diff --git a/apps/photocraft-cli/src/main.rs b/apps/photocraft-cli/src/main.rs
index ea5598f99d..6e21c2ac44 100644
--- a/apps/photocraft-cli/src/main.rs
+++ b/apps/photocraft-cli/src/main.rs
@@ -1,6 +1,8 @@
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
 
 fn main() {
+    // May re-execute this process with glibc tuned to return freed document memory (#8743).
+    photocraft_engine::malloc_tuning::apply();
     // `args_os`, not `args`: a non-Unicode argument (a Latin-1 file name on Linux) must reach clap,
     // not panic before anything is printed (issue #1108).
     let code = photocraft_cli::run(std::env::args_os().skip(1), &mut std::io::stdout(), &mut std::io::stderr());
diff --git a/apps/photocraft-cli/tests/it/main.rs b/apps/photocraft-cli/tests/it/main.rs
index 65092cdee4..2729f74251 100644
--- a/apps/photocraft-cli/tests/it/main.rs
+++ b/apps/photocraft-cli/tests/it/main.rs
@@ -1,6 +1,8 @@
 //! The crate's integration tests, linked into one test binary.
 
 mod cli;
+#[cfg(all(target_os = "linux", target_env = "gnu"))]
+mod malloc_tuning;
 mod man_and_completions;
 mod orientation;
 
diff --git a/apps/photocraft-cli/tests/it/malloc_tuning.rs b/apps/photocraft-cli/tests/it/malloc_tuning.rs
new file mode 100644
index 0000000000..a7513a714a
--- /dev/null
+++ b/apps/photocraft-cli/tests/it/malloc_tuning.rs
@@ -0,0 +1,41 @@
+//! The binary re-executes itself with glibc's trim threshold set (#8743), keeping its arguments
+//! and a value the user set.
+
+use std::io::{BufRead, BufReader, Write};
+use std::process::{Command, Stdio};
+
+use photocraft_engine::malloc_tuning::{TRIM_THRESHOLD, TRIM_THRESHOLD_VAR};
+
+/// The environment of a running `serve` once it answered a request, as `NAME=value` entries.
+fn serve_environ(set: Option<&str>) -> Vec<String> {
+    let mut cmd = Command::new(crate::binary());
+    for var in [TRIM_THRESHOLD_VAR, "MALLOC_MMAP_THRESHOLD_", "MALLOC_TOP_PAD_", "MALLOC_MMAP_MAX_", "MALLOC_ARENA_MAX", "GLIBC_TUNABLES"] {
+        cmd.env_remove(var);
+    }
+    if let Some(v) = set {
+        cmd.env(TRIM_THRESHOLD_VAR, v);
+    }
+    let mut child = cmd.arg("serve").stdin(Stdio::piped()).stdout(Stdio::piped()).stderr(Stdio::null()).spawn().unwrap();
+    let mut stdin = child.stdin.take().unwrap();
+    writeln!(stdin, r#"{{"id":1,"method":"session.list"}}"#).unwrap();
+    let mut reply = String::new();
+    BufReader::new(child.stdout.take().unwrap()).read_line(&mut reply).unwrap();
+    assert!(reply.contains(r#""id":1"#), "serve answered after the re-exec: {reply}");
+    // The same process: `exec` keeps the PID, so this is the re-executed program's environment.
+    let environ = std::fs::read(format!("/proc/{}/environ", child.id())).unwrap();
+    drop(stdin);
+    child.wait().unwrap();
+    environ.split(|&b| b == 0).map(|e| String::from_utf8_lossy(e).into_owned()).collect()
+}
+
+#[test]
+fn sets_the_trim_threshold() {
+    let env = serve_environ(None);
+    assert!(env.contains(&format!("{TRIM_THRESHOLD_VAR}={TRIM_THRESHOLD}")), "{env:?}");
+}
+
+#[test]
+fn keeps_a_value_the_user_set() {
+    let env = serve_environ(Some("999999"));
+    assert!(env.contains(&format!("{TRIM_THRESHOLD_VAR}=999999")), "{env:?}");
+}
diff --git a/apps/photocraft/src/main.rs b/apps/photocraft/src/main.rs
index e19a9d45e8..3738ffc8d1 100644
--- a/apps/photocraft/src/main.rs
+++ b/apps/photocraft/src/main.rs
@@ -340,7 +340,10 @@ fn write_start_marker(sentinel: &gpu_startup::SharedSentinel, plan: &gpu_startup
 }
 
 fn main() -> eframe::Result {
-    // First, so the panic hook and every start-up warning are recorded (`logging`).
+    // Before anything starts a thread: may re-execute this process with glibc tuned to return
+    // the memory of closed documents (#8743).
+    photocraft_engine::malloc_tuning::apply();
+    // Then, so the panic hook and every start-up warning are recorded (`logging`).
     let logger = logging::install();
     crash_guard::install_hook();
     #[cfg(not(target_arch = "wasm32"))]
diff --git a/crates/algo/src/blur.rs b/crates/algo/src/blur.rs
index 819bf6fa78..7ca9d34f99 100644
--- a/crates/algo/src/blur.rs
+++ b/crates/algo/src/blur.rs
@@ -1,7 +1,7 @@
 //! Blurs: Gaussian, box, motion, radial, surface.
 
 use photocraft_geom::Rect;
-use photocraft_raster::Interrupt;
+use photocraft_raster::{Interrupt, scratch};
 
 use crate::image::{Edge, Image, premultiply, unpremultiply};
 use crate::photo_util::{par_map, par_rows};
@@ -78,7 +78,7 @@ pub(crate) fn conv_sep(src: &Image, out: Rect, kx: &[f32], ky: &[f32], alpha: bo
     // Premultiplied copy of the needed source window.
     let win = Rect::new(out.x0 - rx, out.y0 - ry, out.x1 + rx, out.y1 + ry);
     let ww = win.width() as usize;
-    let mut p = vec![0.0f32; ww * win.height() as usize * n];
+    let mut p = scratch::Buf::new(ww * win.height() as usize * n, 0.0f32);
     for y in win.y0..win.y1 {
         for x in win.x0..win.x1 {
             let o = ((y - win.y0) as usize * ww + (x - win.x0) as usize) * n;
@@ -89,7 +89,7 @@ pub(crate) fn conv_sep(src: &Image, out: Rect, kx: &[f32], ky: &[f32], alpha: bo
     }
     premultiply(&mut p, n, alpha);
     // Horizontal pass: (ow × th).
-    let mut tmp = vec![0.0f32; ow * th * n];
+    let mut tmp = scratch::Buf::new(ow * th * n, 0.0f32);
     for ty in 0..th {
         let row = &p[ty * ww * n..(ty + 1) * ww * n];
         let dst = &mut tmp[ty * ow * n..(ty + 1) * ow * n];
@@ -113,7 +113,7 @@ pub(crate) fn conv_sep(src: &Image, out: Rect, kx: &[f32], ky: &[f32], alpha: bo
         }
     }
     // Vertical pass.
-    let mut res = vec![0.0f32; ow * oh * n];
+    let mut res = scratch::take(ow * oh * n, 0.0f32);
     for oy in 0..oh {
         let d = &mut res[oy * ow * n..(oy + 1) * ow * n];
         for (i, kv) in ky.iter().enumerate() {
@@ -182,11 +182,27 @@ pub(crate) fn box_widths(params: &FilterParams) -> Option<Vec<usize>> {
 }
 
 /// Scratch buffers of one worker for [`box_blur`].
-#[derive(Default)]
 struct Scratch {
     line: Vec<f32>,
     next: Vec<f32>,
     acc: Vec<f32>,
+    /// The source row being read (horizontal passes only).
+    row: Vec<f32>,
+}
+
+impl Scratch {
+    /// Buffers with room for lines of `line` floats (and the shorter ones after the first pass).
+    fn new(line: usize, row: usize) -> Self {
+        Scratch { line: scratch::take_cap(line), next: scratch::take_cap(line), acc: Vec::new(), row: scratch::take_cap(row) }
+    }
+}
+
+impl Drop for Scratch {
+    fn drop(&mut self) {
+        scratch::give(std::mem::take(&mut self.line));
+        scratch::give(std::mem::take(&mut self.next));
+        scratch::give(std::mem::take(&mut self.row));
+    }
 }
 
 /// One running-sum box pass of radius `r` along a line of elements of `w` floats each (a pixel's
@@ -252,7 +268,7 @@ fn box_pass_px<const N: usize>(src: &[f32], dst: &mut [f32], r: usize) {
 /// `dst` unfinished) when `ctl` is cancelled before a pass: a column strip's passes take tens of
 /// milliseconds on a tall image, too long to finish once cancelled (#6205).
 fn line_passes(dst: &mut [f32], w: usize, radii: &[usize], s: &mut Scratch, ctl: &Interrupt) {
-    let Scratch { line, next, acc } = s;
+    let Scratch { line, next, acc, .. } = s;
     let Some(len) = dst.len().checked_div(w) else { return };
     let mut tail: usize = radii.iter().sum();
     for (k, &r) in radii.iter().enumerate() {
@@ -306,21 +322,21 @@ pub(crate) fn box_blur(
     // Horizontal passes over `used`'s rows only (the repeated rows above and below it would just
     // repeat their results), for the output columns. Each row is extended to the passes' reach by
     // repeating its end pixels.
-    let mut h = vec![0.0f32; used.height() as usize * ow * n];
+    let mut h = scratch::Buf::new(used.height() as usize * ow * n, 0.0f32);
     let (left, right) = ((used.x0 - out.x0.saturating_sub(reach)) as usize, (out.x1.saturating_add(reach) - used.x1) as usize);
     par_rows(&mut h, ow * ROWS_PER_TASK, n, |task, chunk| {
-        let (mut row, mut s) = (Vec::new(), Scratch::default());
+        let mut s = Scratch::new((used.width() as usize + left + right) * n, used.width() as usize * n);
         for (k, dst) in chunk.chunks_exact_mut(ow * n).enumerate() {
             if ctl.cancelled() {
                 return;
             }
             let y = used.y0 + (task * ROWS_PER_TASK + k) as i32;
-            read(Rect::new(used.x0, y, used.x1, y + 1), &mut row);
-            premultiply(&mut row, n, alpha);
-            let (Some(first), Some(last)) = (row.get(..n), row.get(row.len().saturating_sub(n)..)) else { return };
+            read(Rect::new(used.x0, y, used.x1, y + 1), &mut s.row);
+            premultiply(&mut s.row, n, alpha);
+            let (Some(first), Some(last)) = (s.row.get(..n), s.row.get(s.row.len().saturating_sub(n)..)) else { return };
             s.line.clear();
             (0..left).for_each(|_| s.line.extend_from_slice(first));
-            s.line.extend_from_slice(&row);
+            s.line.extend_from_slice(&s.row);
             (0..right).for_each(|_| s.line.extend_from_slice(last));
             line_passes(dst, n, &radii, &mut s, ctl);
         }
@@ -336,11 +352,11 @@ pub(crate) fn box_blur(
         }
         let (sx, w) = ((t.x0 - out.x0) as usize * n, t.width() as usize * n);
         let row = |y: usize| &h[y * stride + sx..y * stride + sx + w];
-        let mut s = Scratch::default();
+        let mut s = Scratch::new((rows + top + bottom) * w, 0);
         (0..top).for_each(|_| s.line.extend_from_slice(row(0)));
         (0..rows).for_each(|y| s.line.extend_from_slice(row(y)));
         (0..bottom).for_each(|_| s.line.extend_from_slice(row(rows - 1)));
-        let mut res = vec![0.0f32; oh * w];
+        let mut res = scratch::take(oh * w, 0.0f32);
         line_passes(&mut res, w, &radii, &mut s, ctl);
         if ctl.cancelled() {
             return (t, Vec::new());
@@ -367,7 +383,7 @@ fn box_passes(src: &Image, out: Rect, alpha: bool, boxes: &[usize]) -> Vec<f32>
         buf.extend_from_slice(src.row(r));
     };
     let ow = out.width() as usize * n;
-    let mut res = vec![0.0f32; ow * out.height() as usize];
+    let mut res = scratch::take(ow * out.height() as usize, 0.0f32);
     if res.is_empty() {
         return res;
     }
@@ -376,6 +392,7 @@ fn box_passes(src: &Image, out: Rect, alpha: bool, boxes: &[usize]) -> Vec<f32>
         for (dst, s) in res.chunks_exact_mut(ow).zip(data.chunks_exact(w)) {
             dst[x0..x0 + w].copy_from_slice(s);
         }
+        scratch::give(data);
     }
     res
 }
diff --git a/crates/algo/src/blur/tests.rs b/crates/algo/src/blur/tests.rs
index 028ac65dcc..74cf7ab20c 100644
--- a/crates/algo/src/blur/tests.rs
+++ b/crates/algo/src/blur/tests.rs
@@ -204,7 +204,7 @@ fn direct_boxes(img: &Image, out: Rect, boxes: &[usize], alpha: bool) -> Vec<f32
         let rect = out.inflate(left);
         cur = Image { rect, ch: img.ch, data: conv_sep(&cur, rect, &k, &k, alpha) };
     }
-    cur.data
+    cur.into_data()
 }
 
