catalog.apply(Op::AddPhoto { photo: Box::new(file_photo(1, "/p/IMG_1.JPG")) }).unwrap();
+        let plans = s.plan_rename_with(&fs, &[PhotoId(1)], "img_1", 1);
+        assert_eq!(plans[0].to, "img_1.JPG", "not a collision with itself");
+        move_file_with(&fs, "/p/IMG_1.JPG", "/p/img_1.JPG").unwrap();
+        assert_eq!(fs.listing(), vec![("/p/img_1.JPG".into(), "first".into()), ("/p/img_1.xmp".into(), "sc1".into())]);
+        // case-insensitive, another file under another name: still a collision
+        let fs = FakeFs::new(true, &[("/p/A.JPG", "a"), ("/p/b.JPG", "b")]);
+        assert!(move_file_with(&fs, "/p/A.JPG", "/p/B.JPG").is_err());
+    }
+
+    /// Issue #105: a rollback that fails is reported, and the library follows the files that kept
+    /// their new names (an undoable partial rename), so nothing goes missing.
+    #[test]
+    fn failed_rollbacks_are_reported_and_followed() {
+        let fs = FakeFs::new(false, &[("/p/a.jpg", "A"), ("/p/a.xmp", "As"), ("/p/b.jpg", "B"), ("/p/c.jpg", "C")]);
+        let mut s = Session::new();
+        for (i, f) in ["/p/a.jpg", "/p/b.jpg", "/p/c.jpg"].iter().enumerate() {
+            s.catalog.apply(Op::AddPhoto { photo: Box::new(file_photo(i as u64 + 1, f)) }).unwrap();
+        }
+        let ids = [PhotoId(1), PhotoId(2), PhotoId(3)];
+        let plans = s.plan_rename_with(&fs, &ids, "Trip-{seq}", 1);
+        // c can't be renamed (the share went away), and neither can Trip-1 be moved back
+        fs.fail.borrow_mut().extend(["c.jpg".to_string(), "Trip-1".to_string()]);
+        let err = s.apply_rename_with(&fs, &plans).unwrap_err().to_string();
+        assert!(err.contains("rename /p/c.jpg"), "{err}");
+        assert!(err.contains("/p/Trip-1.jpg could not be moved back"), "{err}");
+        assert!(err.contains("/p/a.jpg → /p/Trip-1.jpg"), "lists what stayed renamed: {err}");
+        assert_eq!(
+            fs.listing(),
+            vec![
+                ("/p/Trip-1.jpg".into(), "A".into()),
+                ("/p/Trip-1.xmp".into(), "As".into()),
+                ("/p/b.jpg".into(), "B".into()),
+                ("/p/c.jpg".into(), "C".into())
+            ]
+        );
+        // the catalog matches the disk
+        let path = |s: &Session, id: u64| match &s.catalog.photo(PhotoId(id)).unwrap().source {
+            Source::File { path } => path.clone(),
+            Source::Demo { .. } => String::new(),
+        };
+        assert_eq!(path(&s, 1), "/p/Trip-1.jpg");
+        assert_eq!(s.catalog.photo(PhotoId(1)).unwrap().file_name, "Trip-1.jpg");
+        assert_eq!((path(&s, 2), path(&s, 3)), ("/p/b.jpg".into(), "/p/c.jpg".into()));
+        assert_eq!(s.undo.last().map(|e| e.label.as_str()), Some("Rename 1 Photo (partly)"));
+
+        // a sidecar that won't move, and a file that won't go back: the file keeps its new name
+        // with the sidecars that did move, and says so
+        let fs = FakeFs::new(false, &[("/p/d.jpg", "D"), ("/p/d.xmp", "Ds"), ("/p/d.jpg.xmp", "Df")]);
+        fs.fail.borrow_mut().extend(["d.jpg.xmp".to_string(), "/p/e.jpg".to_string()]);
+        let e = move_file_with(&fs, "/p/d.jpg", "/p/e.jpg").unwrap_err();
+        assert!(e.moved, "{e}");
+        assert!(e.message.contains("it is now /p/e.jpg with its sidecar /p/e.xmp"), "{e}");
+        assert_eq!(fs.listing(), vec![("/p/d.jpg.xmp".into(), "Df".into()), ("/p/e.jpg".into(), "D".into()), ("/p/e.xmp".into(), "Ds".into())]);
+        // … and when the file does go back, its sidecars follow it
+        let fs = FakeFs::new(false, &[("/p/d.jpg", "D"), ("/p/d.xmp", "Ds"), ("/p/d.jpg.xmp", "Df")]);
+        fs.fail.borrow_mut().push("d.jpg.xmp".to_string());
+        let e = move_file_with(&fs, "/p/d.jpg", "/p/e.jpg").unwrap_err();
+        assert!(!e.moved);
+        assert_eq!(fs.listing().len(), 3);
+        assert!(fs.listing().iter().all(|(p, _)| p.starts_with("/p/d.")));
+    }
+
+    /// Issue #92 (comment): renaming one of `IMG_1.CR3` + `IMG_1.JPG` copies their shared
+    /// `IMG_1.xmp` instead of taking it away from the other; the last one renamed takes it.
+    #[test]
+    fn shared_stem_sidecar_is_copied_not_taken() {
+        let fs = FakeFs::new(false, &[("/p/IMG_1.CR3", "raw"), ("/p/IMG_1.JPG", "jpg"), ("/p/IMG_1.xmp", "shared"), ("/p/IMG_1.CR3.xmp", "own")]);
+        move_file_with(&fs, "/p/IMG_1.CR3", "/p/Trip_1.CR3").unwrap();
+        assert_eq!(
+            fs.listing(),
+            vec![
+                ("/p/IMG_1.JPG".into(), "jpg".into()),
+                ("/p/IMG_1.xmp".into(), "shared".into()),
+                ("/p/Trip_1.CR3".into(), "raw".into()),
+                ("/p/Trip_1.CR3.xmp".into(), "own".into()),
+                ("/p/Trip_1.xmp".into(), "shared".into()),
+            ]
+        );
+        // the JPEG is the last one using it: it moves
+        move_file_with(&fs, "/p/IMG_1.JPG", "/p/Trip_2.JPG").unwrap();
+        assert!(fs.listing().contains(&("/p/Trip_2.xmp".into(), "shared".into())));
+        assert!(!fs.exists(Path::new("/p/IMG_1.xmp")));
+        // a failure after the copy removes the copy and keeps the original
+        let fs = FakeFs::new(false, &[("/p/A.CR3", "raw"), ("/p/A.JPG", "jpg"), ("/p/A.xmp", "shared"), ("/p/A.CR3.xmp", "own")]);
+        fs.fail.borrow_mut().push("A.CR3.xmp".into());
+        assert!(move_file_with(&fs, "/p/A.CR3", "/p/B.CR3").is_err());
+        assert_eq!(fs.listing().len(), 4);
+        assert!(fs.listing().contains(&("/p/A.xmp".into(), "shared".into())) && !fs.exists(Path::new("/p/B.xmp")));
+    }
+
+    /// Issue #95 on the real disk, whichever kind of volume the temp folder is on.
+    #[test]
+    fn case_only_rename_on_disk() {
+        let dir = std::env::temp_dir().join(format!("lc-rename-case-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        std::fs::create_dir_all(&dir).unwrap();
+        let (upper, lower) = (dir.join("IMG_1.JPG"), dir.join("img_1.JPG"));
+        std::fs::write(&upper, b"first").unwrap();
+        let case_sensitive = !lower.exists();
+        let p = |q: &Path| q.to_string_lossy().to_string();
+        if case_sensitive {
+            std::fs::write(&lower, b"second").unwrap();
+            assert!(move_file(&p(&upper), &p(&lower)).is_err());
+            assert_eq!(std::fs::read(&lower).unwrap(), b"second");
+            assert_eq!(std::fs::read(&upper).unwrap(), b"first");
+        } else {
+            move_file(&p(&upper), &p(&lower)).unwrap();
+            let names: Vec<String> = std::fs::read_dir(&dir).unwrap().flatten().map(|e| e.file_name().to_string_lossy().to_string()).collect();
+            assert_eq!(names, vec!["img_1.JPG".to_string()]);
+            assert_eq!(std::fs::read(&lower).unwrap(), b"first");
+        }
+        // a plain rename never replaces
+        std::fs::write(dir.join("other.JPG"), b"other").unwrap();
+        assert!(move_file(&p(&dir.join("other.JPG")), &p(&lower)).is_err());
+        assert_eq!(std::fs::read(dir.join("other.JPG")).unwrap(), b"other");
+        let _ = std::fs::remove_dir_all(&dir);
+    }
 
     #[test]
     fn folder_templates_stay_inside_the_destination() {

crates/engine/src/sidecar.rs

@@ -5,12 +5,25 @@
 //! creator, keywords, capture time and GPS in the standard namespaces, plus our complete develop
 //! settings (`lc:settings`, JSON), the pick/reject flag (`lc:flag`) and location (`lc:location`).
 //!
+//! An existing sidecar is never replaced wholesale (issue #92): LightCraft's properties
+//! ([`OWNED`], [`OWNED_IF_STATED`]) are merged into it ([`lightcraft_meta::merge_xmp`]) and
+//! everything else — another editor's `crs:` develop settings, `xmpMM` history, unknown
+//! namespaces — is kept byte for byte. A sidecar that can't be read as XMP is first copied to
+//! `<name>.xmp.bak-<time>` (never overwritten), then replaced. Writes are atomic (temp file,
+//! fsync, rename).
+//!
+//! **Shared names** (Stem naming): `IMG_0001.CR3` and `IMG_0001.JPG` would share `IMG_0001.xmp`.
+//! When two catalogued files map to one stem sidecar, it belongs to one of them (a raw first, then
+//! the first by file name — [`Session::sidecar_naming`]); the others use `<file>.xmp`
+//! (`IMG_0001.JPG.xmp`) for writing and reading, so neither overwrites the other.
+//!
 //! **Read** (on import, and `photo.readMetadataFromFile`): the sidecar wins for metadata, except
 //! the capture time: a time embedded in the file wins, and the sidecar's (`exif:DateTimeOriginal`,
 //! else `photoshop:DateCreated`, else `xmp:CreateDate`) fills in only when the file has none; develop
 //! settings are restored from `lc:settings` when present, else mapped from interoperable `crs:`
 //! fields ([`crate::crs`]). For raw/DNG files without a sidecar the file's embedded XMP is used.
 
+use std::collections::HashMap;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
@@ -258,11 +271,101 @@ pub fn sidecar_packet(p: &Photo, cat: &lightcraft_catalog::Catalog) -> String {
     lightcraft_meta::write_xmp_lc(&meta, &lc)
 }
 
-/// Write `data` to `path` atomically (temp file + sync + rename).
+/// The properties LightCraft writes and owns in a sidecar: replaced on every save (removed when
+/// LightCraft has no value, so clearing a field clears it in the file too). All of them are read
+/// back on import and by Read Metadata from File.
+pub const OWNED: &[&str] = &[
+    "xmp:Rating",
+    "xmp:Label",
+    "dc:title",
+    "dc:description",
+    "dc:rights",
+    "dc:creator",
+    "dc:subject",
+    "Iptc4xmpCore:Location",
+    "Iptc4xmpCore:AltTextAccessibility",
+    "Iptc4xmpCore:ExtDescrAccessibility",
+    "photoshop:City",
+    "photoshop:State",
+    "photoshop:Country",
+    "xmpRights:Marked",
+    "xmpRights:UsageTerms",
+    "xmpRights:WebStatement",
+    "lc:*",
+];
+
+/// Properties replaced only when LightCraft has a value (capture time; GPS, which LightCraft
+/// doesn't read from sidecars): otherwise the sidecar's own value stays. Anything else LightCraft
+/// writes (`xmp:CreatorTool`) goes only into new sidecars.
+pub const OWNED_IF_STATED: &[&str] = &["exif:DateTimeOriginal", "photoshop:DateCreated", "exif:GPSLatitude", "exif:GPSLongitude"];
+
+/// Write `data` to `path` atomically: a temp file next to it, synced, then renamed over it.
 fn write_atomic(path: &Path, data: &[u8]) -> std::io::Result<()> {
     lightcraft_catalog::safe_file::write_atomic(path, data)
 }
 
+/// Copy `path` to a new `<name>.bak-<stamp>` (`-1`, `-2`… if taken; never overwriting).
+fn backup(path: &Path, stamp: &str) -> std::io::Result<PathBuf> {
+    use std::io::Write;
+    let bytes = std::fs::read(path)?;
+    let stamp: String = stamp.chars().filter(char::is_ascii_alphanumeric).collect();
+    let name = path.file_name().map(|n| n.to_string_lossy().to_string()).unwrap_or_default();
+    for k in 0..1000 {
+        let b = path.with_file_name(if k == 0 { format!("{name}.bak-{stamp}") } else { format!("{name}.bak-{stamp}-{k}") });
+        match std::fs::OpenOptions::new().write(true).create_new(true).open(&b) {
+            Ok(mut f) => {
+                f.write_all(&bytes)?;
+                f.sync_all()?;
+                return Ok(b);
+            }
+            Err(e) if e.kind() == std::io::ErrorKind::AlreadyExists => continue,
+            Err(e) => return Err(e),
+        }
+    }
+    Err(std::io::Error::other("no free backup name"))
+}
+
+/// What [`Session::save_sidecar`] did.
+#[derive(Clone, Debug, PartialEq)]
+pub struct SidecarSaved {
+    pub path: PathBuf,
+    /// An existing sidecar was merged into (its other contents kept).
+    pub merged: bool,
+    /// An existing sidecar that couldn't be read as XMP was copied here before being replaced.
+    pub backup: Option<PathBuf>,
+}
+
+/// The new contents for the sidecar at `path`: `fresh` merged into the existing file, if any.
+/// Returns (contents, merged, backup).
+fn sidecar_contents(path: &Path, fresh: String, stamp: &str) -> std::io::Result<(String, bool, Option<PathBuf>)> {
+    let bytes = match std::fs::read(path) {
+        Ok(b) => b,
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok((fresh, false, None)),
+        // can't see what is there: never overwrite it blindly
+        Err(e) => return Err(e),
+    };
+    if bytes.iter().all(u8::is_ascii_whitespace) {
+        return Ok((fresh, false, None));
+    }
+    let rules = lightcraft_meta::MergeRules { owned: OWNED, owned_if_present: OWNED_IF_STATED };
+    match std::str::from_utf8(&bytes)
+        .map_err(|e| e.to_string())
+        .and_then(|old| lightcraft_meta::merge_xmp(old, &fresh, rules).map_err(|e| e.to_string()))
+    {
+        Ok(merged) => Ok((merged, true, None)),
+        Err(why) => {
+            let b = backup(path, stamp)?;
+            log::warn!("{}: not readable as XMP ({why}); kept a copy as {} before replacing it", path.display(), b.display());
+            Ok((fresh, false, Some(b)))
+        }
+    }
+}
+
+/// Key of the stem sidecar a file maps to (case-insensitive).
+fn stem_key(original: &str) -> String {
+    sidecar_path(original, SidecarNaming::Stem).to_string_lossy().to_lowercase()
+}
+
 fn file_path(p: &Photo) -> Option<&str> {
     match &p.source {
         Source::File { path } => Some(path),
@@ -298,24 +401,70 @@ pub(crate) fn op_photos(op: &Op, out: &mut Vec<PhotoId>) {
     }
 }
 
+/// Which photo owns each stem sidecar that several catalogued files map to (see
+/// [`Session::sidecar_naming`]).
+pub(crate) struct StemOwners(HashMap<String, PhotoId>);
+
+impl StemOwners {
+    pub(crate) fn of(cat: &lightcraft_catalog::Catalog) -> StemOwners {
+        // per stem: (raw first, then file name, then id) of the best candidate; and how many
+        let mut best: HashMap<String, ((bool, String, u64), PhotoId, usize)> = HashMap::new();
+        for p in cat.photos().filter(|p| p.copy_of.is_none()) {
+            let Some(path) = file_path(p) else { continue };
+            let rank = (p.kind != MediaKind::Raw, path.to_lowercase(), p.id.0);
+            let e = best.entry(stem_key(path)).or_insert_with(|| (rank.clone(), p.id, 0));
+            e.2 += 1;
+            if rank < e.0 {
+                (e.0, e.1) = (rank, p.id);
+            }
+        }
+        StemOwners(best.into_iter().filter(|(_, v)| v.2 > 1).map(|(k, v)| (k, v.1)).collect())
+    }
+
+    /// `naming` for photo `p`, except that a stem sidecar another file owns becomes Full.
+    fn naming(&self, p: &Photo, naming: SidecarNaming) -> SidecarNaming {
+        match (naming, file_path(p)) {
+            (SidecarNaming::Stem, Some(path)) if self.0.get(&stem_key(path)).is_some_and(|owner| *owner != p.id) => SidecarNaming::Full,
+            _ => naming,
+        }
+    }
+}
+
 impl Session {
-    /// Write the photo's XMP sidecar; returns its path.
-    pub fn save_sidecar(&self, id: PhotoId) -> Result<PathBuf> {
+    /// The sidecar naming for photo `id`: the library's, except under Stem naming when another
+    /// catalogued file shares the stem (`IMG_0001.CR3` + `IMG_0001.JPG`) and owns the stem
+    /// sidecar — a raw first, else the first by file name. The others use Full naming
+    /// (`IMG_0001.JPG.xmp`), so their metadata never overwrites each other.
+    pub fn sidecar_naming(&self, id: PhotoId) -> SidecarNaming {
+        match self.catalog.photo(id) {
+            Some(p) if self.xmp.naming == SidecarNaming::Stem => StemOwners::of(&self.catalog).naming(p, self.xmp.naming),
+            _ => self.xmp.naming,
+        }
+    }
+
+    /// Write the photo's XMP sidecar, merged into an existing one (see the module docs).
+    pub fn save_sidecar(&self, id: PhotoId) -> Result<SidecarSaved> {
+        self.save_sidecar_with(id, &StemOwners::of(&self.catalog))
+    }
+
+    pub(crate) fn save_sidecar_with(&self, id: PhotoId, owners: &StemOwners) -> Result<SidecarSaved> {
         let p = self.catalog.photo(id).ok_or(lightcraft_catalog::CatalogError::NoPhoto(id))?;
         if p.copy_of.is_some() {
             return Err(EngineError::Other(format!("{} is a virtual copy: its settings live only in the library", p.file_name)));
         }
         let orig = file_path(p).ok_or_else(|| EngineError::Other(format!("{} is not a file on disk", p.file_name)))?;
-        let path = sidecar_path(orig, self.xmp.naming);
-        write_atomic(&path, sidecar_packet(p, &self.catalog).as_bytes()).map_err(|e| EngineError::Other(format!("{}: {e}", path.display())))?;
-        Ok(path)
+        let path = sidecar_path(orig, owners.naming(p, self.xmp.naming));
+        let err = |e: std::io::Error| EngineError::Other(format!("{}: {e}", path.display()));
+        let (data, merged, backup) = sidecar_contents(&path, sidecar_packet(p, &self.catalog), &(self.clock)()).map_err(err)?;
+        write_atomic(&path, data.as_bytes()).map_err(err)?;
+        Ok(SidecarSaved { path, merged, backup })
     }
 
     /// The op that applies a photo's sidecar (or embedded XMP) to the catalog, if there is one.
     pub fn read_sidecar_op(&self, id: PhotoId) -> Result<Option<(Op, PathBuf)>> {
         let p = self.catalog.photo(id).ok_or(lightcraft_catalog::CatalogError::NoPhoto(id))?;
         let Some(orig) = file_path(p) else { return Ok(None) };
-        let Some((packet, from)) = read_packet(orig, p.kind, self.xmp.naming) else { return Ok(None) };
+        let Some((packet, from)) = read_packet(orig, p.kind, self.sidecar_naming(id)) else { return Ok(None) };
         let sc = parse_sidecar(&packet, p.kind == MediaKind::Raw)
             .map_err(|e| EngineError::Other(format!("{}: {e}", from.display())))?
             .resolve_label(&self.catalog);
@@ -340,9 +489,13 @@ impl Session {
     pub(crate) fn auto_write_sidecars(&self, ops: &[Op]) {
         let mut ids = Vec::new();
         ops.iter().for_each(|o| op_photos(o, &mut ids));
+        if ids.is_empty() {
+            return;
+        }
+        let owners = StemOwners::of(&self.catalog);
         for id in ids {
             if self.catalog.photo(id).is_some_and(|p| file_path(p).is_some() && p.copy_of.is_none())
-                && let Err(e) = self.save_sidecar(id)
+                && let Err(e) = self.save_sidecar_with(id, &owners)
             {
                 log::warn!("auto-write XMP: {e}");
             }

crates/engine/src/smart.rs

@@ -1,13 +1,16 @@
 //! Smart previews: a compact proxy of each photo (its decoded preview-size source, about 1 MB)
 //! kept in the library, so photos stay editable — and exportable at proxy size — while their
 //! originals are offline (an unplugged drive). The proxy is the scene-linear source scaled into
-//! 0..1 by a stored factor, sRGB-encoded and saved as a JPEG after a one-line header.
+//! 0..1 by a stored factor, sRGB-encoded and saved as a JPEG after a one-line header. The header
+//! also keeps the decoder's file-local camera tone curve (Sony ARW camera look), which is applied
+//! at render time and is not baked into the pixels.
 
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
 use lightcraft_catalog::Photo;
 use lightcraft_color::transfer::linear_to_srgb;
+use lightcraft_pipeline::tone::CameraTone;
 use lightcraft_raster::{Rgb32f, Rgba8};
 
 const MAGIC: &[u8] = b"LCSP1\n";
@@ -18,8 +21,11 @@ pub fn file_name(p: &Photo) -> String {
     format!("{:032x}.lcsp", h.0)
 }
 
-/// Encode a source image as a smart preview.
-pub fn encode(img: &Rgb32f) -> Result<Vec<u8>, String> {
+/// The most header [`is_valid`] reads (the JSON line before the JPEG).
+const HEADER_MAX: u64 = 4096;
+
+/// Encode a source image (and the decoder's camera tone curve, if any) as a smart preview.
+pub fn encode(img: &Rgb32f, tone: Option<&CameraTone>) -> Result<Vec<u8>, String> {
     // scale so all but the brightest 0.05 % fit into 0..1
     let mut lum: Vec<f32> = img.data.iter().map(|c| c[0].max(c[1]).max(c[2])).filter(|v| v.is_finite()).collect();
     let scale = if lum.is_empty() {
@@ -47,22 +53,29 @@ pub fn encode(img: &Rgb32f) -> Result<Vec<u8>, String> {
     )
     .map_err(|e| e.to_string())?;
     let mut out = MAGIC.to_vec();
-    out.extend_from_slice(format!("{{\"w\":{},\"h\":{},\"scale\":{scale}}}\n", img.width, img.height).as_bytes());
+    let mut head = serde_json::json!({"w": img.width, "h": img.height, "scale": scale});
+    if let Some(t) = tone {
+        head["tone"] = serde_json::to_value(t).map_err(|e| e.to_string())?;
+    }
+    out.extend_from_slice(head.to_string().as_bytes());
+    out.push(b'\n');
     out.extend_from_slice(&jpg);
     Ok(out)
 }
 
-/// Decode a smart preview back into a source image.
-pub fn decode(bytes: &[u8]) -> Result<Rgb32f, String> {
+/// Decode a smart preview back into a source image and its stored camera tone curve (an invalid
+/// curve is ignored, like a missing one).
+pub fn decode(bytes: &[u8]) -> Result<(Rgb32f, Option<CameraTone>), String> {
     let rest = bytes.strip_prefix(MAGIC).ok_or("not a smart preview")?;
     let nl = rest.iter().position(|b| *b == b'\n').ok_or("bad smart preview")?;
     let head: serde_json::Value = serde_json::from_slice(&rest[..nl]).map_err(|e| e.to_string())?;
     let scale = head["scale"].as_f64().unwrap_or(1.0) as f32;
+    let tone = head.get("tone").and_then(|t| serde_json::from_value::<CameraTone>(t.clone()).ok());
     let d = lightcraft_codecs::decode(&rest[nl + 1..], Default::default()).map_err(|e| e.to_string())?;
     // the decoder undoes the sRGB encoding; the values are the source's own primaries
     let mut img = d.image;
     img.data.iter_mut().for_each(|c| *c = c.map(|v| v * scale));
-    Ok(img)
+    Ok((img, tone))
 }
 
 /// Where a library keeps its smart previews.
@@ -130,11 +143,16 @@ pub fn migrate(from: &Path, to: &Path, what: Existing) -> (usize, Vec<String>) {
             Existing::Discard => std::fs::remove_file(&src),
             _ => {
                 let dst = to.join(e.file_name());
-                if dst.exists() {
-                    // named by content: the copy already there is the same preview
+                if is_valid(&dst) {
+                    // named by content: the complete copy already there is the same preview
                     std::fs::remove_file(&src)
                 } else {
-                    std::fs::rename(&src, &dst).or_else(|_| std::fs::copy(&src, &dst).and_then(|_| std::fs::remove_file(&src)))
+                    // across drives: copied atomically (never a partial proxy at the new place)
+                    std::fs::rename(&src, &dst).or_else(|_| {
+                        std::fs::read(&src)
+                            .and_then(|b| lightcraft_catalog::safe_file::write_atomic(&dst, &b))
+                            .and_then(|()| std::fs::remove_file(&src))
+                    })
                 }
             }
         };
@@ -146,10 +164,33 @@ pub fn migrate(from: &Path, to: &Path, what: Existing) -> (usize, Vec<String>) {
     (done, failed)
 }
 
+/// A cheap check that the smart preview at `path` is complete: our header, then a JPEG from its
+/// start marker to its end marker. A file cut short by a crash, a full drive or an unplugged one
+/// fails it (and is then rebuilt by Build Smart Previews, not counted as there).
+pub fn is_valid(path: &Path) -> bool {
+    use std::io::{Read, Seek, SeekFrom};
+    let Ok(mut f) = std::fs::File::open(path) else { return false };
+    let mut head = Vec::with_capacity(1024);
+    if (&mut f).take(HEADER_MAX).read_to_end(&mut head).is_err() {
+        return false;
+    }
+    let Some(rest) = head.strip_prefix(MAGIC) else { return false };
+    let Some(nl) = rest.iter().position(|b| *b == b'\n') else { return false };
+    let size_ok = rest
+        .get(..nl)
+        .and_then(|h| serde_json::from_slice::<serde_json::Value>(h).ok())
+        .is_some_and(|h| h["w"].as_u64().is_some_and(|w| w > 0) && h["h"].as_u64().is_some_and(|h| h > 0));
+    if !size_ok || rest.get(nl + 1..nl + 3) != Some(&[0xFF, 0xD8][..]) {
+        return false;
+    }
+    let mut end = [0u8; 2];
+    f.seek(SeekFrom::End(-2)).is_ok() && f.read_exact(&mut end).is_ok() && end == [0xFF, 0xD9]
+}
+
 /// Load the proxy at `path`.
-pub fn load(path: &Path) -> Result<Arc<Rgb32f>, String> {
+pub fn load(path: &Path) -> Result<crate::media::DecodedSource, String> {
     let b = std::fs::read(path).map_err(|e| format!("{}: {e}", path.display()))?;
-    decode(&b).map(Arc::new)
+    decode(&b).map(|(image, camera_tone)| crate::media::DecodedSource { image: Arc::new(image), info: None, camera_tone })
 }
 
 #[cfg(test)]
@@ -193,11 +234,66 @@ mod tests {
         let _ = std::fs::remove_dir_all(&base);
     }
 
+    #[test]
+    fn damaged_proxies_are_invalid_and_never_kept_over_good_ones() {
+        let base = temp("valid");
+        let (a, b) = (base.join("a"), base.join("b"));
+        std::fs::create_dir_all(&a).unwrap();
+        std::fs::create_dir_all(&b).unwrap();
+        let img = lightcraft_scenes::demo_library()[0].render(64, 40);
+        let good = encode(&img, None).unwrap();
+        std::fs::write(a.join("1.lcsp"), &good).unwrap();
+        assert!(is_valid(&a.join("1.lcsp")));
+        for cut in [good.len() - 1, good.len() / 2, 10, 0] {
+            std::fs::write(b.join("1.lcsp"), &good[..cut]).unwrap();
+            assert!(!is_valid(&b.join("1.lcsp")), "cut at {cut}");
+        }
+        assert!(!is_valid(&b.join("missing.lcsp")));
+        // moving onto a damaged copy replaces it instead of deleting the good one
+        assert_eq!(migrate(&a, &b, Existing::Move).0, 1);
+        assert_eq!(std::fs::read(b.join("1.lcsp")).unwrap(), good);
+        let _ = std::fs::remove_dir_all(&base);
+    }
+
+    #[test]
+    fn camera_tone_travels_with_the_proxy() {
+        let tone = CameraTone::new(std::array::from_fn(|i| {
+            let x = 0.004 * 1.17f32.powi(i as i32);
+            [x, 0.95 * (1.0 - (-2.7 * x).exp())]
+        }))
+        .unwrap();
+        let img = lightcraft_scenes::demo_library()[0].render(64, 40);
+        let bytes = encode(&img, Some(&tone)).unwrap();
+        assert_eq!(decode(&bytes).unwrap().1, Some(tone));
+        let dir = temp("tone");
+        let path = dir.join("t.lcsp");
+        std::fs::write(&path, &bytes).unwrap();
+        // the longer header is still read by the validity check, and the curve by `load`
+        assert!(is_valid(&path));
+        let loaded = load(&path).unwrap();
+        assert_eq!(loaded.camera_tone, Some(tone));
+        let header = lightcraft_pipeline::SourceInfo { raw: true, ..Default::default() };
+        assert_eq!(loaded.info_or(header).camera_tone, Some(tone));
+        // a hostile curve (reversing knots) is ignored, not trusted
+        let nl = MAGIC.len() + bytes[MAGIC.len()..].iter().position(|b| *b == b'\n').unwrap();
+        let mut head: serde_json::Value = serde_json::from_slice(&bytes[MAGIC.len()..nl]).unwrap();
+        let mut knots: Vec<[f32; 2]> = serde_json::from_value(head["tone"]["knots"].clone()).unwrap();
+        knots.swap(3, 4);
+        head["tone"]["knots"] = serde_json::json!(knots);
+        let mut hostile = MAGIC.to_vec();
+        hostile.extend_from_slice(head.to_string().as_bytes());
+        hostile.extend_from_slice(&bytes[nl..]);
+        let (pixels, tone) = decode(&hostile).unwrap();
+        assert_eq!((pixels.width, tone), (img.width, None));
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
     #[test]
     fn roundtrip_keeps_the_picture() {
         let img = lightcraft_scenes::demo_library()[0].render(160, 100);
-        let back = decode(&encode(&img).unwrap()).unwrap();
+        let (back, tone) = decode(&encode(&img, None).unwrap()).unwrap();
         assert_eq!((back.width, back.height), (img.width, img.height));
+        assert!(tone.is_none());
         let mut err = 0.0f64;
         for (a, b) in img.data.iter().zip(&back.data) {
             for k in 0..3 {

crates/engine/src/tests.rs

@@ -10,6 +10,30 @@ fn active_dev(s: &Session) -> lightcraft_develop::DevelopSettings {
     (*s.develop_of(s.active().unwrap()).unwrap()).clone()
 }
 
+#[test]
+fn changing_one_wb_control_resolves_as_shot_without_stale_tint() {
+    use lightcraft_catalog::{Photo, PhotoId, Source};
+    use lightcraft_develop::{DevelopSettings, WbMode};
+    let mut s = demo();
+    let id = PhotoId(100);
+    let mut p = Photo::new(id, Source::File { path: "synthetic.arw".into() }, "synthetic.arw", "ARW", 16, 16, "");
+    // A catalog made by the old generic-matrix Kelvin inference.
+    p.as_shot_wb = Some((6829.0, -127.0));
+    p.develop = std::sync::Arc::new(DevelopSettings::for_raw(6829.0, -127.0));
+    s.catalog.apply(lightcraft_catalog::Op::AddPhoto { photo: Box::new(p) }).unwrap();
+    s.execute("library.select", &json!({"ids": [100], "active": 100})).unwrap();
+    s.execute("develop.set", &json!({"control": "wb.temp", "value": 8000})).unwrap();
+    let d = active_dev(&s);
+    assert_eq!(d.wb.mode, WbMode::Custom);
+    assert_eq!(d.wb.temp, 8000.0);
+    assert_eq!(d.wb.tint, 0.0, "untouched tint comes from the current as-shot reference");
+    s.execute("develop.wb", &json!({"mode": "asShot"})).unwrap();
+    s.execute("develop.set", &json!({"control": "wb.tint", "value": 10})).unwrap();
+    assert_eq!(active_dev(&s).wb.temp, 6500.0);
+    s.execute("develop.reset", &json!({})).unwrap();
+    assert_eq!((active_dev(&s).wb.temp, active_dev(&s).wb.tint), (6500.0, 0.0));
+}
+
 #[test]
 fn demo_library_loads() {
     let mut s = demo();

crates/engine/src/tests_import.rs

@@ -144,6 +144,99 @@ fn browsing_a_folder_lists_its_photos_without_adding_them() {
     let _ = std::fs::remove_dir_all(&dir);
 }
 
+/// Photos a.png, b.png, c.png imported from `old`, then: a renamed into `moved`; b renamed, with
+/// an impostor (same name and size, other bytes) under its old name; c gone, with two impostors.
+fn renamed_and_ambiguous_scene(tag: &str) -> (std::path::PathBuf, Session) {
+    let dir = temp_dir(tag);
+    std::fs::create_dir_all(dir.join("old")).unwrap();
+    std::fs::create_dir_all(dir.join("moved/real")).unwrap();
+    for (n, seed) in [("a.png", 1), ("b.png", 2), ("c.png", 3)] {
+        write_png(&dir.join("old").join(n), seed);
+    }
+    let mut s = Session::new().with_fs();
+    s.execute("library.import", &json!({"paths": [dir.join("old").to_string_lossy()]})).unwrap();
+    let impostor = |src: &Path, dst: &Path| {
+        let mut b = std::fs::read(src).unwrap();
+        let k = b.len() - 20;
+        b[k] ^= 0xff;
+        std::fs::write(dst, b).unwrap();
+    };
+    std::fs::rename(dir.join("old/a.png"), dir.join("moved/Trip-001.png")).unwrap();
+    impostor(&dir.join("old/b.png"), &dir.join("moved/b.png"));
+    std::fs::rename(dir.join("old/b.png"), dir.join("moved/real/Trip-002.png")).unwrap();
+    impostor(&dir.join("old/c.png"), &dir.join("moved/c.png"));
+    impostor(&dir.join("old/c.png"), &dir.join("moved/real/c.png"));
+    std::fs::remove_file(dir.join("old/c.png")).unwrap();
+    (dir, s)
+}
+
+/// Issue #105: Find Missing finds renamed files by content, prefers the content match over a
+/// same-name same-size impostor, and skips (reports) photos it can't tell apart.
+#[test]
+fn find_missing_matches_renamed_files_by_content() {
+    let (dir, mut s) = renamed_and_ambiguous_scene("missing-content");
+    let r = s.execute("library.findMissing", &json!({"folder": dir.join("moved").to_string_lossy()})).unwrap();
+    let found = r["found"].as_array().unwrap();
+    assert_eq!(found.len(), 2, "{r}");
+    let to = |name: &str| {
+        found.iter().find(|f| f["from"].as_str().unwrap().ends_with(name)).map(|f| (f["to"].as_str().unwrap().to_string(), f["by"].clone()))
+    };
+    assert_eq!(to("a.png"), Some((dir.join("moved/Trip-001.png").to_string_lossy().to_string(), json!("content"))));
+    assert_eq!(to("b.png"), Some((dir.join("moved/real/Trip-002.png").to_string_lossy().to_string(), json!("content"))), "not the impostor");
+    assert_eq!(r["missing"], 1);
+    assert_eq!(r["ambiguous"][0]["candidates"].as_array().map(Vec::len), Some(2), "{r}");
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
+/// Issue #104: the app plans Find Missing on a worker thread (no session) and relinks the plan
+/// afterwards; that gives exactly what the synchronous command gives — renamed files by content,
+/// impostors and look-alikes skipped (`ambiguous`).
+#[test]
+fn find_missing_planned_on_a_worker_matches_the_command() {
+    use crate::cmd::missing::{find_candidates, plan_find_missing};
+    let (dir, mut s) = renamed_and_ambiguous_scene("missing-worker");
+    let folder = dir.join("moved").to_string_lossy().to_string();
+    let candidates = find_candidates(&s.catalog);
+    let f = folder.clone();
+    let plan = std::thread::spawn(move || plan_find_missing(&candidates, &f)).join().unwrap().unwrap();
+    assert_eq!((plan.found.len(), plan.missing, plan.ambiguous.len()), (2, 1, 1), "{plan:?}");
+    let applied = s.execute("library.findMissing", &plan.to_json()).unwrap();
+    s.execute("edit.undo", &json!({})).unwrap();
+    assert_eq!(s.execute("library.missing", &json!({})).unwrap().as_array().map(Vec::len), Some(3), "undo restores all three");
+    let direct = s.execute("library.findMissing", &json!({"folder": folder})).unwrap();
+    assert_eq!(applied, direct);
+    assert_eq!(direct["found"].as_array().map(Vec::len), Some(2), "{direct}");
+    assert_eq!(direct["ambiguous"].as_array().map(Vec::len), Some(1), "{direct}");
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
+/// Issue #104: a plan made on a worker is re-checked when it is applied: a photo relinked
+/// meanwhile is left alone, and a file that is now another photo's original isn't used.
+#[test]
+fn find_missing_plan_is_rechecked_when_applied() {
+    use crate::cmd::missing::{find_candidates, plan_find_missing};
+    let (dir, mut s) = renamed_and_ambiguous_scene("missing-recheck");
+    let plan = plan_find_missing(&find_candidates(&s.catalog), &dir.join("moved").to_string_lossy()).unwrap();
+    let to = |name: &str| plan.found.iter().find(|f| f.from.ends_with(name)).unwrap().clone();
+    let (a, b) = (to("a.png"), to("b.png"));
+    // meanwhile: a is relinked by hand (elsewhere), and the ambiguous c is pointed at b's file
+    std::fs::copy(&a.to, dir.join("a-elsewhere.png")).unwrap();
+    s.execute("photo.relink", &json!({"id": a.id.0, "path": dir.join("a-elsewhere.png").to_string_lossy()})).unwrap();
+    let c = plan.ambiguous[0].id;
+    s.execute("photo.relink", &json!({"id": c.0, "path": b.to})).unwrap();
+    let r = s.execute("library.findMissing", &plan.to_json()).unwrap();
+    assert_eq!(r["found"].as_array().map(Vec::len), Some(0), "{r}");
+    assert_eq!(r["ambiguous"].as_array().map(Vec::len), Some(0), "c isn't missing any more: {r}");
+    assert_eq!(r["missing"], 1, "b stays missing: its file is c's now: {r}");
+    let path_of = |id: lightcraft_catalog::PhotoId| match &s.catalog.photo(id).unwrap().source {
+        lightcraft_catalog::Source::File { path } => path.clone(),
+        _ => String::new(),
+    };
+    assert_eq!(path_of(a.id), dir.join("a-elsewhere.png").to_string_lossy());
+    assert_eq!(path_of(b.id), b.from);
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
 #[test]
 fn missing_files_are_found_and_relinked() {
     let dir = std::env::temp_dir().join(format!("lc-missing-{}", std::process::id()));
@@ -352,6 +445,58 @@ fn smart_previews_stand_in_for_offline_originals() {
     let _ = std::fs::remove_dir_all(&lib);
 }
 
+/// Issue #106: a smart preview cut short (crash, full drive) counted as built forever and failed
+/// exactly when the original went offline. Writes are atomic now, and a damaged proxy is not
+/// reported as present and is rebuilt.
+#[test]
+fn damaged_smart_previews_are_rebuilt_and_failed_writes_leave_none() {
+    let src = temp_dir("smartdmg-src");
+    let lib = temp_dir("smartdmg-lib");
+    write_png(&src.join("a.png"), 5);
+    let mut s = Session::new().with_fs();
+    s.open_library(&lib, false).unwrap();
+    s.execute("library.import", &json!({"paths": [src.join("a.png").to_string_lossy()]})).unwrap();
+    let id = s.active().unwrap();
+    let dir = s.media.smart_dir.clone().unwrap();
+    let file = dir.join(crate::smart::file_name(s.catalog.photo(id).unwrap()));
+    {
+        let _fault = lightcraft_catalog::safe_file::fail_writes_after(64);
+        let r = s.execute("library.smartPreviews", &json!({})).unwrap();
+        assert_eq!((r["built"].as_u64(), r["failed"].as_array().map(Vec::len)), (Some(0), Some(1)), "{r}");
+    }
+    assert!(!file.exists(), "no partial proxy");
+    assert_eq!(std::fs::read_dir(&dir).unwrap().count(), 0, "no temp file left");
+    assert_eq!(s.execute("photo.smartPreview", &json!({})).unwrap()["smartPreview"], false);
+
+    let r = s.execute("library.smartPreviews", &json!({})).unwrap();
+    assert_eq!((r["built"].as_u64(), r["repaired"].as_u64()), (Some(1), Some(0)), "{r}");
+    assert!(crate::smart::is_valid(&file));
+    // cut short, as by a crash before the fix
+    let full = std::fs::read(&file).unwrap();
+    std::fs::write(&file, &full[..full.len() / 2]).unwrap();
+    assert!(!crate::smart::is_valid(&file));
+    assert_eq!(s.execute("photo.smartPreview", &json!({})).unwrap()["smartPreview"], false, "not counted as there");
+    let r = s.execute("library.smartPreviews", &json!({})).unwrap();
+    assert_eq!((r["built"].as_u64(), r["repaired"].as_u64()), (Some(1), Some(1)), "{r}");
+    assert_eq!(std::fs::read(&file).unwrap(), full, "rebuilt whole");
+    // the app's background build (issue #104) checks and repairs the same way, on a worker thread
+    std::fs::write(&file, &full[..full.len() / 2]).unwrap();
+    let r = s.execute("library.smartPreviews", &json!({"background": true})).unwrap();
+    assert_eq!(r["what"], "smart previews", "{r}");
+    let t0 = std::time::Instant::now();
+    let r = loop {
+        let r = s.execute("library.previewProgress", &json!({})).unwrap();
+        if r["running"] == false || t0.elapsed() > std::time::Duration::from_secs(60) {
+            break r;
+        }
+        std::thread::sleep(std::time::Duration::from_millis(5));
+    };
+    assert_eq!((r["done"].as_u64(), r["failed"].as_u64(), r["repaired"].as_u64()), (Some(1), Some(0), Some(1)), "{r}");
+    assert_eq!(std::fs::read(&file).unwrap(), full, "rebuilt whole in the background");
+    let _ = std::fs::remove_dir_all(&src);
+    let _ = std::fs::remove_dir_all(&lib);
+}
+
 /// LUT profiles: a .cube imports as a creative profile (into the library), renders differently
 /// (Amount 0 = no change), is listed in the profile browser and comes back with the library.
 #[test]
@@ -441,6 +586,70 @@ fn folders_rename_and_move_with_their_photos() {
     let _ = std::fs::remove_dir_all(&root);
 }
 