 /// Noisy pixels over `r` (alpha varying, some fully transparent).
@@ -481,7 +481,8 @@ fn line_passes_stop_between_passes_when_cancelled() {
     let reach: usize = radii.iter().sum();
     let line: Vec<f32> = (0..(len + 2 * reach) * w).map(|i| (i % 7) as f32 + 1.0).collect();
     let run = |ctl: &Interrupt| {
-        let mut s = Scratch { line: line.clone(), ..Scratch::default() };
+        let mut s = Scratch::new(0, 0);
+        s.line.extend_from_slice(&line);
         let mut dst = vec![0.0f32; len * w];
         line_passes(&mut dst, w, &radii, &mut s, ctl);
         dst
diff --git a/crates/algo/src/image.rs b/crates/algo/src/image.rs
index 6a17e08b01..c521f04348 100644
--- a/crates/algo/src/image.rs
+++ b/crates/algo/src/image.rs
@@ -1,7 +1,7 @@
 //! Interleaved `f32` image regions and sampling helpers.
 
 use photocraft_geom::Rect;
-use photocraft_raster::Surface;
+use photocraft_raster::{Surface, scratch};
 
 /// How samples outside an image are read.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
@@ -14,8 +14,9 @@ pub enum Edge {
     Wrap,
 }
 
-/// A rectangle of interleaved, normalized samples.
-#[derive(Clone, Debug, PartialEq)]
+/// A rectangle of interleaved, normalized samples. The samples come from, and go back to, the
+/// scratch pool.
+#[derive(Debug, PartialEq)]
 pub struct Image {
     pub rect: Rect,
     /// Channels per pixel (alpha last when the surface has alpha).
@@ -23,6 +24,20 @@ pub struct Image {
     pub data: Vec<f32>,
 }
 
+impl Clone for Image {
+    fn clone(&self) -> Self {
+        let mut data = scratch::take(self.data.len(), 0.0f32);
+        data.copy_from_slice(&self.data);
+        Image { rect: self.rect, ch: self.ch, data }
+    }
+}
+
+impl Drop for Image {
+    fn drop(&mut self) {
+        scratch::give(std::mem::take(&mut self.data));
+    }
+}
+
 impl Image {
     /// Reads `rect` from a surface.
     pub fn read(s: &Surface, rect: Rect) -> Self {
@@ -53,9 +68,15 @@ impl Image {
         img
     }
 
+    /// The samples, taken out of the image (it can't be destructured: it returns them to the
+    /// pool on drop).
+    pub fn into_data(mut self) -> Vec<f32> {
+        std::mem::take(&mut self.data)
+    }
+
     /// New zeroed image.
     pub fn new(rect: Rect, ch: usize) -> Self {
-        Image { rect, ch, data: vec![0.0; rect.width() as usize * rect.height() as usize * ch] }
+        Image { rect, ch, data: scratch::take(rect.width() as usize * rect.height() as usize * ch, 0.0) }
     }
 
     #[inline]
diff --git a/crates/algo/src/lib.rs b/crates/algo/src/lib.rs
index 03ffe38144..bda29cb2ea 100644
--- a/crates/algo/src/lib.rs
+++ b/crates/algo/src/lib.rs
@@ -1269,7 +1269,10 @@ fn apply_tiled_with_impl(
         }
         for (t, data) in results {
             match data {
-                TileData::Samples(data) => out.write_region(t, &data),
+                TileData::Samples(data) => {
+                    out.write_region(t, &data);
+                    photocraft_raster::scratch::give(data);
+                }
                 TileData::Encoded(data) => out.write_interleaved(t, &data),
             }
         }
@@ -1324,6 +1327,7 @@ fn apply_box_blur(
                     mix_selection(data, *t, sel, &Image::read(surface, *t), fmt.alpha);
                 }
                 s.write_region(*t, data);
+                photocraft_raster::scratch::give(std::mem::take(data));
             }
         };
         #[cfg(not(target_arch = "wasm32"))]
diff --git a/crates/algo/src/sharpen/tests.rs b/crates/algo/src/sharpen/tests.rs
index 4699bb3a10..aef62259a3 100644
--- a/crates/algo/src/sharpen/tests.rs
+++ b/crates/algo/src/sharpen/tests.rs
@@ -267,7 +267,12 @@ fn malformed_inputs_and_allocations_stop_gracefully() {
         assert!(crate::apply_in_with(&s, &p, rect, rect, None, rect, &Interrupt::NONE).is_none());
         assert_eq!(crate::apply_in(&s, &p, rect, rect, None, rect), s);
     }
-    for bad in [Image { ch: 0, ..src.clone() }, Image { data: vec![0.0], ..src.clone() }, Image { rect: Rect::new(5, 0, 0, 2), ..src.clone() }] {
+    let with = |edit: &dyn Fn(&mut Image)| {
+        let mut bad = src.clone();
+        edit(&mut bad);
+        bad
+    };
+    for bad in [with(&|i| i.ch = 0), with(&|i| i.data = vec![0.0]), with(&|i| i.rect = Rect::new(5, 0, 0, 2))] {
         assert!(exact::run(&bad, rect, &ctx, 100.0, 1.0, 0.0, &Interrupt::NONE).is_none());
     }
     for rect in [Rect::new(i32::MIN, 0, i32::MAX, 2), Rect::new(0, 0, 300_000, 300_000), Rect::new(2, 0, 0, 2)] {
diff --git a/crates/algo/src/transform.rs b/crates/algo/src/transform.rs
index 1ed0ec7c04..b1f7bacaae 100644
--- a/crates/algo/src/transform.rs
+++ b/crates/algo/src/transform.rs
@@ -521,6 +521,7 @@ fn warp(
                 outp[o + a] = al as f32;
             }
         }
+        photocraft_raster::scratch::give(px);
         Ok(any.then_some((*t, outp)))
     };
     // Each tile is written as soon as it is warped, so only the tiles in flight hold their `f32`
diff --git a/crates/automation/src/headless.rs b/crates/automation/src/headless.rs
index 6722c5c00b..8b08daa6aa 100644
--- a/crates/automation/src/headless.rs
+++ b/crates/automation/src/headless.rs
@@ -358,6 +358,8 @@ impl Headless {
         if let Some(d) = self.session.close(i) {
             self.writers.remove(&d.doc.id.0);
         }
+        // The closed document's buffers went to the scratch pool: hand them back to the OS.
+        photocraft_raster::scratch::release();
         Ok(self.session_list())
     }
 
diff --git a/crates/compose/src/advanced.rs b/crates/compose/src/advanced.rs
index 8ea5a86c6d..7a4068012d 100644
--- a/crates/compose/src/advanced.rs
+++ b/crates/compose/src/advanced.rs
@@ -32,6 +32,7 @@ use std::borrow::Cow;
 use photocraft_doc::{Knockout, Layer, LayerContent};
 use photocraft_geom::Rect;
 
+use crate::extents::recycle_mask;
 use crate::{Buffer, Ctx, composite_atop, composite_layer, effects, mask_vals, render_content};
 
 /// Where a layer stack sits, for knockouts: at the document's top level, and/or inside an
@@ -157,6 +158,7 @@ pub(crate) fn knockout(layer: &Layer, backdrop: &mut Buffer, target: &Buffer, cl
     if target.rect != backdrop.rect || shape.len() != backdrop.px.len() {
         // Never reached (targets are built over the backdrop's rect); compositing without the
         // knockout beats a wrong pixel or a panic.
+        recycle_mask(Some(shape));
         draw(backdrop);
         return;
     }
@@ -172,7 +174,10 @@ pub(crate) fn knockout(layer: &Layer, backdrop: &mut Buffer, target: &Buffer, cl
     }
     let knocked = (layer.opacity < 1.0).then(|| backdrop.clone());
     draw(backdrop);
-    let Some(knocked) = knocked else { return };
+    let Some(knocked) = knocked else {
+        recycle_mask(Some(shape));
+        return;
+    };
     let rest = 1.0 - layer.opacity.clamp(0.0, 1.0);
     for (((p, b), k), s) in backdrop.px.iter_mut().zip(&before.px).zip(&knocked.px).zip(&shape) {
         if *s <= 0.0 {
@@ -186,6 +191,7 @@ pub(crate) fn knockout(layer: &Layer, backdrop: &mut Buffer, target: &Buffer, cl
         let a = pm[3].clamp(0.0, 1.0);
         *p = if a > 0.0 { [(pm[0] / a).clamp(0.0, 1.0), (pm[1] / a).clamp(0.0, 1.0), (pm[2] / a).clamp(0.0, 1.0), a] } else { [0.0; 4] };
     }
+    recycle_mask(Some(shape));
 }
 
 /// Composite a clipping group's clipped layers atop `base` (the base's isolated content, Blend
@@ -220,7 +226,12 @@ pub(crate) fn composite_clipped_individually(layer: &Layer, clipped: &[Layer], b
     let op = layer.opacity.clamp(0.0, 1.0);
     let clip: Vec<f32> = match render_content(layer, rect, cx) {
         Some(b) => b.px.iter().map(|p| p[3] * op).collect(),
-        None => mask_vals(layer, rect, cx).unwrap_or_else(|| vec![1.0; n]).iter().map(|m| m * op).collect(),
+        None => {
+            let mv = mask_vals(layer, rect, cx);
+            let clip = mv.as_ref().map_or_else(|| vec![op; n], |m| m.iter().map(|m| m * op).collect());
+            recycle_mask(mv);
+            clip
+        }
     };
     if clip.len() != n {
         return;
diff --git a/crates/compose/src/advanced_tests.rs b/crates/compose/src/advanced_tests.rs
index 608c6188e2..15d3cf2346 100644
--- a/crates/compose/src/advanced_tests.rs
+++ b/crates/compose/src/advanced_tests.rs
@@ -395,7 +395,7 @@ fn shapeless_stroke_tile_skips_match_full_region_across_blending_settings() {
                         .unwrap();
                         let mut band_pixels = Vec::with_capacity(whole.px.len());
                         for band in bands {
-                            band_pixels.extend(band.px);
+                            band_pixels.extend(band.into_px());
                         }
                         assert_eq!(whole.px, band_pixels, "banded: {depth:?}, {position:?}, {blend:?}, fill={fill}, blend_if={blend_if}");
                     }
@@ -639,7 +639,7 @@ fn transparency_shapes_off_ignores_masks_and_reaches_groups() {
                 l.mask = Some(LayerMask { surface: photocraft_raster::Surface::with_default(PixelFormat::GRAY8, &[77.0 / 255.0]), ..LayerMask::reveal_all() });
                 l.advanced.transparency_shapes = tsl;
                 d.layers.push(l);
-                render(&d, d.bounds()).px
+                render(&d, d.bounds()).into_px()
             };
             let (off, on) = (render_with(false), render_with(true));
             assert!(off.iter().zip(&on).all(|(a, b)| close(*a, *b)), "{mode:?} ({depth:?}): a mask isn't the layer's transparency");
@@ -691,13 +691,13 @@ fn transparency_shapes_off_keeps_the_base_alpha_under_a_clipped_knockout() {
             base.advanced.transparency_shapes = false;
             base.vector_mask = Some(photocraft_doc::vector::VectorMask { feather: 1.5, ..photocraft_doc::vector::VectorMask::new(square.clone()) });
             d.layers.push(base);
-            let alone = render(&d, d.bounds()).px;
+            let alone = render(&d, d.bounds()).into_px();
             let mut red = solid(&d, "red", full(&d), [1.0, 0.0, 0.0, 0.5]);
             red.clipped = true;
             let mut knock = knocker(&d, k);
             knock.clipped = true;
             d.layers.extend([red, knock]);
-            let got = render(&d, d.bounds()).px;
+            let got = render(&d, d.bounds()).into_px();
             let what = format!("{k:?} ({depth:?})");
             for (i, (g, a)) in got.iter().zip(&alone).enumerate() {
                 if i % 12 < 6 {
diff --git a/crates/compose/src/cmyk.rs b/crates/compose/src/cmyk.rs
index 96a6df0ceb..2f8eaa8861 100644
--- a/crates/compose/src/cmyk.rs
+++ b/crates/compose/src/cmyk.rs
@@ -27,6 +27,7 @@ use photocraft_doc::adjust::ToneSpace;
 use photocraft_doc::{Adjustment, Document, Knockout, Layer, LayerContent};
 use photocraft_geom::Rect;
 
+use super::extents::recycle_mask;
 use super::{Ctx, RENDER_TILE, advanced, empty_in, mask_vals, pattern};
 
 #[path = "cmyk_split.rs"]
@@ -355,6 +356,7 @@ fn apply_mask(l: &Layer, buf: &mut CmykBuffer, cx: &Ctx) {
         for (p, k) in buf.px.iter_mut().zip(&m) {
             p[4] *= clean(*k).max(0.0);
         }
+        recycle_mask(Some(m));
     }
 }
 
@@ -425,6 +427,7 @@ fn mix_adjusted(l: &Layer, base: &mut CmykBuffer, adjusted: &CmykBuffer, cx: &Ct
             *v = if k >= 1.0 { b } else { *v + (b - *v) * k };
         }
     }
+    recycle_mask(mv);
 }
 
 /// Rounds to the document's levels after an adjustment layer, as the compositor does (on the
@@ -534,6 +537,7 @@ fn composite_layer(l: &Layer, clipped: &[Layer], backdrop: &mut CmykBuffer, cx:
                         [0.0; 5]
                     };
                 }
+                recycle_mask(mv);
             }
             return;
         }
diff --git a/crates/compose/src/composite.rs b/crates/compose/src/composite.rs
index 8436ff7428..4ef497672f 100644
--- a/crates/compose/src/composite.rs
+++ b/crates/compose/src/composite.rs
@@ -1,6 +1,6 @@
-use super::content::{channel_weights, empty_in, recycle_buffer, render_content, restore_channels, scratch_buffer, surface_to_buffer};
+use super::content::{channel_weights, empty_in, render_content, restore_channels, surface_to_buffer};
 use super::ctx::Ctx;
-use super::extents::{effects_frame, mask_k, mask_vals, shapeless_stroke_bounds};
+use super::extents::{effects_frame, mask_k, mask_vals, recycle_mask, shapeless_stroke_bounds};
 use super::fx_cache::effect_maps;
 use super::{BlendMode, Buffer, Fill, Layer, LayerContent, Rect, Surface, advanced, blend, effects, psblend, shape_split};
 
@@ -339,6 +339,7 @@ pub(crate) fn composite_pixel_layer(layer: &Layer, surf: &Surface, backdrop: &mu
         }
         blend_span_fill(dst, &row, rect.x0, y, layer.blend, layer.opacity, layer.fill_opacity, gamma);
     }
+    recycle_mask(mv);
 }
 
 pub(crate) fn composite_layer_plain(layer: &Layer, clipped: &[Layer], backdrop: &mut Buffer, cx: &Ctx, scope: advanced::Scope) {
@@ -389,6 +390,7 @@ pub(crate) fn composite_layer_plain(layer: &Layer, clipped: &[Layer], backdrop:
                     [0.0; 4]
                 };
             }
+            recycle_mask(mv);
         }
         // A Frame's stroke over the frame's content, at the group's opacity.
         if let Some(stroke) = shape_split::frame_stroke(layer, cx.canvas, cx.depth) {
@@ -425,9 +427,10 @@ pub(crate) fn composite_layer_plain(layer: &Layer, clipped: &[Layer], backdrop:
     if let LayerContent::Adjustment(adj) = &layer.content {
         let mv = mask_vals(layer, rect, cx);
         if mv.as_ref().is_some_and(|values| values.iter().all(|&value| opacity * value <= 0.0)) {
+            recycle_mask(mv);
             return;
         }
-        let mut adjusted = scratch_buffer(rect);
+        let mut adjusted = Buffer::transparent(rect);
         adjusted.px.copy_from_slice(&backdrop.px);
         cx.apply_adjustment(adj, &mut adjusted);
         // Clipped layers onto an adjustment are uncommon; they composite atop the adjusted result.
@@ -455,7 +458,7 @@ pub(crate) fn composite_layer_plain(layer: &Layer, clipped: &[Layer], backdrop:
                 None => blend_back(&mut backdrop.px, &adjusted.px, std::iter::repeat(k), layer.blend, fill),
             }
         }
-        recycle_buffer(adjusted);
+        recycle_mask(mv);
         return;
     }
 
@@ -469,6 +472,7 @@ pub(crate) fn composite_layer_plain(layer: &Layer, clipped: &[Layer], backdrop:
         if let (Some(m), Some(b)) = (&hide, &before) {
             advanced::apply_hiding_mask(backdrop, b, m);
         }
+        recycle_mask(hide);
         return;
     }
     if let Some((mut content, stroke, mask)) = shape_parts(layer, clipped, rect, cx) {
@@ -478,6 +482,7 @@ pub(crate) fn composite_layer_plain(layer: &Layer, clipped: &[Layer], backdrop:
             p[3] *= mask_k(&mask, i);
         }
         blend_layer_into(backdrop, &content, layer, cx, 1.0);
+        recycle_mask(mask);
         return;
     }
     if !matches!(layer.content, LayerContent::Group(_) | LayerContent::Fill(_) | LayerContent::Adjustment(_))
@@ -512,7 +517,6 @@ pub(crate) fn composite_layer_plain(layer: &Layer, clipped: &[Layer], backdrop:
     let Some(mut content) = render_content(layer, rect, cx) else { return };
     advanced::composite_clipped(clipped, &mut content, cx);
     blend_layer_into(backdrop, &content, layer, cx, text_gamma(layer));
-    recycle_buffer(content);
 }
 
 /// A layer with effects (and its clipping group) onto `backdrop`.
@@ -521,7 +525,7 @@ fn composite_layer_effects(layer: &Layer, clipped: &[Layer], backdrop: &mut Buff
     // Neighbourhoods are already captured by the full-region effect maps;
     // content and effect application only need the output rectangle.
     // A stroked shape's vector stroke stays above its clipped layers and interior effects.
-    let (mut content, vstroke) = match split_parts(layer, rect, cx) {
+    let (mut content, parts) = match split_parts(layer, rect, cx) {
         Some((fill, stroke, mask)) => (fill, Some((stroke, mask))),
         None => {
             let Some(content) = render_content(layer, rect, cx) else { return };
@@ -529,9 +533,12 @@ fn composite_layer_effects(layer: &Layer, clipped: &[Layer], backdrop: &mut Buff
         }
     };
     advanced::composite_clipped(clipped, &mut content, cx);
-    let vstroke = vstroke.as_ref().map(|(s, m)| effects::VectorStroke { stroke: s, mask: m.as_deref() });
+    let vstroke = parts.as_ref().map(|(s, m)| effects::VectorStroke { stroke: s, mask: m.as_deref() });
     let maps = effect_maps(layer, rect, cx);
     effects::composite_with_effects_prepared(layer, &content, backdrop, &maps, effects_frame(layer, cx.canvas), cx.patterns, vstroke);
+    if let Some((_, mask)) = parts {
+        recycle_mask(mask);
+    }
 }
 
 /// The coverage-mixing gamma of a layer: the text blending gamma
@@ -605,6 +612,7 @@ fn composite_atop_any(layer: &Layer, base: &mut Buffer, cx: &Ctx) {
                 p[c] += (bl[c] - p[c]) * k;
             }
         }
+        recycle_mask(mv);
         return;
     }
     if effects::has_effects(layer) {
@@ -615,21 +623,28 @@ fn composite_atop_any(layer: &Layer, base: &mut Buffer, cx: &Ctx) {
         let hide = advanced::hiding_mask(layer, rect, cx);
         let src = advanced::effects_source(layer);
         let layer = src.as_ref();
-        let (content, vstroke) = match split_parts(layer, rect, cx) {
+        let (content, parts) = match split_parts(layer, rect, cx) {
             Some((fill, stroke, mask)) => (fill, Some((stroke, mask))),
             None => {
-                let Some(content) = render_content(layer, rect, cx) else { return };
+                let Some(content) = render_content(layer, rect, cx) else {
+                    recycle_mask(hide);
+                    return;
+                };
                 (content, None)
             }
         };
-        let vstroke = vstroke.as_ref().map(|(s, m)| effects::VectorStroke { stroke: s, mask: m.as_deref() });
+        let vstroke = parts.as_ref().map(|(s, m)| effects::VectorStroke { stroke: s, mask: m.as_deref() });
         let mut opaque = Buffer { rect, px: base.px.iter().map(|p| [p[0], p[1], p[2], 1.0]).collect() };
         let maps = effect_maps(layer, rect, cx);
         effects::composite_with_effects_prepared(layer, &content, &mut opaque, &maps, effects_frame(layer, cx.canvas), cx.patterns, vstroke);
+        if let Some((_, mask)) = parts {
+            recycle_mask(mask);
+        }
         if let Some(m) = &hide {
             let plain = Buffer { rect, px: base.px.iter().map(|p| [p[0], p[1], p[2], 1.0]).collect() };
             advanced::apply_hiding_mask(&mut opaque, &plain, m);
         }
+        recycle_mask(hide);
         for (p, o) in base.px.iter_mut().zip(&opaque.px) {
             if p[3] > 0.0 {
                 *p = [o[0], o[1], o[2], p[3]];
@@ -689,6 +704,7 @@ fn blend_layer_into(backdrop: &mut Buffer, src: &Buffer, layer: &Layer, cx: &Ctx
         let alpha = (s[3] / m).clamp(0.0, 1.0);
         *b = psblend::composite_fill(mode, *b, [s[0], s[1], s[2], m], opacity, fill * alpha, gamma);
     }
+    recycle_mask(mv);
 }
 