+/// Rename / Move Folder are undo steps (issue #97): undo renames the folder back on disk (files and
+/// sidecars along) and restores the photos' paths, redo repeats it; a destination taken in the
+/// meantime is never overwritten — the step is refused, reported and stays on the stack.
+#[test]
+fn folder_rename_and_move_undo_and_redo_on_disk() {
+    let root = temp_dir("folders-undo");
+    let a = root.join("Trip");
+    write_png(&a.join("one.png"), 3);
+    std::fs::write(a.join("one.xmp"), "<x:xmpmeta xmlns:x=\"adobe:ns:meta/\"/>").unwrap();
+    let mut s = Session::new().with_fs();
+    s.execute("library.import", &json!({"paths": [a.to_string_lossy()]})).unwrap();
+    let id = s.active().unwrap();
+    let path = |s: &Session| match &s.catalog.photo(id).unwrap().source {
+        lightcraft_catalog::Source::File { path } => path.clone(),
+        _ => panic!(),
+    };
+    let undo0 = s.undo.len();
+    let b = root.join("Italy");
+    s.execute("folder.rename", &json!({"path": a.to_string_lossy(), "name": "Italy"})).unwrap();
+    assert_eq!(s.undo.len(), undo0 + 1, "one undo step");
+    assert!(s.undo.last().unwrap().label.contains("Rename Folder"));
+    assert!(b.join("one.png").exists() && !a.exists());
+
+    s.execute("edit.undo", &json!({})).unwrap();
+    assert!(a.join("one.png").exists() && a.join("one.xmp").exists() && !b.exists(), "renamed back on disk");
+    assert_eq!(path(&s), a.join("one.png").to_string_lossy());
+    s.media.forget(id);
+    assert!(s.render_now(id, 16, 16).is_ok());
+
+    s.execute("edit.redo", &json!({})).unwrap();
+    assert!(b.join("one.png").exists() && b.join("one.xmp").exists() && !a.exists());
+    assert_eq!(path(&s), b.join("one.png").to_string_lossy());
+
+    // the old name is taken now: undo is refused, nothing is overwritten, the step stays
+    std::fs::create_dir_all(&a).unwrap();
+    std::fs::write(a.join("keep.txt"), "mine").unwrap();
+    let undo_n = s.undo.len();
+    let e = s.execute("edit.undo", &json!({})).unwrap_err().to_string();
+    assert!(e.contains("already exists"), "{e}");
+    assert_eq!(s.undo.len(), undo_n, "the step stays on the stack");
+    assert_eq!(std::fs::read_to_string(a.join("keep.txt")).unwrap(), "mine");
+    assert!(b.join("one.png").exists());
+    assert_eq!(path(&s), b.join("one.png").to_string_lossy());
+    std::fs::remove_dir_all(&a).unwrap();
+
+    // move into another folder, undo, redo
+    let into = root.join("Archive");
+    s.execute("folder.move", &json!({"path": b.to_string_lossy(), "into": into.to_string_lossy()})).unwrap();
+    let moved = into.join("Italy");
+    assert_eq!(path(&s), moved.join("one.png").to_string_lossy());
+    s.execute("edit.undo", &json!({})).unwrap();
+    assert!(b.join("one.png").exists() && !moved.exists());
+    assert_eq!(path(&s), b.join("one.png").to_string_lossy());
+    // the redo target is taken (even by an empty folder): refused, nothing replaced
+    std::fs::create_dir_all(&moved).unwrap();
+    assert!(s.execute("edit.redo", &json!({})).is_err());
+    assert!(b.join("one.png").exists());
+    std::fs::remove_dir(&moved).unwrap();
+    s.execute("edit.redo", &json!({})).unwrap();
+    assert!(moved.join("one.png").exists() && moved.join("one.xmp").exists() && !b.exists());
+    assert_eq!(path(&s), moved.join("one.png").to_string_lossy());
+    let _ = std::fs::remove_dir_all(&root);
+}
+
 /// Assisted culling: a burst (same scene, seconds apart) of a sharp and two soft shots, plus an
 /// unrelated photo: the burst is grouped, the sharp one is its best, blurry shots can be rejected.
 #[test]
@@ -590,6 +799,7 @@ fn smart_previews_folder_is_chosen_per_library() {
     assert_eq!(s.execute("photo.smartPreview", &json!({})).unwrap()["smartPreview"], true);
 
     // the setting is saved with the library
+    drop(s); // one session per library (issue #99)
     let mut again = Session::new().with_fs();
     again.open_library(&lib, false).unwrap();
     assert_eq!(again.execute("library.smartPreviewsLocation", &json!({})).unwrap()["path"], to.to_string_lossy().as_ref());

crates/engine/src/tests_import_move.rs

@@ -163,6 +163,50 @@ fn a_failed_or_corrupt_copy_keeps_the_source() {
     }
 }
 
+/// Issue #96: Import → Copy used a plain unverified copy (and check-then-copy naming that could
+/// replace a file). It now gets the same verified copy as Move: a copy that fails or comes out
+/// different is removed and reported as a failed import, nothing is catalogued, and the card
+/// is untouched; a good copy never replaces an existing file.
+#[test]
+fn copy_import_verifies_each_copy() {
+    let import_copy = |s: &mut Session, card: &Path, dest: &Path| {
+        s.execute(
+            "library.import",
+            &json!({"paths": [card.to_string_lossy()], "mode": "copy", "destination": dest.to_string_lossy(), "organize": "flat"}),
+        )
+        .unwrap()
+    };
+    for fault in [Fault::FailWrite, Fault::Corrupt] {
+        let base = temp_dir(&format!("copyfail-{fault:?}"));
+        let (card, dest) = (base.join("card"), base.join("out"));
+        write_png(&card.join("a.png"), 3);
+        let bytes = std::fs::read(card.join("a.png")).unwrap();
+        let mut s = session();
+        inject(fault);
+        let r = import_copy(&mut s, &card, &dest);
+        inject(Fault::None);
+        assert_eq!(len(&r, "failed"), 1, "{fault:?}: {r}");
+        assert_eq!(len(&r, "imported"), 0, "{fault:?}: {r}");
+        assert!(r.to_string().contains("the original is untouched"), "{r}");
+        assert_eq!(s.catalog.len(), 0);
+        assert_eq!(std::fs::read(card.join("a.png")).unwrap(), bytes, "{fault:?}: source intact");
+        assert_eq!(files_under(&dest), Vec::<String>::new(), "{fault:?}: no bad copy left");
+        let _ = std::fs::remove_dir_all(&base);
+    }
+    // a good copy: verified, and a taken name gets -1 instead of being replaced
+    let base = temp_dir("copyok");
+    let (card, dest) = (base.join("card"), base.join("out"));
+    write_png(&card.join("a.png"), 4);
+    std::fs::create_dir_all(&dest).unwrap();
+    std::fs::write(dest.join("a.png"), b"someone else's file").unwrap();
+    let mut s = session();
+    let r = import_copy(&mut s, &card, &dest);
+    assert_eq!(len(&r, "imported"), 1, "{r}");
+    assert_eq!(std::fs::read(dest.join("a.png")).unwrap(), b"someone else's file");
+    assert_eq!(std::fs::read(dest.join("a-1.png")).unwrap(), std::fs::read(card.join("a.png")).unwrap());
+    let _ = std::fs::remove_dir_all(&base);
+}
+
 /// A source that can't be removed (a read-only card) stays and is reported; the photo is
 /// imported from its copy.
 #[test]

crates/engine/src/tests_library.rs

@@ -113,6 +113,7 @@ fn close_writes_snapshot_and_view_state() {
     let expect = s.catalog.to_snapshot();
     s.close_library().unwrap();
     assert_eq!(std::fs::metadata(dir.join("catalog.log")).unwrap().len(), 0);
+    drop(s); // one session per library (issue #99)
 
     let s2 = open(&dir, true);
     let r = &s2.library.as_ref().unwrap().report;
@@ -178,6 +179,7 @@ fn new_library_without_seed_is_empty_and_compacts() {
     assert!(p["snapshots"].as_u64() >= Some(1), "{p}");
     assert!(p["lastSnapshot"]["bytes"].as_u64() > Some(0), "{p}");
     assert!(p["lastSnapshot"]["totalMs"].as_f64() >= p["lastSnapshot"]["serializeMs"].as_f64(), "{p}");
+    drop(s); // one session per library (issue #99)
     let s2 = open(&dir, true);
     assert_eq!(s2.catalog.len(), 0, "an existing library is never seeded");
     assert_eq!(s2.catalog.albums().count(), 1);
@@ -376,3 +378,32 @@ fn scale_100k_library_queries() {
     worst.sort_by(|a, b| b.1.total_cmp(&a.1));
     eprintln!("slowest: {:?}", &worst[..3]);
 }
+
+/// Issue #99: a library is open in one session at a time. A second opener is refused (nothing
+/// read or written), the owning session can reopen it, and it is free again once closed.
+#[test]
+fn a_library_open_elsewhere_is_refused() {
+    let dir = temp_dir("locked");
+    let mut s = open(&dir, true);
+    s.execute("photo.rate", &json!({"rating": 3})).unwrap();
+    let log = std::fs::read(dir.join("catalog.log")).unwrap();
+
+    let mut other = Session::new();
+    let e = other.open_library(&dir, true).unwrap_err();
+    assert!(matches!(e, crate::EngineError::LibraryInUse(_)), "{e:?}");
+    assert!(e.to_string().contains("already open in"), "{e}");
+    assert!(other.library.is_none());
+    assert_eq!(std::fs::read(dir.join("catalog.log")).unwrap(), log, "the refused opener wrote nothing");
+
+    // the session that has it open may reopen it (Settings → Open Library on the same folder)
+    s.close_library().unwrap();
+    s.open_library(&dir, true).unwrap();
+    assert!(other.open_library(&dir, true).is_err(), "still locked after reopening");
+    s.execute("photo.rate", &json!({"rating": 4})).unwrap();
+    let expect = s.catalog.to_snapshot();
+
+    drop(s);
+    other.open_library(&dir, true).unwrap();
+    assert_eq!(other.catalog.to_snapshot(), expect);
+    let _ = std::fs::remove_dir_all(&dir);
+}

crates/engine/src/tests_persist.rs

@@ -17,6 +17,8 @@ struct Flaky {
     fail: Arc<AtomicBool>,
     /// Only snapshots fail (appends work).
     snapshots_only: bool,
+    /// Only appends fail (a dead log handle; fresh files can still be written).
+    appends_only: bool,
 }
 
 impl Flaky {
@@ -39,7 +41,7 @@ impl Store for Flaky {
         self.files.read(name)
     }
     fn write_atomic(&mut self, name: &str, data: &[u8]) -> std::io::Result<()> {
-        if self.failing() {
+        if self.failing() && !self.appends_only {
             return Err(std::io::Error::other("disk full"));
         }
         self.files.write_atomic(name, data)
@@ -145,3 +147,47 @@ fn failed_snapshot_does_not_fail_the_command() {
     store.set_failing(false);
     assert_eq!(open(&store, false).catalog.albums().count(), 2);
 }
+
+/// Issue #101: quitting while the log can't be appended to still saves the queued changes in the
+/// closing snapshot (a fresh file), and reports success; they are not appended again later.
+#[test]
+fn close_saves_queued_changes_in_the_snapshot_when_appends_fail() {
+    let store = Flaky { appends_only: true, ..Default::default() };
+    let mut s = open(&store, true);
+    let id = s.selection.active.unwrap();
+    store.set_failing(true);
+    assert!(matches!(s.execute("photo.rate", &json!({"rating": 4})), Err(EngineError::NotSaved(_))));
+    assert!(matches!(s.execute("photo.flag", &json!({"flag": "pick"})), Err(EngineError::NotSaved(_))));
+    assert_eq!(s.unsaved().map(|u| u.0), Some(2));
+    s.close_library().unwrap();
+    assert_eq!(s.unsaved(), None);
+    assert!(s.pending_log.is_empty());
+    let expect = s.catalog.to_snapshot();
+    drop(s);
+    store.set_failing(false);
+    let mut s2 = open(&store, true);
+    assert_eq!(s2.catalog.to_snapshot(), expect);
+    let p = s2.catalog.photo(id).unwrap();
+    assert_eq!((p.rating, p.flag), (4, Flag::Pick));
+    // later edits continue after the absorbed ops
+    s2.execute("photo.rate", &json!({"rating": 2})).unwrap();
+    let expect = s2.catalog.to_snapshot();
+    drop(s2);
+    assert_eq!(open(&store, true).catalog.to_snapshot(), expect);
+}
+
+/// When neither the log nor the snapshot can be written, closing fails with `NotSaved` and the
+/// changes stay queued (a later retry can still save them).
+#[test]
+fn close_fails_when_nothing_can_be_saved() {
+    let store = Flaky::default();
+    let mut s = open(&store, true);
+    store.set_failing(true);
+    assert!(s.execute("photo.rate", &json!({"rating": 4})).is_err());
+    let e = s.close_library().unwrap_err();
+    assert!(matches!(e, EngineError::NotSaved(_)), "{e:?}");
+    assert_eq!(s.unsaved().map(|u| u.0), Some(1));
+    store.set_failing(false);
+    s.close_library().unwrap();
+    assert_eq!(s.unsaved(), None);
+}

crates/engine/src/tests_prefs.rs

@@ -126,11 +126,13 @@ fn preferences_persist_with_the_library() {
     assert_eq!(r["persistent"], true);
     // export presets are library preferences too
     s.execute("export.savePreset", &json!({"name": "Proof", "params": {"format": "jpeg", "percent": 25}})).unwrap();
+    drop(s); // one session per library (issue #99)
     let mut s = Session::new().with_fs();
     s.open_library(&lib, false).unwrap();
     assert_eq!(s.export_params(&json!({"preset": "Proof"})).unwrap(), json!({"format": "jpeg", "percent": 25}));
     // older prefs.json files (snake_case `last_export`, no import section) still load
     std::fs::write(lib.join("prefs.json"), r#"{"xmp": {"autoWrite": false}, "last_export": {"format": "png"}}"#).unwrap();
+    drop(s);
     let mut s = Session::new().with_fs();
     s.open_library(&lib, false).unwrap();
     assert_eq!(s.last_export, Some(json!({"format": "png"})));

crates/engine/src/tests_settings_files.rs

@@ -0,0 +1,97 @@
+//! Issue #103: a damaged or unreadable settings file (prefs.json, presets.json, view.json) is
+//! never silently replaced by the defaults: a damaged one is kept aside, an unreadable one is not
+//! written this session, and the user is told.
+
+use std::sync::{Arc, Mutex};
+
+use lightcraft_catalog::{MemStore, Store};
+use serde_json::json;
+
+use crate::Session;
+use crate::library::LibraryStores;
+
+fn temp_dir(tag: &str) -> std::path::PathBuf {
+    let d = std::env::temp_dir().join(format!("lc-settings-{tag}-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&d);
+    std::fs::create_dir_all(&d).unwrap();
+    d
+}
+
+#[test]
+fn damaged_prefs_are_kept_aside_and_reported() {
+    let lib = temp_dir("damaged");
+    let bad = br#"{"exportPresets": [{"name": "Proof", "par"#;
+    std::fs::write(lib.join("prefs.json"), bad).unwrap();
+    let mut s = Session::new().with_fs();
+    s.open_library(&lib, false).unwrap();
+    let kept: Vec<_> = std::fs::read_dir(&lib)
+        .unwrap()
+        .map(|e| e.unwrap().file_name().to_string_lossy().to_string())
+        .filter(|n| n.starts_with("prefs.json.corrupt-"))
+        .collect();
+    assert_eq!(kept.len(), 1, "{kept:?}");
+    assert_eq!(std::fs::read(lib.join(&kept[0])).unwrap(), bad);
+    let warnings = s.take_library_warnings();
+    assert_eq!(warnings.len(), 1);
+    assert!(warnings[0].contains("prefs.json is damaged") && warnings[0].contains(&kept[0]), "{warnings:?}");
+    assert!(s.take_library_warnings().is_empty(), "each warning is handed out once");
+    let info = s.execute("library.info", &json!({})).unwrap();
+    assert_eq!(info["settingsWarnings"].as_array().map(Vec::len), Some(1), "{info}");
+    // saving goes on (the damaged original is safe in its copy)
+    s.execute("library.preferences", &json!({"cacheMb": 300})).unwrap();
+    assert!(String::from_utf8(std::fs::read(lib.join("prefs.json")).unwrap()).unwrap().contains("300"));
+    assert_eq!(std::fs::read(lib.join(&kept[0])).unwrap(), bad);
+    drop(s);
+    let _ = std::fs::remove_dir_all(&lib);
+}
+
+/// `presets.json` and `prefs.json` can't be read (locked by another program, an I/O error).
+#[derive(Clone, Default)]
+struct Unreadable {
+    files: MemStore,
+    unreadable: Arc<Mutex<Vec<String>>>,
+}
+
+impl Store for Unreadable {
+    fn read(&mut self, name: &str) -> std::io::Result<Option<Vec<u8>>> {
+        if self.unreadable.lock().unwrap().iter().any(|n| n == name) {
+            return Err(std::io::Error::other("locked by another process"));
+        }
+        self.files.read(name)
+    }
+    fn write_atomic(&mut self, name: &str, data: &[u8]) -> std::io::Result<()> {
+        self.files.write_atomic(name, data)
+    }
+    fn append(&mut self, name: &str, data: &[u8]) -> std::io::Result<()> {
+        self.files.append(name, data)
+    }
+    fn truncate(&mut self, name: &str, len: u64) -> std::io::Result<()> {
+        self.files.truncate(name, len)
+    }
+    fn describe(&self) -> String {
+        "unreadable".into()
+    }
+}
+
+#[test]
+fn unreadable_settings_are_not_overwritten() {
+    let files = Unreadable::default();
+    let presets = br#"{"user": [{"id": "user.mine", "name": "Mine", "group": "User Presets", "settings": {}}]}"#.to_vec();
+    let prefs = br#"{"cacheMb": 777}"#.to_vec();
+    files.files.set("presets.json", presets.clone());
+    files.files.set("prefs.json", prefs.clone());
+    *files.unreadable.lock().unwrap() = vec!["presets.json".into(), "prefs.json".into()];
+    let mut s = Session::new();
+    let stores = LibraryStores { dir: "unreadable".into(), catalog: Box::new(MemStore::new()), files: Box::new(files.clone()), on_disk: false };
+    s.open_library_in(stores, true).unwrap();
+    let warnings = s.take_library_warnings();
+    assert_eq!(warnings.len(), 2, "{warnings:?}");
+    assert!(warnings.iter().all(|w| w.contains("couldn't be read") && w.contains("won't overwrite")), "{warnings:?}");
+
+    // a preset change and a preference change: neither file is replaced by defaults
+    s.execute("preset.create", &json!({"name": "New"})).unwrap();
+    let e = s.execute("library.preferences", &json!({"cacheMb": 300}));
+    assert!(e.is_err(), "saving preferences is refused, not done over the unread file");
+    assert_eq!(files.files.get("presets.json").unwrap(), presets);
+    assert_eq!(files.files.get("prefs.json").unwrap(), prefs);
+}

crates/engine/src/tests_xmp.rs

@@ -329,6 +329,55 @@ fn convert_raw_to_dng() {
     let _ = std::fs::remove_dir_all(&dir);
 }
 
+/// Issue #106: Convert to DNG wrote straight to the final name (no temp file, sync or check) and
+/// relinked the photo even when the write was cut short. A failed write now leaves no DNG and
+/// the photo on its raw; a good one is verified and never replaces an existing file.
+#[test]
+fn convert_to_dng_is_verified_and_atomic() {
+    let dir = temp_dir("todng-safe");
+    // a synthetic raw (stored as DNG, catalogued as a NEF so Convert to DNG takes it)
+    let raw = dir.join("shot.dng");
+    let bytes = synthetic_dng_with(None, Default::default());
+    std::fs::write(&raw, &bytes).unwrap();
+    let mut s = Session::new().with_fs();
+    s.execute("library.import", &json!({"paths": [raw.to_string_lossy()]})).unwrap();
+    let id = s.catalog.photos().next().unwrap().id;
+    let path = raw.to_string_lossy().to_string();
+    s.catalog
+        .apply(lightcraft_catalog::Op::Relink {
+            id,
+            file_name: "shot.dng".into(),
+            source: lightcraft_catalog::Source::File { path: path.clone() },
+            format: Some("NEF".into()),
+        })
+        .unwrap();
+    s.execute("library.select", &json!({"ids": [id.0]})).unwrap();
+    let names = || {
+        let mut v: Vec<String> = std::fs::read_dir(&dir).unwrap().flatten().map(|e| e.file_name().to_string_lossy().to_string()).collect();
+        v.sort();
+        v
+    };
+    {
+        // the drive fills up part-way
+        let _fault = lightcraft_catalog::safe_file::fail_writes_after(200);
+        let r = s.execute("photo.convertToDng", &json!({})).unwrap();
+        assert_eq!(r["converted"].as_array().unwrap().len(), 0, "{r}");
+        assert!(r["skipped"][0][1].as_str().unwrap().contains("the raw is kept"), "{r}");
+    }
+    assert_eq!(names(), ["shot.dng"], "no partial DNG");
+    assert_eq!(s.catalog.photo(id).unwrap().source, lightcraft_catalog::Source::File { path: path.clone() }, "not relinked");
+    // a good conversion: a new name (the existing file is not replaced), decodable, relinked
+    let r = s.execute("photo.convertToDng", &json!({})).unwrap();
+    let out = r["converted"][0]["path"].as_str().unwrap().to_string();
+    assert!(out.ends_with("shot-2.dng"), "{r}");
+    assert_eq!(std::fs::read(&raw).unwrap(), bytes, "the raw is untouched");
+    let back = lightcraft_raw::decode(&std::fs::read(&out).unwrap()).unwrap();
+    assert_eq!(back.data, lightcraft_raw::decode(&bytes).unwrap().data);
+    assert_eq!(s.catalog.photo(id).unwrap().source, lightcraft_catalog::Source::File { path: out });
+    assert_eq!(names(), ["shot-2.dng", "shot.dng"], "no temp file left");
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
 /// Edit in External Editor (engine half): a 16-bit TIFF `-Edit` copy with the edits, next to
 /// the original, added and stacked on top of it; a second one doesn't overwrite the first.
 #[test]
@@ -576,3 +625,132 @@ fn copyright_status_usage_terms_and_url_round_trip() {
     let _ = std::fs::remove_dir_all(&src);
     let _ = std::fs::remove_dir_all(&lib);
 }
+
+/// A sidecar another raw developer wrote: develop settings in attributes and elements, a
+/// structured edit history, an unknown namespace.
+const OTHER_APP_SIDECAR: &str = r#"<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
+<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Other Toolkit">
+ <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
+  <rdf:Description rdf:about=""
+    xmlns:xmp="http://ns.adobe.com/xap/1.0/"
+    xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/"
+    xmlns:stEvt="http://ns.adobe.com/xap/1.0/sType/ResourceEvent#"
+    xmlns:crs="http://ns.adobe.com/camera-raw-settings/1.0/"
+    xmlns:other="http://example.com/other/1.0/"
+    xmp:Rating="2"
+    crs:Version="99.0"
+    crs:Exposure2012="+0.65"
+    crs:HasSettings="True"
+    other:Secret="keep me">
+   <xmpMM:History>
+    <rdf:Seq>
+     <rdf:li stEvt:action="derived" stEvt:parameters="converted from image/x-raw to image/png"/>
+    </rdf:Seq>
+   </xmpMM:History>
+   <crs:ToneCurvePV2012>
+    <rdf:Seq>
+     <rdf:li>0, 0</rdf:li>
+     <rdf:li>128, 140</rdf:li>
+     <rdf:li>255, 255</rdf:li>
+    </rdf:Seq>
+   </crs:ToneCurvePV2012>
+  </rdf:Description>
+ </rdf:RDF>
+</x:xmpmeta>
+<?xpacket end="w"?>"#;
+
+/// Issue #92: saving merges into another app's sidecar instead of replacing it.
+#[test]
+fn saving_merges_into_another_apps_sidecar() {
+    let src = temp_dir("merge");
+    let lib = temp_dir("merge-lib");
+    write_png(&src.join("shot.png"), 1);
+    std::fs::write(src.join("shot.xmp"), OTHER_APP_SIDECAR).unwrap();
+    let mut s = Session::new().with_fs();
+    s.open_library(&lib, false).unwrap();
+    s.execute("library.import", &json!({"paths": [src.join("shot.png").to_string_lossy()]})).unwrap();
+    let id = only(&s);
+    s.execute("library.select", &json!({"ids": [id.0]})).unwrap();
+    s.execute("photo.rate", &json!({"rating": 5})).unwrap();
+    s.execute("photo.setMeta", &json!({"title": "Harbour", "keywords": ["boats"]})).unwrap();
+    s.execute("develop.set", &json!({"control": "effects.clarity", "value": 30})).unwrap();
+    let r = s.execute("photo.saveMetadataToFile", &json!({})).unwrap();
+    assert_eq!(r["merged"][0], src.join("shot.xmp").to_string_lossy().as_ref(), "{r}");
+    let out = std::fs::read_to_string(src.join("shot.xmp")).unwrap();
+    // the other app's data, byte for byte
+    for part in [
+        "crs:Exposure2012=\"+0.65\"",
+        "other:Secret=\"keep me\"",
+        "   <xmpMM:History>\n    <rdf:Seq>\n     <rdf:li stEvt:action=\"derived\" stEvt:parameters=\"converted from image/x-raw to image/png\"/>\n    </rdf:Seq>\n   </xmpMM:History>",
+        "   <crs:ToneCurvePV2012>\n    <rdf:Seq>\n     <rdf:li>0, 0</rdf:li>\n     <rdf:li>128, 140</rdf:li>",
+    ] {
+        assert!(out.contains(part), "lost {part:?}:\n{out}");
+    }
+    let d = lightcraft_meta::parse_xmp(&out).unwrap();
+    assert_eq!(d.metadata.rating, Some(5), "ours replaces theirs");
+    assert_eq!(d.metadata.title.as_deref(), Some("Harbour"));
+    assert_eq!(d.properties.get("crs:Version"), Some(&vec!["99.0".to_string()]));
+    let saved = s.catalog.photo(id).unwrap().develop.clone();
+    // reading it back restores our settings (lc:settings wins over crs:)
+    s.execute("develop.set", &json!({"control": "effects.clarity", "value": 0})).unwrap();
+    s.execute("photo.readMetadataFromFile", &json!({})).unwrap();
+    assert_eq!(s.catalog.photo(id).unwrap().develop, saved);
+    // saving again keeps one LightCraft description and the other app's data
+    s.execute("photo.rate", &json!({"rating": 3})).unwrap();
+    s.execute("photo.saveMetadataToFile", &json!({})).unwrap();
+    let again = std::fs::read_to_string(src.join("shot.xmp")).unwrap();
+    assert_eq!(again.matches("<rdf:Description").count(), 2, "{again}");
+    assert!(again.contains("other:Secret=\"keep me\"") && again.contains("crs:Exposure2012=\"+0.65\""));
+    assert_eq!(lightcraft_meta::parse_xmp(&again).unwrap().metadata.rating, Some(3));
+
+    // a sidecar that isn't XMP is kept as a backup before it is replaced
+    std::fs::write(src.join("shot.xmp"), b"<not xmp").unwrap();
+    let r = s.execute("photo.saveMetadataToFile", &json!({})).unwrap();
+    let backup = r["backups"][0]["backup"].as_str().unwrap().to_string();
+    assert!(backup.contains("shot.xmp.bak-"), "{r}");
+    assert_eq!(std::fs::read(&backup).unwrap(), b"<not xmp");
+    assert_eq!(lightcraft_meta::parse_xmp(&std::fs::read_to_string(src.join("shot.xmp")).unwrap()).unwrap().metadata.rating, Some(3));
+    // … and another one never overwrites the first backup
+    std::fs::write(src.join("shot.xmp"), b"<still not xmp").unwrap();
+    let r = s.execute("photo.saveMetadataToFile", &json!({})).unwrap();
+    let second = r["backups"][0]["backup"].as_str().unwrap().to_string();
+    assert_ne!(second, backup);
+    assert_eq!(std::fs::read(&backup).unwrap(), b"<not xmp");
+    assert_eq!(std::fs::read(&second).unwrap(), b"<still not xmp");
+    let _ = std::fs::remove_dir_all(&src);
+    let _ = std::fs::remove_dir_all(&lib);
+}
+
+/// Issue #92: two catalogued files with one stem (`IMG_1.jpg` + `IMG_1.png`) don't share a
+/// Stem-named sidecar: the first by name keeps `IMG_1.xmp`, the other writes and reads
+/// `IMG_1.png.xmp`.
+#[test]
+fn files_sharing_a_stem_get_their_own_sidecars() {
+    let src = temp_dir("stem");
+    let lib = temp_dir("stem-lib");
+    write_png(&src.join("IMG_1.png"), 1);
+    let img = lightcraft_raster::Rgba8::from_fn(40, 24, |x, y| [(x * 6) as u8, (y * 9) as u8, 7, 255]);
+    let jpg =
+        crate::export::encode_image(&img, &crate::export::ExportOptions { format: crate::export::ExportFormat::Jpeg, ..Default::default() }).unwrap();
+    std::fs::write(src.join("IMG_1.jpg"), jpg).unwrap();
+    let mut s = Session::new().with_fs();
+    s.open_library(&lib, false).unwrap();
+    s.execute("library.import", &json!({"paths": [src.to_string_lossy()]})).unwrap();
+    let id = |s: &Session, name: &str| s.catalog.photos().find(|p| p.file_name == name).unwrap().id;
+    let (j, p) = (id(&s, "IMG_1.jpg"), id(&s, "IMG_1.png"));
+    assert_eq!(s.sidecar_naming(j), crate::sidecar::SidecarNaming::Stem);
+    assert_eq!(s.sidecar_naming(p), crate::sidecar::SidecarNaming::Full);
+    s.execute("photo.rate", &json!({"ids": [j.0], "rating": 2})).unwrap();
+    s.execute("photo.rate", &json!({"ids": [p.0], "rating": 5})).unwrap();
+    let r = s.execute("photo.saveMetadataToFile", &json!({"ids": [j.0, p.0]})).unwrap();
+    assert_eq!(r["written"].as_array().unwrap().len(), 2, "{r}");
+    let rating = |f: &str| lightcraft_meta::parse_xmp(&std::fs::read_to_string(src.join(f)).unwrap()).unwrap().metadata.rating;
+    assert_eq!(rating("IMG_1.xmp"), Some(2));
+    assert_eq!(rating("IMG_1.png.xmp"), Some(5));
+    // each reads its own back
+    s.execute("photo.rate", &json!({"ids": [j.0, p.0], "rating": 0})).unwrap();
+    s.execute("photo.readMetadataFromFile", &json!({"ids": [j.0, p.0]})).unwrap();
+    assert_eq!((s.catalog.photo(j).unwrap().rating, s.catalog.photo(p).unwrap().rating), (2, 5));
+    let _ = std::fs::remove_dir_all(&src);
+    let _ = std::fs::remove_dir_all(&lib);
+}

crates/gpu/tests/equivalence.rs

@@ -22,6 +22,27 @@ fn gpu() -> bool {
     ok
 }
 
+#[test]
+fn camera_tone_and_relative_wb() {
+    if !gpu() {
+        return;
+    }
+    let src = scene(2, 320, 240);
+    let curve = lightcraft_pipeline::tone::CameraTone::new(std::array::from_fn(|i| {
+        let x = 0.004 * 1.18f32.powi(i as i32);
+        [x, 1.0 - (-2.0 * x).exp()]
+    }))
+    .unwrap();
+    let info = SourceInfo { raw: true, relative_wb: true, camera_tone: Some(curve), ..Default::default() };
+    let mut s = DevelopSettings::default();
+    check("camera tone neutral", &src, &info, &s, &RenderRequest::fit(320, 240));
+    s.light.exposure = 1.0;
+    s.light.contrast = 40.0;
+    s.wb.mode = WbMode::Custom;
+    s.wb.temp = 8000.0;
+    check("camera tone edited", &src, &info, &s, &RenderRequest::fit(320, 240));
+}
+
 fn scene(i: usize, w: usize, h: usize) -> Arc<Rgb32f> {
     Arc::new(lightcraft_scenes::demo_library()[i].render(w, h))
 }

crates/meta/src/lib.rs

@@ -17,6 +17,7 @@ mod gpx;
 mod iptc;
 pub mod tags;
 mod xmp;
+mod xmp_merge;
 
 pub use container::{Embedded, embedded, jpeg_segments, png_chunks, webp_chunks};
 pub use datetime::DateTime;
@@ -26,6 +27,7 @@ pub use iptc::parse_iptc;
 pub use lightcraft_geom::Orientation;
 pub use tags::{TagRow, file_tag_rows, tag_rows};
 pub use xmp::{CRS_NS, LC_NS, XmpData, XmpError, XmpValue, parse_xmp, write_xmp, write_xmp_lc};
+pub use xmp_merge::{MergeRules, merge_xmp};
 
 use serde::{Deserialize, Serialize};
 

crates/meta/src/xmp.rs

@@ -145,6 +145,11 @@ impl Node {
 const MAX_DEPTH: usize = 64;
 const MAX_NODES: usize = 200_000;
 
+/// `prefix:local` with the prefix canonicalised by namespace URI (see [`NAMESPACES`]).
+pub(crate) fn canonical_name(qname: &str, scopes: &[Vec<(String, String)>]) -> String {
+    canonical(qname, scopes)
+}
+
 fn canonical(qname: &str, scopes: &[Vec<(String, String)>]) -> String {
     let (prefix, local) = qname.split_once(':').unwrap_or(("", qname));
     if prefix == "xml" || prefix == "xmlns" {