 /// [`blend_into_g`] for a layer's own `opacity` and `fill`: Fill is part of the blend for
diff --git a/crates/compose/src/content.rs b/crates/compose/src/content.rs
index ea868d715e..1f91c6a942 100644
--- a/crates/compose/src/content.rs
+++ b/crates/compose/src/content.rs
@@ -1,63 +1,29 @@
 use super::composite::{adjustment_quantum, blend_into, composite_stack};
 use super::ctx::Ctx;
-use super::extents::{effect_shape, effect_source_bounds, mask_vals, shapeless_stroke_bounds, transparent_outside};
+use super::extents::{effect_shape, effect_source_bounds, mask_vals, recycle_mask, shapeless_stroke_bounds, transparent_outside};
 use super::fx_cache::effect_maps;
 use super::{BlendMode, Buffer, Document, Fill, Layer, LayerContent, Pattern, Rect, Surface, bounds, effects, gradient_fill, pattern, shape_split};
 
 /// Tile size for parallel rendering (tile results are independent).
 pub const RENDER_TILE: i32 = 256;
 
-// One tile of scratch per worker; nested rendering takes its own buffer.
-thread_local! {
-    static SCRATCH: std::cell::RefCell<Vec<[f32; 4]>> = const { std::cell::RefCell::new(Vec::new()) };
-}
-
-pub(crate) fn scratch_buffer(rect: Rect) -> Buffer {
-    if rect.width() as usize * rect.height() as usize > (RENDER_TILE * RENDER_TILE) as usize {
-        return Buffer::transparent(rect);
-    }
-    let mut px = SCRATCH.with(|slot| std::mem::take(&mut *slot.borrow_mut()));
-    px.resize(rect.width() as usize * rect.height() as usize, [0.0; 4]);
-    Buffer { rect, px }
-}
-
-pub(crate) fn recycle_buffer(buf: Buffer) {
-    if buf.px.capacity() <= (RENDER_TILE * RENDER_TILE) as usize {
-        SCRATCH.with(|slot| {
-            let mut slot = slot.borrow_mut();
-            if slot.capacity() < buf.px.capacity() {
-                *slot = buf.px;
-            }
-        });
-    }
-}
-
 #[cfg(test)]
 #[test]
-fn scratch_reuse_preserves_pixels_and_bounds_retention() {
-    SCRATCH.with(|slot| slot.borrow_mut().clear());
-    let rect = Rect::new(-2, -3, 18, 11);
+fn scratch_reuse_preserves_pixels() {
+    // 256 × 256 pixels of [f32; 4] (1 MiB): over `MIN_POOLED_BYTES`, so the pool keeps it.
+    let rect = Rect::new(-2, -3, 254, 253);
     for fmt in [photocraft_color::PixelFormat::RGBA8, photocraft_color::PixelFormat::RGBA16, photocraft_color::PixelFormat::RGBA32F] {
         let s = Surface::with_default(fmt, &[0.2, 0.4, 0.6, 0.8]);
-        let buf = surface_to_scratch(&s, rect);
+        let mut buf = surface_to_scratch(&s, rect);
         assert_eq!(buf, surface_to_buffer(&s, rect));
-        let ptr = buf.px.as_ptr();
-        recycle_buffer(buf);
-        let reused = surface_to_scratch(&Surface::new(fmt), rect);
-        assert_eq!(reused.px.as_ptr(), ptr);
+        buf.px.fill([1.0; 4]);
+        // A dropped buffer goes back to the pool; the next one must come out cleared.
+        drop(buf);
+        let reused = Buffer::transparent(rect);
         assert!(reused.px.iter().all(|p| p == &[0.0; 4]));
-        let nested = scratch_buffer(rect);
+        let nested = Buffer::transparent(rect);
         assert_ne!(nested.px.as_ptr(), reused.px.as_ptr());
-        recycle_buffer(nested);
-        recycle_buffer(reused);
     }
-    let cached = SCRATCH.with(|slot| slot.borrow().as_ptr());
-    let huge = scratch_buffer(Rect::new(0, 0, RENDER_TILE + 1, RENDER_TILE));
-    recycle_buffer(huge);
-    SCRATCH.with(|slot| {
-        assert_eq!(slot.borrow().as_ptr(), cached);
-        assert!(slot.borrow().capacity() <= (RENDER_TILE * RENDER_TILE) as usize);
-    });
 }
 
 /// Render a layer's own content (no blending into the backdrop yet) into an isolated buffer.
@@ -93,6 +59,7 @@ pub(crate) fn render_content(layer: &Layer, rect: Rect, cx: &Ctx) -> Option<Buff
         for (p, k) in buf.px.iter_mut().zip(&m) {
             p[3] *= k;
         }
+        recycle_mask(Some(m));
     }
     // A Frame's stroke lies over its masked content; the frame doesn't clip it.
     if let Some(stroke) = shape_split::frame_stroke(layer, cx.canvas, cx.depth) {
@@ -125,13 +92,13 @@ pub fn stroke_frame(doc: &Document, layer: &Layer, st: &photocraft_doc::StrokeFx
 }
 
 pub fn surface_to_buffer(s: &Surface, rect: Rect) -> Buffer {
-    let mut px = vec![[0.0f32; 4]; rect.width() as usize * rect.height() as usize];
-    s.read_rgba_into(rect, &mut px);
-    Buffer { rect, px }
+    let mut buf = Buffer::transparent(rect);
+    s.read_rgba_into(rect, &mut buf.px);
+    buf
 }
 
 fn surface_to_scratch(s: &Surface, rect: Rect) -> Buffer {
-    let mut buf = scratch_buffer(rect);
+    let mut buf = Buffer::transparent(rect);
     s.read_rgba_into(rect, &mut buf.px);
     buf
 }
diff --git a/crates/compose/src/extents.rs b/crates/compose/src/extents.rs
index d895f14bc9..7e4f8d234e 100644
--- a/crates/compose/src/extents.rs
+++ b/crates/compose/src/extents.rs
@@ -134,6 +134,7 @@ pub(crate) fn effect_shape(layer: &Layer, rect: Rect, cx: &Ctx) -> Vec<f32> {
             out[i] = v * mask_k(&mv, i);
         }
     }
+    recycle_mask(mv);
     out
 }
 
@@ -283,13 +284,13 @@ pub(crate) fn mask_vals(layer: &Layer, rect: Rect, cx: &Ctx) -> Option<Vec<f32>>
     if masks::has_feather(layer)
         && let Some(s) = masks::combined_mask(layer, cx.canvas)
     {
-        let mut v = Vec::new();
+        let mut v = photocraft_raster::scratch::take_cap(rect.width() as usize * rect.height() as usize);
         s.read_region_into(rect, &mut v);
         return Some(v);
     }
     let vector = layer.vector_mask.as_ref().map(|vm| cx.vector_masks.values(vm, rect));
     let Some(m) = layer.mask.as_ref() else { return vector };
-    let mut v = Vec::new();
+    let mut v = photocraft_raster::scratch::take_cap(rect.width() as usize * rect.height() as usize);
     m.values_into(rect, &mut v);
     if let Some(vm) = vector {
         for (a, b) in v.iter_mut().zip(vm) {
@@ -299,6 +300,13 @@ pub(crate) fn mask_vals(layer: &Layer, rect: Rect, cx: &Ctx) -> Option<Vec<f32>>
     Some(v)
 }
 
+/// Hand a [`mask_vals`] result back to the scratch pool once its tile is done.
+pub(crate) fn recycle_mask(m: Option<Vec<f32>>) {
+    if let Some(v) = m {
+        photocraft_raster::scratch::give(v);
+    }
+}
+
 #[inline]
 pub(crate) fn mask_k(m: &Option<Vec<f32>>, i: usize) -> f32 {
     m.as_ref().map_or(1.0, |v| v[i])
diff --git a/crates/compose/src/lib.rs b/crates/compose/src/lib.rs
index e593290571..25dc55984a 100644
--- a/crates/compose/src/lib.rs
+++ b/crates/compose/src/lib.rs
@@ -84,18 +84,39 @@ pub use render::{
 };
 
 /// Straight-alpha RGBA float buffer covering a rectangle.
-#[derive(Clone, Debug, PartialEq)]
+///
+/// The pixel storage comes from, and goes back to, the scratch pool.
+#[derive(Debug, PartialEq)]
 pub struct Buffer {
     pub rect: Rect,
     pub px: Vec<[f32; 4]>,
 }
 