crates/meta/src/xmp_merge.rs

@@ -0,0 +1,403 @@
+//! Merging a freshly written XMP packet into an existing one (a sidecar another application
+//! wrote, e.g. with its develop settings and edit history), keeping everything the writer does not
+//! own byte for byte.
+//!
+//! The existing packet is scanned once (namespace-resolved, with byte positions). Only top-level
+//! properties of the `rdf:Description` elements directly under `rdf:RDF` are considered, in
+//! attribute form (`xmp:Rating="3"`) and element form (`<dc:subject>…</dc:subject>`):
+//! - properties the writer owns ([`MergeRules::owned`]) are removed, and written from the fresh
+//!   packet when it has them (so a cleared field is cleared in the file too);
+//! - properties owned only when stated ([`MergeRules::owned_if_present`]) are replaced when the
+//!   fresh packet has them and kept otherwise;
+//! - any other property of the fresh packet (e.g. `xmp:CreatorTool`) is not written: the file
+//!   keeps describing itself as its creator left it;
+//! - everything else — other namespaces (e.g. `crs:`), `xmpMM:History`, unknown properties,
+//!   comments, the packet wrapper and padding — is copied unchanged.
+//!
+//! The written properties go into one new `rdf:Description` (declaring its own namespaces, so
+//! the existing prefix bindings never matter) just before `</rdf:RDF>`. A description left empty
+//! by the removals is dropped, so repeated saves don't accumulate. The result is checked by
+//! parsing it again: every written property must read back as in the fresh packet.
+
+use std::collections::BTreeSet;
+
+use quick_xml::events::Event;
+
+use crate::xmp::{XmpError, canonical_name, parse_xmp};
+
+/// Which properties [`merge_xmp`] takes from the fresh packet. Names are canonical
+/// `prefix:name` (prefixes as [`crate::parse_xmp`] reports them); `prefix:*` is a whole namespace.
+#[derive(Clone, Copy, Debug, Default)]
+pub struct MergeRules<'a> {
+    /// Always replaced: removed from the existing packet, written from the fresh one if stated.
+    pub owned: &'a [&'a str],
+    /// Replaced only when the fresh packet states them; otherwise the existing value stays.
+    pub owned_if_present: &'a [&'a str],
+}
+
+fn listed(list: &[&str], name: &str) -> bool {
+    list.iter().any(|p| match p.strip_suffix('*') {
+        Some(ns) => name.starts_with(ns),
+        None => *p == name,
+    })
+}
+
+#[derive(Debug)]
+struct Attr {
+    raw: String,
+    name: String,
+    /// The value as written (still escaped).
+    value: String,
+}
+
+#[derive(Debug)]
+struct Prop {
+    name: String,
+    start: usize,
+    end: usize,
+}
+
+#[derive(Debug, Default)]
+struct Desc {
+    tag_start: usize,
+    tag_end: usize,
+    /// The element name as written (`rdf:Description`, or another prefix for the RDF namespace).
+    raw_name: String,
+    empty: bool,
+    attrs: Vec<Attr>,
+    props: Vec<Prop>,
+    /// The end of `</rdf:Description>` (`tag_end` when self-closing).
+    end: usize,
+}
+
+#[derive(Debug, Default)]
+struct Scan {
+    descs: Vec<Desc>,
+    /// Where the first `</rdf:RDF>` starts.
+    rdf_close: Option<usize>,
+}
+
+enum Kind {
+    Other,
+    Rdf,
+    Desc(usize),
+    Prop { desc: usize, start: usize, name: String },
+}
+
+fn is_meta_attr(name: &str) -> bool {
+    name.starts_with("xmlns")
+        || matches!(name, "rdf:about" | "rdf:ID" | "rdf:nodeID" | "xml:lang" | "rdf:parseType" | "rdf:resource" | "rdf:datatype")
+}
+
+fn pos(r: &quick_xml::Reader<&[u8]>) -> usize {
+    usize::try_from(r.buffer_position()).unwrap_or(usize::MAX)
+}
+
+/// Locate the descriptions, their top-level properties and `</rdf:RDF>` in a packet.
+fn scan(s: &str) -> Result<Scan, XmpError> {
+    let mut reader = quick_xml::Reader::from_reader(s.as_bytes());
+    reader.config_mut().check_end_names = true;
+    let mut out = Scan::default();
+    let mut stack: Vec<Kind> = Vec::new();
+    let mut scopes: Vec<Vec<(String, String)>> = vec![vec![("xml".into(), "http://www.w3.org/XML/1998/namespace".into())]];
+    let mut count = 0usize;
+    loop {
+        let before = pos(&reader);
+        let ev = reader.read_event().map_err(|e| XmpError::Xml(e.to_string()))?;
+        let after = pos(&reader);
+        match ev {
+            Event::Start(ref e) | Event::Empty(ref e) => {
+                count += 1;
+                if count > 200_000 || stack.len() > 64 {
+                    return Err(XmpError::TooComplex);
+                }
+                let empty = matches!(ev, Event::Empty(_));
+                let mut scope = Vec::new();
+                let mut raw_attrs = Vec::new();
+                for a in e.attributes() {
+                    let a = a.map_err(|e| XmpError::Xml(e.to_string()))?;
+                    let k = String::from_utf8_lossy(a.key.as_ref()).into_owned();
+                    let v = String::from_utf8_lossy(&a.value).into_owned();
+                    if k == "xmlns" {
+                        scope.push((String::new(), v.clone()));
+                    } else if let Some(p) = k.strip_prefix("xmlns:") {
+                        scope.push((p.to_string(), v.clone()));
+                    }
+                    raw_attrs.push((k, v));
+                }
+                scopes.push(scope);
+                let raw_name = String::from_utf8_lossy(e.name().as_ref()).into_owned();
+                let name = canonical_name(&raw_name, &scopes);
+                let kind = match stack.last() {
+                    Some(Kind::Rdf) if name == "rdf:Description" => {
+                        let attrs = raw_attrs.into_iter().map(|(raw, value)| Attr { name: canonical_name(&raw, &scopes), raw, value }).collect();
+                        out.descs.push(Desc { tag_start: before, tag_end: after, raw_name, empty, attrs, props: Vec::new(), end: after });
+                        Kind::Desc(out.descs.len() - 1)
+                    }
+                    Some(Kind::Desc(i)) => Kind::Prop { desc: *i, start: before, name },
+                    _ if name == "rdf:RDF" && out.rdf_close.is_none() => Kind::Rdf,
+                    _ => Kind::Other,
+                };
+                if empty {
+                    scopes.pop();
+                    if let Kind::Prop { desc, start, name } = kind
+                        && let Some(d) = out.descs.get_mut(desc)
+                    {
+                        d.props.push(Prop { name, start, end: after });
+                    }
+                } else {
+                    stack.push(kind);
+                }
+            }
+            Event::End(_) => {
+                scopes.pop();
+                match stack.pop() {
+                    Some(Kind::Prop { desc, start, name }) => {
+                        if let Some(d) = out.descs.get_mut(desc) {
+                            d.props.push(Prop { name, start, end: after });
+                        }
+                    }
+                    Some(Kind::Desc(i)) => {
+                        if let Some(d) = out.descs.get_mut(i) {
+                            d.end = after;
+                        }
+                    }
+                    Some(Kind::Rdf) => out.rdf_close = out.rdf_close.or(Some(before)),
+                    Some(Kind::Other) => {}
+                    None => return Err(XmpError::Xml("unbalanced end tag".into())),
+                }
+            }
+            Event::Eof => break,
+            _ => {}
+        }
+    }
+    if !stack.is_empty() {
+        return Err(XmpError::Xml("unclosed element".into()));
+    }
+    Ok(out)
+}
+
+/// `start` moved back over the indentation and line break before it (so a removed property
+/// takes its line with it).
+fn line_start(s: &str, start: usize) -> usize {
+    let b = s.as_bytes();
+    let mut i = start;
+    while i > 0 && matches!(b.get(i - 1), Some(b' ' | b'\t')) {
+        i -= 1;
+    }
+    if i > 0 && b.get(i - 1) == Some(&b'\n') {
+        i -= 1;
+        if i > 0 && b.get(i - 1) == Some(&b'\r') {
+            i -= 1;
+        }
+    }
+    i
+}
+
+/// Merge `fresh` (a packet as [`crate::write_xmp_lc`] writes it) into `existing` following
+/// `rules` (see the module docs). Fails — and the caller must not overwrite `existing` blindly —
+/// when `existing` isn't a well-formed XMP packet.
+pub fn merge_xmp(existing: &str, fresh: &str, rules: MergeRules) -> Result<String, XmpError> {
+    let (bom, old) = match existing.strip_prefix('\u{feff}') {
+        Some(rest) => ("\u{feff}", rest),
+        None => ("", existing),
+    };
+    parse_xmp(old)?;
+    let ex = scan(old)?;
+    let rdf_close = ex.rdf_close.ok_or_else(|| XmpError::Xml("no rdf:RDF element".into()))?;
+    let new = scan(fresh)?;
+    let fresh_desc = new.descs.first().ok_or_else(|| XmpError::Xml("the new packet has no rdf:Description".into()))?;
+    let fresh_names: BTreeSet<&str> = fresh_desc.props.iter().map(|p| p.name.as_str()).collect();
+    let remove = |name: &str| listed(rules.owned, name) || (listed(rules.owned_if_present, name) && fresh_names.contains(name));
+    let write = |name: &str| listed(rules.owned, name) || listed(rules.owned_if_present, name);
+
+    // edits on `old`: (start, end, replacement), applied back to front
+    let mut edits: Vec<(usize, usize, String)> = Vec::new();
+    for d in &ex.descs {
+        let gone_attrs: Vec<&Attr> = d.attrs.iter().filter(|a| !is_meta_attr(&a.name) && remove(&a.name)).collect();
+        let gone_props: Vec<&Prop> = d.props.iter().filter(|p| remove(&p.name)).collect();
+        if gone_attrs.is_empty() && gone_props.is_empty() {
+            continue;
+        }
+        let attrs_left = d.attrs.iter().any(|a| !is_meta_attr(&a.name) && !remove(&a.name));
+        if !attrs_left && gone_props.len() == d.props.len() {
+            // nothing of its own left: drop the whole description
+            edits.push((line_start(old, d.tag_start), d.end, String::new()));
+            continue;
+        }
+        if !gone_attrs.is_empty() {
+            let mut tag = format!("<{}", d.raw_name);
+            for a in d.attrs.iter().filter(|a| is_meta_attr(&a.name) || !remove(&a.name)) {
+                tag.push_str(&format!("\n    {}=\"{}\"", a.raw, a.value.replace('"', "&quot;")));
+            }
+            tag.push_str(if d.empty { "/>" } else { ">" });
+            edits.push((d.tag_start, d.tag_end, tag));
+        }
+        for p in gone_props {
+            edits.push((line_start(old, p.start), p.end, String::new()));
+        }
+    }
+    // the new description: its own namespace declarations, the properties to write
+    let mut block = String::from("\n  <rdf:Description rdf:about=\"\"\n    xmlns:rdf=\"http://www.w3.org/1999/02/22-rdf-syntax-ns#\"");
+    for a in fresh_desc.attrs.iter().filter(|a| a.raw.starts_with("xmlns:") && a.raw != "xmlns:rdf") {
+        block.push_str(&format!("\n    {}=\"{}\"", a.raw, a.value));
+    }
+    block.push('>');
+    let mut written = 0;
+    for p in fresh_desc.props.iter().filter(|p| write(&p.name)) {
+        let text = fresh.get(p.start..p.end).ok_or_else(|| XmpError::Xml("bad property span".into()))?;
+        block.push_str("\n   ");
+        block.push_str(text);
+        written += 1;
+    }
+    block.push_str("\n  </rdf:Description>");
+    if written > 0 {
+        let at = old.get(..rdf_close).map_or(rdf_close, |h| h.trim_end().len());
+        edits.push((at, at, block));
+    }
+    edits.sort_by_key(|e| (e.0, e.1));
+    // overlapping edits can't happen (properties sit inside their description, which is either
+    // dropped whole or edited piecewise), but never splice blindly
+    let mut out = String::with_capacity(old.len() + 4096);
+    out.push_str(bom);
+    let mut at = 0;
+    for (s, e, r) in &edits {
+        if *s < at {
+            return Err(XmpError::Xml("overlapping edits".into()));
+        }
+        out.push_str(old.get(at..*s).ok_or_else(|| XmpError::Xml("bad span".into()))?);
+        out.push_str(r);
+        at = *e;
+    }
+    out.push_str(old.get(at..).ok_or_else(|| XmpError::Xml("bad span".into()))?);
+
+    // read back: everything written must come out as written
+    let merged = parse_xmp(&out)?;
+    let want = parse_xmp(fresh)?;
+    for (k, v) in &want.properties {
+        let top = k.split('/').next().unwrap_or(k);
+        if write(top) && merged.properties.get(k) != Some(v) {
+            return Err(XmpError::Xml(format!("{k} did not survive the merge")));
+        }
+    }
+    Ok(out)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const RULES: MergeRules =
+        MergeRules { owned: &["xmp:Rating", "xmp:Label", "dc:subject", "dc:title", "lc:*"], owned_if_present: &["exif:DateTimeOriginal"] };
+
+    /// A sidecar as another raw developer writes it: attribute-form simple properties, develop
+    /// settings, a structured history, an unknown namespace.
+    const FOREIGN: &str = "<?xpacket begin=\"\u{feff}\" id=\"W5M0MpCehiHzreSzNTczkc9d\"?>
+<x:xmpmeta xmlns:x=\"adobe:ns:meta/\" x:xmptk=\"Some Toolkit 1.0\">
+ <rdf:RDF xmlns:rdf=\"http://www.w3.org/1999/02/22-rdf-syntax-ns#\">
+  <rdf:Description rdf:about=\"\"
+    xmlns:xmp=\"http://ns.adobe.com/xap/1.0/\"
+    xmlns:xmpMM=\"http://ns.adobe.com/xap/1.0/mm/\"
+    xmlns:stEvt=\"http://ns.adobe.com/xap/1.0/sType/ResourceEvent#\"
+    xmlns:crs=\"http://ns.adobe.com/camera-raw-settings/1.0/\"
+    xmlns:dc=\"http://purl.org/dc/elements/1.1/\"
+    xmlns:foo=\"http://example.com/foo/\"
+    xmp:Rating=\"2\"
+    xmp:CreatorTool=\"Other App\"
+    crs:Exposure2012=\"+0.50\"
+    crs:Contrast2012=\"-12\"
+    foo:Thing=\"a &amp; b\">
+   <xmpMM:History>
+    <rdf:Seq>
+     <rdf:li stEvt:action=\"saved\" stEvt:when=\"2026-01-02T03:04:05\"/>
+    </rdf:Seq>
+   </xmpMM:History>
+   <crs:ToneCurvePV2012>
+    <rdf:Seq>
+     <rdf:li>0, 0</rdf:li>
+     <rdf:li>255, 255</rdf:li>
+    </rdf:Seq>
+   </crs:ToneCurvePV2012>
+   <dc:subject>
+    <rdf:Bag>
+     <rdf:li>old</rdf:li>
+    </rdf:Bag>
+   </dc:subject>
+  </rdf:Description>
+ </rdf:RDF>
+</x:xmpmeta>
+";
+
+    /// With the packet's whitespace padding and trailer.
+    fn foreign() -> String {
+        format!("{FOREIGN}{}\n<?xpacket end=\"w\"?>", " ".repeat(100))
+    }
+
+    fn fresh(rating: i8, keywords: &[&str]) -> String {
+        let m = crate::Metadata {
+            software: Some("LightCraft".into()),
+            rating: Some(rating),
+            keywords: keywords.iter().map(|k| k.to_string()).collect(),
+            ..Default::default()
+        };
+        crate::write_xmp_lc(&m, &[("settings", "{\"a\":1}"), ("flag", "pick")])
+    }
+
+    #[test]
+    fn keeps_foreign_properties_and_replaces_owned_ones() {
+        let out = merge_xmp(&foreign(), &fresh(4, &["new", "two"]), RULES).unwrap();
+        let d = parse_xmp(&out).unwrap();
+        let p = |k: &str| d.properties.get(k).cloned().unwrap_or_default();
+        assert_eq!(p("xmp:Rating"), vec!["4"]);
+        assert_eq!(p("dc:subject"), vec!["new", "two"]);
+        assert_eq!(p("lc:settings"), vec!["{\"a\":1}"]);
+        assert_eq!(p("lc:flag"), vec!["pick"]);
+        assert_eq!(p("xmp:CreatorTool"), vec!["Other App"], "not ours: kept");
+        assert_eq!(p("crs:Exposure2012"), vec!["+0.50"]);
+        assert_eq!(p("foo:Thing").len(), 1);
+        // untouched parts are byte for byte the same
+        for part in [
+            "   <xmpMM:History>\n    <rdf:Seq>\n     <rdf:li stEvt:action=\"saved\" stEvt:when=\"2026-01-02T03:04:05\"/>\n    </rdf:Seq>\n   </xmpMM:History>",
+            "   <crs:ToneCurvePV2012>\n    <rdf:Seq>\n     <rdf:li>0, 0</rdf:li>",
+            "crs:Contrast2012=\"-12\"",
+            "foo:Thing=\"a &amp; b\"",
+            "<?xpacket begin=\"\u{feff}\" id=\"W5M0MpCehiHzreSzNTczkc9d\"?>\n<x:xmpmeta xmlns:x=\"adobe:ns:meta/\" x:xmptk=\"Some Toolkit 1.0\">",
+            &format!("</x:xmpmeta>\n{}\n<?xpacket end=\"w\"?>", " ".repeat(100)),
+        ] {
+            assert!(out.contains(part), "lost {part:?} in\n{out}");
+        }
+        assert!(!out.contains("xmp:Rating=\"2\""));
+        assert!(!out.contains("<rdf:li>old</rdf:li>"));
+        // saving again changes only our part, and doesn't pile up descriptions
+        let again = merge_xmp(&out, &fresh(1, &[]), RULES).unwrap();
+        let d = parse_xmp(&again).unwrap();
+        assert_eq!(d.properties.get("xmp:Rating"), Some(&vec!["1".to_string()]));
+        assert!(!d.properties.contains_key("dc:subject"), "a cleared field is cleared");
+        assert_eq!(again.matches("<rdf:Description").count(), 2, "{again}");
+        assert_eq!(merge_xmp(&again, &fresh(1, &[]), RULES).unwrap(), again, "idempotent");
+    }
+
+    #[test]
+    fn owned_if_present_and_prefix_independence() {
+        // the existing packet binds the namespaces to other prefixes, and has a capture time
+        let ex = "<x:xmpmeta xmlns:x=\"adobe:ns:meta/\"><r:RDF xmlns:r=\"http://www.w3.org/1999/02/22-rdf-syntax-ns#\">\
+            <r:Description r:about=\"\" xmlns:a=\"http://ns.adobe.com/xap/1.0/\" xmlns:e=\"http://ns.adobe.com/exif/1.0/\" \
+            a:Rating=\"5\" e:DateTimeOriginal=\"2020-01-01T00:00:00\"/></r:RDF></x:xmpmeta>";
+        let out = merge_xmp(ex, &fresh(3, &[]), RULES).unwrap();
+        let d = parse_xmp(&out).unwrap();
+        assert_eq!(d.properties.get("xmp:Rating"), Some(&vec!["3".to_string()]));
+        assert_eq!(d.properties.get("exif:DateTimeOriginal"), Some(&vec!["2020-01-01T00:00:00".to_string()]), "fresh has none: kept");
+        let mut m = crate::Metadata { rating: Some(3), ..Default::default() };
+        m.capture_time = crate::DateTime::parse_iso("2024-05-06T07:08:09");
+        let out = merge_xmp(ex, &crate::write_xmp_lc(&m, &[]), RULES).unwrap();
+        let d = parse_xmp(&out).unwrap();
+        assert_eq!(d.properties.get("exif:DateTimeOriginal"), Some(&vec!["2024-05-06T07:08:09".to_string()]));
+    }
+
+    #[test]
+    fn refuses_what_it_cannot_read() {
+        for bad in ["", "not xml at all", "<x:xmpmeta xmlns:x=\"adobe:ns:meta/\"><rdf:RDF", "<a><b></a>", "<x:xmpmeta xmlns:x=\"adobe:ns:meta/\"/>"] {
+            assert!(merge_xmp(bad, &fresh(1, &[]), RULES).is_err(), "{bad:?}");
+        }
+    }
+}

crates/meta/tests/robust.rs

@@ -1,4 +1,4 @@
-use lightcraft_meta::{Metadata, extract, parse_iptc, parse_xmp, read_exif, write_xmp};
+use lightcraft_meta::{MergeRules, Metadata, extract, merge_xmp, parse_iptc, parse_xmp, read_exif, write_xmp};
 use proptest::prelude::*;
 
 proptest! {
@@ -21,6 +21,23 @@ proptest! {
         let _ = parse_xmp(&s);
     }
 
+    /// Merging into arbitrary (also damaged) packets never panics, and a merge that succeeds
+    /// reads back with the written values.
+    #[test]
+    fn merge_never_panics(cut in 0usize..900, junk in ".{0,20}", rating in 0i8..=5) {
+        let base = write_xmp(&Metadata { title: Some("t".into()), rating: Some(1), ..Default::default() }, Some("{}"));
+        let mut s: String = base.chars().take(cut).collect();
+        s.push_str(&junk);
+        s.extend(base.chars().skip(cut));
+        let fresh = write_xmp(&Metadata { rating: Some(rating), ..Default::default() }, Some("{\"x\":1}"));
+        let rules = MergeRules { owned: &["xmp:Rating", "dc:title", "lc:*"], owned_if_present: &[] };
+        if let Ok(out) = merge_xmp(&s, &fresh, rules) {
+            let d = parse_xmp(&out).unwrap();
+            prop_assert_eq!(d.metadata.rating, Some(rating));
+            prop_assert_eq!(d.lc_settings.as_deref(), Some("{\"x\":1}"));
+        }
+    }
+
     #[test]
     fn user_text_roundtrips(title in "[a-zA-Z0-9 &<>\"'éü€;|/\\\\]{1,40}", kw in proptest::collection::vec("[a-zA-Z0-9 &<>\"'|]{1,12}", 0..5), rating in -1i8..=5) {
         let title = title.trim().to_string();

crates/pipeline/src/finish.rs

@@ -221,7 +221,9 @@ impl FinishParams {
         FinishParams {
             calib: if calibration { crate::colorops::calibration_matrix(&s.calibration) } else { None },
             shadow_tint: if calibration { (s.calibration.shadows_tint / 100.0) as f32 } else { 0.0 },
-            tone: if info.raw {
+            tone: if let Some(curve) = info.camera_tone.as_ref().filter(|_| info.raw) {
+                ToneMap::camera(curve, s.light.contrast, s.light.whites, s.light.blacks)
+            } else if info.raw {
                 ToneMap::new(s.light.contrast, s.light.whites, s.light.blacks)
             } else {
                 ToneMap::display(s.light.contrast, s.light.whites, s.light.blacks)

crates/pipeline/src/lib.rs

@@ -64,11 +64,14 @@ pub struct SourceInfo {
     pub raw: bool,
     pub as_shot_temp: f64,
     pub as_shot_tint: f64,
+    /// No measured camera illuminant: WB adjustments are relative to the camera's rendered look.
+    pub relative_wb: bool,
+    pub camera_tone: Option<tone::CameraTone>,
 }
 
 impl Default for SourceInfo {
     fn default() -> Self {
-        Self { raw: false, as_shot_temp: 6500.0, as_shot_tint: 0.0, lens: None }
+        Self { raw: false, as_shot_temp: 6500.0, as_shot_tint: 0.0, lens: None, relative_wb: false, camera_tone: None }
     }
 }
 

crates/pipeline/src/local.rs

@@ -61,7 +61,7 @@ pub fn effective_wb(info: &SourceInfo, s: &DevelopSettings) -> (f64, f64) {
     use lightcraft_develop::WbMode;
     match s.wb.mode {
         WbMode::AsShot => (info.as_shot_temp, info.as_shot_tint),
-        m if info.raw => m.preset().unwrap_or((s.wb.temp, s.wb.tint)),
+        m if info.raw && !info.relative_wb => m.preset().unwrap_or((s.wb.temp, s.wb.tint)),
         _ => (s.wb.temp, s.wb.tint),
     }
 }

crates/pipeline/src/tone.rs

@@ -14,12 +14,75 @@ pub const LUT_MIN_EV: f32 = -14.0;
 pub const LUT_MAX_EV: f32 = 10.0;
 pub const LUT_N: usize = 4096;
 
+/// A file-local camera look, fitted independently of the scene-linear colour transform.
+/// Knots are scene/display-linear luminance pairs. Keeping this in the finish stage preserves
+/// RAW exposure and highlight headroom; it is never baked into the decoded sensor pixels.
+#[derive(Clone, Copy, Debug, PartialEq, serde::Serialize)]
+pub struct CameraTone {
+    knots: [[f32; 2]; 32],
+}
+
+impl<'de> serde::Deserialize<'de> for CameraTone {
+    fn deserialize<D: serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
+        #[derive(serde::Deserialize)]
+        struct Wire {
+            knots: [[f32; 2]; 32],
+        }
+        let w = Wire::deserialize(d)?;
+        Self::new(w.knots).ok_or_else(|| serde::de::Error::custom("invalid camera tone curve"))
+    }
+}
+
+impl CameraTone {
+    pub fn new(knots: [[f32; 2]; 32]) -> Option<Self> {
+        let mut previous = [0.0, 0.0];
+        for p in knots {
+            if !p.iter().all(|v| v.is_finite()) || p[0] <= previous[0] || p[1] < previous[1] || p[1] >= 1.0 {
+                return None;
+            }
+            previous = p;
+        }
+        Some(Self { knots })
+    }
+
+    pub fn apply(&self, y: f32) -> f32 {
+        if !y.is_finite() || y <= 0.0 {
+            return 0.0;
+        }
+        let mut previous = [0.0, 0.0];
+        for p in self.knots {
+            if y <= p[0] {
+                let t = (y - previous[0]) / (p[0] - previous[0]);
+                return previous[1] + t * (p[1] - previous[1]);
+            }
+            previous = p;
+        }
+        let a = self.knots[30];
+        let b = self.knots[31];
+        // Extend beyond observed (unclipped) highlights with a continuous, bounded shoulder.
+        let slope = ((b[1] - a[1]) / (b[0] - a[0])).clamp(0.1, 16.0);
+        1.0 - (1.0 - b[1]) * (-(y - b[0]) * slope / (1.0 - b[1]).max(0.01)).exp()
+    }
+}
+
 #[derive(Clone, Debug)]
 pub struct ToneMap {
     lut: Vec<f32>,
 }
 
 impl ToneMap {
+    pub fn camera(curve: &CameraTone, contrast: f64, whites: f64, blacks: f64) -> ToneMap {
+        let adjustment = Self::display(contrast, whites, blacks);
+        let neutral = contrast == 0.0 && whites == 0.0 && blacks == 0.0;
+        let lut = (0..LUT_N)
+            .map(|i| {
+                let ev = LUT_MIN_EV + (LUT_MAX_EV - LUT_MIN_EV) * i as f32 / (LUT_N - 1) as f32;
+                let y = curve.apply(GREY * 2f32.powf(ev));
+                if neutral { y } else { adjustment.apply(y) }
+            })
+            .collect();
+        ToneMap { lut }
+    }
     /// `contrast`, `whites`, `blacks` in −100..100 (Lightroom slider units).
     pub fn new(contrast: f64, whites: f64, blacks: f64) -> ToneMap {
         let c = (contrast / 100.0) as f32;
@@ -116,6 +179,32 @@ fn smooth(e0: f32, e1: f32, x: f32) -> f32 {
 mod tests {
     use super::*;
 
+    #[test]
+    fn camera_curve_preserves_black_and_extends_headroom() {
+        let knots = std::array::from_fn(|i| {
+            let x = 0.005 * 1.15f32.powi(i as i32);
+            [x, 1.0 - (-3.0 * x).exp()]
+        });
+        let curve = CameraTone::new(knots).unwrap();
+        let base = ToneMap::camera(&curve, 0.0, 0.0, 0.0);
+        assert_eq!(base.apply(0.0), 0.0);
+        assert!(base.apply(0.1) < base.apply(0.2));
+        let mut previous = 0.0;
+        for i in 0..2000 {
+            let y = 1e-6 * 1.01f32.powi(i);
+            let v = base.apply(y);
+            assert!((0.0..=1.0).contains(&v));
+            assert!(v >= previous - 1e-6);
+            previous = v;
+        }
+        assert!((base.apply(0.1) - curve.apply(0.1)).abs() < 0.001);
+        assert!(ToneMap::camera(&curve, 50.0, 0.0, 0.0).apply(0.3) > base.apply(0.3));
+        let mut invalid = knots;
+        invalid[1][0] = invalid[0][0];
+        assert!(CameraTone::new(invalid).is_none());
+        assert!(serde_json::from_value::<CameraTone>(serde_json::json!({"knots": invalid})).is_err());
+    }
+
     #[test]
     fn monotone_and_bounded() {
         for (c, w, b) in [(0.0, 0.0, 0.0), (100.0, 100.0, -100.0), (-100.0, -100.0, 100.0), (50.0, -30.0, -40.0)] {

crates/preview/src/disk.rs

@@ -4,6 +4,11 @@
 //! files) but not fsynced; unreadable files are deleted and re-rendered. When the total size
 //! exceeds the budget, the least recently used files (by modification time, refreshed on read)
 //! are removed down to 80 % of the budget.
+//!
+//! The cache only ever lists, counts or deletes files of its own name shape
+//! (`<2 hex>/<32 hex>.jpg` and the `<32 hex>.tmp…` temp files of [`DiskCache::put`], see
+//! [`is_cache_file`]): the directory may be shared with other files (e.g. a library opened on a
+//! photo folder that already has a `thumbs/` folder), and those are never touched (issue #98).
 
 use std::path::{Path, PathBuf};
 use std::sync::Mutex;
@@ -96,13 +101,25 @@ impl DiskCache {
         }
     }
 
-    /// All cache files: (path, size, modified).
+    /// All cache files (only names of the cache's own shape, see [`is_cache_file`]):
+    /// (path, size, modified).
     fn scan(&self) -> Vec<(PathBuf, u64, std::time::SystemTime)> {
         let mut out = Vec::new();
         let Ok(rd) = std::fs::read_dir(&self.dir) else { return out };
         for sub in rd.flatten() {
+            let sub_name = sub.file_name();
+            let Some(sub_name) = sub_name.to_str() else { continue };
+            if !is_shard_name(sub_name) {
+                continue;
+            }
             let Ok(files) = std::fs::read_dir(sub.path()) else { continue };
             for f in files.flatten() {
+                let name = f.file_name();
+                let Some(name) = name.to_str() else { continue };
+                if !is_cache_file(sub_name, name) {
+                    continue;
+                }
+                // `DirEntry::metadata` does not follow symlinks: a link is never a cache file
                 if let Ok(m) = f.metadata()
                     && m.is_file()
                 {
@@ -144,6 +161,29 @@ impl DiskCache {
     }
 }
 
+fn is_lower_hex(s: &str) -> bool {
+    s.bytes().all(|b| b.is_ascii_digit() || (b'a'..=b'f').contains(&b))
+}
+
+/// A shard directory name: two lowercase hex digits.
+fn is_shard_name(s: &str) -> bool {
+    s.len() == 2 && is_lower_hex(s)
+}
+
+/// Whether `name` inside shard directory `shard` is a file this cache wrote: `<32 hex>.jpg`
+/// (whose first two digits are the shard) or a `<32 hex>.tmp<alphanumeric>` temp file of
+/// [`DiskCache::put`]. Anything else in the cache directory belongs to someone else.
+pub fn is_cache_file(shard: &str, name: &str) -> bool {
+    if !is_shard_name(shard) {
+        return false;
+    }
+    let Some((stem, ext)) = name.split_once('.') else { return false };
+    if stem.len() != 32 || !is_lower_hex(stem) || !stem.starts_with(shard) {
+        return false;
+    }
+    ext == "jpg" || ext.strip_prefix("tmp").is_some_and(|t| !t.is_empty() && t.bytes().all(|b| b.is_ascii_alphanumeric()))
+}
+
 /// Encode a thumbnail as the cache stores it (JPEG, RGB, 4:2:0).
 pub fn encode_jpeg(img: &Rgba8) -> Option<Vec<u8>> {
     if img.width == 0 || img.height == 0 || img.width > u16::MAX as usize || img.height > u16::MAX as usize {

crates/preview/src/tests.rs

@@ -154,3 +154,41 @@ fn pool_runs_inline() {
     assert_eq!(p.run_inline(10), 1);
     assert_eq!(p.try_recv().map(|d| d.result), Some(1));
 }
+
+#[test]
+fn disk_cache_never_touches_foreign_files() {
+    // issue #98: a library opened on a folder that already has a `thumbs/` folder
+    let dir = temp_dir("foreign");
+    let foreign = [
+        dir.join("readme.txt"),
+        dir.join("ab").join("holiday.jpg"),
+        dir.join("ab").join("0123456789abcdef0123456789abcdef.jpg"), // wrong shard
+        dir.join("small").join("0123456789abcdef0123456789abcdef.jpg"),
+        dir.join("01").join("0123456789ABCDEF0123456789ABCDEF.jpg"), // upper case
+        dir.join("01").join("0123456789abcdef0123456789abcdef.jpeg"),
+        dir.join("01").join("0123456789abcdef0123456789abcdef.tmp"),
+    ];
+    for p in &foreign {
+        std::fs::create_dir_all(p.parent().unwrap()).unwrap();
+        std::fs::write(p, vec![7u8; 50_000]).unwrap();
+    }
+    // a stale temp file of our own is cleaned up
+    let own_tmp = dir.join("01").join("0123456789abcdef0123456789abcdef.tmpThreadId9");
+    std::fs::write(&own_tmp, b"partial").unwrap();
+    let d = DiskCache::new(&dir, 40_000);
+    assert_eq!(d.size(), 7, "only the cache's own temp file counts");
+    // fill past the budget (forces prunes), then clear
+    for i in 0..40u8 {
+        d.put(hash_bytes(&[i, 2]), &gradient(160, 100, i));
+    }
+    assert!(d.size() <= 40_000);
+    d.clear();
+    assert_eq!(d.size(), 0);
+    assert!(!own_tmp.exists());
+    for p in &foreign {
+        assert!(p.exists(), "foreign file deleted: {}", p.display());
+    }
+    assert!(disk::is_cache_file("01", "0123456789abcdef0123456789abcdef.jpg"));
+    assert!(!disk::is_cache_file("01", "0123456789abcdef0123456789abcdef.jpg.bak"));
+    let _ = std::fs::remove_dir_all(&dir);
+}

crates/ui-egui/Cargo.toml

@@ -25,3 +25,6 @@ log = { workspace = true }
 
 [dev-dependencies]
 lightcraft-codecs = { workspace = true }
+
+[build-dependencies]
+serde_json = { workspace = true }

crates/ui-egui/build.rs

@@ -0,0 +1,18 @@
+//! Compile translated format strings so Rust checks both languages' placeholders.
+use std::{collections::BTreeMap, env, fs, path::PathBuf};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    println!("cargo:rerun-if-changed=locales/ja-formats.json");
+    let messages: BTreeMap<String, String> = serde_json::from_str(&fs::read_to_string("locales/ja-formats.json")?)?;
+    let mut source = String::from("macro_rules! tr_format {\n");
+    for (english, japanese) in messages {
+        let en = serde_json::to_string(&english)?;
+        let ja = serde_json::to_string(&japanese)?;
+        source.push_str(&format!(
+            "({en} $(, $($args:tt)*)?) => {{ if $crate::i18n::is_japanese() {{ format!({ja} $(, $($args)*)?) }} else {{ format!({en} $(, $($args)*)?) }} }};\n"
+        ));
+    }
+    source.push_str("}\npub(crate) use tr_format;\n");
+    fs::write(PathBuf::from(env::var("OUT_DIR")?).join("ja-formats.rs"), source)?;
+    Ok(())
+}

crates/ui-egui/locales/ja-formats.json

@@ -0,0 +1,104 @@
+{
+  " · {skipped} skipped (file exists)": "・{skipped}件は同名ファイルのためスキップ",
+  " · {} duplicate{} skipped": "・重複{}枚をスキップ{:.0}",
+  " · {} failed: {}": "・{}件失敗：{}",
+  " · {} moved": "・{}件移動",
+  " · {} not readable": "・{}件は読み込み不可",
+  ", {failed} file{} not readable": "、{failed}件を読み込めません{:.0}",
+  "Add {local_n} to My Photos": "{local_n}枚をマイフォトに追加",
+  "Add {} Photo{}": "{}枚の写真を追加{:.0}",
+  "Add “{}” to Favorites": "「{}」をお気に入りに追加",
+  "Added {n} photo{} to My Photos": "マイフォトに{n}枚を追加しました{:.0}",
+  "Added {n} photo{} to “{}”": "「{1}」に{n}枚を追加しました{0:.0}",
+  "All {n} selected photos move by the same amount.": "選択中の{n}枚を同じ時間だけずらします",
+  "Auto Sync: edits apply to {n} photos": "自動同期：{n}枚に編集を適用",
+  "Automatic ({} MB)": "自動（{}MB）",
+  "Click {}:1": "クリック時 {}:1",
+  "Create {n} Virtual Copies": "{n}枚の仮想コピーを作成",
+  "Decoder: {reason}": "デコーダー：{reason}",
+  "Delete \"{label}\"": "「{label}」を削除",
+  "Delete \"{label}\" (and the mask)": "「{label}」とマスクを削除",
+  "Delete {n} Photos": "{n}枚の写真を削除",
+  "Delete “{current}”": "「{current}」を削除",
+  "Duplicate \"{label}\"": "「{label}」を複製",
+  "Example: {example}": "例：{example}",
+  "Exported {n} photo{}": "{n}枚を書き出しました{:.0}",
+  "Exported {ok} of {total} photo{}": "{total}枚中{ok}枚を書き出しました{:.0}",
+  "Exported {} point curve preset{}": "{}件のポイントカーブを書き出しました{:.0}",
+  "Exported {} preset{}": "{}件のプリセットを書き出しました{:.0}",
+  "Exporting {} of {total}": "書き出し中：{total}枚中{}枚",
+  "Filter bar — {active} active filter{}": "フィルターバー：{active}件適用中{:.0}",
+  "Healed {n} dust spot{}": "{n}か所のほこりを修復しました{:.0}",
+  "Imported {n} point curve preset{}": "{n}件のポイントカーブを読み込みました{:.0}",
+  "Imported {n} preset{}": "{n}件のプリセットを読み込みました{:.0}",
+  "Imported {n} preset{}, {f} file{} not readable": "{n}件のプリセットを読み込みました{:.0}。{f}件は読み込めません{:.0}",
+  "Imported {} photo{}": "{}枚を読み込みました{:.0}",
+  "Matches: {}": "一致条件：{}",
+  "Merging… {stage} {:.0}%": "合成中… {stage} {:.0}%",
+  "Move {what} to Recently Deleted?": "{what}を「最近削除した写真」に移動しますか？",
+  "Named ({named_n})": "名前付き（{named_n}）",
+  "Paste into {n} photo{} — only settings that were copied are pasted": "{n}枚に貼り付け{:.0}（コピーされた設定だけを適用）",
+  "Preset: {name}": "プリセット：{name}",
+  "Preview only — editing the camera's embedded JPEG ({})": "プレビューのみ：カメラ内蔵のJPEGを編集中（{}）",
+  "Preview only — {}": "プレビューのみ：{}",
+  "Profile: {}": "プロファイル：{}",
+  "Proof Copy ({})": "校正用コピー（{}）",
+  "Proof Preview · {}": "校正プレビュー・{}",
+  "Quick Develop · {n} photos": "クイック現像・{n}枚",
+  "Rated {}": "評価：{}",
+  "Reading photos… {done} of {total}": "写真を読み込み中：{total}枚中{done}枚",
+  "Redo {}": "やり直す：{}",
+  "Remove “{}” from Favorites": "「{}」をお気に入りから削除",
+  "Rename {n} Photos…": "{n}枚の写真の名前を変更…",
+  "Rename “{name}”": "「{name}」の名前を変更",
+  "Rendering on the CPU: {why}": "CPUで描画：{why}",
+  "Reset {} Channel": "{}チャンネルをリセット",
+  "Saved export preset “{}”": "書き出しプリセット「{}」を保存しました",
+  "Show {hidden} hidden location{}": "非表示の{hidden}か所を表示{:.0}",
+  "Showing {n} of {}": "{}枚中{n}枚を表示",
+  "Smart album: {}": "スマートアルバム：{}",
+  "Undo {}": "取り消す：{}",
+  "Version {} — a clean-room, pure-Rust photo library and raw developer.": "バージョン{} — Rust製の写真管理・RAW現像アプリ",
+  "Version: {}": "バージョン：{}",
+  "none (CPU rendering): {why}": "なし（CPU描画）：{why}",
+  "the {n} selected photos": "選択中の{n}枚",
+  "the {} photos in view": "表示中の{}枚",
+  "these {count} photos": "この{count}枚の写真",
+  "{count} smart preview{} · {:.1} MB": "スマートプレビュー{count}枚{:.0}・{:.1}MB",
+  "{f} folders (and their subfolders)": "{f}個のフォルダとそのサブフォルダ",
+  "{label} Grading": "{label}のカラーグレーディング",
+  "{label} {d:+} on every selected photo": "選択したすべての写真の{label}を{d:+}調整",
+  "{label}, {n} photos": "{label}、{n}枚",
+  "{matching} of {t} photos": "{t}枚中{matching}枚",
+  "{matching} photos": "{matching}枚",
+  "{mode} spot {} of {}": "{mode}：{1}か所中{0}か所",
+  "{msg} ({failed} failed)": "{msg}（{failed}件失敗）",
+  "{name} Label": "{name}のラベル",
+  "{name} Off": "{name}を無効にする",
+  "{name} On": "{name}を有効にする",
+  "{name} — double-click to reset it": "{name}：ダブルクリックでリセット",
+  "{n} change{} saved in memory but not written to disk: {e}\nLightCraft retries automatically; quitting now would lose {}.": "{n}件の変更{:.0}をディスクに保存できません：{e}\n自動で再試行します。終了すると変更が失われます{:.0}",
+  "{n} found · {sel} selected": "{n}枚検出・{sel}枚選択",
+  "{n} photos": "{n}枚",
+  "{n} photos in {} are hidden by the filters above": "{}の{n}枚は上のフィルターで非表示になっています",
+  "{n} photo{}": "{n}枚{:.0}",
+  "{n} photo{} match · updates automatically as photos change": "{n}枚が一致{:.0}・写真の変更に応じて自動更新",
+  "{n} photo{} now · updates automatically as photos change": "現在{n}枚{:.0}・写真の変更に応じて自動更新",
+  "{sel_n} selected · {counted}": "{sel_n}枚選択・{counted}",
+  "{stage}… {:.0}%": "{stage}… {:.0}%",
+  "{what} merge added": "{what}合成を追加しました",
+  "{what} merge failed: {e}": "{what}合成に失敗：{e}",
+  "{} and higher": "{}以上",
+  "{} files": "{}個のファイル",
+  "{} files and {f} folder{}": "{}個のファイルと{f}個のフォルダ{:.0}",
+  "{} of 4 guides — drag along lines that should be vertical or horizontal.": "ガイド4本中{}本：垂直または水平にする線に沿ってドラッグ",
+  "{} photos": "{}枚",
+  "{} photo{} not readable": "{}枚を読み込めません{:.0}",
+  "{} spot(s) on this photo": "この写真に{}か所のスポット",
+  "· {dups} already in the library": "・{dups}枚は読み込み済み",
+  "· {n} photo{}": "・{n}枚{:.0}",
+  "… and {more} more": "…ほか{more}件",
+  "Import cancelled · {} photo{} added": "読み込みを中止しました・{}枚を追加{:.0}",
+  "Reading photos… {} of {}": "写真を確認中：{1}枚中{0}枚",
+  "Adding photos… {} of {}": "写真を追加中：{1}枚中{0}枚"
+}

crates/ui-egui/src/control.rs

@@ -82,9 +82,14 @@ pub fn inspect(app: &LightcraftApp, ctx: &egui::Context) -> Value {
         "loupe": app.loupe_shown.map(|(p, src)| json!({"photo": p.0, "source": src, "pending": app.renderer.is_pending(crate::render::Slot::Main)})),
         "hoverPreview": app.hover_preview.as_ref().map(|h| h.label.clone()),
         "status": app.ui.status,
+        "notices": app.notices,
+        "quitPrompt": app.quit_prompt,
         "unsaved": app.session.unsaved().map(|(n, e)| json!({"ops": n, "error": e})),
+        "libraryProblem": app.library_problem.as_ref().map(crate::panels::library_problem::LibraryProblem::to_json),
         "scan": app.scan.as_ref().map(crate::import::ScanTask::status),
         "export": {"running": app.export.as_ref().map(crate::export_task::ExportTask::status), "last": app.last_export_result},
+        "import": app.import.as_ref().map(crate::import::ImportTask::status),
+        "tasks": app.tasks.labels(),
         "memory": memory(app),
     })
 }

crates/ui-egui/src/export_task.rs

@@ -75,12 +75,13 @@ pub fn poll(app: &mut LightcraftApp, ctx: &egui::Context) {
                     let ok = files.iter().filter(|f| f.get("path").is_some()).count();
                     let failed: Vec<&Value> = files.iter().filter(|f| f.get("error").is_some()).collect();
                     let skipped = files.iter().filter(|f| f.get("skipped").is_some()).count();
-                    let mut m = format!("Exported {ok} of {total} photo{}", if total == 1 { "" } else { "s" });
+                    let mut m =
+                        crate::i18n::tr_format!("Exported {ok} of {total} photo{}", if total == 1 { "" } else { "s" }, ok = ok, total = total);
                     if skipped > 0 {
-                        m += &format!(" · {skipped} skipped (file exists)");
+                        m += &crate::i18n::tr_format!(" · {skipped} skipped (file exists)", skipped = skipped);
                     }
                     if let Some(first) = failed.first() {
-                        m += &format!(" · {} failed: {}", failed.len(), first["error"].as_str().unwrap_or("error"));
+                        m += &crate::i18n::tr_format!(" · {} failed: {}", failed.len(), first["error"].as_str().unwrap_or("error"));
                     }
                     if cancelled {
                         m += " · cancelled";
@@ -96,14 +97,17 @@ pub fn poll(app: &mut LightcraftApp, ctx: &egui::Context) {
             let (done, current) = task.progress.lock().map(|g| g.clone()).unwrap_or_default();
             let (total, cancel) = (task.total, task.cancel.clone());
             let t = Tokens::get(ctx);
-            egui::Window::new("Exporting")
+            egui::Window::new(crate::i18n::tr("Exporting"))
                 .title_bar(false)
                 .resizable(false)
                 .anchor(Align2::LEFT_BOTTOM, [16.0, -56.0])
                 .fixed_size([300.0, 64.0])
                 .show(ctx, |ui| {
                     ui.horizontal(|ui| {
-                        ui.label(egui::RichText::new(format!("Exporting {} of {total}", (done + 1).min(total))).color(t.text));
+                        ui.label(
+                            egui::RichText::new(crate::i18n::tr_format!("Exporting {} of {total}", (done + 1).min(total), total = total))
+                                .color(t.text),
+                        );
                         ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
                             let stopping = cancel.load(Ordering::Relaxed);
                             if crate::widgets::text_button(ui, "exportCancel", if stopping { "Stopping…" } else { "Cancel" }, false).clicked() {

crates/ui-egui/src/headless.rs

@@ -176,6 +176,7 @@ impl Headless {
             || self.app.scan.is_some()
             || self.app.import.is_some()
             || self.app.export.is_some()
+            || !self.app.tasks.is_empty()
             || !self.app.synthetic.is_empty()
             || !self.events.is_empty()
     }

crates/ui-egui/src/i18n.rs

@@ -1,24 +1,27 @@
-//! Interface translations. Command ids, document text and file names remain stable.
-//! Untranslated labels fall back to English so coverage can grow incrementally.
+//! Presentation-only localization. Command ids, user names and catalog data remain unchanged.
+use std::{cell::Cell, collections::BTreeMap, sync::OnceLock};
 
-#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
-#[serde(rename_all = "lowercase")]
+use serde::{Deserialize, Serialize};
+
+include!(concat!(env!("OUT_DIR"), "/ja-formats.rs"));
+
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
 pub enum Language {
     #[default]
+    #[serde(rename = "en")]
     En,
+    #[serde(rename = "ja")]
     Ja,
 }
 
 impl Language {
     pub const ALL: [Self; 2] = [Self::En, Self::Ja];
-
     pub fn name(self) -> &'static str {
         match self {
             Self::En => "English",
             Self::Ja => "日本語",
         }
     }
-
     pub fn parse(code: &str) -> Option<Self> {
         match code {
             "en" => Some(Self::En),
@@ -26,129 +29,134 @@ impl Language {
             _ => None,
         }
     }
-
-    pub fn tr(self, text: &str) -> &str {
-        if self == Self::Ja
-            && let Some((_, japanese)) = JAPANESE.iter().find(|(english, _)| *english == text)
-        {
-            return japanese;
-        }
-        text
+    pub fn tr(self, source: &str) -> &str {
+        if self == Self::Ja { japanese().get(source).map(String::as_str).unwrap_or(source) } else { source }
     }
 }
 
-const JAPANESE: &[(&str, &str)] = &[
-    ("Photo", "写真"),
-    ("Import Photos…", "写真を読み込み…"),
-    ("Detail", "詳細"),
-    ("Photo Grid", "写真グリッド"),
-    ("Square Grid", "正方形グリッド"),
-    ("Object", "オブジェクト"),
-    ("Effect", "効果"),
-    ("Settings…", "環境設定…"),
-    ("Image", "画像"),
-    ("Layer", "レイヤー"),
-    ("Type", "書式"),
-    ("Select", "選択"),
-    ("Filter", "フィルター"),
-    ("Window", "ウィンドウ"),
-    ("Language", "表示言語"),
-    ("Save As…", "別名で保存…"),
-    ("Exit", "終了"),
-    ("New…", "新規…"),
-    ("New", "新規"),
-    ("Horizontal", "横書き"),
-    ("Vertical", "縦書き"),
-    ("Orientation", "組み方向"),
-    ("Layers", "レイヤー"),
-    ("History", "履歴"),
-    ("Properties", "プロパティ"),
-    ("Color", "カラー"),
-    ("Brush Settings", "ブラシ設定"),
-    ("Tools", "ツール"),
-    ("Options", "オプション"),
-    ("Zoom In", "ズームイン"),
-    ("Zoom Out", "ズームアウト"),
-    ("Fit on Screen", "画面に合わせる"),
-    ("Copy", "コピー"),
-    ("Cut", "切り取り"),
-    ("Paste", "貼り付け"),
-    ("Select All", "すべて選択"),
-    ("Deselect", "選択を解除"),
-    ("Export", "書き出し"),
-    ("Export As…", "形式を指定して書き出し…"),
-    ("Search…", "検索…"),
-    ("Theme", "テーマ"),
-    ("Menu", "メニュー"),
-    ("File", "ファイル"),
-    ("Edit", "編集"),
-    ("Pages", "ページ"),
-    ("View", "表示"),
-    ("Help", "ヘルプ"),
-    ("Preferences", "環境設定"),
-    ("Preferences…", "環境設定…"),
-    ("Interface language", "表示言語"),
-    ("Open…", "開く…"),
-    ("New blank PDF", "空白の PDF を作成"),
-    ("Create PDF from file…", "ファイルから PDF を作成…"),
-    ("Create PDF from images…", "画像から PDF を作成…"),
-    ("Create PDF from clipboard", "クリップボードから PDF を作成"),
-    ("Combine files…", "ファイルを結合…"),
-    ("Save", "保存"),
-    ("Save as…", "別名で保存…"),
-    ("Close file", "ファイルを閉じる"),
-    ("Close all", "すべて閉じる"),
-    ("Revert", "保存済みの状態に戻す"),
-    ("Print…", "印刷…"),
-    ("Document properties…", "文書のプロパティ…"),
-    ("Undo", "取り消し"),
-    ("Redo", "やり直し"),
-    ("Find…", "検索…"),
-    ("Advanced search…", "高度な検索…"),
-    ("Copy pages", "ページをコピー"),
-    ("Cut pages", "ページを切り取り"),
-    ("Paste pages", "ページを貼り付け"),
-    ("Fit visible", "表示範囲に合わせる"),
-    ("Marquee zoom", "範囲指定ズーム"),
-    ("Take a snapshot", "スナップショットを作成"),
-    ("Full screen mode", "全画面表示"),
-    ("Read mode", "閲覧モード"),
-    ("Switch light / dark theme", "明るい／暗いテーマを切り替え"),
-    ("Comments panel", "コメントパネル"),
-    ("Form fields panel", "フォームフィールドパネル"),
-    ("Clear form", "フォームをクリア"),
-    ("Find tools and commands…", "ツールとコマンドを検索…"),
-    ("Zoom", "ズーム"),
-    ("Actual size", "実際のサイズ"),
-    ("Zoom to page level", "ページ全体を表示"),
-    ("Fit to width", "幅に合わせる"),
-    ("Display theme", "表示テーマ"),
-    ("Side panels", "サイドパネル"),
-    ("OK", "OK"),
-];
+thread_local! {
+    static LANGUAGE: Cell<Language> = const { Cell::new(Language::En) };
+}
+
+pub fn default_language() -> Language {
+    if std::env::var("LIGHTCRAFT_LANGUAGE").as_deref() == Ok("ja") { Language::Ja } else { Language::En }
+}
+
+pub fn set_language(language: Language) {
+    LANGUAGE.with(|value| value.set(language));
+}
+
+pub fn is_japanese() -> bool {
+    LANGUAGE.with(|value| value.get() == Language::Ja)
+}
+
+fn japanese() -> &'static BTreeMap<String, String> {
+    static MESSAGES: OnceLock<BTreeMap<String, String>> = OnceLock::new();
+    MESSAGES.get_or_init(|| {
+        serde_json::from_str(include_str!("../locales/ja.json")).unwrap_or_else(|error| {
+            log::error!("Invalid Japanese message catalog: {error}");
+            BTreeMap::new()
+        })
+    })
+}
+
+/// Translate a built-in display label, preserving unknown labels verbatim.
+/// Never call this on editable user text, filenames or command identifiers.
+pub fn tr(source: &str) -> &str {
+    if is_japanese() { japanese().get(source).map(String::as_str).unwrap_or(source) } else { source }
+}
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
     #[test]
-    fn language_setting_persists() {
-        let state = crate::state::UiState { language: Language::Ja, ..Default::default() };
-        let saved = serde_json::to_string(&state).unwrap();
-        let restored: crate::state::UiState = serde_json::from_str(&saved).unwrap();
-        assert_eq!(restored.language, Language::Ja);
-        assert_eq!(crate::state::UiState::default().language, Language::En);
+    fn catalog_is_valid_and_contains_core_workflows() {
+        let messages: BTreeMap<String, String> = serde_json::from_str(include_str!("../locales/ja.json")).unwrap();
+        for key in ["Import Photos…", "Export…", "Exposure", "White Balance", "Settings", "Language"] {
+            assert!(messages.get(key).is_some_and(|value| !value.is_empty() && value != key), "{key}");
+        }
     }
 
     #[test]
-    fn translations_are_unique_and_preserve_unknown_text() {
-        for (i, (en, ja)) in JAPANESE.iter().enumerate() {
-            assert!(!ja.is_empty());
-            assert!(JAPANESE.iter().take(i).all(|(other, _)| en != other));
-            assert_eq!(Language::En.tr(en), *en);
+    fn language_switches_and_unknown_text_survives() {
+        set_language(Language::Ja);
+        assert_eq!(tr("Exposure"), "露出");
+        assert_eq!(tr("my-photo.jpg"), "my-photo.jpg");
+        assert_eq!(tr("develop.set"), "develop.set");
+        assert_eq!(crate::menubar::display_item_label("album.addPhotos", &serde_json::json!({"id": 1}), "Color"), "Color");
+        assert_eq!(crate::menubar::display_item_label("app.export", &serde_json::json!({"preset": "Color"}), "Color"), "Color");
+        assert_eq!(crate::menubar::display_item_label("view.photoGrid", &serde_json::Value::Null, "Color"), "カラー");
+        set_language(Language::En);
+        assert_eq!(tr("Exposure"), "Exposure");
+    }
+
+    #[test]
+    fn translated_formats_preserve_counts_and_remove_english_plural_suffixes() {
+        set_language(Language::Ja);
+        assert_eq!(tr_format!("{n} photo{}", "s", n = 12), "12枚");
+        assert_eq!(tr_format!("Exported {ok} of {total} photo{}", "s", ok = 4, total = 12), "12枚中4枚を書き出しました");
+        set_language(Language::En);
+        assert_eq!(tr_format!("{n} photo{}", "s", n = 12), "12 photos");
+    }
+
+    #[test]
+    fn preferences_round_trip_and_old_settings_remain_readable() {
+        let old: crate::state::UiState = serde_json::from_str("{}").unwrap();
+        assert_eq!(old.language, Language::En);
+        let settings = crate::state::UiState { language: Language::Ja, ..old };
+        let saved = serde_json::to_string(&settings).unwrap();
+        let restored: crate::state::UiState = serde_json::from_str(&saved).unwrap();
+        assert_eq!(restored.language, Language::Ja);
+    }
+
+    #[test]
+    fn japanese_is_painted_and_both_font_weights_cover_the_catalog() {
+        let ctx = egui::Context::default();
+        crate::theme::install_fonts(&ctx);
+        let mut app = crate::LightcraftApp::new(lightcraft_engine::Session::with_demo(), Default::default());
+        app.ui.language = Language::Ja;
+        app.ui.left_panel = true;
+        let mut text = String::new();
+        fn collect(shape: &egui::epaint::Shape, text: &mut String) {
+            match shape {
+                egui::epaint::Shape::Text(shape) => {
+                    text.push_str(&shape.galley.job.text);
+                    text.push('\n');
+                }
+                egui::epaint::Shape::Vec(shapes) => shapes.iter().for_each(|shape| collect(shape, text)),
+                _ => {}
+            }
         }
-        assert_eq!(Language::Ja.tr("File"), "ファイル");
-        assert_eq!(Language::Ja.tr("日本語の文書.pdf"), "日本語の文書.pdf");
-        assert_eq!(Language::parse("xx"), None);
+        for frame in 0..4 {
+            let input = crate::headless::HeadlessView::raw_input(egui::vec2(1600.0, 1000.0), 1.0, frame as f64 / 60.0, vec![]);
+            let mut out = ctx.run_ui(input, |ui| {
+                app.logic(ui.ctx());
+                app.ui(ui);
+            });
+            // This assertion inspects shapes without a renderer; discard texture uploads explicitly.
+            out.textures_delta.clear();
+            text.clear();
+            for shape in out.shapes {
+                collect(&shape.shape, &mut text);
+            }
+        }
+        assert!(text.contains("マイフォト"), "{text}");
+        assert!(text.contains("すべての写真"), "{text}");
+        ctx.fonts_mut(|fonts| {
+            for family in [egui::FontFamily::Proportional, egui::FontFamily::Name(crate::theme::FONT_SEMIBOLD.into())] {
+                let font = egui::FontId::new(13.0, family);
+                for message in japanese().values() {
+                    for ch in message.chars().filter(|ch| !ch.is_whitespace()) {
+                        assert!(fonts.has_glyph(&font, ch), "Missing glyph {ch} in {message}");
+                    }
+                }
+            }
+        });
+        // Locale affects presentation only: command ids remain the same.
+        let ids = |app: &crate::LightcraftApp| crate::menus::menu_entries(app).into_iter().map(|entry| entry.id).collect::<Vec<_>>();
+        let japanese_ids = ids(&app);
+        set_language(Language::En);
+        assert_eq!(japanese_ids, ids(&app));
     }
 }

crates/ui-egui/src/import.rs

@@ -3,8 +3,9 @@
 //! a grid of thumbnails with checkboxes (duplicates marked and unchecked), the destination (add in
 //! place / copy or move into the library's `Originals/` or a chosen folder, filed by day, by month,
 //! into one folder or by a custom folder template, optionally renamed), an album
-//! (existing or new), a preset and keywords to apply. Importing runs in small batches, one per
-//! frame, with a progress window; the whole import is one undo step.
+//! (existing or new), a preset and keywords to apply. Importing runs on a worker thread (files are
+//! probed, copied or moved there) and its batches join the catalog between frames, with a progress
+//! window and Cancel; the whole import is one undo step.
 
 use egui::{Align2, Color32, Rect, Sense, Stroke, StrokeKind, pos2, vec2};
 use lightcraft_engine::import::{ImportCandidate, ScanInput, ScanOutput, ScanProgress, scan_with};
@@ -17,7 +18,7 @@ use crate::render::Slot;
 use crate::theme::Tokens;
 use crate::widgets::register;
 
-/// Files per batch (one batch per frame, so the progress window updates).
+/// Files per batch (each batch joins the catalog as it is ready, so the progress window updates).
 pub(crate) const BATCH: usize = 8;
 
 #[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
@@ -91,9 +92,13 @@ impl ImportDialog {
     }
 }
 
-/// A running import (see the module docs).
+/// A running import (see the module docs). The file-system work — expanding folders, probing,
+/// reading sidecars, copying or placing files — runs on a worker thread
+/// ([`lightcraft_engine::import::ImportJob`]); each batch it readies is added to the catalog on the
+/// UI thread between frames, so a slow drive never stalls the window.
 #[derive(Debug, Default)]
 pub struct ImportTask {
+    /// Files and folders to import (handed to the worker when the task starts).
     queue: Vec<String>,
     pub total: usize,
     pub done: usize,
@@ -109,6 +114,156 @@ pub struct ImportTask {
     /// Reading a folder for the Local view: the photos stay out of the library, and nothing is
     /// selected or announced as added.
     browse: bool,
+    /// Cancel was pressed: no further files are started; batches already readied are added.
+    pub cancelled: bool,
+    /// Auto Import (the watched folder): the selection stays as it is, a short toast when done.
+    auto: bool,
+    /// Auto Import: the selection to keep.
+    keep_selection: Option<lightcraft_engine::Selection>,
+    run: Option<ImportRun>,
+}
+
+impl ImportTask {
+    /// An import of `paths` (files or folders) with `library.import` params (without `paths`).
+    pub fn new(paths: Vec<String>, params: Value, undo0: usize, browse: bool) -> Self {
+        ImportTask { total: paths.len(), queue: paths, params, undo0, browse, ..Default::default() }
+    }
+
+    /// An Auto Import (see [`ImportTask::auto`]).
+    pub fn auto(mut self) -> Self {
+        self.auto = true;
+        self
+    }
+
+    /// `{done, total, imported, cancelled}` for `ui.inspect`.
+    pub fn status(&self) -> Value {
+        json!({"done": self.done, "total": self.total, "imported": self.imported, "cancelled": self.cancelled})
+    }
+}
+
+/// Where an import's batches are readied: a worker thread, or (browser build: no threads, and no
+/// slow drives) inline, one batch per frame.
+enum Runner {
+    #[cfg(not(target_arch = "wasm32"))]
+    Thread(std::sync::mpsc::Receiver<lightcraft_engine::import::Prepared>),
+    #[cfg(target_arch = "wasm32")]
+    Inline { job: Box<lightcraft_engine::import::ImportJob>, queue: Vec<String>, files: Option<std::collections::VecDeque<String>> },
+}
+
+struct ImportRun {
+    runner: Runner,
+    cancel: std::sync::Arc<std::sync::atomic::AtomicBool>,
+    total: std::sync::Arc<std::sync::atomic::AtomicUsize>,
+    done: std::sync::Arc<std::sync::atomic::AtomicUsize>,
+    opts: lightcraft_engine::import::ImportOptions,
+    now: String,
+    album: Option<u64>,
+    album_name: Option<String>,
+}
+
+impl std::fmt::Debug for ImportRun {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("ImportRun").field("cancel", &self.cancel.load(Ordering::Relaxed)).finish()
+    }
+}
+
+impl Drop for ImportRun {
+    /// A dropped import (replaced, or the app closing) stops its worker at the next file.
+    fn drop(&mut self) {
+        self.cancel.store(true, Ordering::Relaxed);
+    }
+}
+
+impl ImportRun {
+    fn start(
+        job: lightcraft_engine::import::ImportJob,
+        queue: Vec<String>,
+        album: Option<u64>,
+        album_name: Option<String>,
+        ctx: &egui::Context,
+    ) -> Result<Self, String> {
+        let cancel = std::sync::Arc::new(std::sync::atomic::AtomicBool::new(false));
+        let (total, done) = (job.total.clone(), job.done.clone());
+        let (opts, now) = (job.opts.clone(), job.now().to_string());
+        let runner = Self::spawn(job, queue, cancel.clone(), ctx)?;
+        Ok(ImportRun { runner, cancel, total, done, opts, now, album, album_name })
+    }
+
+    #[cfg(not(target_arch = "wasm32"))]
+    fn spawn(
+        mut job: lightcraft_engine::import::ImportJob,
+        queue: Vec<String>,
+        cancel: std::sync::Arc<std::sync::atomic::AtomicBool>,
+        ctx: &egui::Context,
+    ) -> Result<Runner, String> {
+        let (tx, rx) = std::sync::mpsc::channel();
+        let ctx = ctx.clone();
+        let work = move || {
+            let files = job.expand(&queue);
+            for chunk in files.chunks(BATCH) {
+                if cancel.load(Ordering::Relaxed) {
+                    break;
+                }
+                let prepared = match lightcraft_engine::guard::catch("import", || job.prepare_files(chunk.to_vec(), &cancel)) {
+                    Ok(p) => p,
+                    Err(_) => break, // logged; the files readied so far are added
+                };
+                if let Err(unsent) = tx.send(prepared) {
+                    // the import was dropped: nothing will add these, so take back what a Move placed
+                    unsent.0.rollback();
+                    break;
+                }
+                ctx.request_repaint();
+            }
+            ctx.request_repaint();
+        };
+        std::thread::Builder::new().name("lc-import".into()).spawn(work).map(|_| Runner::Thread(rx)).map_err(|e| format!("could not start: {e}"))
+    }
+
+    #[cfg(target_arch = "wasm32")]
+    fn spawn(
+        job: lightcraft_engine::import::ImportJob,
+        queue: Vec<String>,
+        _cancel: std::sync::Arc<std::sync::atomic::AtomicBool>,
+        _ctx: &egui::Context,
+    ) -> Result<Runner, String> {
+        Ok(Runner::Inline { job: Box::new(job), queue, files: None })
+    }
+
+    /// Readied batches (at most a few per frame). `None` once the worker is done.
+    fn next_batches(&mut self) -> Option<Vec<lightcraft_engine::import::Prepared>> {
+        match &mut self.runner {
+            #[cfg(not(target_arch = "wasm32"))]
+            Runner::Thread(rx) => {
+                let mut out = Vec::new();
+                while out.len() < 4 {
+                    match rx.try_recv() {
+                        Ok(p) => out.push(p),
+                        Err(std::sync::mpsc::TryRecvError::Empty) => return Some(out),
+                        Err(std::sync::mpsc::TryRecvError::Disconnected) => return if out.is_empty() { None } else { Some(out) },
+                    }
+                }
+                Some(out)
+            }
+            #[cfg(target_arch = "wasm32")]
+            Runner::Inline { job, queue, files } => {
+                if self.cancel.load(Ordering::Relaxed) {
+                    return None;
+                }
+                if files.is_none() {
+                    *files = Some(job.expand(queue).into());
+                    return Some(Vec::new());
+                }
+                let Some(files) = files.as_mut() else { return None };
+                if files.is_empty() {
+                    return None;
+                }
+                let n = files.len().min(BATCH);
+                let batch: Vec<String> = files.drain(..n).collect();
+                Some(vec![job.prepare_files(batch, &self.cancel)])
+            }
+        }
+    }
 }
 
 /// A folder scan running on a worker thread (a network share can take minutes to read; the
@@ -232,7 +387,8 @@ pub fn poll_scan(app: &mut LightcraftApp, ctx: &egui::Context) {
         if !queue.is_empty() {
             let undo0 = app.session.undo.len();
             let total = queue.len();
-            app.import = Some(ImportTask { queue, total, params: json!({"mode": "add", "local": true}), undo0, browse: true, ..Default::default() });
+            let _ = total;
+            app.import = Some(ImportTask::new(queue, json!({"mode": "add", "local": true}), undo0, true));
         }
         return;
     }
@@ -256,19 +412,21 @@ pub fn scan_progress(app: &mut LightcraftApp, ctx: &egui::Context) {
     let text = if total == 0 {
         if task.browse { "Reading folder…" } else { "Looking for photos…" }.to_string()
     } else {
-        format!("Reading photos… {done} of {total}")
+        crate::i18n::tr_format!("Reading photos… {done} of {total}", done = done, total = total)
     };
     let mut cancel = false;
-    egui::Window::new("Scanning").title_bar(false).resizable(false).anchor(Align2::CENTER_BOTTOM, [0.0, -80.0]).fixed_size([340.0, 80.0]).show(
-        ctx,
-        |ui| {
+    egui::Window::new(crate::i18n::tr("Scanning"))
+        .title_bar(false)
+        .resizable(false)
+        .anchor(Align2::CENTER_BOTTOM, [0.0, -80.0])
+        .fixed_size([340.0, 80.0])
+        .show(ctx, |ui| {
             ui.label(egui::RichText::new(text).color(t.text));
             ui.add(egui::ProgressBar::new(done as f32 / total.max(1) as f32).desired_width(320.0));
-            let r = ui.button("Cancel");
+            let r = ui.button(crate::i18n::tr("Cancel"));
             register(ui.ctx(), "button:scanCancel", r.rect);
             cancel = r.clicked();
-        },
-    );
+        });
     if cancel {
         // the worker stops at its next file; don't wait for it (a NAS read can take a while)
         task.progress.cancel.store(true, Ordering::Relaxed);
@@ -326,28 +484,82 @@ pub fn start(app: &mut LightcraftApp, d: &ImportDialog) -> Result<Value, String>
         }
     }
     let total = queue.len();
-    app.import = Some(ImportTask { queue, total, params, undo0, ..Default::default() });
+    app.import = Some(ImportTask::new(queue, params, undo0, false));
     app.renderer.forget_imports();
     Ok(json!({"importing": total}))
 }
 
-/// Run one batch of the import in progress (called every frame).
-pub fn tick(app: &mut LightcraftApp, ctx: &egui::Context) {
-    let Some(task) = app.import.as_mut() else { return };
-    // (browsing reads a sidecar per file, slow on a network share: keep each frame short)
-    let n = task.queue.len().min(if task.browse { 2 } else { BATCH });
-    let batch: Vec<String> = task.queue.drain(..n).collect();
-    let mut p = task.params.clone();
-    p["paths"] = json!(batch);
-    // renamed copies keep counting across batches
-    if p.get("rename").is_some() {
-        p["renameStart"] = json!(1 + task.imported);
+/// Start importing `paths` (files or folders) in the background, e.g. dropped on the window.
+pub fn start_paths(app: &mut LightcraftApp, paths: Vec<String>) -> Result<Value, String> {
+    if app.import.is_some() || app.scan.as_ref().is_some_and(|t| !t.browse) {
+        return Err("an import is running".into());
     }
-    let r = app.session.execute("library.import", &p);
-    let Some(task) = app.import.as_mut() else { return };
-    task.done += n;
+    let undo0 = app.session.undo.len();
+    let total = paths.len();
+    app.import = Some(ImportTask::new(paths, json!({"mode": "add"}), undo0, false));
+    Ok(json!({"importing": total}))
+}
+
+/// Advance the import in progress (called every frame): start its worker, then add the batches it
+/// has readied to the catalog.
+pub fn tick(app: &mut LightcraftApp, ctx: &egui::Context) {
+    let Some(mut task) = app.import.take() else { return };
+    if task.run.is_none() {
+        let mut p = task.params.clone();
+        p["paths"] = json!(task.queue);
+        let started = lightcraft_engine::cmd::library::import_params(&app.session, &p)
+            .and_then(|req| Ok((lightcraft_engine::import::ImportJob::new(&mut app.session, req.opts)?, req.album, req.album_name)))
+            .map_err(|e| e.to_string())
+            .and_then(|(job, album, name)| ImportRun::start(job, std::mem::take(&mut task.queue), album, name, ctx));
+        if task.auto {
+            task.keep_selection = Some(app.session.selection.clone());
+        }
+        match started {
+            Ok(run) => task.run = Some(run),
+            Err(e) => {
+                log::warn!("import: {e}");
+                app.toast(ctx, format!("Import failed: {e}"));
+                return;
+            }
+        }
+    }
+    ctx.request_repaint_after(std::time::Duration::from_millis(100));
+    let Some(run) = task.run.as_mut() else { return };
+    let batches = run.next_batches();
+    let finished = batches.is_none();
+    for prepared in batches.into_iter().flatten() {
+        commit_batch(app, &mut task, prepared);
+        // arriving photos don't take over the selection
+        if let Some(sel) = &task.keep_selection {
+            app.session.selection = sel.clone();
+        }
+    }
+    if let Some(run) = &task.run {
+        task.total = run.total.load(Ordering::Relaxed).max(task.total);
+        task.done = run.done.load(Ordering::Relaxed);
+    }
+    if !finished {
+        app.import = Some(task);
+        return;
+    }
+    finish(app, ctx, task);
+}
+
+/// Add one readied batch to the catalog (an undo step merged into the import's at the end).
+fn commit_batch(app: &mut LightcraftApp, task: &mut ImportTask, prepared: lightcraft_engine::import::Prepared) {
+    let Some(run) = task.run.as_ref() else { return };
+    let n = prepared.len();
+    let (opts, now, album, album_name) = (&run.opts, run.now.as_str(), run.album, run.album_name.clone());
+    let r = app.session.execute_fn("library.import", |s| {
+        let report = lightcraft_engine::import::commit_prepared(s, opts, now, prepared)?;
+        lightcraft_engine::cmd::library::import_batch_done(s, report, album, album_name.as_deref())
+    });
     match r {
         Ok(v) => {
+            // a new album (named in the params) is created with the first photos; later batches join it
+            if let (Some(a), Some(run)) = (v["album"].as_u64(), task.run.as_mut()) {
+                run.album = Some(a);
+            }
             let len = |k: &str| v[k].as_array().map_or(0, Vec::len);
             task.imported += len("imported");
             task.duplicates += len("duplicates");
@@ -366,17 +578,22 @@ pub fn tick(app: &mut LightcraftApp, ctx: &egui::Context) {
             task.failed += n;
         }
     }
-    ctx.request_repaint();
-    if !task.queue.is_empty() {
+}
+
+/// The import is done (or cancelled): one undo step, select the first photo, say what happened.
+fn finish(app: &mut LightcraftApp, ctx: &egui::Context, task: ImportTask) {
+    let steps = app.session.undo.len().saturating_sub(task.undo0);
+    let label = crate::i18n::tr_format!("Add {} Photo{}", task.imported, if task.imported == 1 { "" } else { "s" });
+    app.session.merge_undo(steps, &label);
+    if task.auto {
+        if task.imported > 0 {
+            app.toast(ctx, format!("Auto Import: added {} photo{}", task.imported, if task.imported == 1 { "" } else { "s" }));
+        }
         return;
     }
-    let Some(task) = app.import.take() else { return };
-    let steps = app.session.undo.len().saturating_sub(task.undo0);
-    let label = format!("Add {} Photo{}", task.imported, if task.imported == 1 { "" } else { "s" });
-    app.session.merge_undo(steps, &label);
     if task.browse {
         if task.failed > 0 {
-            app.toast(ctx, format!("{} photo{} not readable", task.failed, if task.failed == 1 { "" } else { "s" }));
+            app.toast(ctx, crate::i18n::tr_format!("{} photo{} not readable", task.failed, if task.failed == 1 { "" } else { "s" }));
         }
         return;
     }
@@ -384,35 +601,58 @@ pub fn tick(app: &mut LightcraftApp, ctx: &egui::Context) {
         let _ = app.run("library.select", json!({"ids": [f]}));
     }
     let plural = |n: usize| if n == 1 { "" } else { "s" };
-    let mut msg = format!("Imported {} photo{}", task.imported, plural(task.imported));
+    let mut msg = if task.cancelled {
+        crate::i18n::tr_format!("Import cancelled · {} photo{} added", task.imported, plural(task.imported))
+    } else {
+        crate::i18n::tr_format!("Imported {} photo{}", task.imported, plural(task.imported))
+    };
     if task.params["mode"] == "move" {
-        msg.push_str(&format!(" · {} moved", task.moved));
+        msg.push_str(&crate::i18n::tr_format!(" · {} moved", task.moved));
         if task.kept > 0 {
             msg.push_str(&format!(" · {} original{} left at the source", task.kept, plural(task.kept)));
         }
     }
     if task.duplicates > 0 {
-        msg.push_str(&format!(" · {} duplicate{} skipped", task.duplicates, if task.duplicates == 1 { "" } else { "s" }));
+        msg.push_str(&crate::i18n::tr_format!(" · {} duplicate{} skipped", task.duplicates, if task.duplicates == 1 { "" } else { "s" }));
     }
     if task.failed > 0 {
-        msg.push_str(&format!(" · {} not readable", task.failed));
+        msg.push_str(&crate::i18n::tr_format!(" · {} not readable", task.failed));
     }
     app.toast(ctx, msg);
 }
 
-/// The progress window while an import runs.
+/// The progress window while an import runs, with Cancel (files already copied or added stay;
+/// nothing new is started).
 pub fn progress(app: &mut LightcraftApp, ctx: &egui::Context) {
     let Some(task) = &app.import else { return };
     let t = Tokens::get(ctx);
     let frac = task.done as f32 / task.total.max(1) as f32;
-    let text = format!("{} photos… {} of {}", if task.browse { "Reading" } else { "Adding" }, task.done, task.total);
-    egui::Window::new("Importing").title_bar(false).resizable(false).anchor(Align2::CENTER_BOTTOM, [0.0, -80.0]).fixed_size([340.0, 60.0]).show(
-        ctx,
-        |ui| {
+    let text = if task.cancelled {
+        crate::i18n::tr("Stopping…").to_string()
+    } else if task.browse {
+        crate::i18n::tr_format!("Reading photos… {} of {}", task.done, task.total)
+    } else {
+        crate::i18n::tr_format!("Adding photos… {} of {}", task.done, task.total)
+    };
+    let mut cancel = false;
+    egui::Window::new(crate::i18n::tr("Importing"))
+        .title_bar(false)
+        .resizable(false)
+        .anchor(Align2::CENTER_BOTTOM, [0.0, -80.0])
+        .fixed_size([340.0, 80.0])
+        .show(ctx, |ui| {
             ui.label(egui::RichText::new(text).color(t.text));
             ui.add(egui::ProgressBar::new(frac).desired_width(320.0));
-        },
-    );
+            let r = ui.add_enabled(!task.cancelled, egui::Button::new(crate::i18n::tr("Cancel")));
+            register(ui.ctx(), "button:importCancel", r.rect);
+            cancel = r.clicked();
+        });
+    if cancel && let Some(task) = app.import.as_mut() {
+        task.cancelled = true;
+        if let Some(run) = &task.run {
+            run.cancel.store(true, Ordering::Relaxed);
+        }
+    }
 }
 
 /// The dialog body: options, then the candidate grid.
@@ -422,15 +662,15 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &mut ImportDialog) {
     let dups = d.candidates.iter().filter(|c| c.duplicate.is_some()).count();
     let sel = d.selected_paths().len();
     ui.horizontal(|ui| {
-        ui.label(egui::RichText::new(format!("{n} found · {sel} selected")).color(t.text));
+        ui.label(egui::RichText::new(crate::i18n::tr_format!("{n} found · {sel} selected", n = n, sel = sel)).color(t.text));
         if dups > 0 {
-            ui.label(egui::RichText::new(format!("· {dups} already in the library")).color(t.text_dim));
+            ui.label(egui::RichText::new(crate::i18n::tr_format!("· {dups} already in the library", dups = dups)).color(t.text_dim));
         }
         ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
-            if crate::widgets::text_button(ui, "importNone", "Uncheck All", false).clicked() {
+            if crate::widgets::text_button(ui, "importNone", crate::i18n::tr("Uncheck All"), false).clicked() {
                 d.checked.iter_mut().for_each(|c| *c = false);
             }
-            if crate::widgets::text_button(ui, "importAll", "Check All", false).clicked() {
+            if crate::widgets::text_button(ui, "importAll", crate::i18n::tr("Check All"), false).clicked() {
                 for i in 0..n {
                     d.checked[i] = d.importable(i);
                 }
@@ -458,29 +698,42 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &mut ImportDialog) {
     // options
     if !d.sources.is_empty() {
         field(ui, "Source", |ui| {
-            let r = ui.label(egui::RichText::new(source_summary(&d.sources)).color(t.text_label)).on_hover_text(d.sources.join("\n"));
+            // (whether each source is a folder is checked off the UI thread, once)
+            let joined = d.sources.join("\n");
+            let summary = crate::panels::left::fs_cached(ui, "import-source", &joined, f64::INFINITY, |s| {
+                source_summary(&s.split('\n').map(str::to_string).collect::<Vec<_>>())
+            })
+            .unwrap_or_else(|| format!("{} item{}", d.sources.len(), if d.sources.len() == 1 { "" } else { "s" }));
+            let r = ui.label(egui::RichText::new(summary).color(t.text_label)).on_hover_text(joined);
             register(ui.ctx(), "label:importSource", r.rect);
         });
         ui.label(
-            egui::RichText::new("Importing scans the source for photos; it doesn't add the folder to Local (use Local → Browse Folder… to work in a folder without importing).")
+            egui::RichText::new(crate::i18n::tr("Importing scans the source for photos; it doesn't add the folder to Local (use Local → Browse Folder… to work in a folder without importing)."))
                 .color(t.text_dim)
                 .small(),
         );
     }
     field(ui, "Transfer", |ui| {
         ui.spacing_mut().item_spacing.x = 4.0;
-        if crate::widgets::text_button(ui, "importAdd", "Add in place", !d.copy).on_hover_text("Reference the files where they are").clicked() {
+        if crate::widgets::text_button(ui, "importAdd", crate::i18n::tr("Add in place"), !d.copy)
+            .on_hover_text(crate::i18n::tr("Reference the files where they are"))
+            .clicked()
+        {
             d.copy = false;
             d.move_files = false;
         }
         let can_copy = app.session.library.as_ref().is_some_and(|l| l.on_disk) || app.services.pick_folder.is_some();
-        let r = ui.add_enabled_ui(can_copy, |ui| crate::widgets::text_button(ui, "importCopy", "Copy", d.copy && !d.move_files)).inner;
-        if r.on_hover_text("Copy the files (into the library's Originals/, or a folder you choose)").clicked() {
+        let r =
+            ui.add_enabled_ui(can_copy, |ui| crate::widgets::text_button(ui, "importCopy", crate::i18n::tr("Copy"), d.copy && !d.move_files)).inner;
+        if r.on_hover_text(crate::i18n::tr("Copy the files (into the library's Originals/, or a folder you choose)")).clicked() {
             d.copy = true;
             d.move_files = false;
         }
-        let r = ui.add_enabled_ui(can_copy, |ui| crate::widgets::text_button(ui, "importMove", "Move", d.copy && d.move_files)).inner;
-        if r.on_hover_text("Move the files (into the library's Originals/, or a folder you choose), removing them from the source").clicked() {
+        let r =
+            ui.add_enabled_ui(can_copy, |ui| crate::widgets::text_button(ui, "importMove", crate::i18n::tr("Move"), d.copy && d.move_files)).inner;
+        if r.on_hover_text(crate::i18n::tr("Move the files (into the library's Originals/, or a folder you choose), removing them from the source"))
+            .clicked()
+        {
             d.copy = true;
             d.move_files = true;
         }
@@ -505,12 +758,12 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &mut ImportDialog) {
             let shown = if d.destination.trim().is_empty() { "Library Originals".to_string() } else { d.destination.clone() };
             ui.label(egui::RichText::new(shown).color(Tokens::get(ui.ctx()).text_label));
             if app.services.pick_folder.is_some()
-                && crate::widgets::text_button(ui, "importDest", "Choose…", false).clicked()
+                && crate::widgets::text_button(ui, "importDest", crate::i18n::tr("Choose…"), false).clicked()
                 && let Some(f) = app.services.pick_folder.as_mut().and_then(|f| f())
             {
                 d.destination = f;
             }
-            if !d.destination.is_empty() && crate::widgets::text_button(ui, "importDestReset", "Library", false).clicked() {
+            if !d.destination.is_empty() && crate::widgets::text_button(ui, "importDestReset", crate::i18n::tr("Library"), false).clicked() {
                 d.destination.clear();
             }
         });
@@ -557,14 +810,16 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &mut ImportDialog) {
                 None => unknown_tags_warning(ui, &d.folder_template),
             }
             ui.label(
-                egui::RichText::new("Each / starts a folder level; tags are filled in per photo (a level with missing metadata is \"unknown\").")
-                    .color(t.text_dim)
-                    .small(),
+                egui::RichText::new(crate::i18n::tr(
+                    "Each / starts a folder level; tags are filled in per photo (a level with missing metadata is \"unknown\").",
+                ))
+                .color(t.text_dim)
+                .small(),
             );
         }
         if !d.move_files {
             field(ui, "Raw files", |ui| {
-                let r = ui.checkbox(&mut d.dng, "Copy as DNG");
+                let r = ui.checkbox(&mut d.dng, crate::i18n::tr("Copy as DNG"));
                 register(ui.ctx(), "check:importDng", r.rect);
             });
         }
@@ -582,10 +837,12 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &mut ImportDialog) {
         unknown_tags_warning(ui, &d.rename);
         if let Some(example) = example_destination(app, d) {
             let t = Tokens::get(ui.ctx());
-            let r = ui.label(egui::RichText::new(format!("Example: {example}")).color(t.text_dim));
+            let r = ui.label(egui::RichText::new(crate::i18n::tr_format!("Example: {example}", example = example)).color(t.text_dim));
             register(ui.ctx(), "label:importExample", r.rect);
             ui.label(
-                egui::RichText::new("Folders and {date} use the capture time; a photo without one uses today's date.").color(t.text_dim).small(),
+                egui::RichText::new(crate::i18n::tr("Folders and {date} use the capture time; a photo without one uses today's date."))
+                    .color(t.text_dim)
+                    .small(),
             );
         }
     }
@@ -602,11 +859,11 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &mut ImportDialog) {
             None => "None".into(),
         };
         egui::ComboBox::from_id_salt("import-album").selected_text(cur).show_ui(ui, |ui| {
-            if ui.selectable_label(d.album.is_none() && d.new_album.is_empty(), "None").clicked() {
+            if ui.selectable_label(d.album.is_none() && d.new_album.is_empty(), crate::i18n::tr("None")).clicked() {
                 d.album = None;
                 d.new_album.clear();
             }
-            if ui.selectable_label(d.album.is_none() && !d.new_album.is_empty(), "New album…").clicked() {
+            if ui.selectable_label(d.album.is_none() && !d.new_album.is_empty(), crate::i18n::tr("New album…")).clicked() {
                 d.album = None;
                 if d.new_album.is_empty() {
                     d.new_album = "Imported Photos".into();
@@ -627,7 +884,7 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &mut ImportDialog) {
     field(ui, "Preset", |ui| {
         let cur = app.session.presets.iter().find(|p| p.id == d.preset).map(|p| p.name.clone()).unwrap_or_else(|| "None".into());
         egui::ComboBox::from_id_salt("import-preset").selected_text(cur).height(300.0).show_ui(ui, |ui| {
-            if ui.selectable_label(d.preset.is_empty(), "None").clicked() {
+            if ui.selectable_label(d.preset.is_empty(), crate::i18n::tr("None")).clicked() {
                 d.preset.clear();
             }
             for p in &app.session.presets {
@@ -641,7 +898,7 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &mut ImportDialog) {
         field(ui, "Metadata", |ui| {
             let cur = if d.metadata_preset.is_empty() { "None".to_string() } else { d.metadata_preset.clone() };
             egui::ComboBox::from_id_salt("import-metadata").selected_text(cur).show_ui(ui, |ui| {
-                if ui.selectable_label(d.metadata_preset.is_empty(), "None").clicked() {
+                if ui.selectable_label(d.metadata_preset.is_empty(), crate::i18n::tr("None")).clicked() {
                     d.metadata_preset.clear();
                 }
                 for m in &app.session.metadata_presets {
@@ -653,7 +910,7 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &mut ImportDialog) {
         });
     }
     field(ui, "Keywords", |ui| {
-        let r = ui.add(egui::TextEdit::singleline(&mut d.keywords).hint_text("comma, separated").desired_width(f32::INFINITY));
+        let r = ui.add(egui::TextEdit::singleline(&mut d.keywords).hint_text(crate::i18n::tr("comma, separated")).desired_width(f32::INFINITY));
         register(ui.ctx(), "field:importKeywords", r.rect);
     });
 }
@@ -726,7 +983,8 @@ fn candidate_cell(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &mut ImportDial
 pub(crate) fn tag_toggle(ui: &mut egui::Ui, key: &str) -> bool {
     let id = egui::Id::new((key, "tags-open"));
     let mut open = ui.ctx().data(|d| d.get_temp::<bool>(id)).unwrap_or(false);
-    let r = crate::widgets::text_button(ui, &format!("{key}Tags"), "Tags", open).on_hover_text("Show the template tags; click one to insert it");
+    let r = crate::widgets::text_button(ui, &format!("{key}Tags"), crate::i18n::tr("Tags"), open)
+        .on_hover_text(crate::i18n::tr("Show the template tags; click one to insert it"));
     if r.clicked() {
         open = !open;
         ui.ctx().data_mut(|d| d.insert_temp(id, open));
@@ -770,7 +1028,9 @@ pub(crate) fn tag_help(ui: &mut egui::Ui, key: &str, text: &mut String, edit_id:
     let t = Tokens::get(ui.ctx());
     egui::Frame::new().fill(t.inset).corner_radius(4.0).inner_margin(6.0).show(ui, |ui| {
         ui.label(
-            egui::RichText::new("Click a tag to insert it. Examples are for IMG_0042.CR3 taken 14 Jan 2026, 05:58:48.").color(t.text_dim).small(),
+            egui::RichText::new(crate::i18n::tr("Click a tag to insert it. Examples are for IMG_0042.CR3 taken 14 Jan 2026, 05:58:48."))
+                .color(t.text_dim)
+                .small(),
         );
         egui::ScrollArea::vertical().id_salt((key, "tags")).max_height(170.0).show(ui, |ui| {
             egui::Grid::new((key, "tag-grid")).num_columns(3).spacing([10.0, 2.0]).show(ui, |ui| {
@@ -848,9 +1108,9 @@ pub fn source_summary(sources: &[String]) -> String {
         many => {
             let folders = many.iter().filter(|p| std::path::Path::new(p.as_str()).is_dir()).count();
             match folders {
-                0 => format!("{} files", many.len()),
-                f if f == many.len() => format!("{f} folders (and their subfolders)"),
-                f => format!("{} files and {f} folder{}", many.len() - f, if f == 1 { "" } else { "s" }),
+                0 => crate::i18n::tr_format!("{} files", many.len()),
+                f if f == many.len() => crate::i18n::tr_format!("{f} folders (and their subfolders)", f = f),
+                f => crate::i18n::tr_format!("{} files and {f} folder{}", many.len() - f, if f == 1 { "" } else { "s" }, f = f),
             }
         }
     }

crates/ui-egui/src/lib.rs

@@ -21,6 +21,7 @@ pub mod render;
 pub mod shortcuts;
 pub mod softpaint;
 pub mod state;
+pub mod tasks;
 pub mod theme;
 pub mod widgets;
 
@@ -29,10 +30,16 @@ mod tests_curve;
 #[cfg(test)]
 mod tests_grid;
 #[cfg(test)]
+mod tests_library_problem;
+#[cfg(test)]
 mod tests_masking;
 #[cfg(test)]
+mod tests_offline;
+#[cfg(test)]
 mod tests_panels;
 #[cfg(test)]
+mod tests_quit_unsaved;
+#[cfg(test)]
 mod tests_scroll;
 #[cfg(test)]
 mod tests_unsaved;
@@ -60,6 +67,9 @@ pub type RevealFn = Box<dyn FnMut(&str) -> Result<(), String>>;
 pub type OpenUrlFn = Box<dyn FnMut(&str) -> Result<(), String>>;
 /// Open a file in an application (`app` = "" for the system's default one).
 pub type OpenWithFn = Box<dyn FnMut(&str, &str) -> Result<(), String>>;
+/// Something the host does with the session (web: back up or restore the library in browser
+/// storage); the work may finish asynchronously.
+pub type HostAction = Box<dyn FnMut(&mut Session) -> Result<Value, String>>;
 
 /// Platform services injected by the host app (desktop or web).
 #[derive(Default)]
@@ -89,6 +99,12 @@ pub struct Services {
     pub open_url: Option<OpenUrlFn>,
     /// Open a file in an external editor (Edit in External Editor; desktop only).
     pub open_with: Option<OpenWithFn>,
+    /// File ▸ Back Up Library…: save the whole library (catalog and originals) as one file the
+    /// user keeps (web only: there the library lives in browser storage, which the browser may
+    /// clear; on the desktop it is a folder backed up like any other).
+    pub backup_library: Option<HostAction>,
+    /// File ▸ Restore Library from Backup… (web only; keeps the current library).
+    pub restore_library: Option<HostAction>,
 }
 
 #[derive(Clone, Copy, Debug, Default)]
@@ -123,6 +139,12 @@ pub struct LightcraftApp {
     pub native_shortcuts: std::collections::HashSet<String>,
     /// The host is [`headless::Headless`] (it answers viewport screenshot commands itself).
     pub headless_host: bool,
+    /// Warnings to show one at a time (damaged settings files…, issue #103).
+    pub notices: Vec<String>,
+    /// Quitting was stopped because changes couldn't be saved: the prompt's text.
+    pub quit_prompt: Option<String>,
+    /// Quit Anyway was chosen: the window may close with unsaved changes.
+    pub quit_confirmed: bool,
     control_rx: Option<Receiver<ControlRequest>>,
     pending_screenshots: Vec<PendingShot>,
     screenshot_token: u64,
@@ -159,6 +181,8 @@ pub struct LightcraftApp {
     pub scan: Option<import::ScanTask>,
     /// A background export in progress.
     pub export: Option<export_task::ExportTask>,
+    /// Background file-system work of other commands (Find Missing Photos, auto import…).
+    pub tasks: tasks::Tasks,
     /// The files of the last finished background export (`ui.inspect` → `export.last`).
     pub last_export_result: Option<Value>,
     /// The look the loupe shows while the pointer rests on a preset or profile (set by the
@@ -170,6 +194,9 @@ pub struct LightcraftApp {
     gpu_applied: Option<bool>,
     /// The memory budget setting last applied (MB, 0 = automatic).
     memory_applied: Option<u32>,
+    /// The library failed to open at launch: the blocking window, then the temporary-session
+    /// banner (issue #100). Cleared once a library opens.
+    pub library_problem: Option<panels::library_problem::LibraryProblem>,
 }
 
 impl LightcraftApp {
@@ -187,6 +214,9 @@ impl LightcraftApp {
             native_menu: false,
             native_shortcuts: Default::default(),
             headless_host: false,
+            notices: vec![],
+            quit_prompt: None,
+            quit_confirmed: false,
             control_rx: None,
             pending_screenshots: vec![],
             screenshot_token: 0,
@@ -208,11 +238,13 @@ impl LightcraftApp {
             import: None,
             scan: None,
             export: None,
+            tasks: Default::default(),
             last_export_result: None,
             hover_preview: None,
             window_is_fullscreen: false,
             gpu_applied: None,
             memory_applied: None,
+            library_problem: None,
         }
     }
 