+impl Clone for Buffer {
+    fn clone(&self) -> Self {
+        let mut px = photocraft_raster::scratch::take(self.px.len(), [0.0; 4]);
+        px.copy_from_slice(&self.px);
+        Self { rect: self.rect, px }
+    }
+}
+
+impl Drop for Buffer {
+    fn drop(&mut self) {
+        photocraft_raster::scratch::give(std::mem::take(&mut self.px));
+    }
+}
+
 impl Buffer {
     pub fn transparent(rect: Rect) -> Self {
-        Self { rect, px: vec![[0.0; 4]; rect.width() as usize * rect.height() as usize] }
+        Self::filled(rect, [0.0; 4])
     }
     pub fn filled(rect: Rect, c: [f32; 4]) -> Self {
-        Self { rect, px: vec![c; rect.width() as usize * rect.height() as usize] }
+        Self { rect, px: photocraft_raster::scratch::take(rect.width() as usize * rect.height() as usize, c) }
+    }
+    /// The pixels, taken out of the buffer (it can't be destructured: it returns them to the
+    /// pool on drop).
+    pub fn into_px(mut self) -> Vec<[f32; 4]> {
+        std::mem::take(&mut self.px)
     }
     #[inline]
     pub fn get(&self, x: i32, y: i32) -> [f32; 4] {
diff --git a/crates/compose/src/render.rs b/crates/compose/src/render.rs
index b739d3f42a..250a3ebce1 100644
--- a/crates/compose/src/render.rs
+++ b/crates/compose/src/render.rs
@@ -229,14 +229,12 @@ pub fn composite_to_surface(doc: &Document, rect: Rect, fmt: photocraft_color::P
     let mut s = Surface::new(fmt);
     let n = fmt.channels();
     let empty = s.default_pixel();
-    let mut data = Vec::new();
     let _ = render_bands(doc, rect, 0, |band| -> Result<(), ()> {
         let band = match background {
             Some(bg) => band.over_background(bg),
             None => band,
         };
-        data.clear();
-        data.resize(band.px.len() * n, 0.0);
+        let mut data = photocraft_raster::scratch::take(band.px.len() * n, 0.0f32);
         photocraft_color::convert::with_cmyk_space(space.as_ref(), || {
             for (p, out) in band.px.iter().zip(data.chunks_exact_mut(n)) {
                 if fmt.alpha && (p[3] <= 0.0 || p[3].is_nan()) && empty.len() == n {
@@ -247,6 +245,7 @@ pub fn composite_to_surface(doc: &Document, rect: Rect, fmt: photocraft_color::P
             }
         });
         s.write_region(band.rect, &data);
+        photocraft_raster::scratch::give(data);
         Ok(())
     });
     s.prune();
diff --git a/crates/compose/src/soft_shape_tests.rs b/crates/compose/src/soft_shape_tests.rs
index 37575beef5..9332f31af1 100644
--- a/crates/compose/src/soft_shape_tests.rs
+++ b/crates/compose/src/soft_shape_tests.rs
@@ -115,7 +115,7 @@ fn soft_shape_matches_an_equal_vector_mask() {
 fn soft_shape_keeps_its_stroke_crisp() {
     let stroke = ShapeStroke { width: 4.0, paint: Fill::Solid(Color::rgb(1.0, 0.0, 0.0)), ..ShapeStroke::default() };
     let d = shape_doc(SampleType::U8, 0.5, 10.0, Some(stroke));
-    let px = render(&d, Rect::new(0, 100, 200, 101)).px;
+    let px = render(&d, Rect::new(0, 100, 200, 101)).into_px();
     // Centred 4 px stroke over x = 48..52: opaque red.
     for x in [48, 49, 50, 51] {
         let p = px[x];
diff --git a/crates/compose/src/tests.rs b/crates/compose/src/tests.rs
index 917192f44a..7ea8655099 100644
--- a/crates/compose/src/tests.rs
+++ b/crates/compose/src/tests.rs
@@ -3001,7 +3001,7 @@ fn levels_steps_match_photoshop() {
         let px = xs.iter().map(|&x| f32::from(x) / 255.0).map(|v| [v, v, v, 1.0]).collect();
         let mut b = Buffer { rect: Rect::new(0, 0, xs.len() as i32, 1), px };
         adjust::apply_depth(adj, &mut b, adjust::Transfer::Srgb, Some(SampleType::U8));
-        b.px
+        b.into_px()
     };
     let rgb = levels(ch(0.0, 213.0, 1.22, 48.0, 255.0), [ch(0.0, 255.0, 0.47, 0.0, 194.0), id.clone(), ch(61.0, 255.0, 0.47, 0.0, 213.0)]);
     let xs = [2, 8, 9, 15, 16, 43, 45, 48, 55, 61, 72, 79, 84, 89, 90, 101, 106, 120, 150, 180, 200];
@@ -3364,7 +3364,7 @@ fn render_bands_cover_the_rect_in_order() {
     render_bands(&d, r, 100, |b| -> Result<(), ()> {
         assert_eq!((b.rect.x0, b.rect.x1), (r.x0, r.x1));
         rows.push((b.rect.y0, b.rect.y1));
-        px.extend(b.px);
+        px.extend(b.into_px());
         Ok(())
     })
     .unwrap();
@@ -4469,13 +4469,13 @@ fn dissolve_adjustment_resolves_opacity_to_binary_coverage() {
     layer.blend = BlendMode::Dissolve;
     layer.opacity = 0.5;
     d.layers.push(layer);
-    let pixels = render(&d, d.bounds()).px;
+    let pixels = render(&d, d.bounds()).into_px();
     let black = pixels.iter().filter(|p| p[0] < 0.01).count();
     let white = pixels.iter().filter(|p| p[0] > 0.99).count();
     assert!(black > 0 && white > 0, "Dissolve must select both original and adjusted pixels");
     assert_eq!(black + white, pixels.len(), "no intermediate gray pixels");
     d.layers.last_mut().unwrap().blend = BlendMode::Normal;
-    let continuous = render(&d, d.bounds()).px;
+    let continuous = render(&d, d.bounds()).into_px();
     assert!(continuous.iter().all(|p| (p[0] - 0.5).abs() < E), "Normal remains continuously interpolated");
 }
 
@@ -4486,14 +4486,14 @@ fn clipped_dissolve_fill_matches_opaque_unclipped_coverage() {
     fill.blend = BlendMode::Dissolve;
     fill.opacity = 0.5;
     d.layers.push(fill);
-    let control = render(&d, d.bounds()).px;
+    let control = render(&d, d.bounds()).into_px();
     d.layers.last_mut().unwrap().clipped = true;
-    let clipped = render(&d, d.bounds()).px;
+    let clipped = render(&d, d.bounds()).into_px();
     assert_eq!(clipped, control, "clipping over a fully opaque base must preserve dissolve pixels");
     let black = clipped.iter().filter(|p| p[0] < 0.01).count();
     assert!(black > 0 && black < clipped.len());
     d.layers.last_mut().unwrap().blend = BlendMode::Normal;
-    let continuous = render(&d, d.bounds()).px;
+    let continuous = render(&d, d.bounds()).into_px();
     assert!(continuous.iter().all(|p| (p[0] - 0.5).abs() < E));
 }
 
@@ -4504,17 +4504,17 @@ fn dissolve_color_overlay_preserves_binary_layer_coverage() {
     layer.blend = BlendMode::Dissolve;
     layer.opacity = 0.5;
     d.layers.push(layer);
-    let control = render(&d, d.bounds()).px;
+    let control = render(&d, d.bounds()).into_px();
     d.layers
         .last_mut()
         .unwrap()
         .effects
         .items
         .push(photocraft_doc::Effect::ColorOverlay { common: photocraft_doc::FxCommon::new(BlendMode::Normal, 1.0), color: Color::BLACK });
-    let styled = render(&d, d.bounds()).px;
+    let styled = render(&d, d.bounds()).into_px();
     assert_eq!(styled, control, "an identity overlay should not turn dissolve pixels gray");
     d.layers.last_mut().unwrap().blend = BlendMode::Normal;
-    let continuous = render(&d, d.bounds()).px;
+    let continuous = render(&d, d.bounds()).into_px();
     assert!(continuous.iter().all(|p| (p[0] - 0.5).abs() < E));
 }
 
diff --git a/crates/compose/tests/buffer_reuse.rs b/crates/compose/tests/buffer_reuse.rs
new file mode 100644
index 0000000000..f07bf8b69f
--- /dev/null
+++ b/crates/compose/tests/buffer_reuse.rs
@@ -0,0 +1,27 @@
+use photocraft_compose::Buffer;
+use photocraft_geom::Rect;
+use photocraft_raster::scratch;
+
+/// Restores idle release even when an assertion fails.
+struct IdleReleaseOff;
+impl Drop for IdleReleaseOff {
+    fn drop(&mut self) {
+        scratch::release();
+        scratch::set_idle_release(true);
+    }
+}
+
+/// Runs in its own binary so other compositor tests cannot consume the pooled allocation.
+#[test]
+fn dropped_buffer_storage_is_reused() {
+    scratch::set_idle_release(false);
+    let _idle = IdleReleaseOff;
+    scratch::release();
+    let rect = Rect::from_xywh(0, 0, 256, 256);
+    let buf = Buffer::transparent(rect);
+    let ptr = buf.px.as_ptr();
+    drop(buf);
+    let reused = Buffer::transparent(rect);
+    assert_eq!(reused.px.as_ptr(), ptr);
+    assert!(reused.px.iter().all(|p| *p == [0.0; 4]));
+}
diff --git a/crates/engine/examples/indexed_color_perf.rs b/crates/engine/examples/indexed_color_perf.rs
index 6dba948ff2..112f6eb0d9 100644
--- a/crates/engine/examples/indexed_color_perf.rs
+++ b/crates/engine/examples/indexed_color_perf.rs
@@ -25,7 +25,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     let path = std::env::args().nth(1).ok_or("provide a local image path")?;
     let bytes = photocraft_format::read::read_file(std::path::Path::new(&path))?;
     let doc = photocraft_io::import(&path, &bytes)?.document;
-    let px = photocraft_compose::flatten(&doc).px;
+    let px = photocraft_compose::flatten(&doc).into_px();
     println!("{}", json!({"width":doc.size.width,"height":doc.size.height,"preview_factor":1}));
     for count in [8usize, 16, 32, 64, 128, 256] {
         for run in 0..4 {
diff --git a/crates/engine/src/cmd/adjust_cmds.rs b/crates/engine/src/cmd/adjust_cmds.rs
index 39ab43c7a6..f5301979dc 100644
--- a/crates/engine/src/cmd/adjust_cmds.rs
+++ b/crates/engine/src/cmd/adjust_cmds.rs
@@ -459,9 +459,9 @@ fn stats_pixels(doc: &Document, layer: Option<u64>, use_selection: bool) -> Resu
     let px: Vec<[f32; 4]> = match layer {
         Some(id) => {
             let l = doc.layer(photocraft_doc::LayerId(id)).ok_or(EngineError::NoLayer(photocraft_doc::LayerId(id)))?;
-            photocraft_compose::render_layer(l, area).px
+            photocraft_compose::render_layer(l, area).into_px()
         }
-        None => photocraft_compose::flatten(doc).px,
+        None => photocraft_compose::flatten(doc).into_px(),
     };
     let mask = doc.selection.as_ref().filter(|_| use_selection).map(|sel| photocraft_algo::selection::mask_from_surface(Some(sel), area));
     Ok((px, mask))
@@ -521,7 +521,7 @@ fn hdr_toning(s: &mut Session, p: &Value) -> Result<Value> {
     s.edit("HDR Toning", |doc, active| {
         let buf = photocraft_compose::flatten(doc).over_background([1.0, 1.0, 1.0]);
         let (w, hgt) = (buf.rect.width() as usize, buf.rect.height() as usize);
-        let mut px = buf.px;
+        let mut px = buf.into_px();
         tone::hdr_toning(&mut px, w, hgt, &h);
         let fmt = doc.pixel_format();
         let data: Vec<f32> = px.iter().flat_map(|q| photocraft_raster::from_rgba(&fmt, *q)).collect();
diff --git a/crates/engine/src/cmd/adjust_cmds/tests.rs b/crates/engine/src/cmd/adjust_cmds/tests.rs
index d60fa26d10..51843ae022 100644
--- a/crates/engine/src/cmd/adjust_cmds/tests.rs
+++ b/crates/engine/src/cmd/adjust_cmds/tests.rs
@@ -480,7 +480,7 @@ fn smart_session() -> Session {
 }
 
 fn flatten(s: &Session) -> Vec<[f32; 4]> {
-    photocraft_compose::flatten(doc(s)).px
+    photocraft_compose::flatten(doc(s)).into_px()
 }
 
 fn max_diff(a: &[[f32; 4]], b: &[[f32; 4]]) -> f32 {
diff --git a/crates/engine/src/cmd/face_cmds.rs b/crates/engine/src/cmd/face_cmds.rs
index d48df95b84..0ae0af3d35 100644
--- a/crates/engine/src/cmd/face_cmds.rs
+++ b/crates/engine/src/cmd/face_cmds.rs
@@ -36,7 +36,7 @@ pub fn faces_in(doc: &Document, active: Option<LayerId>, all_layers: bool, min_s
             surf.read_rgba_into(area, &mut px);
             px
         }
-        None => photocraft_compose::render(doc, area).px,
+        None => photocraft_compose::render(doc, area).into_px(),
     };
     let found = detect(&px, w, h, min_score)?;
     let (x0, y0) = (area.x0 as f32, area.y0 as f32);
diff --git a/crates/engine/src/cmd/layer_menu_cmds.rs b/crates/engine/src/cmd/layer_menu_cmds.rs
index 34a1f914ee..75701d9ddd 100644
--- a/crates/engine/src/cmd/layer_menu_cmds.rs
+++ b/crates/engine/src/cmd/layer_menu_cmds.rs
@@ -230,7 +230,7 @@ fn mask_all_objects(s: &mut Session, p: &Value) -> Result<Value> {
             struct Composite<'a>(&'a Document);
             impl photocraft_algo::segment::Sampler for Composite<'_> {
                 fn rgba(&self, r: Rect) -> Vec<[f32; 4]> {
-                    photocraft_compose::render(self.0, r).px
+                    photocraft_compose::render(self.0, r).into_px()
                 }
             }
             photocraft_algo::segment::subject::select_subject(&Composite(&doc), doc.bounds())
diff --git a/crates/engine/src/cmd/layer_menu_cmds/tests.rs b/crates/engine/src/cmd/layer_menu_cmds/tests.rs
index 702d65891b..62522ccc39 100644
--- a/crates/engine/src/cmd/layer_menu_cmds/tests.rs
+++ b/crates/engine/src/cmd/layer_menu_cmds/tests.rs
@@ -757,11 +757,11 @@ fn applying_a_feathered_mask_preserves_its_soft_composite() {
             Ok(())
         })
         .unwrap();
-        let before = photocraft_compose::flatten(doc(&s)).px;
+        let before = photocraft_compose::flatten(doc(&s)).into_px();
         assert!(before[15 * 40 + 19][3] > 0.0 && before[15 * 40 + 19][3] < 1.0, "mask must start with a soft edge");
         s.execute("layer.layerMask.apply", json!({})).unwrap();
         assert!(active(&s).mask.is_none(), "Apply removes the pixel mask");
-        let after = photocraft_compose::flatten(doc(&s)).px;
+        let after = photocraft_compose::flatten(doc(&s)).into_px();
         for (a, b) in before.iter().zip(&after) {
             assert!((a[3] - b[3]).abs() <= 1.0 / 255.0 + 1e-5, "depth {depth}: alpha {a:?} became {b:?}");
         }
@@ -791,13 +791,13 @@ fn from_transparency_preserves_mask_coverage_outside_the_canvas() {
     for depth in DEPTHS {
         let mut s = session(depth, "rgb");
         paint(&mut s, |_, _| [1.0, 0.0, 0.0, 0.5]);
-        let before = photocraft_compose::flatten(doc(&s)).px;
+        let before = photocraft_compose::flatten(doc(&s)).into_px();
         s.execute("layer.translate", json!({"dx": 20})).unwrap();
         s.execute("layer.layerMask.fromTransparency", json!({})).unwrap();
         let mask = active(&s).mask.as_ref().unwrap();
         assert!((mask.value(50, 10) - 0.5).abs() < 1.0 / 255.0 + 1e-6, "off-canvas mask at depth {depth}");
         s.execute("layer.translate", json!({"dx": -20})).unwrap();
-        let after = photocraft_compose::flatten(doc(&s)).px;
+        let after = photocraft_compose::flatten(doc(&s)).into_px();
         for (a, b) in before.iter().zip(&after) {
             assert!((a[3] - b[3]).abs() <= 1.0 / 255.0 + 1e-6, "alpha changed at depth {depth}: {a:?} -> {b:?}");
         }
diff --git a/crates/engine/src/cmd/mask_view_cmds/tests.rs b/crates/engine/src/cmd/mask_view_cmds/tests.rs
index ce9bffa744..82179a5456 100644
--- a/crates/engine/src/cmd/mask_view_cmds/tests.rs
+++ b/crates/engine/src/cmd/mask_view_cmds/tests.rs
@@ -44,7 +44,7 @@ fn modes_toggle_and_show_in_inspect_without_history() {
 fn a_mask_view_never_alters_pixels() {
     let (mut s, masked, _) = session();
     let before = s.active().unwrap().doc.clone();
-    let px = |s: &Session| photocraft_compose::render(&s.active().unwrap().doc, Rect::new(0, 0, 40, 20)).px;
+    let px = |s: &Session| photocraft_compose::render(&s.active().unwrap().doc, Rect::new(0, 0, 40, 20)).into_px();
     let composite = px(&s);
     for mode in ["gray", "overlay", "toggleOverlay", "toggleGray", "off"] {
         s.execute(ID, json!({"layer": masked, "mode": mode})).unwrap();
diff --git a/crates/engine/src/cmd/mode_cmds.rs b/crates/engine/src/cmd/mode_cmds.rs
index ac30023d92..3043f080e6 100644
--- a/crates/engine/src/cmd/mode_cmds.rs
+++ b/crates/engine/src/cmd/mode_cmds.rs
@@ -186,7 +186,7 @@ fn with_released_movement_locks<R>(l: &mut Layer, f: impl FnOnce(&mut Layer) ->
 /// The flattened image as straight RGBA (over white when `opaque`).
 fn composite(doc: &Document, opaque: bool) -> Vec<[f32; 4]> {
     let buf = photocraft_compose::flatten(doc);
-    if opaque { buf.over_background([1.0, 1.0, 1.0]).px } else { buf.px }
+    if opaque { buf.over_background([1.0, 1.0, 1.0]).into_px() } else { buf.into_px() }
 }
 
 /// Replace the document's layers by one 8-bit layer holding `px` in `mode`'s storage format.
diff --git a/crates/engine/src/cmd/mode_cmds/tests.rs b/crates/engine/src/cmd/mode_cmds/tests.rs
index 0d3f9b3cea..4d3c97b02b 100644
--- a/crates/engine/src/cmd/mode_cmds/tests.rs
+++ b/crates/engine/src/cmd/mode_cmds/tests.rs
@@ -568,7 +568,7 @@ fn bitmap_budgets_a_conversion_at_the_document_resolution_too() {
 
 /// The Bitmap conversion of `d` the pre-#8477 way, from one full-canvas composite over white.
 fn bitmap_oracle(d: &Document, method: Option<BitmapMethod>, custom: Option<(&[f32], usize, usize)>) -> Vec<f32> {
-    let px = photocraft_compose::flatten(d).over_background([1.0; 3]).px;
+    let px = photocraft_compose::flatten(d).over_background([1.0; 3]).into_px();
     let mut gray: Vec<f32> = px.iter().map(|q| photocraft_color::convert::rgb_to_gray([q[0], q[1], q[2]])).collect();
     let w = d.size.width as usize;
     match (method, custom) {
@@ -730,7 +730,7 @@ fn duotone_to_colour_modes_keeps_the_ink_colours() {
                 s.execute("image.mode.duotone", cfg.clone()).unwrap();
                 let before = s.active().unwrap().doc.clone();
                 let gray: Vec<f32> = (0..16).map(|x| before.layers[0].surface().unwrap().pixel(x, 1)[0]).collect();
-                let shown = photocraft_compose::render(&display_document(&before).unwrap(), Rect::from_xywh(0, 1, 16, 1)).px;
+                let shown = photocraft_compose::render(&display_document(&before).unwrap(), Rect::from_xywh(0, 1, 16, 1)).into_px();
                 s.execute(&format!("image.mode.{mode}"), json!({})).unwrap();
                 let d = doc(&s);
                 assert!(d.duotone.is_none(), "{ctx}");
diff --git a/crates/engine/src/cmd/select_extra_cmds.rs b/crates/engine/src/cmd/select_extra_cmds.rs
index 8ca012266d..9fd7b309cc 100644
--- a/crates/engine/src/cmd/select_extra_cmds.rs
+++ b/crates/engine/src/cmd/select_extra_cmds.rs
@@ -40,7 +40,7 @@ struct CompositeSampler<'a>(&'a Document);
 
 impl Sampler for CompositeSampler<'_> {
     fn rgba(&self, r: Rect) -> Vec<[f32; 4]> {
-        photocraft_compose::render(self.0, r).px
+        photocraft_compose::render(self.0, r).into_px()
     }
 }
 
diff --git a/crates/engine/src/cmd/selection_cmds.rs b/crates/engine/src/cmd/selection_cmds.rs
index e8d206285e..024f6b088b 100644
--- a/crates/engine/src/cmd/selection_cmds.rs
+++ b/crates/engine/src/cmd/selection_cmds.rs
@@ -70,7 +70,7 @@ fn sample_pixels(s: &Session, all_layers: bool, window: Option<Rect>) -> Result<
             surf.read_rgba_into(area, &mut px);
             Ok((area, px))
         }
-        _ => Ok((area, photocraft_compose::render(&d.doc, area).px)),
+        _ => Ok((area, photocraft_compose::render(&d.doc, area).into_px())),
     }
 }
 
diff --git a/crates/engine/src/cmd/smart_cmds/rendering.rs b/crates/engine/src/cmd/smart_cmds/rendering.rs
index 907c7d6947..ab862d5545 100644
--- a/crates/engine/src/cmd/smart_cmds/rendering.rs
+++ b/crates/engine/src/cmd/smart_cmds/rendering.rs
@@ -39,7 +39,7 @@ pub fn stack_image(file_name: &str, bytes: &[u8], fmt: PixelFormat, mode: photoc
             let mut one = l.clone();
             one.blend = BlendMode::Normal;
             one.clipped = false;
-            photocraft_compose::render_layer(&one, bounds).px
+            photocraft_compose::render_layer(&one, bounds).into_px()
         })
         .collect();
     if frames.is_empty() {
diff --git a/crates/engine/src/cmd/smart_cmds/tests.rs b/crates/engine/src/cmd/smart_cmds/tests.rs
index d6306f0d18..6e8ce37f9c 100644
--- a/crates/engine/src/cmd/smart_cmds/tests.rs
+++ b/crates/engine/src/cmd/smart_cmds/tests.rs
@@ -110,7 +110,7 @@ fn paint(s: &mut Session) {
 }
 
 fn flat(s: &Session) -> Vec<[f32; 4]> {
-    photocraft_compose::flatten(&s.active().unwrap().doc).px
+    photocraft_compose::flatten(&s.active().unwrap().doc).into_px()
 }
 
 fn max_diff(a: &[[f32; 4]], b: &[[f32; 4]]) -> f32 {
diff --git a/crates/engine/src/cmd/smartselect_cmds.rs b/crates/engine/src/cmd/smartselect_cmds.rs
index c04df742a8..adbf9b5f46 100644
--- a/crates/engine/src/cmd/smartselect_cmds.rs
+++ b/crates/engine/src/cmd/smartselect_cmds.rs
@@ -49,7 +49,7 @@ struct CompositeSampler<'a>(&'a Document);
 
 impl Sampler for CompositeSampler<'_> {
     fn rgba(&self, r: Rect) -> Vec<[f32; 4]> {
-        photocraft_compose::render(self.0, r).px
+        photocraft_compose::render(self.0, r).into_px()
     }
 }
 
diff --git a/crates/engine/src/cmd/transform_cmds/tests.rs b/crates/engine/src/cmd/transform_cmds/tests.rs
index e9ed16f245..7bf247466b 100644
--- a/crates/engine/src/cmd/transform_cmds/tests.rs
+++ b/crates/engine/src/cmd/transform_cmds/tests.rs
@@ -366,7 +366,7 @@ fn off_from_fresh(s: &Session) -> f32 {
     let st = s.active().unwrap();
     let mut fresh: Document = (*st.doc).clone();
     fresh.layer_mut(st.active_layer.unwrap()).unwrap().fill_cache = None;
-    let (a, b) = (photocraft_compose::render(&st.doc, st.doc.bounds()).px, photocraft_compose::render(&fresh, fresh.bounds()).px);
+    let (a, b) = (photocraft_compose::render(&st.doc, st.doc.bounds()).into_px(), photocraft_compose::render(&fresh, fresh.bounds()).into_px());
     a.iter().zip(&b).flat_map(|(p, q)| p.iter().zip(q).map(|(x, y)| (x - y).abs())).fold(0.0, f32::max)
 }
 