@@ -269,7 +301,12 @@ impl LightcraftApp {
             if self.ui.preview_build_seen != Some((key, true)) {
                 self.ui.preview_build_seen = Some((key, true));
                 let (done, failed) = (b.done.load(Ordering::Relaxed), b.failed.load(Ordering::Relaxed));
-                let mut msg = format!("Previews ready for {done} photo{}", if done == 1 { "" } else { "s" });
+                let plural = if done == 1 { "" } else { "s" };
+                let mut msg = match (b.error(), b.what) {
+                    (Some(e), what) => format!("{}: {e}", if what.is_empty() { "previews" } else { what }),
+                    (None, "") => format!("Previews ready for {done} photo{plural}"),
+                    (None, what) => format!("Done ({what}): {done} photo{plural}"),
+                };
                 if failed > 0 {
                     msg.push_str(&format!(" · {failed} couldn't be rendered"));
                 }
@@ -278,7 +315,11 @@ impl LightcraftApp {
         } else {
             if self.ui.preview_build_seen != Some((key, false)) {
                 self.ui.preview_build_seen = Some((key, false));
-                self.toast(ctx, format!("Building previews for {} photos…", b.total));
+                let msg = match b.what {
+                    "" => format!("Building previews for {} photos…", b.total),
+                    what => format!("Working on {what} for {} photos…", b.total),
+                };
+                self.toast(ctx, msg);
             }
             ctx.request_repaint_after(std::time::Duration::from_millis(250));
         }
@@ -439,7 +480,9 @@ impl LightcraftApp {
 
     /// Per-frame logic before layout (control channel, renders, shortcuts, drops).
     pub fn logic(&mut self, ctx: &egui::Context) {
+        i18n::set_language(self.ui.language);
         let t0 = now_ms();
+        panels::library_problem::logic(self);
         self.logic_inner(ctx);
         self.perf.logic_ms = now_ms() - t0;
     }
@@ -451,10 +494,19 @@ impl LightcraftApp {
             // File → Add from Device lists cards scanned in the background: show hot-plugs
             let repaint = ctx.clone();
             lightcraft_engine::devices::on_change(move || repaint.request_repaint());
+            // "is the original there?" (grid, Info panel, Missing Photos) answers from a cache a
+            // worker fills: a sleeping NAS or a dropped share never stalls a frame
+            let repaint = ctx.clone();
+            self.session.media.availability.run_in_background(std::sync::Arc::new(move || repaint.request_repaint()));
             self.styled = true;
         } else {
             self.fonts_ready = true;
         }
+        panels::notices::logic(self);
+        // closing the window (or Quit) with changes only in memory: retry, else ask first
+        if ctx.input(|i| i.viewport().close_requested()) && !panels::notices::may_close(self) {
+            ctx.send_viewport_cmd(egui::ViewportCommand::CancelClose);
+        }
         let now = ctx.input(|i| i.time);
         let dt = now - self.last_time;
         if dt > 0.0 {
@@ -470,6 +522,7 @@ impl LightcraftApp {
         merge::poll(self, ctx);
         import::poll_scan(self, ctx);
         import::tick(self, ctx);
+        tasks::poll(self, ctx);
         self.preview_build_status(ctx);
         self.save_status(ctx);
         self.slideshow_tick(ctx);
@@ -484,17 +537,33 @@ impl LightcraftApp {
             }
         }
         self.ui.was_focused = focused;
-        // auto import: scan the watched folder every few seconds
+        // auto import: list the watched folder every few seconds (on a worker thread: it may be on
+        // a network share), then import what's new like any import (also on a worker thread)
         #[cfg(not(target_arch = "wasm32"))]
-        if self.session.import_defaults.auto_folder.is_some() {
+        if let Some(folder) = self.session.import_defaults.auto_folder.clone() {
+            const LABEL: &str = "Auto Import";
             let now = ctx.input(|i| i.time);
-            if now - self.ui.auto_import_at >= 3.0 {
+            if now - self.ui.auto_import_at >= 3.0 && self.import.is_none() && !self.tasks.is_running(LABEL) {
                 self.ui.auto_import_at = now;
-                if let Ok(r) = self.session.execute("library.autoImportScan", &serde_json::json!({})) {
-                    let n = r["imported"].as_array().map_or(0, Vec::len);
-                    if n > 0 {
-                        self.toast(ctx, format!("Auto Import: added {n} photo{}", if n == 1 { "" } else { "s" }));
+                let work = move || lightcraft_engine::cmd::library::list_auto_import_folder(&folder);
+                let done = |app: &mut LightcraftApp, _ctx: &egui::Context, listing: Result<Vec<(String, u64)>, String>| {
+                    let listing = match listing {
+                        Ok(l) => l,
+                        Err(e) => return log::debug!("auto import: {e}"),
+                    };
+                    let p = serde_json::json!({"listing": listing, "start": false});
+                    let Ok(r) = app.session.execute("library.autoImportScan", &p) else { return };
+                    let Some(mut params) = r.get("import").cloned().filter(|_| app.import.is_none()) else { return };
+                    let paths: Vec<String> =
+                        params["paths"].as_array().into_iter().flatten().filter_map(|v| v.as_str().map(str::to_string)).collect();
+                    if let Some(o) = params.as_object_mut() {
+                        o.remove("paths");
                     }
+                    let undo0 = app.session.undo.len();
+                    app.import = Some(import::ImportTask::new(paths, params, undo0, false).auto());
+                };
+                if let Err(e) = tasks::spawn(self, LABEL, work, done) {
+                    log::warn!("{e}");
                 }
             }
             ctx.request_repaint_after(std::time::Duration::from_secs(3));
@@ -514,8 +583,11 @@ impl LightcraftApp {
             if !presets.is_empty() {
                 let _ = self.run("file.importPresets", serde_json::json!({"paths": presets}));
             }
-            if !photos.is_empty() {
-                let _ = self.run("library.import", serde_json::json!({"paths": photos}));
+            // read and added on a worker thread (dropped folders can be large, or on a slow drive)
+            if !photos.is_empty()
+                && let Err(e) = import::start_paths(self, photos)
+            {
+                self.toast(ctx, e);
             }
         }
     }
@@ -586,6 +658,7 @@ impl LightcraftApp {
 
     /// Lay out the whole window.
     pub fn ui(&mut self, ui: &mut egui::Ui) {
+        i18n::set_language(self.ui.language);
         let ctx = ui.ctx().clone();
         if !self.fonts_ready {
             ctx.request_repaint();
@@ -601,7 +674,9 @@ impl LightcraftApp {
             // full-screen preview: the photo alone on black
             egui::CentralPanel::default().frame(egui::Frame::NONE.fill(egui::Color32::BLACK)).show(ui, |ui| panels::detail::show(self, ui));
             panels::second::show(self, &ctx);
+            panels::notices::show(self, &ctx);
             panels::dialogs::show(self, &ctx);
+            panels::library_problem::show(self, &ctx);
             panels::toast(self, &ctx);
             self.widgets = widgets::take_registry(&ctx);
             self.end_frame(t0);
@@ -610,6 +685,7 @@ impl LightcraftApp {
         // Order matters: earlier panels take the full edge (top bar spans the window; the tool strip,
         // right panels and left panel run to the bottom; the bottom bar sits between them).
         panels::topbar::show(self, ui);
+        panels::library_problem::banner(self, ui);
         panels::strip::show(self, ui);
         if self.ui.right != state::RightPanel::None {
             panels::right::show(self, ui);
@@ -636,7 +712,9 @@ impl LightcraftApp {
             state::ViewMode::Reference => panels::compare::show_reference(self, ui),
         });
         panels::second::show(self, &ctx);
+        panels::notices::show(self, &ctx);
         panels::dialogs::show(self, &ctx);
+        panels::library_problem::show(self, &ctx);
         import::progress(self, &ctx);
         import::scan_progress(self, &ctx);
         export_task::poll(self, &ctx);

crates/ui-egui/src/menubar.rs

@@ -43,6 +43,15 @@ impl MenuNode {
     }
 }
 
+/// User-defined names in parameterized menus are data, not message keys.
+pub fn display_item_label<'a>(id: &str, params: &Value, label: &'a str) -> &'a str {
+    if matches!(id, "metadata.applyPreset" | "album.addPhotos" | "label.applySet") || (id == "app.export" && params.get("preset").is_some()) {
+        label
+    } else {
+        crate::i18n::tr(label)
+    }
+}
+
 /// Top-level menus in order (the macOS app menu is added by the host).
 pub const MENUS: &[&str] = &["File", "Edit", "View", "Photo", "Window", "Help"];
 
@@ -58,6 +67,8 @@ const LAYOUT: &[(&str, &[&str])] = &[
             "@Import from Device",
             "---",
             "app.openLibrary",
+            "file.backupLibrary",
+            "file.restoreLibrary",
             "---",
             "dialog.newAlbum",
             "dialog.newFolder",
@@ -241,6 +252,15 @@ const HIDDEN: &[&str] = &[
     "preset.create",
 ];
 
+/// Items only some hosts have are left out of the others' menus (the web build's library backup).
+fn host_supports(app: &LightcraftApp, id: &str) -> bool {
+    match id {
+        "file.backupLibrary" => app.services.backup_library.is_some(),
+        "file.restoreLibrary" => app.services.restore_library.is_some(),
+        _ => true,
+    }
+}
+
 fn item(id: &str, params: Value, label: impl Into<String>, shortcut: Option<&str>, enabled: bool, checked: Option<bool>) -> MenuNode {
     MenuNode::Item { id: id.into(), params, label: label.into(), shortcut: shortcut.map(str::to_string), enabled, checked }
 }
@@ -296,11 +316,15 @@ pub fn checked(app: &LightcraftApp, id: &str) -> Option<bool> {
 fn live_label(app: &LightcraftApp, id: &str, label: &str) -> String {
     let n = app.session.selection.ids.len();
     match id {
-        "edit.undo" => app.session.undo.last().map(|e| format!("Undo {}", e.label)).unwrap_or_else(|| "Undo".into()),
-        "edit.redo" => app.session.redo.last().map(|e| format!("Redo {}", e.label)).unwrap_or_else(|| "Redo".into()),
-        "photo.delete" if n > 1 => format!("Delete {n} Photos"),
-        "photo.virtualCopy" if n > 1 => format!("Create {n} Virtual Copies"),
-        "dialog.rename" if n > 1 => format!("Rename {n} Photos…"),
+        "edit.undo" => {
+            app.session.undo.last().map(|e| crate::i18n::tr_format!("Undo {}", crate::i18n::tr(&e.label))).unwrap_or_else(|| "Undo".into())
+        }
+        "edit.redo" => {
+            app.session.redo.last().map(|e| crate::i18n::tr_format!("Redo {}", crate::i18n::tr(&e.label))).unwrap_or_else(|| "Redo".into())
+        }
+        "photo.delete" if n > 1 => crate::i18n::tr_format!("Delete {n} Photos", n = n),
+        "photo.virtualCopy" if n > 1 => crate::i18n::tr_format!("Create {n} Virtual Copies", n = n),
+        "dialog.rename" if n > 1 => crate::i18n::tr_format!("Rename {n} Photos…", n = n),
         _ => label.to_string(),
     }
 }
@@ -325,20 +349,21 @@ fn expanded(app: &LightcraftApp, name: &str) -> Option<Vec<MenuNode>> {
                 item("library.buildPreviews", json!({"size": "full"}), format!("Build 1:1 Previews ({scope})"), None, !running, None),
                 item("library.cancelPreviews", Value::Null, "Stop Building Previews", None, running, None),
                 MenuNode::Separator,
+                // (read and written on a worker thread: the originals may be on a slow drive)
                 item(
                     "library.smartPreviews",
-                    Value::Null,
+                    json!({"background": true}),
                     format!("Build Smart Previews ({scope})"),
                     None,
-                    app.session.media.smart_dir.is_some(),
+                    app.session.media.smart_dir.is_some() && !running,
                     None,
                 ),
                 item(
                     "library.smartPreviews",
-                    json!({"discard": true}),
+                    json!({"discard": true, "background": true}),
                     format!("Discard Smart Previews ({scope})"),
                     None,
-                    app.session.media.smart_dir.is_some(),
+                    app.session.media.smart_dir.is_some() && !running,
                     None,
                 ),
                 MenuNode::Separator,
@@ -464,14 +489,21 @@ fn expanded(app: &LightcraftApp, name: &str) -> Option<Vec<MenuNode>> {
                 .map(|(f, label)| item("library.selectBy", json!({"flag": f}), label, None, true, None))
                 .collect();
             v.push(MenuNode::Separator);
-            v.extend(
-                (1..=5u8).map(|r| item("library.selectBy", json!({"rating": r}), format!("{} and higher", "★".repeat(r as usize)), None, true, None)),
-            );
+            v.extend((1..=5u8).map(|r| {
+                item("library.selectBy", json!({"rating": r}), crate::i18n::tr_format!("{} and higher", "★".repeat(r as usize)), None, true, None)
+            }));
             v.push(item("library.selectBy", json!({"rating": 0, "ratingOp": "eq"}), "Unrated", None, true, None));
             v.push(MenuNode::Separator);
             v.extend(lightcraft_catalog::ColorLabel::ALL.iter().map(|l| {
                 let name = format!("{l:?}");
-                item("library.selectBy", json!({"label": name.to_lowercase()}), format!("{name} Label"), None, true, None)
+                item(
+                    "library.selectBy",
+                    json!({"label": name.to_lowercase()}),
+                    crate::i18n::tr_format!("{name} Label", name = name),
+                    None,
+                    true,
+                    None,
+                )
             }));
             v
         }
@@ -537,7 +569,8 @@ fn tidy(v: Vec<MenuNode>) -> Vec<MenuNode> {
 
 /// The whole menu bar: (title, items) per menu in [`MENUS`] order.
 pub fn menu_bar(app: &LightcraftApp) -> Vec<(String, Vec<MenuNode>)> {
-    let entries: Vec<MenuEntry> = crate::menus::menu_entries(app).into_iter().filter(|e| !HIDDEN.contains(&e.id.as_str())).collect();
+    let entries: Vec<MenuEntry> =
+        crate::menus::menu_entries(app).into_iter().filter(|e| !HIDDEN.contains(&e.id.as_str()) && host_supports(app, &e.id)).collect();
     let mut used = vec![false; entries.len()];
     let mut bar = Vec::new();
     for title in MENUS {
@@ -595,22 +628,6 @@ pub fn menu_bar(app: &LightcraftApp) -> Vec<(String, Vec<MenuNode>)> {
         }
         bar.push((title.to_string(), tidy(items)));
     }
-    fn translate(nodes: &mut [MenuNode], language: crate::i18n::Language) {
-        for node in nodes {
-            match node {
-                MenuNode::Submenu { label, children } => {
-                    *label = language.tr(label).to_string();
-                    translate(children, language);
-                }
-                MenuNode::Item { label, .. } => *label = language.tr(label).to_string(),
-                MenuNode::Separator => {}
-            }
-        }
-    }
-    for (title, nodes) in &mut bar {
-        *title = app.ui.language.tr(title).to_string();
-        translate(nodes, app.ui.language);
-    }
     bar
 }
 
@@ -664,9 +681,9 @@ pub fn shortcut_text(sc: &str, mac: bool) -> String {
 const TITLE_GAP: f32 = 24.0;
 
 /// Width of the in-window menu bar's titles.
-pub fn bar_width(ui: &egui::Ui, language: crate::i18n::Language) -> f32 {
+pub fn bar_width(ui: &egui::Ui) -> f32 {
     let t = crate::theme::Tokens::get(ui.ctx());
-    MENUS.iter().map(|m| ui.painter().layout_no_wrap(language.tr(m).to_string(), t.font(13.0), t.text).size().x + TITLE_GAP).sum::<f32>()
+    MENUS.iter().map(|m| ui.painter().layout_no_wrap(crate::i18n::tr(m).to_string(), t.font(13.0), t.text).size().x + TITLE_GAP).sum::<f32>()
 }
 
 /// The in-window menu bar (hosts without a native one): one dropdown per menu, or a single
@@ -675,8 +692,10 @@ pub fn show_in_window(app: &mut LightcraftApp, ui: &mut egui::Ui, max_width: f32
     let t = crate::theme::Tokens::get(ui.ctx());
     let bar = menu_bar(app);
     let font = t.font(13.0);
-    let widths: Vec<f32> =
-        bar.iter().map(|(title, _)| ui.painter().layout_no_wrap(title.clone(), font.clone(), t.text).size().x + TITLE_GAP).collect();
+    let widths: Vec<f32> = bar
+        .iter()
+        .map(|(title, _)| ui.painter().layout_no_wrap(crate::i18n::tr(title).to_string(), font.clone(), t.text).size().x + TITLE_GAP)
+        .collect();
     let total: f32 = widths.iter().sum();
     let mut clicked: Option<(String, Value)> = None;
     let start = ui.cursor().left();
@@ -684,18 +703,18 @@ pub fn show_in_window(app: &mut LightcraftApp, ui: &mut egui::Ui, max_width: f32
     if total <= max_width {
         let saved = ui.spacing().item_spacing.x;
         ui.spacing_mut().item_spacing.x = TITLE_GAP;
-        for (index, (title, items)) in bar.iter().enumerate() {
-            let r = ui.add(egui::Button::new(egui::RichText::new(title).font(font.clone()).color(t.text_label)).frame(false));
-            crate::widgets::register(ui.ctx(), format!("menu:{}", MENUS.get(index).copied().unwrap_or(title.as_str())), r.rect);
+        for (title, items) in &bar {
+            let r = ui.add(egui::Button::new(egui::RichText::new(crate::i18n::tr(title)).font(font.clone()).color(t.text_label)).frame(false));
+            crate::widgets::register(ui.ctx(), format!("menu:{title}"), r.rect);
             egui::Popup::menu(&r).show(|ui| nodes_ui(ui, items, mac, &mut clicked));
         }
         ui.spacing_mut().item_spacing.x = saved;
     } else {
-        let r = ui.add(egui::Button::new(egui::RichText::new(app.ui.language.tr("Menu")).font(font.clone()).color(t.text_label)).frame(false));
+        let r = ui.add(egui::Button::new(egui::RichText::new(crate::i18n::tr("Menu")).font(font.clone()).color(t.text_label)).frame(false));
         crate::widgets::register(ui.ctx(), "menu:all", r.rect);
         egui::Popup::menu(&r).show(|ui| {
             for (title, items) in &bar {
-                ui.menu_button(title, |ui| nodes_ui(ui, items, mac, &mut clicked));
+                ui.menu_button(crate::i18n::tr(title), |ui| nodes_ui(ui, items, mac, &mut clicked));
             }
         });
     }
@@ -713,11 +732,11 @@ fn nodes_ui(ui: &mut egui::Ui, nodes: &[MenuNode], mac: bool, clicked: &mut Opti
                 ui.separator();
             }
             MenuNode::Submenu { label, children } => {
-                ui.menu_button(format!("      {label}"), |ui| nodes_ui(ui, children, mac, clicked));
+                ui.menu_button(format!("      {}", crate::i18n::tr(label)), |ui| nodes_ui(ui, children, mac, clicked));
             }
             MenuNode::Item { id, params, label, shortcut, enabled, checked } => {
                 // a gutter for check marks, like native menus
-                let mut b = egui::Button::new(format!("      {label}"));
+                let mut b = egui::Button::new(format!("      {}", display_item_label(id, params, label)));
                 if let Some(sc) = shortcut {
                     b = b.shortcut_text(shortcut_text(sc, mac));
                 }
@@ -774,6 +793,34 @@ mod tests {
         assert!(!text.contains("Add Folder") && !text.contains("\"Add Photos"), "no add-folder wording left in the menus");
     }
 
+    /// Back Up / Restore Library are the browser build's (its library lives in browser storage):
+    /// absent from the desktop's menus, present and wired to the host where it provides them.
+    #[test]
+    fn library_backup_items_follow_the_host() {
+        let all = |app: &LightcraftApp| -> Vec<MenuNode> { menu_bar(app).into_iter().flat_map(|(_, v)| v).collect() };
+        let mut desktop = app();
+        assert!(find(&all(&desktop), "file.backupLibrary").is_none() && find(&all(&desktop), "file.restoreLibrary").is_none());
+        assert!(run_item(&mut desktop, "file.backupLibrary", Value::Null).is_err(), "not available without the host");
+        let calls = std::rc::Rc::new(std::cell::Cell::new(0));
+        let c = calls.clone();
+        let services = crate::Services {
+            backup_library: Some(Box::new(move |s: &mut lightcraft_engine::Session| {
+                c.set(c.get() + 1);
+                Ok(json!({"photos": s.catalog.len()}))
+            })),
+            restore_library: Some(Box::new(|_: &mut lightcraft_engine::Session| Ok(json!({"started": true})))),
+            ..Default::default()
+        };
+        let mut web = LightcraftApp::new(lightcraft_engine::Session::with_demo(), services);
+        let bar = all(&web);
+        for id in ["file.backupLibrary", "file.restoreLibrary"] {
+            assert!(matches!(find(&bar, id), Some(MenuNode::Item { enabled: true, .. })), "{id}");
+        }
+        let r = run_item(&mut web, "file.backupLibrary", Value::Null).unwrap();
+        assert!(r["photos"].as_u64().unwrap() > 0);
+        assert_eq!(calls.get(), 1);
+    }
+
     #[test]
     fn bar_follows_the_registry_and_state() {
         let mut app = app();
@@ -936,7 +983,7 @@ mod tests {
         let mut app = LightcraftApp::new(lightcraft_engine::Session::new().with_fs(), Default::default());
         app.session.execute("library.import", &json!({"paths": [dir.join("a").to_string_lossy()]})).unwrap();
         std::fs::rename(dir.join("a/one.png"), dir.join("b/one.png")).unwrap();
-        let r = run_item(&mut app, "file.findMissing", json!({"folder": dir.join("b").to_string_lossy()})).unwrap();
+        let r = run_item(&mut app, "file.findMissing", json!({"folder": dir.join("b").to_string_lossy(), "wait": true})).unwrap();
         assert_eq!(r["found"].as_array().map(Vec::len), Some(1), "{r}");
         // Locate: an explicit file
         std::fs::rename(dir.join("b/one.png"), dir.join("one-renamed.png")).unwrap();

crates/ui-egui/src/menus.rs

@@ -116,6 +116,8 @@ pub const UI_COMMANDS: &[UiCommand] = &[
     ("file.addFolder", "Import from Folder…", None, "File"),
     ("file.addFromDevice", "Import from Device", None, ""),
     ("file.findMissing", "Find Missing Photos…", None, "File"),
+    ("file.backupLibrary", "Back Up Library…", None, "File"),
+    ("file.restoreLibrary", "Restore Library from Backup…", None, "File"),
     ("photo.locate", "Locate Missing File…", None, ""),
     ("dialog.saveMetadataPreset", "Save Metadata Preset…", None, ""),
     ("app.quit", "Quit LightCraft", Some("Cmd+Q"), "File"),
@@ -149,10 +151,10 @@ pub const UI_COMMANDS: &[UiCommand] = &[
 fn panel(app: &mut LightcraftApp, ctx: &egui::Context, p: RightPanel, name: &str) {
     if app.ui.right == p {
         app.ui.right = RightPanel::None;
-        app.toast(ctx, format!("{name} Off"));
+        app.toast(ctx, crate::i18n::tr_format!("{name} Off", name = name));
     } else {
         app.ui.right = p;
-        app.toast(ctx, format!("{name} On"));
+        app.toast(ctx, crate::i18n::tr_format!("{name} On", name = name));
         if p.is_edit_tool() && !matches!(app.ui.view, ViewMode::Detail) {
             app.ui.view = ViewMode::Detail;
         }
@@ -381,6 +383,13 @@ pub fn run_ui_command(app: &mut LightcraftApp, id: &str, p: &Value) -> Option<Re
             Ok(Value::Null)
         }
         "app.openLibrary" => crate::panels::settings::open_library(app, p),
+        "file.backupLibrary" | "file.restoreLibrary" => {
+            let action = if id == "file.backupLibrary" { app.services.backup_library.as_mut() } else { app.services.restore_library.as_mut() };
+            match action {
+                Some(f) => f(&mut app.session),
+                None => Err("not available here: on the desktop the library is a folder; back it up with your other files".into()),
+            }
+        }
         "view.filmstrip" => {
             app.ui.filmstrip = !app.ui.filmstrip;
             Ok(Value::Null)
@@ -865,7 +874,7 @@ pub fn run_ui_command(app: &mut LightcraftApp, id: &str, p: &Value) -> Option<Re
                 (
                     "GPU".to_string(),
                     gpu.unwrap_or_else(|| match lightcraft_engine::gpu::unavailable_reason() {
-                        Some(why) => format!("none (CPU rendering): {why}"),
+                        Some(why) => crate::i18n::tr_format!("none (CPU rendering): {why}", why = why),
                         None => "none (CPU rendering)".into(),
                     }),
                 ),
@@ -928,13 +937,40 @@ pub fn run_ui_command(app: &mut LightcraftApp, id: &str, p: &Value) -> Option<Re
                 None => app.services.pick_folder.as_mut().and_then(|f| f()),
             };
             let Some(folder) = folder else { return Some(Ok(Value::Null)) };
-            let r = app.run("library.findMissing", json!({"folder": folder}));
-            if let Ok(v) = &r {
-                let n = v["found"].as_array().map_or(0, Vec::len);
-                let left = v["missing"].as_u64().unwrap_or(0);
-                app.toast(&egui::Context::default(), format!("Found {n} missing photo{}; {left} still missing", if n == 1 { "" } else { "s" }));
+            // the search (checking every photo's file, walking the folder) runs on a worker thread;
+            // the relinking happens back here, as one undo step
+            const LABEL: &str = "Find Missing Photos";
+            if app.tasks.is_running(LABEL) {
+                return Some(Err("Find Missing Photos is already searching".into()));
             }
-            r
+            let candidates = lightcraft_engine::cmd::missing::find_candidates(&app.session.catalog);
+            let work = move || lightcraft_engine::cmd::missing::plan_find_missing(&candidates, &folder);
+            let done = |app: &mut LightcraftApp, ctx: &egui::Context, plan: Result<lightcraft_engine::cmd::missing::FindPlan, String>| {
+                // relinked under the session as it is now: photos relinked meanwhile and files
+                // now in use are skipped
+                let r = plan.and_then(|plan| app.run("library.findMissing", plan.to_json()));
+                match r {
+                    Ok(v) => {
+                        let n = v["found"].as_array().map_or(0, Vec::len);
+                        let left = v["missing"].as_u64().unwrap_or(0);
+                        let unsure = v["ambiguous"].as_array().map_or(0, Vec::len);
+                        let unsure = if unsure > 0 { format!(" ({unsure} with several look-alike files: use Locate)") } else { String::new() };
+                        app.toast(ctx, format!("Found {n} missing photo{}; {left} still missing{unsure}", if n == 1 { "" } else { "s" }));
+                        app.ui.last_find_missing = Some(v);
+                    }
+                    Err(e) => app.toast(ctx, e),
+                }
+            };
+            app.ui.last_find_missing = None;
+            if let Err(e) = crate::tasks::spawn(app, LABEL, work, done) {
+                return Some(Err(e));
+            }
+            if p.get("wait").and_then(Value::as_bool).unwrap_or(false) {
+                let ctx = app.tasks.repaint.clone().unwrap_or_default();
+                crate::tasks::wait(app, &ctx, std::time::Duration::from_secs(600));
+                return Some(Ok(app.ui.last_find_missing.clone().unwrap_or(Value::Null)));
+            }
+            Ok(json!({"background": true}))
         }
         "photo.tagFromTracklog" => {
             // a GPX file → GPS for the selected photos by capture time (one undo step)
@@ -1059,8 +1095,14 @@ pub fn run_ui_command(app: &mut LightcraftApp, id: &str, p: &Value) -> Option<Re
                 let failed = v["failed"].as_array().map_or(0, Vec::len);
                 let mut msg = match (n, failed) {
                     (0, 0) => "No new presets".to_string(),
-                    (n, 0) => format!("Imported {n} preset{}", if n == 1 { "" } else { "s" }),
-                    (n, f) => format!("Imported {n} preset{}, {f} file{} not readable", if n == 1 { "" } else { "s" }, if f == 1 { "" } else { "s" }),
+                    (n, 0) => crate::i18n::tr_format!("Imported {n} preset{}", if n == 1 { "" } else { "s" }, n = n),
+                    (n, f) => crate::i18n::tr_format!(
+                        "Imported {n} preset{}, {f} file{} not readable",
+                        if n == 1 { "" } else { "s" },
+                        if f == 1 { "" } else { "s" },
+                        f = f,
+                        n = n
+                    ),
                 };
                 // settings with no counterpart here (the other editor's profiles, masks…)
                 let mut skipped: Vec<&str> = v["imported"]
@@ -1105,7 +1147,7 @@ pub fn run_ui_command(app: &mut LightcraftApp, id: &str, p: &Value) -> Option<Re
             }
             let r = app.session.execute("preset.export", &params).map_err(|e| e.to_string());
             if let Ok(v) = &r {
-                app.toast(&ctx, format!("Exported {} preset{}", v["count"], if v["count"] == 1 { "" } else { "s" }));
+                app.toast(&ctx, crate::i18n::tr_format!("Exported {} preset{}", v["count"], if v["count"] == 1 { "" } else { "s" }));
             }
             return Some(r);
         }
@@ -1124,9 +1166,9 @@ pub fn run_ui_command(app: &mut LightcraftApp, id: &str, p: &Value) -> Option<Re
             if let Ok(v) = &r {
                 let n = v["imported"].as_array().map_or(0, Vec::len);
                 let failed = v["failed"].as_array().map_or(0, Vec::len);
-                let mut msg = format!("Imported {n} point curve preset{}", if n == 1 { "" } else { "s" });
+                let mut msg = crate::i18n::tr_format!("Imported {n} point curve preset{}", if n == 1 { "" } else { "s" }, n = n);
                 if failed > 0 {
-                    msg += &format!(", {failed} file{} not readable", if failed == 1 { "" } else { "s" });
+                    msg += &crate::i18n::tr_format!(", {failed} file{} not readable", if failed == 1 { "" } else { "s" }, failed = failed);
                 }
                 app.toast(&ctx, msg);
             }
@@ -1147,7 +1189,7 @@ pub fn run_ui_command(app: &mut LightcraftApp, id: &str, p: &Value) -> Option<Re
             }
             let r = app.session.execute("curve.exportPresets", &params).map_err(|e| e.to_string());
             if let Ok(v) = &r {
-                app.toast(&ctx, format!("Exported {} point curve preset{}", v["count"], if v["count"] == 1 { "" } else { "s" }));
+                app.toast(&ctx, crate::i18n::tr_format!("Exported {} point curve preset{}", v["count"], if v["count"] == 1 { "" } else { "s" }));
             }
             return Some(r);
         }
@@ -1188,6 +1230,8 @@ pub fn ui_enabled(app: &LightcraftApp, id: &str) -> bool {
         "view.compare" => app.session.catalog.len() > 1,
         "view.fullScreenPreview" | "view.infoOverlay" | "view.navigator" => app.session.active().is_some() || app.ui.fullscreen,
         "app.openLibrary" | "file.addFolder" => app.services.pick_folder.is_some(),
+        "file.backupLibrary" => app.services.backup_library.is_some(),
+        "file.restoreLibrary" => app.services.restore_library.is_some(),
         "compare.swap" | "compare.makeSelect" => app.ui.view == ViewMode::Compare,
         s if s.starts_with("dialog.merge") || (s.starts_with("merge.") && s.ends_with("Last")) => {
             app.session.targets(&serde_json::json!({})).len() >= 2 && app.merge.final_task.is_none()

crates/ui-egui/src/merge.rs

@@ -257,18 +257,18 @@ pub fn poll(app: &mut LightcraftApp, ctx: &egui::Context) {
                 match r.map_err(lightcraft_engine::EngineError::Other).and_then(|out| app.session.finish_merge(&t.job, out)) {
                     Ok(v) => {
                         app.merge.last_result = Some(v);
-                        app.toast(ctx, format!("{what} merge added"));
+                        app.toast(ctx, crate::i18n::tr_format!("{what} merge added", what = what));
                     }
                     Err(e) => {
                         app.ui.status = e.to_string();
-                        app.toast(ctx, format!("{what} merge failed: {e}"));
+                        app.toast(ctx, crate::i18n::tr_format!("{what} merge failed: {e}", e = e, what = what));
                     }
                 }
             }
             Err(_) => {
                 let (f, stage) = t.progress.lock().map(|g| g.clone()).unwrap_or_default();
                 let now = ctx.input(|i| i.time);
-                app.ui.toast = Some((format!("Merging… {stage} {:.0}%", f * 100.0), now + 0.5));
+                app.ui.toast = Some((crate::i18n::tr_format!("Merging… {stage} {:.0}%", f * 100.0, stage = stage), now + 0.5));
                 ctx.request_repaint_after(std::time::Duration::from_millis(100));
             }
         }
@@ -299,7 +299,7 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, opts: &mut MergeDialog)
                 ui.painter().text(
                     rect.center_bottom() - egui::vec2(0.0, 14.0),
                     egui::Align2::CENTER_CENTER,
-                    format!("{stage}… {:.0}%", f * 100.0),
+                    crate::i18n::tr_format!("{stage}… {:.0}%", f * 100.0, stage = stage),
                     t.font(12.0),
                     t.text,
                 );
@@ -330,7 +330,7 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, opts: &mut MergeDialog)
         ui.vertical(|ui| {
             ui.set_width(220.0);
             if opts.is_pano() {
-                ui.label(egui::RichText::new("Projection").color(t.text_label));
+                ui.label(egui::RichText::new(crate::i18n::tr("Projection")).color(t.text_label));
                 for (v, l) in [("auto", "Auto Select"), ("spherical", "Spherical"), ("cylindrical", "Cylindrical"), ("perspective", "Perspective")] {
                     if ui.radio(opts.projection == v, l).clicked() {
                         opts.projection = v.to_string();
@@ -341,13 +341,13 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, opts: &mut MergeDialog)
                 if num(ui, &BOUNDARY_WARP, &mut bw) {
                     opts.boundary_warp = bw.round();
                 }
-                ui.checkbox(&mut opts.fill_edges, "Fill Edges");
-                ui.checkbox(&mut opts.auto_crop, "Auto Crop");
+                ui.checkbox(&mut opts.fill_edges, crate::i18n::tr("Fill Edges"));
+                ui.checkbox(&mut opts.auto_crop, crate::i18n::tr("Auto Crop"));
                 ui.add_space(4.0);
             }
             if opts.is_hdr() {
-                ui.checkbox(&mut opts.align, "Auto Align");
-                ui.label(egui::RichText::new("Deghost Amount").color(t.text_label));
+                ui.checkbox(&mut opts.align, crate::i18n::tr("Auto Align"));
+                ui.label(egui::RichText::new(crate::i18n::tr("Deghost Amount")).color(t.text_label));
                 ui.horizontal(|ui| {
                     for (i, (v, l)) in [("none", "None"), ("low", "Low"), ("medium", "Med"), ("high", "High")].iter().enumerate() {
                         if crate::widgets::text_button(ui, &format!("mergeDeghost-{i}"), l, opts.deghost == *v).clicked() {
@@ -356,7 +356,7 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, opts: &mut MergeDialog)
                     }
                 });
                 if opts.command == "merge.hdr" {
-                    ui.add_enabled_ui(opts.deghost != "none", |ui| ui.checkbox(&mut opts.show_overlay, "Show Deghost Overlay"));
+                    ui.add_enabled_ui(opts.deghost != "none", |ui| ui.checkbox(&mut opts.show_overlay, crate::i18n::tr("Show Deghost Overlay")));
                 }
                 if opts.command == "merge.hdrPanorama" {
                     let mut b = opts.bracket as f64;
@@ -366,10 +366,10 @@ pub fn body(app: &mut LightcraftApp, ui: &mut egui::Ui, opts: &mut MergeDialog)
                 }
                 ui.add_space(4.0);
             }
-            ui.checkbox(&mut opts.auto_settings, "Auto Settings");
-            ui.checkbox(&mut opts.stack, "Create Stack");
+            ui.checkbox(&mut opts.auto_settings, crate::i18n::tr("Auto Settings"));
+            ui.checkbox(&mut opts.stack, crate::i18n::tr("Create Stack"));
             ui.add_space(8.0);
-            ui.label(egui::RichText::new(format!("{} photos", app.merge.ids.len())).color(t.text_dim));
+            ui.label(egui::RichText::new(crate::i18n::tr_format!("{} photos", app.merge.ids.len())).color(t.text_dim));
         });
     });
 }

crates/ui-egui/src/panels/bottombar.rs

@@ -104,7 +104,13 @@ fn centre(app: &mut LightcraftApp, ui: &mut egui::Ui, full: Rect, from: f32, to:
     let cresp = ui.interact(copy_r, egui::Id::new("copy-settings"), Sense::click());
     register(ui.ctx(), "button:copySettings", copy_r);
     ui.painter().rect_filled(copy_r, 15.0, if cresp.hovered() { t.hover } else { t.canvas });
-    ui.painter().text(copy_r.center(), Align2::CENTER_CENTER, label, t.font(13.0), if active.is_some() { t.text_label } else { t.text_disabled });
+    ui.painter().text(
+        copy_r.center(),
+        Align2::CENTER_CENTER,
+        crate::i18n::tr(label),
+        t.font(13.0),
+        if active.is_some() { t.text_label } else { t.text_disabled },
+    );
     if cresp.clicked() && active.is_some() {
         let _ = if has_clip { app.run("develop.paste", json!({})) } else { app.run("develop.copy", json!({})) };
         let msg = if has_clip { "Settings pasted" } else { "Edit settings copied" };
@@ -168,7 +174,7 @@ fn right_side(app: &mut LightcraftApp, ui: &mut egui::Ui, full: Rect) -> f32 {
             Zoom::Fill => "Fill".to_string(),
             Zoom::Percent(p) => format!("{p}%"),
         };
-        let zr = crate::widgets::dropdown(&mut child, "zoom", &zoom_label, t.font(13.0), t.text_label);
+        let zr = crate::widgets::dropdown(&mut child, "zoom", crate::i18n::tr(&zoom_label), t.font(13.0), t.text_label);
         egui::Popup::menu(&zr).show(|ui| {
             for (label, z) in [
                 ("Fit", Zoom::Fit),
@@ -185,7 +191,13 @@ fn right_side(app: &mut LightcraftApp, ui: &mut egui::Ui, full: Rect) -> f32 {
             }
         });
         child.add_space(6.0);
-        let cz = crate::widgets::dropdown(&mut child, "clickZoom", &format!("Click {}:1", app.ui.click_zoom / 100), t.font(13.0), t.text_label);
+        let cz = crate::widgets::dropdown(
+            &mut child,
+            "clickZoom",
+            &crate::i18n::tr_format!("Click {}:1", app.ui.click_zoom / 100),
+            t.font(13.0),
+            t.text_label,
+        );
         egui::Popup::menu(&cz).show(|ui| {
             for pct in crate::state::CLICK_ZOOMS {
                 if ui.selectable_label(app.ui.click_zoom == pct, format!("{}:1", pct / 100)).clicked() {
@@ -216,7 +228,7 @@ fn sort_menu(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     use lightcraft_catalog::GroupBy;
     use lightcraft_catalog::SortKey::*;
     let cur = app.session.sort;
-    ui.label(egui::RichText::new("Sort by").weak());
+    ui.label(egui::RichText::new(crate::i18n::tr("Sort by")).weak());
     for (label, key, k) in [
         ("Capture Date", CaptureDate, "captureDate"),
         ("Import Date", ImportDate, "importDate"),
@@ -225,19 +237,19 @@ fn sort_menu(app: &mut LightcraftApp, ui: &mut egui::Ui) {
         ("Rating", Rating, "rating"),
         ("File Size", FileSize, "fileSize"),
     ] {
-        if ui.selectable_label(cur.key == key, label).clicked() {
+        if ui.selectable_label(cur.key == key, crate::i18n::tr(label)).clicked() {
             let _ = app.run("library.sort", json!({"key": k}));
         }
     }
     ui.separator();
-    if ui.selectable_label(cur.ascending, "Ascending").clicked() {
+    if ui.selectable_label(cur.ascending, crate::i18n::tr("Ascending")).clicked() {
         let _ = app.run("library.sort", json!({"ascending": true}));
     }
-    if ui.selectable_label(!cur.ascending, "Descending").clicked() {
+    if ui.selectable_label(!cur.ascending, crate::i18n::tr("Descending")).clicked() {
         let _ = app.run("library.sort", json!({"ascending": false}));
     }
     ui.separator();
-    ui.label(egui::RichText::new("Group by date").weak());
+    ui.label(egui::RichText::new(crate::i18n::tr("Group by date")).weak());
     for (label, g, k) in [
         ("Automatic", GroupBy::Auto, "auto"),
         ("Day", GroupBy::Day, "day"),
@@ -245,7 +257,7 @@ fn sort_menu(app: &mut LightcraftApp, ui: &mut egui::Ui) {
         ("Year", GroupBy::Year, "year"),
         ("None", GroupBy::None, "none"),
     ] {
-        if ui.selectable_label(cur.group == g, label).clicked() {
+        if ui.selectable_label(cur.group == g, crate::i18n::tr(label)).clicked() {
             let _ = app.run("library.sort", json!({"group": k}));
         }
     }

crates/ui-egui/src/panels/chips.rs

@@ -18,8 +18,8 @@ const TAIL: f32 = 170.0;
 /// "14 of 120 photos" when a filter narrows the source, else "14 photos".
 pub fn count_text(matching: usize, total: Option<usize>, filtering: bool) -> String {
     match total {
-        Some(t) if filtering && t != matching => format!("{matching} of {t} photos"),
-        _ => format!("{matching} photos"),
+        Some(t) if filtering && t != matching => crate::i18n::tr_format!("{matching} of {t} photos", matching = matching, t = t),
+        _ => crate::i18n::tr_format!("{matching} photos", matching = matching),
     }
 }
 