diff --git a/crates/engine/src/cmd/video_cmds/tests.rs b/crates/engine/src/cmd/video_cmds/tests.rs
index 66566bdb7d..d08135f60e 100644
--- a/crates/engine/src/cmd/video_cmds/tests.rs
+++ b/crates/engine/src/cmd/video_cmds/tests.rs
@@ -229,7 +229,7 @@ fn animated_gif_keeps_transparency() {
     // Each frame has a transparent index and is cleared before the next (disposal 2).
     let packed: Vec<u8> = gif.windows(4).filter(|w| w[..3] == [0x21, 0xF9, 0x04]).map(|w| w[3]).collect();
     assert_eq!(packed, [0x09, 0x09]);
-    let px = photocraft_compose::flatten(&photocraft_io::import("t.gif", &gif).unwrap().document).px;
+    let px = photocraft_compose::flatten(&photocraft_io::import("t.gif", &gif).unwrap().document).into_px();
     assert_eq!(px[0][3], 0.0, "the corner stays transparent");
     assert_eq!(px[3 * 8 + 3], [1.0, 0.0, 0.0, 1.0], "the square stays red");
 }
diff --git a/crates/engine/src/color_channels/tone.rs b/crates/engine/src/color_channels/tone.rs
index 97d6e8f7b2..c64b1debba 100644
--- a/crates/engine/src/color_channels/tone.rs
+++ b/crates/engine/src/color_channels/tone.rs
@@ -61,7 +61,7 @@ pub(super) fn adjust(surface: &mut Surface, colors: ColorChannels, adjustment: &
                         .collect(),
                 };
                 adjust::apply_in(&scalar, &mut buf, transfer, depth, mode);
-                Arc::new(IntegerTable { adjusted: buf.px.into_iter().map(|p| p[0]).collect(), encoded: Vec::new() })
+                Arc::new(IntegerTable { adjusted: buf.px.iter().map(|p| p[0]).collect(), encoded: Vec::new() })
             })
         });
         let mut component = Component { index, scalar, table, lab_invert };
diff --git a/crates/engine/src/doc_path/tests.rs b/crates/engine/src/doc_path/tests.rs
index 1c9bc88874..049e126a47 100644
--- a/crates/engine/src/doc_path/tests.rs
+++ b/crates/engine/src/doc_path/tests.rs
@@ -157,7 +157,7 @@ fn replayed(s: &mut Session, id: LayerId, params: serde_json::Value) -> Vec<[f32
     })
     .unwrap();
     let doc = &s.active().unwrap().doc;
-    photocraft_compose::render(doc, doc.bounds()).px
+    photocraft_compose::render(doc, doc.bounds()).into_px()
 }
 
 #[test]
@@ -202,12 +202,12 @@ fn smart_displace_keeps_a_relative_map_path() {
     png(&d.join("map.png"), |_| [255, 255, 255]);
     let (mut s, id) = document(&d, &d.join("ramp.png"));
     let path = d.join("map.png").to_string_lossy().into_owned();
-    let unfiltered = photocraft_compose::render(&s.active().unwrap().doc, s.active().unwrap().doc.bounds()).px;
+    let unfiltered = photocraft_compose::render(&s.active().unwrap().doc, s.active().unwrap().doc.bounds()).into_px();
     s.execute("filter.distort.displace", json!({"layer": id.0, "mapPath": path, "horizontal": 50, "vertical": 0})).unwrap();
     let state = |s: &Session| {
         let doc = &s.active().unwrap().doc;
         let Some(LayerContent::Smart(sm)) = doc.layer(id).map(|l| &l.content) else { panic!("a smart object") };
-        (sm.smart_filters[0].params.clone(), photocraft_compose::render(doc, doc.bounds()).px)
+        (sm.smart_filters[0].params.clone(), photocraft_compose::render(doc, doc.bounds()).into_px())
     };
     let (params, displaced) = state(&s);
     assert_eq!(params["mapPath"], json!(path));
diff --git a/crates/engine/src/filters.rs b/crates/engine/src/filters.rs
index aebee03caf..2bcccb7a5c 100644
--- a/crates/engine/src/filters.rs
+++ b/crates/engine/src/filters.rs
@@ -397,6 +397,8 @@ pub(crate) fn keep_alpha(old: &photocraft_raster::Surface, new: &mut photocraft_
                 }
             }
             s.write_region(*r, &v);
+            photocraft_raster::scratch::give(o);
+            photocraft_raster::scratch::give(v);
             true
         })
         .reduce(|| true, |a, b| a && b);
diff --git a/crates/engine/src/jobs.rs b/crates/engine/src/jobs.rs
index 5111fe1635..10d3114e85 100644
--- a/crates/engine/src/jobs.rs
+++ b/crates/engine/src/jobs.rs
@@ -294,6 +294,16 @@ impl Running {
     }
 }
 
+/// A cancelled job's worker that may still be unwinding.
+#[cfg(not(target_arch = "wasm32"))]
+struct Draining {
+    handle: std::thread::JoinHandle<()>,
+    doc: Option<DocId>,
+    /// Its document closed: the worker still holds that document's snapshot, so the scratch
+    /// pool is released again once it exits (the release at close came too early, #10479).
+    release: bool,
+}
+
 /// The session's job table (see the module docs).
 #[derive(Default)]
 pub struct Jobs {
@@ -309,7 +319,7 @@ pub struct Jobs {
     recent: Vec<JobInfo>,
     /// Workers of cancelled jobs that may still be unwinding (native).
     #[cfg(not(target_arch = "wasm32"))]
-    draining: Vec<std::thread::JoinHandle<()>>,
+    draining: Vec<Draining>,
     /// The context inline job work runs under (see [`Session::set_inline_job_ctx`]).
     inline: Option<JobCtx>,
 }
@@ -691,7 +701,17 @@ impl Session {
             }
         }
         #[cfg(not(target_arch = "wasm32"))]
-        self.jobs.draining.retain(|h| !h.is_finished());
+        {
+            let mut release = false;
+            self.jobs.draining.retain(|d| {
+                let done = d.handle.is_finished();
+                release |= done && d.release;
+                !done
+            });
+            if release {
+                photocraft_raster::scratch::release();
+            }
+        }
         std::mem::take(&mut self.jobs.events)
     }
 
@@ -730,8 +750,8 @@ impl Session {
         job.ctx.cancel();
         self.end_job(&job, JobOutcome::Cancelled);
         #[cfg(not(target_arch = "wasm32"))]
-        if let Some(h) = job.handle {
-            self.jobs.draining.push(h);
+        if let Some(handle) = job.handle {
+            self.jobs.draining.push(Draining { handle, doc: job.doc, release: false });
         }
         true
     }
@@ -778,8 +798,15 @@ impl Session {
     /// cancel latency with it). Native only; returns at once on wasm.
     pub fn join_cancelled_jobs(&mut self) {
         #[cfg(not(target_arch = "wasm32"))]
-        for h in self.jobs.draining.drain(..) {
-            let _ = h.join();
+        {
+            let mut release = false;
+            for d in self.jobs.draining.drain(..) {
+                let _ = d.handle.join();
+                release |= d.release;
+            }
+            if release {
+                photocraft_raster::scratch::release();
+            }
         }
     }
 
@@ -798,6 +825,11 @@ impl Session {
         for id in ids {
             self.cancel_job(id);
         }
+        // Workers cancelled now, or earlier and still unwinding, hold the closing document.
+        #[cfg(not(target_arch = "wasm32"))]
+        for d in self.jobs.draining.iter_mut().filter(|d| d.doc == Some(doc)) {
+            d.release = true;
+        }
     }
 
     /// Run the command `id`: inline, or (with `background`) as a job when it is one.
@@ -881,6 +913,7 @@ impl Session {
         // being recorded, nor move the recording mark past the entries it is about to replace.
         let recording = if spec.journal && crate::actions_cmds::replayable(id) { self.actions.recording.take() } else { None };
         let before = self.active().map(|st| st.doc.clone());
+        let docs_before: Vec<_> = self.docs.iter().map(|st| st.doc.id).collect();
         // Last-resort guard (AGENTS.md, Never crash): a command that panics anyway fails with an
         // error instead of taking the app down. `edit` only commits a document after its closure
         // returns, so the documents are unchanged.
@@ -900,7 +933,7 @@ impl Session {
             self.hint_before = None;
         }
         let pending = self.jobs.pending.take();
-        match (r, pending) {
+        let out = match (r, pending) {
             (Err(e), Some(job)) => {
                 job.ctx.cancel();
                 Err(e)
@@ -917,8 +950,8 @@ impl Session {
                 Ok(Started::Job(jid))
             }
             (Ok(v), None) => {
-                if let Some(before) = before {
-                    self.add_relayout_damage(&before);
+                if let Some(before) = &before {
+                    self.add_relayout_damage(before);
                 }
                 if let Some((doc_id, layer_id)) = new_fx_target
                     && let Some(st) = self.active_mut()
@@ -934,7 +967,15 @@ impl Session {
                 self.after_command(id, params, spec.journal, Some(nested_from), pre_selected.as_deref());
                 Ok(Started::Done(v))
             }
+        };
+        // A closed document's freed buffers went to the scratch pool (`before` kept the active
+        // one alive until here): hand them back to the OS (#10479). Compared by id, since Split
+        // and Merge Channels close documents while opening others.
+        if docs_before.iter().any(|id| !self.docs.iter().any(|st| st.doc.id == *id)) {
+            drop(before);
+            photocraft_raster::scratch::release();
         }
+        out
     }
 