@@ -53,7 +53,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, chips: &[FilterChip]) {
         let text_r = Rect::from_min_max(r.min, pos2(r.right() - 22.0, r.max.y));
         ui.painter().with_clip_rect(text_r).text(pos2(r.left() + 10.0, r.center().y), egui::Align2::LEFT_CENTER, &c.label, font.clone(), t.text);
         let xr = Rect::from_center_size(pos2(r.right() - 12.0, r.center().y), vec2(18.0, 18.0));
-        let resp = ui.interact(xr, egui::Id::new(("filter-chip-x", i)), Sense::click()).on_hover_text("Remove this filter");
+        let resp = ui.interact(xr, egui::Id::new(("filter-chip-x", i)), Sense::click()).on_hover_text(crate::i18n::tr("Remove this filter"));
         register(ui.ctx(), format!("chip:{i}"), xr);
         let col = if resp.hovered() { t.text } else { t.text_dim };
         let m = 3.5;
@@ -80,7 +80,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, chips: &[FilterChip]) {
         let more = crate::widgets::text_button(&mut child, "chipsMore", &format!("+{} more", hidden.len()), false);
         egui::Popup::menu(&more).show(|ui| {
             for c in hidden {
-                if ui.button(format!("{}  ✕", c.label)).on_hover_text("Remove this filter").clicked() {
+                if ui.button(format!("{}  ✕", c.label)).on_hover_text(crate::i18n::tr("Remove this filter")).clicked() {
                     let _ = app.run("library.filter", c.clear.clone());
                     if c.clear.get("text").is_some() {
                         app.ui.search.clear();
@@ -89,7 +89,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, chips: &[FilterChip]) {
             }
         });
     }
-    if crate::widgets::text_button(&mut child, "chipsClearAll", "Clear all", false).clicked() {
+    if crate::widgets::text_button(&mut child, "chipsClearAll", crate::i18n::tr("Clear all"), false).clicked() {
         app.ui.search.clear();
         let _ = app.run("library.clearFilter", json!({}));
     }

crates/ui-egui/src/panels/compare.rs

@@ -263,10 +263,10 @@ pub fn show_compare(app: &mut LightcraftApp, ui: &mut egui::Ui) {
             app.ui.zoom = if app.ui.zoom == Zoom::Fit { Zoom::Percent(100) } else { Zoom::Fit };
         }
         resp.context_menu(|ui| {
-            if ui.button("Swap").clicked() {
+            if ui.button(crate::i18n::tr("Swap")).clicked() {
                 let _ = swap(app);
             }
-            if ui.button("Make Candidate the Select").clicked() {
+            if ui.button(crate::i18n::tr("Make Candidate the Select")).clicked() {
                 let _ = make_select(app);
             }
             ui.separator();
@@ -321,7 +321,7 @@ pub fn show_survey(app: &mut LightcraftApp, ui: &mut egui::Ui) {
         // remove from the survey (deselect) on hover
         if resp.hovered() && photos.len() > 1 {
             let xr = Rect::from_min_size(pos2(img.right() - 26.0, img.top() + 6.0), vec2(20.0, 20.0));
-            let xresp = ui.interact(xr, egui::Id::new(("survey-x", id.0)), Sense::click()).on_hover_text("Remove from survey");
+            let xresp = ui.interact(xr, egui::Id::new(("survey-x", id.0)), Sense::click()).on_hover_text(crate::i18n::tr("Remove from survey"));
             ui.painter().circle_filled(xr.center(), 10.0, Color32::from_black_alpha(if xresp.hovered() { 230 } else { 160 }));
             paint(ui.painter(), xr.shrink(4.0), Icon::Close, t.text);
             if xresp.clicked() {
@@ -331,8 +331,11 @@ pub fn show_survey(app: &mut LightcraftApp, ui: &mut egui::Ui) {
         resp.context_menu(|ui| super::grid::context_menu(app, ui, *id));
     }
     let n = photos.len();
-    let msg =
-        if app.session.selection.ids.len() > SURVEY_MAX { format!("Showing {n} of {}", app.session.selection.ids.len()) } else { String::new() };
+    let msg = if app.session.selection.ids.len() > SURVEY_MAX {
+        crate::i18n::tr_format!("Showing {n} of {}", app.session.selection.ids.len(), n = n)
+    } else {
+        String::new()
+    };
     if !msg.is_empty() {
         ui.painter().text(pos2(canvas.right() - 16.0, canvas.top() + 10.0), Align2::RIGHT_TOP, msg, t.font(12.0), t.text_dim);
     }
@@ -357,7 +360,7 @@ pub fn show_reference(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     app.image_rect = Some(img);
     pan(app, &resp, img);
     lresp.context_menu(|ui| {
-        if ui.button("Clear Reference").clicked() {
+        if ui.button(crate::i18n::tr("Clear Reference")).clicked() {
             app.ui.reference = None;
             app.ui.view = ViewMode::Detail;
         }

crates/ui-egui/src/panels/detail.rs

@@ -267,7 +267,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     // soft proofing: a paper-white surround and the proof's name, as Lightroom shows it
     if app.ui.soft_proof && !fullscreen {
         p.rect_filled(canvas, 0.0, Color32::from_gray(238));
-        let label = format!("Proof Preview · {}", app.ui.proof.space.label());
+        let label = crate::i18n::tr_format!("Proof Preview · {}", app.ui.proof.space.label());
         p.text(pos2(canvas.right() - 16.0, canvas.top() + 14.0), Align2::RIGHT_CENTER, label, t.font(12.5), Color32::from_gray(60));
     }
     let shown;
@@ -275,11 +275,11 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui) {
         let br = fit_rect(areas[0], aspect, app.ui.zoom, native, ppp, app.ui.pan);
         draw(Slot::Before, br);
         shown = draw(Slot::Main, img_rect);
-        p.text(pos2(br.left(), br.bottom() + 14.0), Align2::LEFT_CENTER, "Before", t.font(12.0), t.text_dim);
-        p.text(pos2(img_rect.left(), img_rect.bottom() + 14.0), Align2::LEFT_CENTER, "After", t.font(12.0), t.text_dim);
+        p.text(pos2(br.left(), br.bottom() + 14.0), Align2::LEFT_CENTER, crate::i18n::tr("Before"), t.font(12.0), t.text_dim);
+        p.text(pos2(img_rect.left(), img_rect.bottom() + 14.0), Align2::LEFT_CENTER, crate::i18n::tr("After"), t.font(12.0), t.text_dim);
     } else if show_before {
         shown = draw(Slot::Before, img_rect);
-        p.text(pos2(img_rect.left() + 8.0, img_rect.top() + 14.0), Align2::LEFT_CENTER, "Before", t.font(12.0), t.text);
+        p.text(pos2(img_rect.left() + 8.0, img_rect.top() + 14.0), Align2::LEFT_CENTER, crate::i18n::tr("Before"), t.font(12.0), t.text);
     } else if let Some((key, label)) = &hover_key
         && let Some(tex) = app.renderer.textures.get(&Slot::Hover).filter(|t| t.photo == id && t.key == *key)
     {
@@ -294,11 +294,17 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui) {
         if shown == "none" {
             match app.renderer.failure(Slot::Main) {
                 Some(e) => {
-                    p.text(canvas.center() - vec2(0.0, 10.0), Align2::CENTER_CENTER, "This photo can't be opened", t.semibold(14.0), t.text);
+                    p.text(
+                        canvas.center() - vec2(0.0, 10.0),
+                        Align2::CENTER_CENTER,
+                        crate::i18n::tr("This photo can't be opened"),
+                        t.semibold(14.0),
+                        t.text,
+                    );
                     p.text(canvas.center() + vec2(0.0, 12.0), Align2::CENTER_CENTER, e, t.font(12.0), t.text_dim);
                 }
                 None => {
-                    p.text(canvas.center(), Align2::CENTER_CENTER, "Rendering…", t.font(13.0), t.text_dim);
+                    p.text(canvas.center(), Align2::CENTER_CENTER, crate::i18n::tr("Rendering…"), t.font(13.0), t.text_dim);
                 }
             }
         }
@@ -354,7 +360,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui) {
         preview_only_pill(ui, canvas, why);
     }
     resp.context_menu(|ui| {
-        ui.menu_button("Zoom", |ui| {
+        ui.menu_button(crate::i18n::tr("Zoom"), |ui| {
             for (label, cmd) in [("Fit", "view.zoomFit"), ("100%", "view.zoom100"), ("Zoom In", "view.zoomIn"), ("Zoom Out", "view.zoomOut")] {
                 if ui.button(label).clicked() {
                     let _ = app.run(cmd, json!({}));
@@ -419,7 +425,7 @@ fn info_overlay(app: &LightcraftApp, p: &egui::Painter, canvas: Rect, photo: &li
 fn preview_only_pill(ui: &mut egui::Ui, canvas: Rect, reason: &str) {
     let t = Tokens::get(ui.ctx());
     let p = ui.painter_at(canvas);
-    let text = format!("Preview only — editing the camera's embedded JPEG ({})", crate::widgets::preview_only_variant(reason));
+    let text = crate::i18n::tr_format!("Preview only — editing the camera's embedded JPEG ({})", crate::widgets::preview_only_variant(reason));
     let g = p.layout_no_wrap(text, t.font(12.0), Color32::WHITE);
     let size = vec2(g.size().x + 40.0, 26.0);
     let r = Rect::from_min_size(pos2(canvas.center().x - size.x / 2.0, canvas.top() + 12.0), size);

crates/ui-egui/src/panels/dialogs.rs

@@ -7,6 +7,53 @@ use crate::LightcraftApp;
 use crate::state::Dialog;
 use crate::theme::Tokens;
 
+/// Rows the Rename dialog previews.
+const RENAME_PREVIEW_ROWS: usize = 6;
+
+/// The Rename dialog's preview: its first rows (`None` while being planned) and how many files
+/// are renamed. Which names are taken is checked on disk, which can block on a slow drive, so the
+/// rows are planned on a worker thread, and only when the template, start number, photos or
+/// catalog change — never once per frame.
+pub(crate) fn rename_preview(
+    app: &mut LightcraftApp,
+    ctx: &egui::Context,
+    template: &str,
+    start: usize,
+) -> (Option<Vec<lightcraft_engine::rename::RenamePlan>>, usize) {
+    use std::hash::{Hash, Hasher};
+    type Rows = std::sync::Arc<std::sync::Mutex<Option<Vec<lightcraft_engine::rename::RenamePlan>>>>;
+    let ids = app.session.targets(&json!({}));
+    let photos = lightcraft_engine::rename::rename_photos(&app.session.catalog, &ids);
+    let total = photos.len();
+    let mut h = std::collections::hash_map::DefaultHasher::new();
+    (template, start, app.session.catalog.revision, &ids).hash(&mut h);
+    let key = h.finish();
+    let id = egui::Id::new("rename-preview-rows");
+    let read = |rows: &Rows| rows.lock().unwrap_or_else(std::sync::PoisonError::into_inner).clone();
+    if let Some((k, rows)) = ctx.data(|d| d.get_temp::<(u64, Rows)>(id))
+        && k == key
+    {
+        return (read(&rows), total);
+    }
+    let rows: Rows = Default::default();
+    let first: Vec<_> = photos.into_iter().take(RENAME_PREVIEW_ROWS).collect();
+    let (out, template, repaint) = (rows.clone(), template.to_string(), ctx.clone());
+    let exists = app.session.media.availability.probe();
+    let work = move || {
+        let plans = lightcraft_engine::rename::plan_rename_photos(&first, &template, start, &|f| exists(f));
+        *out.lock().unwrap_or_else(std::sync::PoisonError::into_inner) = Some(plans);
+        repaint.request_repaint();
+    };
+    #[cfg(not(target_arch = "wasm32"))]
+    if let Err(e) = std::thread::Builder::new().name("lc-rename-preview".into()).spawn(work) {
+        log::warn!("rename preview: {e}");
+    }
+    #[cfg(target_arch = "wasm32")]
+    work();
+    ctx.data_mut(|d| d.insert_temp(id, (key, rows.clone())));
+    (read(&rows), total)
+}
+
 /// Help ▸ What's New (docs/whats-new.md).
 pub const WHATS_NEW: &str = include_str!("../../../../docs/whats-new.md");
 
@@ -52,7 +99,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
     }
     .to_string();
     let frame = egui::Frame::window(&ctx.global_style()).inner_margin(egui::Margin::symmetric(16, 12));
-    let shown = egui::Window::new(title)
+    let shown = egui::Window::new(crate::i18n::tr(&title)).id(egui::Id::new("lightcraft-dialog"))
         .collapsible(false)
         .resizable(false)
         .frame(frame)
@@ -67,7 +114,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
             ui.spacing_mut().item_spacing.y = 8.0;
             match &mut dlg {
                 Dialog::AutoStack { gap } => {
-                    ui.label(egui::RichText::new("Stack photos taken within this time of each other:").color(t.text_label));
+                    ui.label(egui::RichText::new(crate::i18n::tr("Stack photos taken within this time of each other:")).color(t.text_label));
                     ui.add(
                         egui::Slider::new(gap, 0.0..=86400.0)
                             .logarithmic(true)
@@ -83,15 +130,15 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                 }
                 Dialog::Cull { reject_below, pick_best } => {
                     let n = app.session.selection.ids.len();
-                    let scope = if n > 1 { format!("the {n} selected photos") } else { format!("the {} photos in view", app.session.visible_cloned().len()) };
+                    let scope = if n > 1 { crate::i18n::tr_format!("the {n} selected photos", n = n) } else { crate::i18n::tr_format!("the {} photos in view", app.session.visible_cloned().len()) };
                     ui.label(egui::RichText::new(format!("Scores {scope} for focus and exposure and finds similar shots taken within seconds of each other (bursts).")).color(t.text_label));
                     ui.add_space(6.0);
                     let r = ui.add(egui::Slider::new(reject_below, 0.0..=80.0).text("Reject below focus").step_by(1.0));
                     crate::widgets::register(ui.ctx(), "field:cullReject", r.rect);
                     ui.label(egui::RichText::new(if *reject_below > 0.0 { "Blurry photos below the score are flagged as rejects." } else { "0: nothing is rejected." }).color(t.text_dim));
-                    let r = ui.checkbox(pick_best, "Pick the sharpest photo of each burst");
+                    let r = ui.checkbox(pick_best, crate::i18n::tr("Pick the sharpest photo of each burst"));
                     crate::widgets::register(ui.ctx(), "check:cullPick", r.rect);
-                    ui.label(egui::RichText::new("Scores stay on the photos: filter or make smart albums with Focus and Best of Similar Shots.").color(t.text_dim));
+                    ui.label(egui::RichText::new(crate::i18n::tr("Scores stay on the photos: filter or make smart albums with Focus and Best of Similar Shots.")).color(t.text_dim));
                 }
                 Dialog::WhatsNew => {
                     egui::ScrollArea::vertical().max_height(460.0).auto_shrink([false, true]).show(ui, |ui| {
@@ -120,14 +167,14 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                             ui.end_row();
                         }
                     });
-                    if ui.button("Copy to Clipboard").clicked() {
+                    if ui.button(crate::i18n::tr("Copy to Clipboard")).clicked() {
                         let text: String = rows.iter().map(|(k, v)| format!("{k}: {v}\n")).collect();
                         ui.ctx().copy_text(text);
                     }
                 }
                 Dialog::AllMetadata { title, rows, search } => {
                     ui.label(egui::RichText::new(title.as_str()).color(t.text_label));
-                    let r = ui.add(egui::TextEdit::singleline(search).hint_text("Filter fields").desired_width(f32::INFINITY));
+                    let r = ui.add(egui::TextEdit::singleline(search).hint_text(crate::i18n::tr("Filter fields")).desired_width(f32::INFINITY));
                     crate::widgets::register(ui.ctx(), "field:metadataSearch", r.rect);
                     let q = search.trim().to_lowercase();
                     let keep = |n: &str, v: &str| q.is_empty() || n.to_lowercase().contains(&q) || v.to_lowercase().contains(&q);
@@ -170,7 +217,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                     });
                 }
                 Dialog::SmartRules { name, rules, .. } => {
-                    let r = ui.add(egui::TextEdit::singleline(name).hint_text("Name").desired_width(f32::INFINITY));
+                    let r = ui.add(egui::TextEdit::singleline(name).hint_text(crate::i18n::tr("Name")).desired_width(f32::INFINITY));
                     crate::widgets::register(ui.ctx(), "field:smartName", r.rect);
                     ui.add_space(6.0);
                     egui::ScrollArea::vertical().max_height(360.0).auto_shrink([false, true]).show(ui, |ui| {
@@ -183,22 +230,22 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                     ui.label(
                         egui::RichText::new(match problems.first() {
                             Some(p) => p.clone(),
-                            None => format!("{n} photo{} match · updates automatically as photos change", if n == 1 { "" } else { "s" }),
+                            None => crate::i18n::tr_format!("{n} photo{} match · updates automatically as photos change", if n == 1 { "" } else { "s" }, n = n),
                         })
                         .color(t.text_dim),
                     );
                 }
                 Dialog::NewSmartAlbum { name } => {
-                    let r = ui.add(egui::TextEdit::singleline(name).hint_text("Name").desired_width(f32::INFINITY));
+                    let r = ui.add(egui::TextEdit::singleline(name).hint_text(crate::i18n::tr("Name")).desired_width(f32::INFINITY));
                     r.request_focus();
                     if r.lost_focus() && ui.input(|i| i.key_pressed(egui::Key::Enter)) {
                         confirm = true;
                     }
                     let rules = app.session.view_rules();
                     let n = app.session.catalog.query(&rules, &Default::default()).len();
-                    ui.label(egui::RichText::new(format!("Matches: {}", rules.describe())).color(t.text_label));
+                    ui.label(egui::RichText::new(crate::i18n::tr_format!("Matches: {}", rules.describe())).color(t.text_label));
                     ui.label(
-                        egui::RichText::new(format!("{n} photo{} now · updates automatically as photos change", if n == 1 { "" } else { "s" }))
+                        egui::RichText::new(crate::i18n::tr_format!("{n} photo{} now · updates automatically as photos change", if n == 1 { "" } else { "s" }, n = n))
                             .color(t.text_dim),
                     );
                 }
@@ -252,7 +299,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                         );
                     }
                     if n > 1 {
-                        ui.label(egui::RichText::new(format!("All {n} selected photos move by the same amount.")).color(t.text_dim));
+                        ui.label(egui::RichText::new(crate::i18n::tr_format!("All {n} selected photos move by the same amount.", n = n)).color(t.text_dim));
                     }
                 }
                 Dialog::LabelNames { names, save_as } => {
@@ -278,17 +325,17 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                         });
                     }
                     field(ui, "Save as set", |ui| {
-                        let te = ui.add(egui::TextEdit::singleline(save_as).hint_text("Optional name").desired_width(f32::INFINITY));
+                        let te = ui.add(egui::TextEdit::singleline(save_as).hint_text(crate::i18n::tr("Optional name")).desired_width(f32::INFINITY));
                         crate::widgets::register(ui.ctx(), "field:labelSetName", te.rect);
                     });
                     ui.label(
-                        egui::RichText::new("Names appear in the label menu, the filter bar and the Info panel, and are written to XMP. Empty = the colour's name.")
+                        egui::RichText::new(crate::i18n::tr("Names appear in the label menu, the filter bar and the Info panel, and are written to XMP. Empty = the colour's name."))
                             .color(t.text_dim),
                     );
                 }
                 Dialog::Rename { template, start } => {
                     let n = app.session.targets(&json!({})).len();
-                    ui.label(egui::RichText::new(format!("{n} photo{}", if n == 1 { "" } else { "s" })).color(t.text_dim));
+                    ui.label(egui::RichText::new(crate::i18n::tr_format!("{n} photo{}", if n == 1 { "" } else { "s" }, n = n)).color(t.text_dim));
                     let template_id = egui::Id::new("rename-template");
                     let tags_open = field(ui, "Template", |ui| {
                         ui.spacing_mut().item_spacing.x = 4.0;
@@ -313,26 +360,33 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                     });
                     field(ui, "Start at", |ui| ui.add(egui::DragValue::new(start).range(0..=999_999)));
                     ui.label(
-                        egui::RichText::new("Tags: see Tags beside the template. Files are renamed on disk (with their XMP sidecars); existing names get -1, -2…")
+                        egui::RichText::new(crate::i18n::tr("Tags: see Tags beside the template. Files are renamed on disk (with their XMP sidecars); existing names get -1, -2…"))
                             .color(t.text_dim),
                     );
-                    let preview = app.session.execute("photo.renamePreview", &json!({"template": template, "start": start})).unwrap_or_default();
-                    egui::Grid::new("rename-preview").num_columns(3).spacing([8.0, 2.0]).show(ui, |ui| {
-                        for pl in preview.as_array().into_iter().flatten().take(6) {
-                            ui.label(egui::RichText::new(pl["from"].as_str().unwrap_or("")).color(t.text_dim));
-                            ui.label(egui::RichText::new("→").color(t.text_dim));
-                            ui.label(egui::RichText::new(pl["to"].as_str().unwrap_or("")).color(t.text));
-                            ui.end_row();
+                    let (preview, total) = rename_preview(app, ui.ctx(), template, *start as usize);
+                    match &preview {
+                        Some(rows) => {
+                            egui::Grid::new("rename-preview").num_columns(3).spacing([8.0, 2.0]).show(ui, |ui| {
+                                for pl in rows {
+                                    ui.label(egui::RichText::new(&pl.from).color(t.text_dim));
+                                    ui.label(egui::RichText::new("→").color(t.text_dim));
+                                    ui.label(egui::RichText::new(&pl.to).color(t.text));
+                                    ui.end_row();
+                                }
+                            });
                         }
-                    });
-                    let more = preview.as_array().map_or(0, Vec::len).saturating_sub(6);
+                        None => {
+                            ui.label(egui::RichText::new("Checking names…").color(t.text_dim));
+                        }
+                    }
+                    let more = total.saturating_sub(RENAME_PREVIEW_ROWS);
                     if more > 0 {
-                        ui.label(egui::RichText::new(format!("… and {more} more")).color(t.text_dim));
+                        ui.label(egui::RichText::new(crate::i18n::tr_format!("… and {more} more", more = more)).color(t.text_dim));
                     }
                 }
                 Dialog::RenameKeyword { from, to } => {
                     let n = app.session.catalog.photos().filter(|p| p.meta.keywords.iter().any(|k| lightcraft_catalog::keywords::is_under(k, from))).count();
-                    let r = ui.add(egui::TextEdit::singleline(to).hint_text("New name").desired_width(f32::INFINITY));
+                    let r = ui.add(egui::TextEdit::singleline(to).hint_text(crate::i18n::tr("New name")).desired_width(f32::INFINITY));
                     crate::widgets::register(ui.ctx(), "field:keywordName", r.rect);
                     r.request_focus();
                     if r.lost_focus() && ui.input(|i| i.key_pressed(egui::Key::Enter)) {
@@ -348,7 +402,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                 }
                 Dialog::MergeKeywords { from, into } => {
                     ui.label(egui::RichText::new(format!("Replace {} with:", from.iter().map(|f| format!("“{f}”")).collect::<Vec<_>>().join(", "))).color(t.text_label));
-                    let r = ui.add(egui::TextEdit::singleline(into).hint_text("Keyword").desired_width(f32::INFINITY));
+                    let r = ui.add(egui::TextEdit::singleline(into).hint_text(crate::i18n::tr("Keyword")).desired_width(f32::INFINITY));
                     crate::widgets::register(ui.ctx(), "field:keywordInto", r.rect);
                     r.request_focus();
                     if r.lost_focus() && ui.input(|i| i.key_pressed(egui::Key::Enter)) {
@@ -377,23 +431,23 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                     }
                 }
                 Dialog::NewAlbum { name, .. } | Dialog::RenameAlbum { name, .. } => {
-                    let r = ui.add(egui::TextEdit::singleline(name).hint_text("Name").desired_width(f32::INFINITY));
+                    let r = ui.add(egui::TextEdit::singleline(name).hint_text(crate::i18n::tr("Name")).desired_width(f32::INFINITY));
                     r.request_focus();
                     if r.lost_focus() && ui.input(|i| i.key_pressed(egui::Key::Enter)) {
                         confirm = true;
                     }
                 }
                 Dialog::CreatePreset { name, group, groups } => {
-                    ui.add(egui::TextEdit::singleline(name).hint_text("Preset name").desired_width(f32::INFINITY));
-                    ui.add(egui::TextEdit::singleline(group).hint_text("Group").desired_width(f32::INFINITY));
-                    ui.label(egui::RichText::new("Settings to include").color(t.text_dim));
+                    ui.add(egui::TextEdit::singleline(name).hint_text(crate::i18n::tr("Preset name")).desired_width(f32::INFINITY));
+                    ui.add(egui::TextEdit::singleline(group).hint_text(crate::i18n::tr("Group")).desired_width(f32::INFINITY));
+                    ui.label(egui::RichText::new(crate::i18n::tr("Settings to include")).color(t.text_dim));
                     group_checklist(ui, "presetInclude", groups);
                 }
                 Dialog::CopySettings { groups } => group_checklist(ui, "copyGroup", groups),
                 Dialog::PasteSettings { groups } => {
                     let n = app.session.targets(&json!({})).len();
                     ui.label(
-                        egui::RichText::new(format!("Paste into {n} photo{} — only settings that were copied are pasted", if n == 1 { "" } else { "s" }))
+                        egui::RichText::new(crate::i18n::tr_format!("Paste into {n} photo{} — only settings that were copied are pasted", if n == 1 { "" } else { "s" }, n = n))
                             .color(t.text_dim),
                     );
                     group_checklist(ui, "pasteGroup", groups);
@@ -401,11 +455,11 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                 Dialog::Export { opts, full_size, resize, preset_name, limit_kb, dir } => {
                     use lightcraft_engine::export::{Anchor as P, ExportFormat as F, MetadataPolicy as M, SharpenAmount as A, SharpenFor as S};
                     let n = app.session.selection.ids.len().max(1);
-                    ui.label(egui::RichText::new(format!("{n} photo{}", if n == 1 { "" } else { "s" })).color(t.text_dim));
+                    ui.label(egui::RichText::new(crate::i18n::tr_format!("{n} photo{}", if n == 1 { "" } else { "s" }, n = n)).color(t.text_dim));
                     // Preset: load a built-in or saved set of options into the dialog
                     field(ui, "Preset", |ui| {
                         let mut chosen = None;
-                        let c = egui::ComboBox::from_id_salt("exportPreset").width(220.0).selected_text("Choose…").show_ui(ui, |ui| {
+                        let c = egui::ComboBox::from_id_salt("exportPreset").width(220.0).selected_text(crate::i18n::tr("Choose…")).show_ui(ui, |ui| {
                             let mut builtin = true;
                             for (p, b) in app.session.all_export_presets() {
                                 if builtin && !b {
@@ -434,7 +488,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                         ui,
                         "Format",
                         "exportFormat",
-                        &[(F::Jpeg, "JPEG"), (F::Png, "PNG"), (F::Tiff, "TIFF"), (F::Webp, "WebP"), (F::Avif, "AVIF"), (F::Dng, "DNG"), (F::Original, "Original")],
+                        &[(F::Jpeg, "JPEG"), (F::Png, "PNG"), (F::Tiff, "TIFF"), (F::Webp, "WebP"), (F::Avif, "AVIF"), (F::Dng, "DNG"), (F::Original, "Original files")],
                         &mut opts.format,
                     );
                     if !opts.format.is_rendered() {
@@ -458,7 +512,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                     }
                     if !rendered {
                     } else if opts.format == F::Avif {
-                        ui.label(egui::RichText::new("Color space: sRGB (AVIF)").color(t.text_dim));
+                        ui.label(egui::RichText::new(crate::i18n::tr("Color space: sRGB (AVIF)")).color(t.text_dim));
                     } else {
                         use lightcraft_engine::export::OutputSpace as C;
                         choices(
@@ -517,10 +571,10 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                         &mut opts.metadata,
                     );
                     if !matches!(opts.metadata, M::None | M::Copyright) {
-                        ui.checkbox(&mut opts.remove_location, "Remove location info");
+                        ui.checkbox(&mut opts.remove_location, crate::i18n::tr("Remove location info"));
                     }
                     let mut wm_on = opts.watermark.is_some();
-                    if ui.checkbox(&mut wm_on, "Watermark").changed() {
+                    if ui.checkbox(&mut wm_on, crate::i18n::tr("Watermark")).changed() {
                         opts.watermark = wm_on.then(|| lightcraft_engine::export::Watermark { text: "© ".into(), ..Default::default() });
                     }
                     if let Some(wm) = &mut opts.watermark {
@@ -538,7 +592,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                             field(ui, "Graphic", |ui| {
                                 trailing_button_row(ui, |ui| {
                                     if app.services.pick_files.is_some()
-                                        && crate::widgets::text_button(ui, "exportWmChoose", "Choose…", false).clicked()
+                                        && crate::widgets::text_button(ui, "exportWmChoose", crate::i18n::tr("Choose…"), false).clicked()
                                         && let Some(f) = app.services.pick_files.as_mut().and_then(|pick| pick().into_iter().next())
                                     {
                                         wm.image = f;
@@ -551,7 +605,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                                 wm.image_width = (width / 100.0) as f32;
                             }
                         } else {
-                            choices(ui, app.ui.language.tr("Orientation"), "exportWmOrientation", &[(false, app.ui.language.tr("Horizontal")), (true, app.ui.language.tr("Vertical"))], &mut wm.vertical);
+                            choices(ui, app.ui.language.tr("Text direction"), "exportWmOrientation", &[(false, app.ui.language.tr("Horizontal text")), (true, app.ui.language.tr("Vertical text"))], &mut wm.vertical);
                             field(ui, "Text", |ui| {
                                 ui.add(egui::TextEdit::multiline(&mut wm.text).desired_rows(2).hint_text("© Your Name").desired_width(f32::INFINITY))
                             });
@@ -572,7 +626,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                             wm.opacity = (op / 100.0) as f32;
                         }
                         if !graphic {
-                            ui.checkbox(&mut wm.shadow, "Shadow");
+                            ui.checkbox(&mut wm.shadow, crate::i18n::tr("Shadow"));
                         }
                     }
                     }
@@ -605,7 +659,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                     field(ui, "Folder", |ui| {
                         trailing_button_row(ui, |ui| {
                             if app.services.pick_folder.is_some()
-                                && crate::widgets::text_button(ui, "exportChooseFolder", "Choose…", false).clicked()
+                                && crate::widgets::text_button(ui, "exportChooseFolder", crate::i18n::tr("Choose…"), false).clicked()
                                 && let Some(pick) = app.services.pick_folder.as_mut()
                                 && let Some(d) = pick()
                             {
@@ -615,7 +669,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                         });
                     });
                     field(ui, "Subfolder", |ui| {
-                        ui.add(egui::TextEdit::singleline(&mut opts.subfolder).hint_text("none").desired_width(f32::INFINITY))
+                        ui.add(egui::TextEdit::singleline(&mut opts.subfolder).hint_text(crate::i18n::tr("none")).desired_width(f32::INFINITY))
                     });
                     use lightcraft_engine::export::Conflict as K;
                     choices(
@@ -629,17 +683,17 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                     field(ui, "Save preset", |ui| {
                         trailing_button_row(ui, |ui| {
                             let named = !preset_name.trim().is_empty();
-                            if crate::widgets::text_button(ui, "exportSavePreset", "Save", false).clicked() && named {
+                            if crate::widgets::text_button(ui, "exportSavePreset", crate::i18n::tr("Save"), false).clicked() && named {
                                 let params = export_dialog_params(opts, *full_size, resize, *limit_kb);
                                 match app.run("export.savePreset", json!({"name": preset_name.trim(), "params": params})) {
                                     Ok(_) => {
-                                        app.toast(ui.ctx(), format!("Saved export preset “{}”", preset_name.trim()));
+                                        app.toast(ui.ctx(), crate::i18n::tr_format!("Saved export preset “{}”", preset_name.trim()));
                                         preset_name.clear();
                                     }
                                     Err(e) => app.toast(ui.ctx(), e),
                                 }
                             }
-                            ui.add(egui::TextEdit::singleline(preset_name).hint_text("Preset name").desired_width(ui.available_width()));
+                            ui.add(egui::TextEdit::singleline(preset_name).hint_text(crate::i18n::tr("Preset name")).desired_width(ui.available_width()));
                         });
                     });
                 }
@@ -647,14 +701,14 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                 Dialog::Import { opts } => crate::import::body(app, ui, opts),
                 Dialog::Settings { tab } => crate::panels::settings::body(app, ui, tab),
                 Dialog::ConfirmDelete { count } => {
-                    let what = if *count == 1 { "this photo".to_string() } else { format!("these {count} photos") };
-                    ui.label(format!("Move {what} to Recently Deleted?"));
-                    ui.label(egui::RichText::new("They can be restored from Recently Deleted until it is emptied.").color(t.text_dim));
+                    let what = if *count == 1 { "this photo".to_string() } else { crate::i18n::tr_format!("these {count} photos", count = count) };
+                    ui.label(crate::i18n::tr_format!("Move {what} to Recently Deleted?", what = what));
+                    ui.label(egui::RichText::new(crate::i18n::tr("They can be restored from Recently Deleted until it is emptied.")).color(t.text_dim));
                 }
                 Dialog::About => {
                     ui.label(egui::RichText::new("LightCraft").font(t.semibold(20.0)).color(t.text));
-                    ui.label(format!("Version {} — a clean-room, pure-Rust photo library and raw developer.", env!("CARGO_PKG_VERSION")));
-                    ui.label("MIT OR Apache-2.0. Font: Inter (OFL). Icons: original.");
+                    ui.label(crate::i18n::tr_format!("Version {} — a clean-room, pure-Rust photo library and raw developer.", env!("CARGO_PKG_VERSION")));
+                    ui.label("MIT OR Apache-2.0. Fonts: Inter / BIZ UDPGothic (OFL). Icons: original.");
                     ui.add_space(10.0);
                     let discord = egui::Button::new(egui::RichText::new("Join the ArtCraft Discord").font(t.semibold(15.0)).color(egui::Color32::WHITE))
                         .fill(t.accent)
@@ -681,7 +735,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                         egui::Grid::new("shortcuts").striped(true).show(ui, |ui| {
                             for (id, label, sc, _) in crate::menus::UI_COMMANDS {
                                 if let Some(sc) = sc {
-                                    ui.label(*label);
+                                    ui.label(crate::i18n::tr(label));
                                     ui.label(*sc);
                                     ui.label(egui::RichText::new(*id).color(t.text_dim));
                                     ui.end_row();
@@ -689,7 +743,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                             }
                             for c in lightcraft_engine::command_specs() {
                                 if let Some(sc) = c.shortcut {
-                                    ui.label(c.label);
+                                    ui.label(crate::i18n::tr(c.label));
                                     ui.label(sc);
                                     ui.label(egui::RichText::new(c.id).color(t.text_dim));
                                     ui.end_row();
@@ -702,7 +756,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                                     .map(|c| c.1)
                                     .or_else(|| lightcraft_engine::find_command(id).map(|c| c.label))
                                     .unwrap_or(id);
-                                ui.label(label);
+                                ui.label(crate::i18n::tr(label));
                                 ui.label(*sc);
                                 ui.label(egui::RichText::new(*id).color(t.text_dim));
                                 ui.end_row();
@@ -714,7 +768,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
             ui.add_space(4.0);
             ui.horizontal(|ui| {
                 let informational = matches!(dlg, Dialog::About | Dialog::Shortcuts | Dialog::Settings { .. });
-                if !informational && ui.button("Cancel").clicked() {
+                if !informational && ui.button(crate::i18n::tr("Cancel")).clicked() {
                     close = true;
                 }
                 let add_label;
@@ -730,7 +784,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                     _ if informational => "Close",
                     _ => "OK",
                 };
-                if ui.button(ok).clicked() {
+                if ui.button(crate::i18n::tr(ok)).clicked() {
                     if informational {
                         close = true;
                     } else {
@@ -929,15 +983,15 @@ fn export_size(ui: &mut egui::Ui, full: &mut bool, r: &mut lightcraft_engine::ex
         (R::Megapixels, "Megapixels"),
         (R::Percent, "Percentage"),
     ];
-    let r_full = ui.checkbox(full, "Full size");
+    let r_full = ui.checkbox(full, crate::i18n::tr("Full size"));
     crate::widgets::register(ui.ctx(), "check:exportFullSize", r_full.rect);
     if !*full {
         field(ui, "Resize to", |ui| {
             let cur = MODES.iter().find(|m| m.0 == r.mode).map_or("Long Edge", |m| m.1);
             let before = r.mode;
-            let c = egui::ComboBox::from_id_salt("exportResizeMode").width(150.0).selected_text(cur).show_ui(ui, |ui| {
+            let c = egui::ComboBox::from_id_salt("exportResizeMode").width(150.0).selected_text(crate::i18n::tr(cur)).show_ui(ui, |ui| {
                 for (m, l) in MODES {
-                    ui.selectable_value(&mut r.mode, m, l);
+                    ui.selectable_value(&mut r.mode, m, crate::i18n::tr(l));
                 }
             });
             crate::widgets::register(ui.ctx(), "combo:exportResizeMode", c.response.rect);
@@ -970,7 +1024,7 @@ fn export_size(ui: &mut egui::Ui, full: &mut bool, r: &mut lightcraft_engine::ex
                 r.height = h as u32;
             }
         }
-        let c = ui.checkbox(&mut r.dont_enlarge, "Don't enlarge");
+        let c = ui.checkbox(&mut r.dont_enlarge, crate::i18n::tr("Don't enlarge"));
         crate::widgets::register(ui.ctx(), "check:exportDontEnlarge", c.rect);
     }
     let mut p = *ppi as f64;
@@ -999,7 +1053,7 @@ fn field<R>(ui: &mut egui::Ui, label: &str, add: impl FnOnce(&mut egui::Ui) -> R
     ui.horizontal(|ui| {
         ui.allocate_ui_with_layout(egui::vec2(LABEL_W, 24.0), egui::Layout::left_to_right(egui::Align::Center), |ui| {
             ui.set_min_width(LABEL_W);
-            ui.label(egui::RichText::new(label).color(t.text_label));
+            ui.label(egui::RichText::new(crate::i18n::tr(label)).color(t.text_label));
         });
         add(ui)
     })

crates/ui-egui/src/panels/edit.rs

@@ -76,7 +76,13 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     let t = Tokens::get(ui.ctx());
     let d = app.session.develop_of(id).unwrap_or_default();
     // a raw shown from its embedded JPEG (preview only) gets the rendered-file white balance scale
-    let raw = app.session.catalog.photo(id).is_some_and(|p| p.develops_raw());
+    let raw = app.session.catalog.photo(id).is_some_and(|p| p.develops_raw() && !p.relative_wb());
+    let mut d = d;
+    if d.wb.mode == WbMode::AsShot && app.session.catalog.photo(id).is_some_and(|p| p.relative_wb()) {
+        let wb = &mut std::sync::Arc::make_mut(&mut d).wb;
+        wb.temp = 6500.0;
+        wb.tint = 0.0;
+    }
     let preview_only = app.session.catalog.photo(id).and_then(|p| p.preview_only.clone());
 
     if app.ui.histogram {
@@ -87,20 +93,21 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     }
     // header: Edit + Auto / B&W / HDR
     let (hr, _) = ui.allocate_exact_size(vec2(ui.available_width(), 40.0), Sense::hover());
-    ui.painter().text(pos2(hr.left() + 24.0, hr.bottom() - 10.0), Align2::LEFT_CENTER, "Edit", t.semibold(15.0), t.text);
+    ui.painter().text(pos2(hr.left() + 24.0, hr.bottom() - 10.0), Align2::LEFT_CENTER, crate::i18n::tr("Edit"), t.semibold(15.0), t.text);
     egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 8, bottom: 14 }).show(ui, |ui| {
         ui.horizontal(|ui| {
             ui.spacing_mut().item_spacing.x = 8.0;
-            if text_button(ui, "auto", "Auto", false).clicked() {
+            if text_button(ui, "auto", crate::i18n::tr("Auto"), false).clicked() {
                 let _ = app.run("develop.auto", json!({}));
                 app.toast(ui.ctx(), "Auto settings applied");
             }
             let bw = crate::is_bw(&d);
-            if text_button(ui, "bw", "B&W", bw).clicked() {
+            if text_button(ui, "bw", crate::i18n::tr("B&W"), bw).clicked() {
                 let _ = app.run("develop.treatment", json!({}));
             }
             ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
-                if text_button(ui, "reset", "Reset", false).on_hover_text("Reset all edits (Cmd+Shift+R)").clicked() {
+                if text_button(ui, "reset", crate::i18n::tr("Reset"), false).on_hover_text(crate::i18n::tr("Reset all edits (Cmd+Shift+R)")).clicked()
+                {
                     let _ = app.run("develop.reset", json!({}));
                 }
             });
@@ -118,9 +125,9 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     if app.session.auto_sync && n > 1 {
         egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 0, bottom: 10 }).show(ui, |ui| {
             ui.horizontal(|ui| {
-                ui.label(egui::RichText::new(format!("Auto Sync: edits apply to {n} photos")).color(t.accent).size(12.0));
+                ui.label(egui::RichText::new(crate::i18n::tr_format!("Auto Sync: edits apply to {n} photos", n = n)).color(t.accent).size(12.0));
                 ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
-                    if text_button(ui, "autoSyncOff", "Turn Off", false).clicked() {
+                    if text_button(ui, "autoSyncOff", crate::i18n::tr("Turn Off"), false).clicked() {
                         let _ = app.run("develop.autoSync", json!({"on": false}));
                     }
                 });
@@ -131,9 +138,10 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     // profile row
     egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 14, bottom: 14 }).show(ui, |ui| {
         ui.horizontal(|ui| {
-            ui.label(egui::RichText::new("Profile").font(t.font(13.0)).color(t.text_dim));
+            ui.label(egui::RichText::new(crate::i18n::tr("Profile")).font(t.font(13.0)).color(t.text_dim));
             let name = lightcraft_engine::presets::profile(&d.profile.id).map(|p| p.name).unwrap_or("Color");
-            let r = crate::widgets::dropdown(ui, "profile", name, t.font(15.0), t.text_label);
+            let r =
+                crate::widgets::dropdown(ui, "profile", if name == "Color" { crate::i18n::tr("Color") } else { name }, t.font(15.0), t.text_label);
             egui::Popup::menu(&r).show(|ui| profile_menu(app, ui, &d));
             ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
                 if crate::widgets::icon_button(ui, "profileBrowser", Icon::ProfileGrid, vec2(28.0, 28.0), false, true, "Browse Profiles").clicked() {
@@ -154,7 +162,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
         }
         ui.add_space(6.0);
         let open = app.ui.flyout_open("curve");
-        if flyout_row(ui, "curve", "Curve", Icon::Curve, open).clicked() {
+        if flyout_row(ui, "curve", crate::i18n::tr("Curve"), Icon::Curve, open).clicked() {
             app.ui.toggle_flyout("curve");
         }
         if open {
@@ -166,8 +174,8 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
         // White balance row
         egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 2, bottom: 2 }).show(ui, |ui| {
             ui.horizontal(|ui| {
-                ui.label(egui::RichText::new("White Balance").font(t.font(13.0)).color(t.text_dim));
-                let r = crate::widgets::dropdown(ui, "wbMode", d.wb.mode.label(), t.font(14.0), t.text_label);
+                ui.label(egui::RichText::new(crate::i18n::tr("White Balance")).font(t.font(13.0)).color(t.text_dim));
+                let r = crate::widgets::dropdown(ui, "wbMode", crate::i18n::tr(d.wb.mode.label()), t.font(14.0), t.text_label);
                 egui::Popup::menu(&r).show(|ui| {
                     for m in WbMode::ALL {
                         if m == WbMode::Custom {
@@ -210,7 +218,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
         }
         if !crate::is_bw(d) {
             let open = app.ui.flyout_open("pointColor");
-            if flyout_row(ui, "pointColor", "Point Color", Icon::Picker, open).clicked() {
+            if flyout_row(ui, "pointColor", crate::i18n::tr("Point Color"), Icon::Picker, open).clicked() {
                 app.ui.toggle_flyout("pointColor");
             }
             if open {
@@ -218,7 +226,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
             }
         }
         let open = app.ui.flyout_open("grading");
-        if flyout_row(ui, "grading", "Color Grading", Icon::Presets, open).clicked() {
+        if flyout_row(ui, "grading", crate::i18n::tr("Color Grading"), Icon::Presets, open).clicked() {
             app.ui.toggle_flyout("grading");
         }
         if open {
@@ -230,7 +238,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
         for c in ["effects.texture", "effects.clarity", "effects.dehaze"] {
             control(app, ui, d, c, true);
         }
-        sub_title(ui, "Vignette");
+        sub_title(ui, crate::i18n::tr("Vignette"));
         {
             use lightcraft_develop::VignetteStyle as V;
             let styles = [
@@ -255,7 +263,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
             let enabled = c == "vignette.amount" || d.vignette.amount != 0.0;
             control(app, ui, d, c, enabled);
         }
-        sub_title(ui, "Grain");
+        sub_title(ui, crate::i18n::tr("Grain"));
         for c in ["grain.amount", "grain.size", "grain.roughness"] {
             control(app, ui, d, c, c == "grain.amount" || d.grain.amount != 0.0);
         }
@@ -265,7 +273,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
         for c in ["detail.sharpenAmount", "detail.sharpenRadius", "detail.sharpenDetail", "detail.sharpenMasking"] {
             control(app, ui, d, c, c == "detail.sharpenAmount" || d.detail.sharpen_amount > 0.0);
         }
-        sub_title(ui, "Noise Reduction");
+        sub_title(ui, crate::i18n::tr("Noise Reduction"));
         for c in ["detail.nrLuminance", "detail.nrDetail", "detail.nrContrast", "detail.nrColor", "detail.nrColorDetail", "detail.nrColorSmoothness"]
         {
             control(app, ui, d, c, true);
@@ -276,16 +284,16 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
         let has_lens = app.session.catalog.photo(id).is_some_and(|p| p.embedded_lens.is_some());
         egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 4, bottom: 4 }).show(ui, |ui| {
             let mut ca = d.optics.remove_ca;
-            if ui.checkbox(&mut ca, "Remove Chromatic Aberration").changed() {
+            if ui.checkbox(&mut ca, crate::i18n::tr("Remove Chromatic Aberration")).changed() {
                 let _ = app.run("develop.merge", json!({"settings": {"optics": {"remove_ca": ca}}, "label": "Remove CA"}));
             }
             let mut lp = d.optics.lens_profile;
-            if ui.checkbox(&mut lp, "Enable Lens Corrections").changed() {
+            if ui.checkbox(&mut lp, crate::i18n::tr("Enable Lens Corrections")).changed() {
                 let _ = app.run("develop.merge", json!({"settings": {"optics": {"lens_profile": lp}}, "label": "Lens Corrections"}));
             }
             if lp && !has_lens {
                 ui.label(
-                    egui::RichText::new("No lens data embedded in this file (DNG lens opcodes only).")
+                    egui::RichText::new(crate::i18n::tr("No lens data embedded in this file (DNG lens opcodes only)."))
                         .size(11.0)
                         .color(Tokens::get(ui.ctx()).text_dim),
                 );
@@ -296,14 +304,14 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
                 control(app, ui, d, c, has_lens);
             }
         }
-        sub_title(ui, "Manual");
+        sub_title(ui, crate::i18n::tr("Manual"));
         for c in ["optics.distortion", "optics.vignetting"] {
             control(app, ui, d, c, true);
         }
         control(app, ui, d, "optics.vignettingMidpoint", d.optics.vignetting != 0.0);
         ui.add_space(6.0);
         let open = app.ui.flyout_open("defringe");
-        if flyout_row(ui, "defringe", "Defringe", Icon::Picker, open).clicked() {
+        if flyout_row(ui, "defringe", crate::i18n::tr("Defringe"), Icon::Picker, open).clicked() {
             app.ui.toggle_flyout("defringe");
         }
         if open {
@@ -315,7 +323,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
             let on = d.optics.defringe_green_amount > 0.0;
             control(app, ui, d, "optics.defringeGreenHueLo", on);
             control(app, ui, d, "optics.defringeGreenHueHi", on);
-            sub_title(ui, "Lateral Chromatic Aberration");
+            sub_title(ui, crate::i18n::tr("Lateral Chromatic Aberration"));
             control(app, ui, d, "optics.caRed", true);
             control(app, ui, d, "optics.caBlue", true);
         }
@@ -323,7 +331,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     });
     // Lightroom Classic's Calibration panel (the cloud app hides it): last, like there.
     section(app, ui, &d, "calibration", "Calibration", |app, ui, d| {
-        sub_title(ui, "Shadows");
+        sub_title(ui, crate::i18n::tr("Shadows"));
         control(app, ui, d, "calibration.shadowsTint", true);
         for (title, k) in [("Red Primary", "red"), ("Green Primary", "green"), ("Blue Primary", "blue")] {
             sub_title(ui, title);
@@ -383,14 +391,18 @@ fn profile_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings)
     ui.separator();
     if let Some(p) = profile(cur) {
         let fav = app.session.profile_favorites.iter().any(|f| f == p.id);
-        let label = if fav { format!("Remove “{}” from Favorites", p.name) } else { format!("Add “{}” to Favorites", p.name) };
+        let label = if fav {
+            crate::i18n::tr_format!("Remove “{}” from Favorites", p.name)
+        } else {
+            crate::i18n::tr_format!("Add “{}” to Favorites", p.name)
+        };
         let r = ui.button(label);
         register(ui.ctx(), "profileMenu:toggleFavorite", r.rect);
         if r.clicked() {
             let _ = app.run("profile.favorite", json!({"id": p.id}));
         }
     }
-    let r = ui.button("Browse…");
+    let r = ui.button(crate::i18n::tr("Browse…"));
     register(ui.ctx(), "profileMenu:browse", r.rect);
     if r.clicked() {
         let _ = app.run("panel.profiles", json!({}));
@@ -402,7 +414,7 @@ fn profile_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings)
         let mut s = d.clone();
         s.profile.id = p.id.to_string();
         s.profile.amount = 100.0;
-        app.hover_preview = Some(crate::HoverPreview { label: format!("Profile: {}", p.name), settings: s });
+        app.hover_preview = Some(crate::HoverPreview { label: crate::i18n::tr_format!("Profile: {}", p.name), settings: s });
     }
     if let Some(id) = pick.0 {
         let _ = app.run("develop.profile", json!({"id": id}));
@@ -412,7 +424,7 @@ fn profile_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings)
 pub fn sub_title(ui: &mut egui::Ui, title: &str) {
     let t = Tokens::get(ui.ctx());
     let (r, _) = ui.allocate_exact_size(vec2(ui.available_width(), 30.0), Sense::hover());
-    ui.painter().text(pos2(r.left() + 24.0, r.center().y + 4.0), Align2::LEFT_CENTER, title, t.semibold(13.0), t.text_label);
+    ui.painter().text(pos2(r.left() + 24.0, r.center().y + 4.0), Align2::LEFT_CENTER, crate::i18n::tr(title), t.semibold(13.0), t.text_label);
 }
 
 fn section(
@@ -531,16 +543,17 @@ fn soft_proofing(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     let t = Tokens::get(ui.ctx());
     egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 8, bottom: 6 }).show(ui, |ui| {
         ui.horizontal(|ui| {
-            ui.label(RichText::new("Soft Proofing").color(t.text).strong());
+            ui.label(RichText::new(crate::i18n::tr("Soft Proofing")).color(t.text).strong());
             ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
                 let mut dest = app.ui.proof.dest_warning;
                 let r = ui
                     .toggle_value(&mut dest, RichText::new("■").color(Color32::from_rgb(255, 40, 40)))
-                    .on_hover_text("Show destination gamut warning");
+                    .on_hover_text(crate::i18n::tr("Show destination gamut warning"));
                 register(ui.ctx(), "button:proofDestWarning", r.rect);
                 let mut disp = app.ui.proof.display_warning;
-                let r2 =
-                    ui.toggle_value(&mut disp, RichText::new("■").color(Color32::from_rgb(40, 90, 255))).on_hover_text("Show display gamut warning");
+                let r2 = ui
+                    .toggle_value(&mut disp, RichText::new("■").color(Color32::from_rgb(40, 90, 255)))
+                    .on_hover_text(crate::i18n::tr("Show display gamut warning"));
                 register(ui.ctx(), "button:proofDisplayWarning", r2.rect);
                 if dest != app.ui.proof.dest_warning || disp != app.ui.proof.display_warning {
                     let _ = app.run("view.softProof", json!({"destWarning": dest, "displayWarning": disp}));
@@ -548,7 +561,7 @@ fn soft_proofing(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
             });
         });
         ui.horizontal(|ui| {
-            ui.label(RichText::new("Profile:").color(t.text_label));
+            ui.label(RichText::new(crate::i18n::tr("Profile:")).color(t.text_label));
             let cur = app.ui.proof.space;
             egui::ComboBox::from_id_salt("proof-space").width(170.0).selected_text(cur.label()).show_ui(ui, |ui| {
                 for s in OutputSpace::ALL {
@@ -558,10 +571,10 @@ fn soft_proofing(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
                 }
             });
         });
-        let r = ui.button("Create Proof Copy");
+        let r = ui.button(crate::i18n::tr("Create Proof Copy"));
         register(ui.ctx(), "button:createProofCopy", r.rect);
         if r.clicked() {
-            let name = format!("Proof Copy ({})", app.ui.proof.space.label());
+            let name = crate::i18n::tr_format!("Proof Copy ({})", app.ui.proof.space.label());
             if app.run("photo.virtualCopy", json!({"ids": [id.0], "name": name})).is_ok() {
                 app.toast(ui.ctx(), "Proof copy created");
             }
@@ -605,7 +618,7 @@ fn curve_editor(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId, d: &Dev
                     "green" => "Green channel",
                     _ => "Blue channel",
                 };
-                let resp = resp.on_hover_text(format!("{name} — double-click to reset it"));
+                let resp = resp.on_hover_text(crate::i18n::tr_format!("{name} — double-click to reset it", name = name));
                 if resp.double_clicked() {
                     app.ui.curve_channel = ch.into();
                     let _ = app.run("curve.reset", json!({"channel": ch}));
@@ -796,7 +809,7 @@ fn curve_footer(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings)
     let t = Tokens::get(ui.ctx());
     egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 2, bottom: 4 }).show(ui, |ui| {
         ui.horizontal(|ui| {
-            ui.label(RichText::new("Point Curve").font(t.font(12.0)).color(t.text_label));
+            ui.label(RichText::new(crate::i18n::tr("Point Curve")).font(t.font(12.0)).color(t.text_label));
             let current = matching_preset(&app.session, &d.curve);
             let r = crate::widgets::dropdown(ui, "curvePreset", current.as_deref().unwrap_or("Custom"), t.font(12.0), t.text);
             egui::Popup::menu(&r).show(|ui| {
@@ -816,7 +829,7 @@ fn curve_footer(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings)
                     }
                     if !p.builtin {
                         r.context_menu(|ui| {
-                            if ui.button("Delete Preset").clicked() {
+                            if ui.button(crate::i18n::tr("Delete Preset")).clicked() {
                                 let _ = app.run("curve.deletePreset", json!({"name": p.name}));
                                 ui.close();
                             }
@@ -825,28 +838,29 @@ fn curve_footer(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings)
                 }
                 ui.separator();
                 let shaped = current.as_deref() != Some("Linear");
-                let r = ui.add_enabled(shaped, egui::Button::new("Save Point Curve…"));
+                let r = ui.add_enabled(shaped, egui::Button::new(crate::i18n::tr("Save Point Curve…")));
                 register(ui.ctx(), "curvePresetMenu:save", r.rect);
                 if r.clicked() {
                     crate::panels::dialogs::prompt(app, "Save Point Curve Preset", "Preset name", "", "curve.savePreset", json!({}), "name");
                     ui.close();
                 }
-                if ui.add_enabled(app.services.pick_curve_preset_files.is_some(), egui::Button::new("Import Presets…")).clicked() {
+                if ui.add_enabled(app.services.pick_curve_preset_files.is_some(), egui::Button::new(crate::i18n::tr("Import Presets…"))).clicked() {
                     let _ = app.run("file.importCurvePresets", json!({}));
                     ui.close();
                 }
                 let can_export = app.services.save_curve_preset_file.is_some() && !app.session.curve_presets.is_empty();
-                if ui.add_enabled(can_export, egui::Button::new("Export Presets…")).clicked() {
+                if ui.add_enabled(can_export, egui::Button::new(crate::i18n::tr("Export Presets…"))).clicked() {
                     let _ = app.run("file.exportCurvePresets", json!({}));
                     ui.close();
                 }
                 if presets.iter().any(|p| !p.builtin) {
-                    ui.label(RichText::new("Right-click a preset to delete it").font(t.font(11.0)).color(t.text_dim));
+                    ui.label(RichText::new(crate::i18n::tr("Right-click a preset to delete it")).font(t.font(11.0)).color(t.text_dim));
                 }
             });
             ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
-                let r = text_button(ui, "curveReset", "Reset", false)
-                    .on_hover_text("Reset all curves: point curves (all channels) and parametric (double-click a channel to reset only that one)");
+                let r = text_button(ui, "curveReset", crate::i18n::tr("Reset"), false).on_hover_text(crate::i18n::tr(
+                    "Reset all curves: point curves (all channels) and parametric (double-click a channel to reset only that one)",
+                ));
                 if r.clicked() {
                     let _ = app.run("curve.reset", json!({"channel": "all"}));
                 }
@@ -857,14 +871,15 @@ fn curve_footer(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings)
 
 /// Right-click menu of the curve graph.
 fn curve_reset_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, ch: &str) {
-    let label = if ch == "parametric" { "Reset Parametric Curve".to_string() } else { format!("Reset {} Channel", channel_label(ch)) };
+    let label =
+        if ch == "parametric" { "Reset Parametric Curve".to_string() } else { crate::i18n::tr_format!("Reset {} Channel", channel_label(ch)) };
     let r = ui.button(label);
     register(ui.ctx(), "curveMenu:resetChannel", r.rect);
     if r.clicked() {
         let _ = app.run("curve.reset", json!({"channel": ch}));
         ui.close();
     }
-    let r = ui.button("Reset All Curves");
+    let r = ui.button(crate::i18n::tr("Reset All Curves"));
     register(ui.ctx(), "curveMenu:resetAll", r.rect);
     if r.clicked() {
         let _ = app.run("curve.reset", json!({"channel": "all"}));
@@ -925,7 +940,7 @@ fn mixer(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings) {
                 let tool = format!("tat:{k}");
                 let active = app.ui.tool == tool;
                 if text_button(ui, &format!("tatMixer-{k}"), label, active)
-                    .on_hover_text("Targeted adjustment: drag up/down on the photo to adjust the colours there")
+                    .on_hover_text(crate::i18n::tr("Targeted adjustment: drag up/down on the photo to adjust the colours there"))
                     .clicked()
                 {
                     app.ui.tool = if active { String::new() } else { tool };
@@ -937,7 +952,10 @@ fn mixer(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings) {
     if crate::is_bw(d) {
         ui.horizontal(|ui| {
             ui.add_space(24.0);
-            if crate::widgets::text_button(ui, "bwAuto", "Auto", false).on_hover_text("Set the mix from the photo's colours").clicked() {
+            if crate::widgets::text_button(ui, "bwAuto", crate::i18n::tr("Auto"), false)
+                .on_hover_text(crate::i18n::tr("Set the mix from the photo's colours"))
+                .clicked()
+            {
                 let _ = app.run("develop.autoBwMix", json!({}));
             }
         });
@@ -994,25 +1012,25 @@ fn point_color(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings)
     });
     if n == 0 {
         egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 2, bottom: 8 }).show(ui, |ui| {
-            ui.label(egui::RichText::new("Pick a colour on the photo with the eyedropper.").size(12.0).color(t.text_dim));
+            ui.label(egui::RichText::new(crate::i18n::tr("Pick a colour on the photo with the eyedropper.")).size(12.0).color(t.text_dim));
         });
         return;
     }
     for k in ["hueShift", "satShift", "lumShift", "variance"] {
         control(app, ui, d, &format!("pointColor.{sel}.{k}"), true);
     }
-    sub_title(ui, "Range");
+    sub_title(ui, crate::i18n::tr("Range"));
     for k in ["range", "hueRange", "satRange", "lumRange"] {
         control(app, ui, d, &format!("pointColor.{sel}.{k}"), true);
     }
     egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 4, bottom: 8 }).show(ui, |ui| {
         ui.horizontal(|ui| {
             let mut v = app.ui.point_color_visualize;
-            if ui.checkbox(&mut v, "Visualize range").changed() {
+            if ui.checkbox(&mut v, crate::i18n::tr("Visualize range")).changed() {
                 app.ui.point_color_visualize = v;
             }
             ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
-                if text_button(ui, "pointColorDelete", "Delete", false).clicked() {
+                if text_button(ui, "pointColorDelete", crate::i18n::tr("Delete"), false).clicked() {
                     let _ = app.run("pointColor.delete", json!({"index": sel}));
                 }
             });
@@ -1047,9 +1065,9 @@ fn grading(app: &mut LightcraftApp, ui: &mut egui::Ui, d: &DevelopSettings) {
         let dot = c + vec2(a.cos(), -a.sin()) * rad * (wh.sat as f32 / 100.0);
         ui.painter().circle_filled(dot, 5.0, Color32::WHITE);
         ui.painter().circle_stroke(dot, 5.0, Stroke::new(1.0, Color32::BLACK));
-        ui.painter().text(pos2(c.x, c.y + rad + 12.0), Align2::CENTER_CENTER, label, t.font(12.0), t.text_label);
+        ui.painter().text(pos2(c.x, c.y + rad + 12.0), Align2::CENTER_CENTER, crate::i18n::tr(label), t.font(12.0), t.text_label);
         if resp.drag_started() {
-            let _ = app.run("develop.beginInteraction", json!({"label": format!("{label} Grading")}));
+            let _ = app.run("develop.beginInteraction", json!({"label": crate::i18n::tr_format!("{label} Grading", label = label)}));
         }
         if (resp.dragged() || resp.clicked())
             && let Some(q) = resp.interact_pointer_pos()
@@ -1093,7 +1111,7 @@ fn paint_wheel(p: &egui::Painter, c: Pos2, rad: f32) {
 fn quick_develop(app: &mut LightcraftApp, ui: &mut egui::Ui, n: usize) {
     let t = Tokens::get(ui.ctx());
     egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 0, bottom: 10 }).show(ui, |ui| {
-        ui.label(egui::RichText::new(format!("Quick Develop · {n} photos")).color(t.text_label).size(12.5));
+        ui.label(egui::RichText::new(crate::i18n::tr_format!("Quick Develop · {n} photos", n = n)).color(t.text_label).size(12.5));
         ui.add_space(4.0);
         let rows: [(&str, &str, f64, f64); 9] = [
             ("Exposure", "light.exposure", 1.0 / 3.0, 1.0),
@@ -1108,11 +1126,11 @@ fn quick_develop(app: &mut LightcraftApp, ui: &mut egui::Ui, n: usize) {
         ];
         egui::Grid::new("quick-develop").num_columns(5).spacing([4.0, 3.0]).show(ui, |ui| {
             for (label, ctl, small, big) in rows {
-                ui.label(egui::RichText::new(label).size(11.5).color(t.text_dim));
+                ui.label(egui::RichText::new(crate::i18n::tr(label)).size(11.5).color(t.text_dim));
                 for (txt, d) in [("◀◀", -big), ("◀", -small), ("▶", small), ("▶▶", big)] {
                     let r = ui.add(egui::Button::new(egui::RichText::new(txt).size(10.0)).min_size(egui::vec2(28.0, 18.0)));
                     crate::widgets::register(ui.ctx(), format!("button:quick-{ctl}-{txt}"), r.rect);
-                    if r.on_hover_text(format!("{label} {d:+} on every selected photo")).clicked() {
+                    if r.on_hover_text(crate::i18n::tr_format!("{label} {d:+} on every selected photo", d = d, label = label)).clicked() {
                         let _ = app.run("develop.quickAdjust", json!({"control": ctl, "delta": d}));
                     }
                 }

crates/ui-egui/src/panels/filterbar.rs

@@ -33,7 +33,7 @@ fn filter(app: &mut LightcraftApp, patch: Value) {
 /// A small label before a group of controls.
 fn caption(ui: &mut egui::Ui, text: &str) {
     let t = Tokens::get(ui.ctx());
-    ui.label(egui::RichText::new(text).font(t.font(12.0)).color(t.text_dim));
+    ui.label(egui::RichText::new(crate::i18n::tr(text)).font(t.font(12.0)).color(t.text_dim));
 }
 
 /// A square toggle with an icon or a colour swatch.
@@ -59,13 +59,13 @@ fn toggle(ui: &mut egui::Ui, id: &str, on: bool, tip: &str, draw: impl FnOnce(&e
             t.icon
         },
     );
-    resp.on_hover_text(tip)
+    resp.on_hover_text(crate::i18n::tr(tip))
 }
 
 /// A dropdown showing `current`; `items` are (label, filter patch, selected).
 fn picker(app: &mut LightcraftApp, ui: &mut egui::Ui, id: &str, current: &str, active: bool, items: Vec<(String, Value, bool)>) {
     let t = Tokens::get(ui.ctx());
-    let r = crate::widgets::dropdown(ui, &format!("filter-{id}"), current, t.font(12.5), if active { t.text } else { t.text_label });
+    let r = crate::widgets::dropdown(ui, &format!("filter-{id}"), crate::i18n::tr(current), t.font(12.5), if active { t.text } else { t.text_label });
     if active {
         ui.painter().rect_stroke(r.rect.expand(2.0), 4.0, Stroke::new(1.0, t.accent.gamma_multiply(0.7)), StrokeKind::Outside);
     }
@@ -73,7 +73,7 @@ fn picker(app: &mut LightcraftApp, ui: &mut egui::Ui, id: &str, current: &str, a
     egui::Popup::menu(&r).show(|ui| {
         egui::ScrollArea::vertical().max_height(320.0).show(ui, |ui| {
             for (label, patch, sel) in &items {
-                if ui.selectable_label(*sel, label).clicked() {
+                if ui.selectable_label(*sel, crate::i18n::tr(label)).clicked() {
                     chosen = Some(patch.clone());
                 }
             }
@@ -260,19 +260,19 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     // save / clear
     ui.add_space(14.0);
     let filtering = app.session.filter != Default::default();
-    let save = ui.add_enabled(filtering, egui::Button::new(egui::RichText::new("Save as Smart Album…").font(t.font(12.5))));
+    let save = ui.add_enabled(filtering, egui::Button::new(egui::RichText::new(crate::i18n::tr("Save as Smart Album…")).font(t.font(12.5))));
     register(ui.ctx(), "button:filterSave", save.rect);
     if save.clicked() {
         let _ = app.run("dialog.newSmartAlbum", json!({}));
     }
-    let clear = ui.add_enabled(filtering, egui::Button::new(egui::RichText::new("Clear").font(t.font(12.5))));
+    let clear = ui.add_enabled(filtering, egui::Button::new(egui::RichText::new(crate::i18n::tr("Clear")).font(t.font(12.5))));
     register(ui.ctx(), "button:filterClear", clear.rect);
     if clear.clicked() {
         app.ui.search.clear();
         let _ = app.run("library.clearFilter", json!({}));
     }
     // filter presets: apply one, save the current filter, delete
-    let presets = ui.button(egui::RichText::new("Presets ▾").font(t.font(12.5)));
+    let presets = ui.button(egui::RichText::new(crate::i18n::tr("Presets ▾")).font(t.font(12.5)));
     register(ui.ctx(), "button:filterPresets", presets.rect);
     egui::Popup::menu(&presets).show(|ui| {
         let names: Vec<String> = app.session.filter_presets.iter().map(|f| f.name.clone()).collect();
@@ -282,16 +282,16 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui) {
                 let _ = app.run("filter.applyPreset", json!({"name": n}));
             }
             r.context_menu(|ui| {
-                if ui.button("Delete Preset").clicked() {
+                if ui.button(crate::i18n::tr("Delete Preset")).clicked() {
                     let _ = app.run("filter.deletePreset", json!({"name": n}));
                 }
             });
         }
         if names.is_empty() {
-            ui.label(egui::RichText::new("No filter presets yet").color(t.text_dim));
+            ui.label(egui::RichText::new(crate::i18n::tr("No filter presets yet")).color(t.text_dim));
         }
         ui.separator();
-        if ui.add_enabled(filtering, egui::Button::new("Save Current Filter as Preset…")).clicked() {
+        if ui.add_enabled(filtering, egui::Button::new(crate::i18n::tr("Save Current Filter as Preset…"))).clicked() {
             crate::panels::dialogs::prompt(app, "Save Filter Preset", "Preset name", "", "filter.savePreset", json!({}), "name");
         }
     });

crates/ui-egui/src/panels/grid.rs

@@ -143,7 +143,7 @@ fn show_inner(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     let chips = lightcraft_engine::filter_chips(&app.session.filter, &app.session.catalog);
     let total = app.session.source_total();
     let counted = super::chips::count_text(ids.len(), total, !chips.is_empty());
-    let cnt = if sel_n > 1 { format!("{sel_n} selected · {counted}") } else { counted };
+    let cnt = if sel_n > 1 { crate::i18n::tr_format!("{sel_n} selected · {counted}", counted = counted, sel_n = sel_n) } else { counted };
     match app.session.browse.clone().filter(|_| app.session.source == lightcraft_engine::LibrarySource::Folder) {
         Some(b) => {
             let local = app.caches.grid.local(&app.session.catalog, &ids, generation);
@@ -163,7 +163,9 @@ fn show_inner(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     if ids.is_empty() {
         if !chips.is_empty() {
             let body = match total {
-                Some(n) if n > 0 => format!("{n} photos in {} are hidden by the filters above", app.session.source.label(&app.session.catalog)),
+                Some(n) if n > 0 => {
+                    crate::i18n::tr_format!("{n} photos in {} are hidden by the filters above", app.session.source.label(&app.session.catalog), n = n)
+                }
                 _ => "Remove a filter above, or choose Clear all".to_string(),
             };
             super::empty_message(ui, ui.max_rect(), "No photos match the active filters", &body);
@@ -412,7 +414,13 @@ fn group_header(app: &mut LightcraftApp, ui: &mut egui::Ui, run: &DateRun, ids:
     let gw = g.size().x;
     p.galley(pos2(x, r.center().y - g.size().y / 2.0), g, t.text);
     let n = run.count;
-    p.text(pos2(x + gw + 10.0, r.center().y), Align2::LEFT_CENTER, format!("· {n} photo{}", if n == 1 { "" } else { "s" }), t.font(12.5), t.text_dim);
+    p.text(
+        pos2(x + gw + 10.0, r.center().y),
+        Align2::LEFT_CENTER,
+        crate::i18n::tr_format!("· {n} photo{}", if n == 1 { "" } else { "s" }, n = n),
+        t.font(12.5),
+        t.text_dim,
+    );
     if resp.clicked() {
         let group: Vec<u64> = ids[run.start..(run.start + run.count).min(ids.len())].iter().map(|p| p.0).collect();
         let m = ui.input(|i| i.modifiers);
@@ -571,7 +579,7 @@ fn cell(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId, r: Rect, square
     if let Some(why) = &photo.preview_only {
         // a raw shown from its embedded JPEG: a small amber "Preview" pill at the image's bottom
         // left, above the badge bar (always shown: it changes what editing does)
-        let g = p.layout_no_wrap("Preview".into(), t.semibold(9.5), Color32::WHITE);
+        let g = p.layout_no_wrap(crate::i18n::tr("Preview").into(), t.semibold(9.5), Color32::WHITE);
         let at = pos2(img_rect.left() + 6.0, img_rect.bottom() - 30.0 - 16.0);
         let br = Rect::from_min_size(at, vec2(g.size().x + 24.0, 16.0));
         p.rect_filled(br, 8.0, Color32::from_black_alpha(170));
@@ -579,7 +587,7 @@ fn cell(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId, r: Rect, square
         p.galley(pos2(br.left() + 17.0, br.center().y - g.size().y / 2.0), g, Color32::WHITE);
         register(ui.ctx(), format!("badge:previewOnly:{}", id.0), br);
         ui.interact(br, egui::Id::new(("preview-only-badge", id.0)), Sense::hover())
-            .on_hover_text(format!("Preview only — {}", crate::widgets::preview_only_explanation(why)));
+            .on_hover_text(crate::i18n::tr_format!("Preview only — {}", crate::widgets::preview_only_explanation(why)));
     }
     if photo.flag == Flag::Reject {
         p.rect_filled(img_rect, 0.0, Color32::from_black_alpha(110));
@@ -656,18 +664,18 @@ fn folder_header(app: &mut LightcraftApp, ui: &mut egui::Ui, hr: Rect, b: &light
         ui.add_space(10.0);
         // counted once per view (cached); the ids are only gathered on a click
         if local_n > 0 {
-            let label = format!("Add {local_n} to My Photos");
+            let label = crate::i18n::tr_format!("Add {local_n} to My Photos", local_n = local_n);
             if crate::widgets::text_button(ui, "addToLibrary", &label, false).clicked() {
                 let local: Vec<u64> = ids.iter().filter(|id| app.session.catalog.photo(**id).is_some_and(|p| p.local)).map(|id| id.0).collect();
                 let n = local.len();
                 match app.run("photo.addToLibrary", json!({"ids": local})) {
-                    Ok(_) => app.toast(ui.ctx(), format!("Added {n} photo{} to My Photos", if n == 1 { "" } else { "s" })),
+                    Ok(_) => app.toast(ui.ctx(), crate::i18n::tr_format!("Added {n} photo{} to My Photos", if n == 1 { "" } else { "s" }, n = n)),
                     Err(e) => app.toast(ui.ctx(), e),
                 }
             }
         }
         let mut sub = b.subfolders;
-        let c = ui.checkbox(&mut sub, "Include subfolders");
+        let c = ui.checkbox(&mut sub, crate::i18n::tr("Include subfolders"));
         register(ui.ctx(), "check:includeSubfolders", c.rect);
         if c.changed() {
             let _ = app.run("library.browse", json!({"path": b.path, "subfolders": sub}));
@@ -690,7 +698,11 @@ pub fn drag_feedback(app: &mut LightcraftApp, ctx: &egui::Context) {
     ctx.set_cursor_icon(egui::CursorIcon::Grabbing);
     egui::Area::new(egui::Id::new("drag-photos")).order(egui::Order::Tooltip).interactable(false).fixed_pos(pos + vec2(14.0, 10.0)).show(ctx, |ui| {
         egui::Frame::NONE.fill(t.accent).corner_radius(10.0).inner_margin(egui::Margin::symmetric(9, 3)).show(ui, |ui| {
-            ui.label(egui::RichText::new(format!("{n} photo{}", if n == 1 { "" } else { "s" })).color(Color32::WHITE).font(t.semibold(12.0)));
+            ui.label(
+                egui::RichText::new(crate::i18n::tr_format!("{n} photo{}", if n == 1 { "" } else { "s" }, n = n))
+                    .color(Color32::WHITE)
+                    .font(t.semibold(12.0)),
+            );
         });
     });
 }
@@ -712,11 +724,11 @@ pub fn label_menu(app: &mut LightcraftApp, ui: &mut egui::Ui) {
             ui.close();
         }
     }
-    if ui.selectable_label(current.is_none(), "None").clicked() {
+    if ui.selectable_label(current.is_none(), crate::i18n::tr("None")).clicked() {
         let _ = app.run("photo.label", json!({"label": "none"}));
     }
     ui.separator();
-    if ui.button("Edit Label Names…").clicked() {
+    if ui.button(crate::i18n::tr("Edit Label Names…")).clicked() {
         let _ = app.run("dialog.labelNames", json!({}));
     }
 }
@@ -755,10 +767,10 @@ pub fn context_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     if !app.session.selection.contains(id) {
         let _ = app.run("library.select", json!({"ids": [id.0]}));
     }
-    if ui.button("Open in Detail").clicked() {
+    if ui.button(crate::i18n::tr("Open in Detail")).clicked() {
         let _ = app.run("view.detail", json!({}));
     }
-    if ui.button("Find Similar Photos").clicked() {
+    if ui.button(crate::i18n::tr("Find Similar Photos")).clicked() {
         match app.run("library.findSimilar", json!({"id": id.0})) {
             Ok(r) => {
                 let n = r["photos"].as_array().map_or(0, Vec::len);
@@ -768,26 +780,26 @@ pub fn context_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
             Err(e) => app.toast(ui.ctx(), e),
         }
     }
-    if ui.button("Set as Reference Photo").clicked() {
+    if ui.button(crate::i18n::tr("Set as Reference Photo")).clicked() {
         let _ = app.run("photo.setReference", json!({"id": id.0}));
     }
     ui.separator();
-    ui.menu_button("Set Rating", |ui| {
+    ui.menu_button(crate::i18n::tr("Set Rating"), |ui| {
         for r in 0..=5 {
             if ui.button(if r == 0 { "No Stars".to_string() } else { "★".repeat(r) }).clicked() {
                 let _ = app.run("photo.rate", json!({"rating": r}));
             }
         }
     });
-    ui.menu_button("Set Flag", |ui| {
+    ui.menu_button(crate::i18n::tr("Set Flag"), |ui| {
         for (l, f) in [("Pick", "pick"), ("Reject", "reject"), ("Unflagged", "none")] {
             if ui.button(l).clicked() {
                 let _ = app.run("photo.flag", json!({"flag": f}));
             }
         }
     });
-    ui.menu_button("Set Color Label", |ui| label_menu(app, ui));
-    ui.menu_button("Add to Album", |ui| {
+    ui.menu_button(crate::i18n::tr("Set Color Label"), |ui| label_menu(app, ui));
+    ui.menu_button(crate::i18n::tr("Add to Album"), |ui| {
         let albums: Vec<_> = app.session.catalog.albums().filter(|a| !a.folder && !a.is_smart()).map(|a| (a.id.0, a.name.clone())).collect();
         for (aid, name) in albums {
             if ui.button(name).clicked() {
@@ -799,23 +811,23 @@ pub fn context_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     if let lightcraft_engine::LibrarySource::Album(aid) = app.session.source
         && app.session.catalog.album(aid).is_some_and(|a| !a.folder && !a.is_smart())
     {
-        if ui.button("Remove from Album").clicked() {
+        if ui.button(crate::i18n::tr("Remove from Album")).clicked() {
             let _ = app.run("album.removePhotos", json!({"id": aid.0}));
         }
-        if ui.button("Set as Album Cover").clicked() {
+        if ui.button(crate::i18n::tr("Set as Album Cover")).clicked() {
             let _ = app.run("album.setCover", json!({"id": aid.0, "photo": id.0}));
         }
     }
-    if ui.button("Rename…").clicked() {
+    if ui.button(crate::i18n::tr("Rename…")).clicked() {
         let _ = app.run("dialog.rename", json!({}));
     }
-    if ui.button("Create Virtual Copy").clicked() {
+    if ui.button(crate::i18n::tr("Create Virtual Copy")).clicked() {
         let _ = app.run("photo.virtualCopy", json!({}));
     }
-    if ui.button("Create Version").clicked() {
+    if ui.button(crate::i18n::tr("Create Version")).clicked() {
         let _ = app.run("version.create", json!({}));
     }
-    ui.menu_button("Stack", |ui| {
+    ui.menu_button(crate::i18n::tr("Stack"), |ui| {
         let stacked = app.session.catalog.stack_of(id).is_some();
         let several = app.session.selection.ids.len() > 1;
         for (label, cmd, on) in [
@@ -833,24 +845,24 @@ pub fn context_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
             }
         }
         ui.separator();
-        if ui.button("Auto-Stack by Capture Time…").clicked() {
+        if ui.button(crate::i18n::tr("Auto-Stack by Capture Time…")).clicked() {
             let _ = app.run("dialog.autoStack", json!({}));
         }
     });
     ui.separator();
-    if ui.button("Copy Edit Settings").clicked() {
+    if ui.button(crate::i18n::tr("Copy Edit Settings")).clicked() {
         let _ = app.run("develop.copy", json!({}));
     }
-    if ui.add_enabled(app.session.clipboard.is_some(), egui::Button::new("Paste Edit Settings")).clicked() {
+    if ui.add_enabled(app.session.clipboard.is_some(), egui::Button::new(crate::i18n::tr("Paste Edit Settings"))).clicked() {
         let _ = app.run("develop.paste", json!({}));
     }
-    if ui.add_enabled(app.session.clipboard.is_some(), egui::Button::new("Paste Selected Settings…")).clicked() {
+    if ui.add_enabled(app.session.clipboard.is_some(), egui::Button::new(crate::i18n::tr("Paste Selected Settings…"))).clicked() {
         let _ = app.run("dialog.pasteSettings", json!({}));
     }
-    if ui.button("Reset Edits").clicked() {
+    if ui.button(crate::i18n::tr("Reset Edits")).clicked() {
         let _ = app.run("develop.reset", json!({}));
     }
-    ui.menu_button("Photo Merge", |ui| {
+    ui.menu_button(crate::i18n::tr("Photo Merge"), |ui| {
         let n = app.session.targets(&json!({})).len();
         for (id, label) in [("dialog.mergeHdr", "HDR…"), ("dialog.mergePanorama", "Panorama…"), ("dialog.mergeHdrPanorama", "HDR Panorama…")] {
             if ui.add_enabled(n >= 2, egui::Button::new(label)).clicked() {
@@ -859,32 +871,33 @@ pub fn context_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
         }
     });
     ui.separator();
-    if ui.button("Rotate Left").clicked() {
+    if ui.button(crate::i18n::tr("Rotate Left")).clicked() {
         let _ = app.run("photo.rotateLeft", json!({}));
     }
-    if ui.button("Rotate Right").clicked() {
+    if ui.button(crate::i18n::tr("Rotate Right")).clicked() {
         let _ = app.run("photo.rotateRight", json!({}));
     }
     ui.separator();
     // the original moved or its drive is gone: point the photo at the file again
-    let missing = matches!(&app.session.catalog.photo(id).map(|p| p.source.clone()), Some(lightcraft_catalog::Source::File { path }) if !std::path::Path::new(path).exists());
-    if missing && ui.button("Locate Missing File…").clicked() {
+    // (a cached answer, checked off the UI thread)
+    let missing = matches!(&app.session.catalog.photo(id).map(|p| p.source.clone()), Some(lightcraft_catalog::Source::File { path }) if app.session.media.availability.is_offline(path));
+    if missing && ui.button(crate::i18n::tr("Locate Missing File…")).clicked() {
         let _ = app.run("photo.locate", json!({}));
     }
-    if ui.add_enabled(crate::menus::ui_enabled(app, "app.showInFinder"), egui::Button::new("Show in Finder")).clicked() {
+    if ui.add_enabled(crate::menus::ui_enabled(app, "app.showInFinder"), egui::Button::new(crate::i18n::tr("Show in Finder"))).clicked() {
         let _ = app.run("app.showInFinder", json!({}));
     }
-    if ui.button("Export…").clicked() {
+    if ui.button(crate::i18n::tr("Export…")).clicked() {
         let _ = app.run("dialog.export", json!({}));
     }
-    ui.menu_button("Export with Preset", |ui| {
+    ui.menu_button(crate::i18n::tr("Export with Preset"), |ui| {
         for (p, _) in app.session.all_export_presets() {
             if ui.button(&p.name).clicked() {
                 match app.run("app.export", json!({"preset": p.name, "background": true})) {
                     Ok(r) if r.get("background").is_some() => {}
                     Ok(r) => {
                         let n = r["files"].as_array().map_or(0, Vec::len);
-                        app.toast(ui.ctx(), format!("Exported {n} photo{}", if n == 1 { "" } else { "s" }));
+                        app.toast(ui.ctx(), crate::i18n::tr_format!("Exported {n} photo{}", if n == 1 { "" } else { "s" }, n = n));
                     }
                     Err(e) => app.toast(ui.ctx(), e),
                 }
@@ -892,7 +905,7 @@ pub fn context_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
         }
     });
     ui.separator();
-    if ui.button("Delete Photo").clicked() {
+    if ui.button(crate::i18n::tr("Delete Photo")).clicked() {
         let _ = app.run("photo.delete", json!({}));
     }
 }

crates/ui-egui/src/panels/left.rs

@@ -20,11 +20,12 @@ fn row(
     selected: bool,
     indent: f32,
 ) -> egui::Response {
+    let label = if matches!(id, "all" | "recentlyAdded" | "picks" | "missing" | "recentlyDeleted") { crate::i18n::tr(label) } else { label };
     let t = Tokens::get(ui.ctx());
     let (r, resp) = ui.allocate_exact_size(vec2(ui.available_width(), 29.0), Sense::click());
     register(ui.ctx(), format!("source:{id}"), r);
     let name = match count {
-        Some(n) => format!("{label}, {n} photos"),
+        Some(n) => crate::i18n::tr_format!("{label}, {n} photos", label = label, n = n),
         None => label.to_string(),
     };
     resp.widget_info(|| egui::WidgetInfo::selected(egui::WidgetType::SelectableLabel, true, selected, &name));
@@ -61,7 +62,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     let resized = super::resizable_side(ui, true, "left_panel", frame, width, crate::state::LEFT_WIDTH, 0.0, |ui| {
         ui.spacing_mut().item_spacing.y = 0.0;
         let (hr, _) = ui.allocate_exact_size(vec2(ui.available_width(), 44.0), Sense::hover());
-        ui.painter().text(pos2(hr.left() + 18.0, hr.center().y), Align2::LEFT_CENTER, "My Photos", t.semibold(15.0), t.text);
+        ui.painter().text(pos2(hr.left() + 18.0, hr.center().y), Align2::LEFT_CENTER, crate::i18n::tr("My Photos"), t.semibold(15.0), t.text);
         let counts = app.caches.counts(&app.session.catalog);
         let (total, picks, deleted) = (counts.total, counts.picks, counts.deleted);
         egui::ScrollArea::vertical().id_salt("left-scroll").auto_shrink([false, false]).show(ui, |ui| {
@@ -85,7 +86,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui) {
             ui.add_space(10.0);
             // Albums header
             let (ar, _) = ui.allocate_exact_size(vec2(ui.available_width(), 34.0), Sense::hover());
-            ui.painter().text(pos2(ar.left() + 18.0, ar.center().y), Align2::LEFT_CENTER, "Albums", t.semibold(13.5), t.text_label);
+            ui.painter().text(pos2(ar.left() + 18.0, ar.center().y), Align2::LEFT_CENTER, crate::i18n::tr("Albums"), t.semibold(13.5), t.text_label);
             let mut hdr = ui.new_child(
                 egui::UiBuilder::new()
                     .max_rect(Rect::from_min_max(pos2(ar.right() - 50.0, ar.top()), ar.right_bottom()))
@@ -93,20 +94,20 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui) {
             );
             let plus = icon_button(&mut hdr, "albumNew", Icon::Plus, vec2(26.0, 26.0), false, true, "Create Album");
             egui::Popup::menu(&plus).show(|ui| {
-                if ui.button("Create Album…").clicked() {
+                if ui.button(crate::i18n::tr("Create Album…")).clicked() {
                     app.ui.dialog = Some(crate::state::Dialog::NewAlbum { name: String::new(), folder: false });
                 }
-                if ui.button("Create Smart Album…").clicked() {
+                if ui.button(crate::i18n::tr("Create Smart Album…")).clicked() {
                     app.ui.dialog = Some(crate::state::Dialog::SmartRules {
                         id: None,
                         name: String::new(),
                         rules: lightcraft_catalog::RuleSet { rules: vec![crate::panels::rules_editor::new_rule()], ..Default::default() },
                     });
                 }
-                if ui.button("Create Smart Album from Filter…").clicked() {
+                if ui.button(crate::i18n::tr("Create Smart Album from Filter…")).clicked() {
                     app.ui.dialog = Some(crate::state::Dialog::NewSmartAlbum { name: String::new() });
                 }
-                if ui.button("Create Folder…").clicked() {
+                if ui.button(crate::i18n::tr("Create Folder…")).clicked() {
                     app.ui.dialog = Some(crate::state::Dialog::NewAlbum { name: String::new(), folder: true });
                 }
             });
@@ -116,7 +117,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui) {
             local_section(app, ui);
             // By date
             let (dr, _) = ui.allocate_exact_size(vec2(ui.available_width(), 34.0), Sense::hover());
-            ui.painter().text(pos2(dr.left() + 18.0, dr.center().y), Align2::LEFT_CENTER, "By Date", t.semibold(13.5), t.text_label);
+            ui.painter().text(pos2(dr.left() + 18.0, dr.center().y), Align2::LEFT_CENTER, crate::i18n::tr("By Date"), t.semibold(13.5), t.text_label);
             for g in app.caches.date_groups(&app.session.catalog).iter() {
                 // year → month → day; a click filters by that prefix, the triangle opens a level
                 if date_row(app, ui, &g.year, &g.year, g.count, 0.0) {
@@ -193,14 +194,15 @@ fn local_section(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     }
     let t = Tokens::get(ui.ctx());
     let (lr, _) = ui.allocate_exact_size(vec2(ui.available_width(), 34.0), Sense::hover());
-    ui.painter().text(pos2(lr.left() + 18.0, lr.center().y), Align2::LEFT_CENTER, "Local", t.semibold(13.5), t.text_label);
+    ui.painter().text(pos2(lr.left() + 18.0, lr.center().y), Align2::LEFT_CENTER, crate::i18n::tr("Local"), t.semibold(13.5), t.text_label);
     let home = std::env::var("HOME").or_else(|_| std::env::var("USERPROFILE")).unwrap_or_default();
     let mut builtin: Vec<(String, String)> = Vec::new();
     if !home.is_empty() {
         for (name, sub) in [("Pictures", "Pictures"), ("Desktop", "Desktop"), ("Downloads", "Downloads"), ("Home", "")] {
             // joined with the platform's separator, like the paths browsing gives back
             let p = if sub.is_empty() { home.clone() } else { std::path::Path::new(&home).join(sub).to_string_lossy().to_string() };
-            if std::path::Path::new(&p).is_dir() {
+            // (checked off the UI thread: a home folder can be on a network share)
+            if fs_cached(ui, "is-dir", &p, 5.0, |p| std::path::Path::new(p).is_dir()) == Some(true) {
                 builtin.push((name.to_string(), p));
             }
         }
@@ -231,9 +233,9 @@ fn local_section(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     }
     let hidden = app.ui.hidden_locations.len();
     if hidden > 0 {
-        let label = format!("Show {hidden} hidden location{}", if hidden == 1 { "" } else { "s" });
+        let label = crate::i18n::tr_format!("Show {hidden} hidden location{}", if hidden == 1 { "" } else { "s" }, hidden = hidden);
         if row(app, ui, "local:restoreHidden", Icon::Folder, &label, None, false, 0.0)
-            .on_hover_text("Put the locations you removed from Local back (no files change)")
+            .on_hover_text(crate::i18n::tr("Put the locations you removed from Local back (no files change)"))
             .clicked()
         {
             let _ = app.run("local.restoreHidden", json!({}));
@@ -305,15 +307,13 @@ pub(crate) fn local_places(
     out
 }
 
-/// The subfolders of `path` (not hidden ones), sorted; listed at most every 2 s per folder.
+/// The subfolders of `path` (not hidden ones), sorted; listed on a worker thread at most every
+/// 2 s per folder (empty until the first listing).
 fn subfolders(ui: &egui::Ui, path: &str) -> Vec<(String, String)> {
-    let id = egui::Id::new(("subfolders", path.to_string()));
-    let now = ui.input(|i| i.time);
-    if let Some((t, v)) = ui.data(|d| d.get_temp::<(f64, Vec<(String, String)>)>(id))
-        && now - t < 2.0
-    {
-        return v;
-    }
+    fs_cached(ui, "subfolders", path, 2.0, list_subfolders).unwrap_or_default()
+}
+
+fn list_subfolders(path: &str) -> Vec<(String, String)> {
     let mut v: Vec<(String, String)> = std::fs::read_dir(path)
         .map(|rd| {
             rd.flatten()
@@ -326,10 +326,59 @@ fn subfolders(ui: &egui::Ui, path: &str) -> Vec<(String, String)> {
         })
         .unwrap_or_default();
     v.sort_by_key(|(n, _)| n.to_lowercase());
-    ui.data_mut(|d| d.insert_temp(id, (now, v.clone())));
     v
 }
 
+/// A file-system answer for `path` (`f(path)`), kept per `kind` and path and refreshed on a worker
+/// thread at most every `every` seconds: a folder on a sleeping NAS, a dropped share or a
+/// spinning-up drive never blocks a frame. `None` until the first answer arrives.
+pub(crate) fn fs_cached<T: Clone + Send + 'static>(ui: &egui::Ui, kind: &'static str, path: &str, every: f64, f: fn(&str) -> T) -> Option<T> {
+    struct Entry<T> {
+        value: Option<T>,
+        at: Option<f64>,
+        running: bool,
+    }
+    type Cell<T> = std::sync::Arc<std::sync::Mutex<Entry<T>>>;
+    let id = egui::Id::new(("fs-cached", kind, path.to_string()));
+    let now = ui.input(|i| i.time);
+    let cell: Cell<T> = match ui.data(|d| d.get_temp::<Cell<T>>(id)) {
+        Some(c) => c,
+        None => {
+            let c: Cell<T> = std::sync::Arc::new(std::sync::Mutex::new(Entry { value: None, at: None, running: false }));
+            ui.data_mut(|d| d.insert_temp(id, c.clone()));
+            c
+        }
+    };
+    let lock = |c: &Cell<T>| c.lock().unwrap_or_else(std::sync::PoisonError::into_inner).value.clone();
+    let start = {
+        let mut e = cell.lock().unwrap_or_else(std::sync::PoisonError::into_inner);
+        let due = !e.running && e.at.is_none_or(|at| now - at >= every || now < at);
+        if due {
+            e.running = true;
+            e.at = Some(now);
+        }
+        due
+    };
+    if start {
+        let (out, path, repaint) = (cell.clone(), path.to_string(), ui.ctx().clone());
+        let work = move || {
+            let v = f(&path);
+            let mut e = out.lock().unwrap_or_else(std::sync::PoisonError::into_inner);
+            e.value = Some(v);
+            e.running = false;
+            drop(e);
+            repaint.request_repaint();
+        };
+        #[cfg(not(target_arch = "wasm32"))]
+        if std::thread::Builder::new().name("lc-fs-list".into()).spawn(work).is_err() {
+            cell.lock().unwrap_or_else(std::sync::PoisonError::into_inner).running = false;
+        }
+        #[cfg(target_arch = "wasm32")]
+        work();
+    }
+    lock(&cell)
+}
+
 /// A folder on disk with a disclosure triangle: click browses it, the triangle lists its
 /// subfolders. In the tree that holds the folder being browsed (`reveal`), the folders on the
 /// way down to it open whenever the browsed folder changes, so it shows highlighted in place.
@@ -384,20 +433,26 @@ fn folder_tree(
     }
     resp.context_menu(|ui| {
         if (transient || indent > 0.0)
-            && ui.button(if transient { "Keep in Local" } else { "Add to Local" }).on_hover_text("List this folder in Local from now on").clicked()
+            && ui
+                .button(if transient { "Keep in Local" } else { "Add to Local" })
+                .on_hover_text(crate::i18n::tr("List this folder in Local from now on"))
+                .clicked()
         {
             let _ = app.run("local.addRoot", json!({"path": path}));
             ui.close();
         }
         if indent == 0.0
-            && ui.button("Remove from Local").on_hover_text("Hides this shortcut only; the folder and its photos stay as they are").clicked()
+            && ui
+                .button(crate::i18n::tr("Remove from Local"))
+                .on_hover_text(crate::i18n::tr("Hides this shortcut only; the folder and its photos stay as they are"))
+                .clicked()
         {
             let _ = app.run("local.hide", json!({"path": path}));
             ui.close();
         }
-        if ui.button("Rename Folder…").clicked() {
+        if ui.button(crate::i18n::tr("Rename Folder…")).clicked() {
             app.ui.dialog = Some(crate::state::Dialog::TextPrompt {
-                title: format!("Rename “{name}”"),
+                title: crate::i18n::tr_format!("Rename “{name}”", name = name),
                 hint: "Folder name (renamed on disk; its photos follow)".into(),
                 value: name.to_string(),
                 command: "folder.rename".into(),
@@ -405,7 +460,7 @@ fn folder_tree(
                 key: "name".into(),
             });
         }
-        if app.services.pick_folder.is_some() && ui.button("Move Folder To…").clicked() {
+        if app.services.pick_folder.is_some() && ui.button(crate::i18n::tr("Move Folder To…")).clicked() {
             let into = app.services.pick_folder.as_mut().and_then(|f| f());
             if let Some(into) = into {
                 match app.run("folder.move", json!({"path": path, "into": into})) {
@@ -415,7 +470,7 @@ fn folder_tree(
             }
         }
         if app.services.reveal.is_some()
-            && ui.button("Show in Finder").clicked()
+            && ui.button(crate::i18n::tr("Show in Finder")).clicked()
             && let Some(f) = app.services.reveal.as_mut()
         {
             let _ = f(path);
@@ -489,7 +544,7 @@ fn albums_tree(app: &mut LightcraftApp, ui: &mut egui::Ui, all: &[Album], parent
                 drop_target(app, ui, &resp, a);
             }
             if let Some(rules) = &a.smart {
-                resp = resp.on_hover_text(format!("Smart album: {}", rules.describe()));
+                resp = resp.on_hover_text(crate::i18n::tr_format!("Smart album: {}", rules.describe()));
             }
             if resp.clicked() {
                 let _ = app.run("library.source", json!({"kind": "album", "id": a.id.0}));
@@ -512,7 +567,7 @@ fn drop_target(app: &mut LightcraftApp, ui: &mut egui::Ui, resp: &egui::Response
     if ui.input(|i| i.pointer.any_released()) {
         let n = ids.len();
         match app.run("album.addPhotos", json!({"id": a.id.0, "ids": ids})) {
-            Ok(_) => app.toast(ui.ctx(), format!("Added {n} photo{} to “{}”", if n == 1 { "" } else { "s" }, a.name)),
+            Ok(_) => app.toast(ui.ctx(), crate::i18n::tr_format!("Added {n} photo{} to “{}”", if n == 1 { "" } else { "s" }, a.name, n = n)),
             Err(e) => app.toast(ui.ctx(), e),
         }
         app.ui.dragging_photos = None;
@@ -521,27 +576,27 @@ fn drop_target(app: &mut LightcraftApp, ui: &mut egui::Ui, resp: &egui::Response
 
 fn folder_menu(app: &mut LightcraftApp, resp: &egui::Response, a: &Album) {
     resp.context_menu(|ui| {
-        if !a.folder && !a.is_smart() && ui.button("Add Selected Photos").clicked() {
+        if !a.folder && !a.is_smart() && ui.button(crate::i18n::tr("Add Selected Photos")).clicked() {
             let _ = app.run("album.addPhotos", json!({"id": a.id.0}));
         }
         if !a.folder && !a.is_smart() {
             let is_target = app.session.target_album == Some(a.id) || (app.session.target_album.is_none() && a.quick);
-            if !is_target && ui.button("Set as Target Album (B adds to it)").clicked() {
+            if !is_target && ui.button(crate::i18n::tr("Set as Target Album (B adds to it)")).clicked() {
                 let _ = app.run("album.setTarget", json!({"id": if a.quick { serde_json::Value::Null } else { json!(a.id.0) }}));
             }
-            if is_target && !a.quick && ui.button("Stop Using as Target Album").clicked() {
+            if is_target && !a.quick && ui.button(crate::i18n::tr("Stop Using as Target Album")).clicked() {
                 let _ = app.run("album.setTarget", json!({"id": null}));
             }
         }
-        if a.quick && ui.button("Clear Quick Collection").clicked() {
+        if a.quick && ui.button(crate::i18n::tr("Clear Quick Collection")).clicked() {
             let _ = app.run("album.clearQuick", json!({}));
         }
-        if a.is_smart() && ui.button("Edit Smart Album…").clicked() {
+        if a.is_smart() && ui.button(crate::i18n::tr("Edit Smart Album…")).clicked() {
             // older smart albums keep their filter fields; the editor works on the rule set
             let rules = a.smart.as_ref().and_then(|f| f.rule_set.clone()).unwrap_or_default();
             app.ui.dialog = Some(crate::state::Dialog::SmartRules { id: Some(a.id.0), name: a.name.clone(), rules });
         }
-        if a.is_smart() && ui.button("Update Rules from Current Filter").clicked() {
+        if a.is_smart() && ui.button(crate::i18n::tr("Update Rules from Current Filter")).clicked() {
             let _ = app.run("album.setRules", json!({"id": a.id.0, "fromView": true}));
         }
         if !a.folder {
@@ -551,12 +606,12 @@ fn folder_menu(app: &mut LightcraftApp, resp: &egui::Response, a: &Album) {
                 let _ = app.run("library.selectAll", json!({}));
             };
             let has_photos = app.session.catalog.album_count(a.id) > 0;
-            if ui.add_enabled(has_photos, egui::Button::new("Export Album…")).clicked() {
+            if ui.add_enabled(has_photos, egui::Button::new(crate::i18n::tr("Export Album…"))).clicked() {
                 show_all(app);
                 let _ = app.run("dialog.export", json!({}));
             }
             ui.add_enabled_ui(has_photos, |ui| {
-                ui.menu_button("Export Album with Preset", |ui| {
+                ui.menu_button(crate::i18n::tr("Export Album with Preset"), |ui| {
                     for (p, _) in app.session.all_export_presets() {
                         if ui.button(&p.name).clicked() {
                             show_all(app);
@@ -573,8 +628,8 @@ fn folder_menu(app: &mut LightcraftApp, resp: &egui::Response, a: &Album) {
         let mut folders: Vec<(u64, String)> =
             app.session.catalog.albums().filter(|f| f.folder && !is_within(app, f.id, a.id)).map(|f| (f.id.0, f.name.clone())).collect();
         folders.sort_by_key(|(_, n)| n.to_lowercase());
-        ui.menu_button("Move to", |ui| {
-            if ui.add_enabled(a.parent.is_some(), egui::Button::new("Top Level")).clicked() {
+        ui.menu_button(crate::i18n::tr("Move to"), |ui| {
+            if ui.add_enabled(a.parent.is_some(), egui::Button::new(crate::i18n::tr("Top Level"))).clicked() {
                 let _ = app.run("album.move", json!({"id": a.id.0, "parent": null}));
             }
             for (fid, name) in &folders {
@@ -583,10 +638,10 @@ fn folder_menu(app: &mut LightcraftApp, resp: &egui::Response, a: &Album) {
                 }
             }
         });
-        if ui.button("Rename…").clicked() {
+        if ui.button(crate::i18n::tr("Rename…")).clicked() {
             app.ui.dialog = Some(crate::state::Dialog::RenameAlbum { id: a.id.0, name: a.name.clone() });
         }
-        if ui.button("Delete").clicked() {
+        if ui.button(crate::i18n::tr("Delete")).clicked() {
             let _ = app.run("album.delete", json!({"id": a.id.0}));
         }
     });
@@ -620,7 +675,7 @@ fn keywords_section(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     }
     ui.add_space(10.0);
     let (kr, _) = ui.allocate_exact_size(vec2(ui.available_width(), 34.0), Sense::hover());
-    ui.painter().text(pos2(kr.left() + 18.0, kr.center().y), Align2::LEFT_CENTER, "Keywords", t.semibold(13.5), t.text_label);
+    ui.painter().text(pos2(kr.left() + 18.0, kr.center().y), Align2::LEFT_CENTER, crate::i18n::tr("Keywords"), t.semibold(13.5), t.text_label);
     keyword_rows(app, ui, &tree, 0.0);
 }
 
@@ -656,20 +711,20 @@ fn keyword_rows(app: &mut LightcraftApp, ui: &mut egui::Ui, nodes: &[KeywordNode
         }
         resp.context_menu(|ui| {
             let has_sel = app.session.active().is_some();
-            if ui.add_enabled(has_sel, egui::Button::new("Add to Selected Photos")).clicked() {
+            if ui.add_enabled(has_sel, egui::Button::new(crate::i18n::tr("Add to Selected Photos"))).clicked() {
                 let _ = app.run("photo.setMeta", json!({"addKeywords": [n.path]}));
             }
-            if ui.add_enabled(has_sel, egui::Button::new("Remove from Selected Photos")).clicked() {
+            if ui.add_enabled(has_sel, egui::Button::new(crate::i18n::tr("Remove from Selected Photos"))).clicked() {
                 let _ = app.run("photo.setMeta", json!({"removeKeywords": [n.path]}));
             }
             ui.separator();
-            if ui.button("Rename Keyword…").clicked() {
+            if ui.button(crate::i18n::tr("Rename Keyword…")).clicked() {
                 app.ui.dialog = Some(crate::state::Dialog::RenameKeyword { from: n.path.clone(), to: n.path.clone() });
             }
-            if ui.button("Merge into…").clicked() {
+            if ui.button(crate::i18n::tr("Merge into…")).clicked() {
                 app.ui.dialog = Some(crate::state::Dialog::MergeKeywords { from: vec![n.path.clone()], into: String::new() });
             }
-            if ui.button("Delete Keyword").clicked() {
+            if ui.button(crate::i18n::tr("Delete Keyword")).clicked() {
                 let _ = app.run("keyword.delete", json!({"keyword": n.path}));
             }
         });

crates/ui-egui/src/panels/library_problem.rs

@@ -0,0 +1,184 @@
+//! The library couldn't be opened at launch (issue #100): never a silent in-memory session. A
+//! blocking window says which library and why, and offers Try Again, Choose Another Library…,
+//! Continue Without Saving and Quit. Continuing shows a banner under the top bar for as long as the
+//! session is temporary.
+
+use egui::{Align2, RichText, vec2};
+use serde_json::json;
+
+use crate::LightcraftApp;
+use crate::theme::Tokens;
+use crate::widgets::register;
+
+/// A library that failed to open (set by the host at launch).
+#[derive(Clone, Debug, Default, PartialEq)]
+pub struct LibraryProblem {
+    /// The library folder ("" when there was none to try, e.g. no home folder).
+    pub path: String,
+    /// Why it didn't open.
+    pub error: String,
+    /// Continue Without Saving was chosen: the banner shows instead of the window.
+    pub dismissed: bool,
+    /// Files from the command line, imported once a library opens.
+    pub pending_import: Vec<String>,
+    /// Try Again reopens `path` as a library folder (`false` in the browser, whose storage isn't
+    /// a folder: reloading the page tries again).
+    pub can_retry: bool,
+}
+
+impl LibraryProblem {
+    pub fn new(path: impl Into<String>, error: impl Into<String>) -> LibraryProblem {
+        LibraryProblem { path: path.into(), error: error.into(), can_retry: true, ..Default::default() }
+    }
+
+    /// `ui.inspect` → `libraryProblem`.
+    pub fn to_json(&self) -> serde_json::Value {
+        json!({"path": self.path, "error": self.error, "temporarySession": self.dismissed, "pendingImport": self.pending_import.len()})
+    }
+}
+
+/// What the user chose.
+enum Choice {
+    Retry,
+    Choose,
+    Temporary,
+    Quit,
+}
+
+/// Open `path` (`None`: ask for a folder) through `app.openLibrary`; on success the problem is
+/// over (and command-line files are imported), else it shows the new error.
+fn open(app: &mut LightcraftApp, path: Option<String>) {
+    let params = match &path {
+        Some(p) => json!({"path": p}),
+        None => json!({}),
+    };
+    match app.run("app.openLibrary", params) {
+        Ok(serde_json::Value::Null) => {} // folder dialog cancelled
+        Ok(_) => {
+            let files = app.library_problem.take().map(|p| p.pending_import).unwrap_or_default();
+            if !files.is_empty() {
+                let _ = app.run("library.import", json!({"paths": files}));
+            }
+        }
+        Err(e) => {
+            if let Some(p) = app.library_problem.as_mut() {
+                if let Some(path) = path {
+                    p.path = path;
+                }
+                p.error = e;
+                p.dismissed = false;
+            }
+        }
+    }
+}
+
+/// Clear the problem once a library is open (e.g. through Settings → Open Library…).
+pub fn logic(app: &mut LightcraftApp) {
+    if app.library_problem.is_some() && app.session.library.is_some() {
+        app.library_problem = None;
+    }
+}
+
+/// The blocking window (until a choice is made).
+pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
+    let Some(problem) = app.library_problem.clone() else { return };
+    if problem.dismissed {
+        return;
+    }
+    let t = Tokens::get(ctx);
+    let screen = ctx.content_rect();
+    egui::Area::new(egui::Id::new("library-problem-dim")).order(egui::Order::Middle).fixed_pos(screen.min).interactable(true).show(ctx, |ui| {
+        // swallows clicks: nothing behind the window can be used meanwhile
+        ui.allocate_rect(screen, egui::Sense::click_and_drag());
+        ui.painter().rect_filled(screen, 0.0, egui::Color32::from_black_alpha(160));
+    });
+    let mut choice = None;
+    let frame = egui::Frame::window(&ctx.global_style()).inner_margin(egui::Margin::symmetric(18, 14));
+    egui::Window::new(crate::i18n::tr("Your library couldn't be opened"))
+        .id(egui::Id::new("library-problem"))
+        .order(egui::Order::Foreground)
+        .collapsible(false)
+        .resizable(false)
+        .frame(frame)
+        .anchor(Align2::CENTER_CENTER, [0.0, 0.0])
+        .default_width(460.0)
+        .show(ctx, |ui| {
+            // a fixed width: a wrapped label in an auto-sized, centred window would move it every frame
+            ui.set_width(440.0);
+            ui.spacing_mut().item_spacing.y = 8.0;
+            if problem.path.is_empty() {
+                ui.label(RichText::new(crate::i18n::tr("LightCraft couldn't find where to keep your library.")).color(t.text));
+            } else {
+                ui.label(RichText::new(crate::i18n::tr("LightCraft couldn't open the library at")).color(t.text_label));
+                ui.label(RichText::new(&problem.path).font(t.semibold(12.5)).color(t.text));
+            }
+            ui.add(egui::Label::new(RichText::new(&problem.error).color(t.caution)).wrap());
+            ui.label(
+                RichText::new(
+                    "Your photos and edits in it are untouched. You can try again (e.g. after closing another program that has it open \
+                     or reconnecting its drive), open a different library or create a new one, or continue without a library — \
+                     then nothing you do is saved.",
+                )
+                .color(t.text_dim),
+            );
+            ui.add_space(4.0);
+            ui.horizontal(|ui| {
+                let mut button = |ui: &mut egui::Ui, id: &str, label: &str, enabled: bool, c: Choice| {
+                    let r = ui.add_enabled(enabled, egui::Button::new(crate::i18n::tr(label)).min_size(vec2(0.0, 26.0)));
+                    register(ui.ctx(), format!("button:{id}"), r.rect);
+                    if r.clicked() {
+                        choice = Some(c);
+                    }
+                };
+                button(ui, "libraryRetry", "Try Again", problem.can_retry && !problem.path.is_empty(), Choice::Retry);
+                button(ui, "libraryChoose", "Choose Another Library…", app.services.pick_folder.is_some(), Choice::Choose);
+                button(ui, "libraryTemporary", "Continue Without Saving", true, Choice::Temporary);
+                button(ui, "libraryQuit", "Quit", true, Choice::Quit);
+            });
+        });
+    match choice {
+        Some(Choice::Retry) => open(app, Some(problem.path)),
+        Some(Choice::Choose) => open(app, None),
+        Some(Choice::Temporary) => {
+            if let Some(p) = app.library_problem.as_mut() {
+                p.dismissed = true;
+            }
+            let files = app.library_problem.as_mut().map(|p| std::mem::take(&mut p.pending_import)).unwrap_or_default();
+            if !files.is_empty() {
+                let _ = app.run("library.import", json!({"paths": files}));
+            }
+        }
+        Some(Choice::Quit) => app.ui.quit = true,
+        None => {}
+    }
+}
+
+/// The banner under the top bar while the session is temporary (Continue Without Saving).
+pub fn banner(app: &mut LightcraftApp, ui: &mut egui::Ui) {
+    if !app.library_problem.as_ref().is_some_and(|p| p.dismissed) {
+        return;
+    }
+    let t = Tokens::get(ui.ctx());
+    let mut reopen = false;
+    egui::Panel::top("library-problem-banner")
+        .exact_size(30.0)
+        .frame(egui::Frame::NONE.fill(t.caution).inner_margin(egui::Margin::symmetric(12, 0)))
+        .show(ui, |ui| {
+            ui.horizontal_centered(|ui| {
+                let r = ui.label(
+                    RichText::new(crate::i18n::tr("Temporary session — your library isn't open, and nothing you do here is saved."))
+                        .font(t.semibold(12.5))
+                        .color(t.canvas),
+                );
+                register(ui.ctx(), "indicator:temporarySession", r.rect);
+                let b = ui.add(
+                    egui::Button::new(RichText::new(crate::i18n::tr("Open Library…")).color(t.canvas)).fill(egui::Color32::from_black_alpha(40)),
+                );
+                register(ui.ctx(), "button:libraryReopen", b.rect);
+                reopen = b.clicked();
+            });
+        });
+    if reopen && let Some(p) = app.library_problem.as_mut() {
+        p.dismissed = false;
+    }
+}

crates/ui-egui/src/panels/masking.rs

@@ -73,7 +73,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     let d = app.session.develop_of(id).unwrap_or_default();
     header(ui, "Masking");
     egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 0, bottom: 10 }).show(ui, |ui| {
-        ui.label(egui::RichText::new("Create New Mask").color(t.text_dim));
+        ui.label(egui::RichText::new(crate::i18n::tr("Create New Mask")).color(t.text_dim));
         ui.add_space(6.0);
         let tiles: [(&str, &str, Icon); 8] = [
             ("subject", "Subject", Icon::Subject),
@@ -123,7 +123,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     // mask list
     egui::Frame::NONE.inner_margin(egui::Margin { left: 16, right: 16, top: 8, bottom: 8 }).show(ui, |ui| {
         ui.horizontal(|ui| {
-            ui.label(egui::RichText::new("Masks").font(t.semibold(13.0)).color(t.text_label));
+            ui.label(egui::RichText::new(crate::i18n::tr("Masks")).font(t.semibold(13.0)).color(t.text_label));
             ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
                 let on = app.ui.mask_overlay;
                 if icon_button(ui, "maskOverlay", Icon::Eye, vec2(24.0, 24.0), on, true, "Show overlay (O)").clicked() {
@@ -132,7 +132,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
             });
         });
         if d.masks.is_empty() {
-            ui.label(egui::RichText::new("No masks yet. Choose a mask type above.").color(t.text_dim));
+            ui.label(egui::RichText::new(crate::i18n::tr("No masks yet. Choose a mask type above.")).color(t.text_dim));
         }
         let count = d.masks.len();
         for (index, m) in d.masks.iter().enumerate() {
@@ -254,7 +254,7 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
                 }
                 resp.context_menu(|ui| component_row_menu(app, ui, m.id, i, &label, m.components.len()));
                 ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
-                    let more = ui.small_button("…").on_hover_text("Component options");
+                    let more = ui.small_button("…").on_hover_text(crate::i18n::tr("Component options"));
                     register(ui.ctx(), format!("button:componentMenu{i}"), more.rect);
                     egui::Popup::menu(&more).show(|ui| component_row_menu(app, ui, m.id, i, &label, m.components.len()));
                 });
@@ -265,13 +265,13 @@ pub fn show(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
         // wraps: the five actions are wider than a narrow panel
         ui.horizontal_wrapped(|ui| {
             ui.spacing_mut().item_spacing.y = 6.0;
-            let add = text_button(ui, "maskAddComp", "Add", false);
+            let add = text_button(ui, "maskAddComp", crate::i18n::tr("Add"), false);
             egui::Popup::menu(&add).show(|ui| component_menu(app, ui, "add"));
-            let sub = text_button(ui, "maskSubComp", "Subtract", false);
+            let sub = text_button(ui, "maskSubComp", crate::i18n::tr("Subtract"), false);
             egui::Popup::menu(&sub).show(|ui| component_menu(app, ui, "subtract"));
-            let int = text_button(ui, "maskIntComp", "Intersect", false);
+            let int = text_button(ui, "maskIntComp", crate::i18n::tr("Intersect"), false);
             egui::Popup::menu(&int).show(|ui| component_menu(app, ui, "intersect"));
-            if text_button(ui, "maskInvert", "Invert", m.invert).clicked() {
+            if text_button(ui, "maskInvert", crate::i18n::tr("Invert"), m.invert).clicked() {
                 let _ = app.run("mask.invert", json!({}));
             }
             if icon_button(ui, "maskDelete", Icon::Trash, vec2(26.0, 24.0), false, true, "Delete mask").clicked() {
@@ -335,11 +335,11 @@ fn mask_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, id: u32, name: &str, vi
     run(ui, "Move Up", index > 0, "mask.move", json!({"id": id, "delta": -1}));
     run(ui, "Move Down", index + 1 < count, "mask.move", json!({"id": id, "delta": 1}));
     ui.separator();
-    if ui.button("Rename…").clicked() {
+    if ui.button(crate::i18n::tr("Rename…")).clicked() {
         app.ui.renaming_mask = Some((id, name.to_string()));
         ui.close();
     }
-    if ui.button("Delete Mask").clicked() {
+    if ui.button(crate::i18n::tr("Delete Mask")).clicked() {
         let _ = app.run("mask.delete", json!({"id": id}));
         ui.close();
     }
@@ -354,7 +354,7 @@ fn overlay_options(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     let t = Tokens::get(ui.ctx());
     let view = MaskView::parse(&app.ui.mask_overlay_mode).unwrap_or_default();
     ui.horizontal(|ui| {
-        ui.label(egui::RichText::new("Overlay").color(t.text_dim));
+        ui.label(egui::RichText::new(crate::i18n::tr("Overlay")).color(t.text_dim));
         let r = crate::widgets::dropdown(ui, "maskOverlayMode", view.label(), t.font(12.5), t.text_label);
         egui::Popup::menu(&r).show(|ui| {
             for v in MaskView::ALL {
@@ -396,7 +396,7 @@ fn overlay_options(app: &mut LightcraftApp, ui: &mut egui::Ui) {
         app.ui.mask_overlay_opacity = v as f32;
     }
     let mut pins = app.ui.mask_pins;
-    if ui.checkbox(&mut pins, "Show Pins").changed() {
+    if ui.checkbox(&mut pins, crate::i18n::tr("Show Pins")).changed() {
         let _ = app.run("view.maskPins", json!({"show": pins}));
     }
 }
@@ -410,7 +410,7 @@ fn range_controls(app: &mut LightcraftApp, ui: &mut egui::Ui, comp: usize, shape
     };
     match shape {
         MaskShape::LuminanceRange { lo, hi, lo_feather, hi_feather } => {
-            ui.label(egui::RichText::new("Select Luminance Range").color(t.text_dim).size(11.5));
+            ui.label(egui::RichText::new(crate::i18n::tr("Select Luminance Range")).color(t.text_dim).size(11.5));
             let (lo, hi) = (*lo, *hi);
             let w = ui.available_width().min(240.0);
             let (rect, resp) = ui.allocate_exact_size(vec2(w, 18.0), Sense::click_and_drag());
@@ -471,7 +471,7 @@ fn range_controls(app: &mut LightcraftApp, ui: &mut egui::Ui, comp: usize, shape
                 app.run("mask.update", json!({"component": comp, "shape": MaskShape::LuminanceRange { lo, hi, lo_feather: f, hi_feather: f }}))
             });
             let mut map = app.ui.mask_overlay && app.ui.mask_overlay_mode == "colorOnBw";
-            let r = ui.checkbox(&mut map, "Show Luminance Map");
+            let r = ui.checkbox(&mut map, crate::i18n::tr("Show Luminance Map"));
             register(ui.ctx(), format!("check:lumMap{comp}"), r.rect);
             if r.changed() {
                 // the luminance map: the photo in black & white with the selected range tinted
@@ -494,8 +494,8 @@ fn range_controls(app: &mut LightcraftApp, ui: &mut egui::Ui, comp: usize, shape
                         .size(11.5),
                 );
                 let picking = app.ui.tool == "colorRange";
-                if text_button(ui, &format!("colorPick{comp}"), "Pick", picking)
-                    .on_hover_text("Click the photo to pick a colour; ⇧-click adds more (up to 5)")
+                if text_button(ui, &format!("colorPick{comp}"), crate::i18n::tr("Pick"), picking)
+                    .on_hover_text(crate::i18n::tr("Click the photo to pick a colour; ⇧-click adds more (up to 5)"))
                     .clicked()
                 {
                     app.ui.tool = if picking { String::new() } else { "colorRange".into() };
@@ -534,22 +534,26 @@ fn component_row_menu(app: &mut LightcraftApp, ui: &mut egui::Ui, mask: u32, k:
         }
     };
     run(ui, "Invert", json!({"action": "invert"}));
-    run(ui, &format!("Duplicate \"{label}\""), json!({"action": "duplicate"}));
+    run(ui, &crate::i18n::tr_format!("Duplicate \"{label}\"", label = label), json!({"action": "duplicate"}));
     if k > 0 {
-        ui.menu_button("Mode", |ui| {
+        ui.menu_button(crate::i18n::tr("Mode"), |ui| {
             for (op, text) in [("add", "Add"), ("subtract", "Subtract"), ("intersect", "Intersect")] {
                 run(ui, text, json!({"action": "op", "op": op}));
             }
         });
     }
-    ui.menu_button("Intersect with", |ui| component_menu(app, ui, "intersect"));
-    ui.menu_button("Subtract", |ui| component_menu(app, ui, "subtract"));
+    ui.menu_button(crate::i18n::tr("Intersect with"), |ui| component_menu(app, ui, "intersect"));
+    ui.menu_button(crate::i18n::tr("Subtract"), |ui| component_menu(app, ui, "subtract"));
     ui.separator();
-    if ui.button("Rename…").clicked() {
+    if ui.button(crate::i18n::tr("Rename…")).clicked() {
         app.ui.renaming_component = Some((mask, k, label.to_string()));
         ui.close();
     }
-    let del = if count == 1 { format!("Delete \"{label}\" (and the mask)") } else { format!("Delete \"{label}\"") };
+    let del = if count == 1 {
+        crate::i18n::tr_format!("Delete \"{label}\" (and the mask)", label = label)
+    } else {
+        crate::i18n::tr_format!("Delete \"{label}\"", label = label)
+    };
     if ui.button(del).clicked() {
         let _ = app.run("mask.component", json!({"id": mask, "component": k, "action": "delete"}));
         ui.close();
@@ -584,16 +588,20 @@ fn brush_settings(app: &mut LightcraftApp, ui: &mut egui::Ui) {
     let t = Tokens::get(ui.ctx());
     egui::Frame::NONE.inner_margin(egui::Margin { left: 24, right: 22, top: 6, bottom: 0 }).show(ui, |ui| {
         ui.horizontal(|ui| {
-            ui.label(egui::RichText::new("Brush").font(t.semibold(13.0)));
-            if text_button(ui, "brushAdd", "Add", !app.ui.brush_erase).clicked() {
+            ui.label(egui::RichText::new(crate::i18n::tr("Brush")).font(t.semibold(13.0)));
+            if text_button(ui, "brushAdd", crate::i18n::tr("Add"), !app.ui.brush_erase).clicked() {
                 app.ui.brush_erase = false;
             }
-            if text_button(ui, "brushErase", "Erase", app.ui.brush_erase).clicked() {
+            if text_button(ui, "brushErase", crate::i18n::tr("Erase"), app.ui.brush_erase).clicked() {
                 app.ui.brush_erase = true;
             }
         });
         let mut auto = app.ui.brush_auto_mask;
-        if ui.checkbox(&mut auto, "Auto Mask").on_hover_text("Paint only areas like the one under the brush").changed() {
+        if ui
+            .checkbox(&mut auto, crate::i18n::tr("Auto Mask"))
+            .on_hover_text(crate::i18n::tr("Paint only areas like the one under the brush"))
+            .changed()
+        {
             app.ui.brush_auto_mask = auto;
         }
     });

crates/ui-egui/src/panels/mod.rs

@@ -10,7 +10,9 @@ pub mod edit;
 pub mod filterbar;
 pub mod grid;
 pub mod left;
+pub mod library_problem;
 pub mod masking;
+pub mod notices;
 pub mod presets;
 pub mod profiles;
 pub mod right;
@@ -69,8 +71,10 @@ pub fn toast(app: &mut LightcraftApp, ctx: &egui::Context) {
     let t = Tokens::get(ctx);
     let fade = ((until - now) / 0.25).clamp(0.0, 1.0) as f32;
     let painter = ctx.layer_painter(egui::LayerId::new(egui::Order::Foreground, egui::Id::new("toast")));
-    let galley = painter.layout_no_wrap(text, t.font(14.0), t.text.gamma_multiply(fade));
-    let size = vec2(galley.size().x + 40.0, 40.0);
+    // long messages (a save warning, the web build's notices) wrap within the canvas
+    let wrap = (canvas.width() - 80.0).clamp(200.0, 720.0);
+    let galley = painter.layout(text, t.font(14.0), t.text.gamma_multiply(fade), wrap);
+    let size = vec2(galley.size().x + 40.0, (galley.size().y + 22.0).max(40.0));
     let r = Rect::from_center_size(pos2(canvas.center().x, canvas.bottom() - 60.0), size);
     painter.rect_filled(r, 6.0, egui::Color32::from_black_alpha((200.0 * fade) as u8));
     painter.galley(r.center() - galley.size() / 2.0, galley, t.text);
@@ -81,6 +85,6 @@ pub fn toast(app: &mut LightcraftApp, ctx: &egui::Context) {
 pub fn empty_message(ui: &egui::Ui, rect: Rect, title: &str, body: &str) {
     let t = Tokens::get(ui.ctx());
     let p = ui.painter();
-    p.text(rect.center() - vec2(0.0, 12.0), Align2::CENTER_CENTER, title, t.semibold(18.0), t.text_label);
-    p.text(rect.center() + vec2(0.0, 14.0), Align2::CENTER_CENTER, body, t.font(13.0), t.text_dim);
+    p.text(rect.center() - vec2(0.0, 12.0), Align2::CENTER_CENTER, crate::i18n::tr(title), t.semibold(18.0), t.text_label);
+    p.text(rect.center() + vec2(0.0, 14.0), Align2::CENTER_CENTER, crate::i18n::tr(body), t.font(13.0), t.text_dim);
 }

crates/ui-egui/src/panels/notices.rs

@@ -0,0 +1,115 @@
+//! Things the user must not miss (issue #103): settings files that were damaged or unreadable when
+//! the library opened (and host warnings such as a damaged `ui.json`), and quitting while changes
+//! are only in memory.
+
+use egui::{Align2, RichText, vec2};
+
+use crate::LightcraftApp;
+use crate::theme::Tokens;
+use crate::widgets::register;
+
+/// Collect the library's settings-file warnings (each is shown once).
+pub fn logic(app: &mut LightcraftApp) {
+    let new = app.session.take_library_warnings();
+    app.notices.extend(new);
+}
+
+/// The window may close now (`true`), or the quit prompt is shown (`false`): changes that
+/// couldn't be written are retried first — the log, then a snapshot of everything in memory.
+pub fn may_close(app: &mut LightcraftApp) -> bool {
+    if app.quit_confirmed || app.session.unsaved().is_none() {
+        return true;
+    }
+    let _ = app.session.persist();
+    if app.session.unsaved().is_some()
+        && let Err(e) = app.session.close_library()
+    {
+        log::error!("quit: library not saved: {e}");
+    }
+    match app.session.unsaved() {
+        None => true,
+        Some((n, e)) => {
+            app.quit_prompt = Some(format!(
+                "{} couldn't be written to disk: {e}\nIf you quit now, {} lost.",
+                if n == 1 { "1 change".to_string() } else { format!("{n} changes") },
+                if n == 1 { "it is" } else { "they are" }
+            ));
+            false
+        }
+    }
+}
+
+enum Choice {
+    Retry,
+    QuitAnyway,
+    Cancel,
+    Ok,
+}
+
+fn window(ctx: &egui::Context, id: &str, title: &str, text: &str, buttons: &[(&str, &str, Choice)]) -> Option<usize> {
+    let t = Tokens::get(ctx);
+    let screen = ctx.content_rect();
+    egui::Area::new(egui::Id::new((id, "dim"))).order(egui::Order::Middle).fixed_pos(screen.min).show(ctx, |ui| {
+        ui.allocate_rect(screen, egui::Sense::click_and_drag());
+        ui.painter().rect_filled(screen, 0.0, egui::Color32::from_black_alpha(140));
+    });
+    let mut chosen = None;
+    let frame = egui::Frame::window(&ctx.global_style()).inner_margin(egui::Margin::symmetric(18, 14));
+    egui::Window::new(title)
+        .id(egui::Id::new(id))
+        .order(egui::Order::Foreground)
+        .collapsible(false)
+        .resizable(false)
+        .frame(frame)
+        .anchor(Align2::CENTER_CENTER, [0.0, 0.0])
+        .default_width(440.0)
+        .show(ctx, |ui| {
+            // a fixed width: a wrapped label in an auto-sized, centred window would move it every frame
+            ui.set_width(420.0);
+            ui.spacing_mut().item_spacing.y = 8.0;
+            ui.add(egui::Label::new(RichText::new(text).color(t.text_label)).wrap());
+            ui.add_space(4.0);
+            ui.horizontal(|ui| {
+                for (i, (bid, label, _)) in buttons.iter().enumerate() {
+                    let r = ui.add(egui::Button::new(*label).min_size(vec2(0.0, 26.0)));
+                    register(ui.ctx(), format!("button:{bid}"), r.rect);
+                    if r.clicked() {
+                        chosen = Some(i);
+                    }
+                }
+            });
+        });
+    chosen
+}
+
+pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
+    if let Some(text) = app.quit_prompt.clone() {
+        let buttons = [
+            ("quitRetry", "Try Saving Again", Choice::Retry),
+            ("quitAnyway", "Quit Anyway", Choice::QuitAnyway),
+            ("quitCancel", "Cancel", Choice::Cancel),
+        ];
+        let Some(i) = window(ctx, "quit-unsaved", "Quit with unsaved changes?", &text, &buttons) else { return };
+        match buttons[i].2 {
+            Choice::Retry => {
+                app.quit_prompt = None;
+                if may_close(app) {
+                    app.ui.quit = true;
+                }
+            }
+            Choice::QuitAnyway => {
+                app.quit_prompt = None;
+                app.quit_confirmed = true;
+                app.ui.quit = true;
+            }
+            Choice::Cancel | Choice::Ok => app.quit_prompt = None,
+        }
+        return;
+    }
+    if let Some(text) = app.notices.first().cloned() {
+        let buttons = [("noticeOk", "OK", Choice::Ok)];
+        if window(ctx, "settings-notice", "Settings file problem", &text, &buttons).is_some() {
+            app.notices.remove(0);
+        }
+    }
+}