     /// Grows the damage a command reported for the pixels it changed by what effects laid out
diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index 5e6cc66ab0..b49675176e 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -29,6 +29,7 @@ pub mod kys;
 pub mod layer_place;
 pub mod layer_style;
 pub mod link_watch;
+pub mod malloc_tuning;
 pub mod new_layer;
 mod param_check;
 mod pixels;
diff --git a/crates/engine/src/malloc_tuning.rs b/crates/engine/src/malloc_tuning.rs
new file mode 100644
index 0000000000..f9c5947c47
--- /dev/null
+++ b/crates/engine/src/malloc_tuning.rs
@@ -0,0 +1,81 @@
+//! glibc malloc tuning for the native binaries (#8743).
+//!
+//! With glibc's defaults, the memory of a closed document stays with the process: freeing a large
+//! buffer raises glibc's dynamic mmap threshold (up to 32 MiB), so later tile buffers come from the
+//! heap, whose freed pages glibc keeps for reuse instead of giving them back. A session that opened
+//! and closed a 5400 × 7200 document held ~540 MiB afterwards; with `MALLOC_TRIM_THRESHOLD_` set it
+//! went back to ~20 MiB, and the peak was lower too. Setting the threshold explicitly turns the
+//! dynamic adjustment off (mallopt(3)), so large buffers are mapped and unmapped on their own and
+//! the heap top is trimmed as it is freed. Mapping fresh pages on every call is slow, so the large
+//! short-lived buffers come from `photocraft_raster::scratch` instead, which reuses them and
+//! releases them when a document closes or the pool goes idle (#10479).
+//!
+//! glibc reads its tunables once, when the process starts, and changing the environment from Rust
+//! needs `unsafe` (and comes too late), so [`apply`] re-executes the binary with the variable set:
+//! the same process (PID), arguments, `argv[0]` and environment, on Linux with glibc only. A value
+//! the user or a package already set, for this or another malloc tunable, is left alone, so setting
+//! `MALLOC_TRIM_THRESHOLD_` to anything opts out. Programs PhotoCraft starts inherit the variable.
+
+use std::ffi::OsString;
+
+/// The glibc environment variable [`apply`] sets.
+pub const TRIM_THRESHOLD_VAR: &str = "MALLOC_TRIM_THRESHOLD_";
+
+/// Its value: glibc's own default trim threshold (128 KiB), now fixed instead of dynamic.
+pub const TRIM_THRESHOLD: &str = "131072";
+
+/// glibc malloc variables that mean someone tuned malloc themselves.
+const MALLOC_VARS: [&str; 5] = [TRIM_THRESHOLD_VAR, "MALLOC_MMAP_THRESHOLD_", "MALLOC_TOP_PAD_", "MALLOC_MMAP_MAX_", "MALLOC_ARENA_MAX"];
+
+/// Whether a start-up should re-execute with [`TRIM_THRESHOLD_VAR`] set, given the environment:
+/// only when no malloc variable or `glibc.malloc.*` tunable is set (which also ends the re-exec).
+pub fn needs_restart(var: impl Fn(&str) -> Option<OsString>) -> bool {
+    if MALLOC_VARS.iter().any(|v| var(v).is_some()) {
+        return false;
+    }
+    !var("GLIBC_TUNABLES").is_some_and(|t| t.to_string_lossy().contains("glibc.malloc."))
+}
+
+/// Re-execute this binary with [`TRIM_THRESHOLD_VAR`] set when [`needs_restart`] says so. Call it
+/// first in `main`, before any thread starts. It returns only when nothing needed to change or the
+/// re-exec failed, and then the process carries on with glibc's defaults.
+#[cfg(all(target_os = "linux", target_env = "gnu"))]
+pub fn apply() {
+    use std::os::unix::process::CommandExt;
+    if !needs_restart(|k| std::env::var_os(k)) {
+        return;
+    }
+    let Ok(exe) = std::env::current_exe() else { return };
+    let mut args = std::env::args_os();
+    let mut cmd = std::process::Command::new(exe);
+    if let Some(argv0) = args.next() {
+        cmd.arg0(argv0);
+    }
+    // `exec` replaces the process and only returns on failure.
+    let err = cmd.args(args).env(TRIM_THRESHOLD_VAR, TRIM_THRESHOLD).exec();
+    eprintln!("PhotoCraft: could not restart with {TRIM_THRESHOLD_VAR} set ({err}); memory of closed documents may not be returned to the system");
+}
+
+/// Nothing to tune off glibc.
+#[cfg(not(all(target_os = "linux", target_env = "gnu")))]
+pub fn apply() {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn env<'a>(vars: &'a [(&'a str, &'a str)]) -> impl Fn(&str) -> Option<OsString> + 'a {
+        move |k| vars.iter().find(|(n, _)| *n == k).map(|(_, v)| OsString::from(v))
+    }
+
+    #[test]
+    fn restarts_only_without_malloc_tuning() {
+        assert!(needs_restart(env(&[])));
+        assert!(needs_restart(env(&[("HOME", "/home/a"), ("GLIBC_TUNABLES", "glibc.cpu.hwcaps=-AVX2")])));
+        assert!(!needs_restart(env(&[(TRIM_THRESHOLD_VAR, TRIM_THRESHOLD)])), "the re-executed process stops");
+        assert!(!needs_restart(env(&[(TRIM_THRESHOLD_VAR, "")])), "any value opts out");
+        assert!(!needs_restart(env(&[("MALLOC_MMAP_THRESHOLD_", "1048576")])));
+        assert!(!needs_restart(env(&[("MALLOC_ARENA_MAX", "2")])));
+        assert!(!needs_restart(env(&[("GLIBC_TUNABLES", "glibc.malloc.trim_threshold=0")])));
+    }
+}
diff --git a/crates/engine/src/pixels.rs b/crates/engine/src/pixels.rs
index 906f0b23c6..f95a3feb0d 100644
--- a/crates/engine/src/pixels.rs
+++ b/crates/engine/src/pixels.rs
@@ -115,6 +115,7 @@ pub fn adjust_surface(s: &mut Surface, adj: &Adjustment, selection: Option<&Surf
             let tr = tc.rect().intersect(&r);
             let out = adjusted(&one, tr, adj, selection, mode);
             one.write_region(tr, &out);
+            photocraft_raster::scratch::give(out);
             one.take_tiles(tc.rect())
         })
         .collect();
@@ -184,6 +185,7 @@ pub(crate) fn adjust_mask_with_transfer(
         for t in &tiles {
             let out = adjusted_with_transfer(s, *t, adj, Some(sel), mode, transfer);
             s.write_region(*t, &out);
+            photocraft_raster::scratch::give(out);
         }
         if !tiles.is_empty() {
             s.prune();
@@ -197,7 +199,9 @@ pub(crate) fn adjust_mask_with_transfer(
     // So only the stored tiles are adjusted, not the (possibly huge) rectangle around them.
     let stored: Vec<Rect> = s.tiles().map(|(c, _)| c.rect()).collect();
     for r in stored {
-        out.write_region(r, &adjusted_with_transfer(s, r, adj, None, mode, transfer));
+        let data = adjusted_with_transfer(s, r, adj, None, mode, transfer);
+        out.write_region(r, &data);
+        photocraft_raster::scratch::give(data);
     }
     out.prune();
     *s = out;
@@ -233,7 +237,10 @@ fn adjusted_with_transfer(
     }
     let n = fmt.channels();
     let raw = s.read_region(r);
-    let mut buf = Buffer { rect: r, px: raw.chunks_exact(n).map(|p| to_rgba(&fmt, p)).collect() };
+    let mut px = photocraft_raster::scratch::take_cap(raw.len() / n.max(1));
+    px.extend(raw.chunks_exact(n).map(|p| to_rgba(&fmt, p)));
+    photocraft_raster::scratch::give(raw);
+    let mut buf = Buffer { rect: r, px };
     let orig = buf.clone();
     // 32-bit documents get the float behaviour of an adjustment layer there (Levels doesn't clip);
     // integer depths keep the unrounded, clipped curves, except that 16-bit Posterize and
@@ -311,7 +318,7 @@ pub(crate) fn mix_through_selection(
     selection: Option<&Surface>,
 ) -> Vec<f32> {
     let w = (r.width() as usize).max(1);
-    let mut out = Vec::with_capacity(orig.len() * fmt.channels());
+    let mut out = photocraft_raster::scratch::take_cap(orig.len() * fmt.channels());
     // The selection's coverage (channel 0) one row at a time, each of its tiles looked up once
     // per row rather than once per pixel.
     let mut coverage = vec![1.0f32; w];
diff --git a/crates/engine/src/select_mask_edits.rs b/crates/engine/src/select_mask_edits.rs
index 9fd29a2757..4285491eb7 100644
--- a/crates/engine/src/select_mask_edits.rs
+++ b/crates/engine/src/select_mask_edits.rs
@@ -239,7 +239,9 @@ fn invert(base: Option<&Surface>, canvas: Rect) -> Option<Surface> {
             if r.is_empty() {
                 continue;
             }
-            let inverted: Vec<f32> = b.read_region(r).chunks_exact(ch).map(|px| 1.0 - px.first().copied().unwrap_or(0.0).clamp(0.0, 1.0)).collect();
+            let read = b.read_region(r);
+            let inverted: Vec<f32> = read.chunks_exact(ch).map(|px| 1.0 - px.first().copied().unwrap_or(0.0).clamp(0.0, 1.0)).collect();
+            photocraft_raster::scratch::give(read);
             s.write_region(r, &inverted);
         }
     }
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index bae9cf4c92..30c2e32f59 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -814,7 +814,7 @@ fn fill_layer_pixel_rewrites_refresh_the_effect_maps() {
     .unwrap();
     let render = |s: &Session| {
         let d = &s.active().unwrap().doc;
-        photocraft_compose::render(d, d.bounds()).px
+        photocraft_compose::render(d, d.bounds()).into_px()
     };
     // Give the layer the cached-pixels state a PSD import produces (the cache is what Image
     // › Transform & friends rewrite in place, without touching the Fill spec).
@@ -901,7 +901,7 @@ fn group_effect_maps_follow_child_visibility_and_opacity() {
     .unwrap();
     let render = |s: &Session| {
         let d = &s.active().unwrap().doc;
-        photocraft_compose::render(d, d.bounds()).px
+        photocraft_compose::render(d, d.bounds()).into_px()
     };
     let mut prev = render(&s); // populate the effect-map cache
     type Edit = (&'static str, fn(&mut photocraft_doc::Layer));
diff --git a/crates/engine/tests/it/atn_crystallize_cell_size.rs b/crates/engine/tests/it/atn_crystallize_cell_size.rs
index 7b72a6ff70..8a015f1497 100644
--- a/crates/engine/tests/it/atn_crystallize_cell_size.rs
+++ b/crates/engine/tests/it/atn_crystallize_cell_size.rs
@@ -24,7 +24,7 @@ fn fixture(depth: u32) -> Session {
 
 /// Compare the actual flattened document rather than just the imported parameters.
 fn pixels(s: &Session) -> Vec<[f32; 4]> {
-    photocraft_compose::flatten(&s.active().unwrap().doc).px
+    photocraft_compose::flatten(&s.active().unwrap().doc).into_px()
 }
 
 /// Fractions remain valid native edits; strict integer ATN conversion must refuse them.
diff --git a/crates/engine/tests/it/atn_ripple_amount.rs b/crates/engine/tests/it/atn_ripple_amount.rs
index b6bde88f7a..0ff38f2036 100644
--- a/crates/engine/tests/it/atn_ripple_amount.rs
+++ b/crates/engine/tests/it/atn_ripple_amount.rs
@@ -24,7 +24,7 @@ fn fixture(depth: u32) -> Session {
 
 /// Flatten the active document to compare direct, native and ATN playback pixels.
 fn pixels(s: &Session) -> Vec<[f32; 4]> {
-    photocraft_compose::flatten(&s.active().unwrap().doc).px
+    photocraft_compose::flatten(&s.active().unwrap().doc).into_px()
 }
 
 /// Fractions are valid native edits, but the existing integer event cannot carry them.
diff --git a/crates/engine/tests/it/atn_selective_color.rs b/crates/engine/tests/it/atn_selective_color.rs
index 454846f59e..92a23aff5e 100644
--- a/crates/engine/tests/it/atn_selective_color.rs
+++ b/crates/engine/tests/it/atn_selective_color.rs
@@ -37,7 +37,7 @@ fn doc_bounds() -> photocraft_doc::Rect {
 }
 
 fn pixels(s: &Session) -> Vec<[f32; 4]> {
-    photocraft_compose::flatten(&s.active().unwrap().doc).px
+    photocraft_compose::flatten(&s.active().unwrap().doc).into_px()
 }
 
 fn check_cases(id: &str, cases: &[Value], require_effect: bool) {
diff --git a/crates/engine/tests/it/atn_stroke_width.rs b/crates/engine/tests/it/atn_stroke_width.rs
index 742359cf38..3034fb2f0a 100644
--- a/crates/engine/tests/it/atn_stroke_width.rs
+++ b/crates/engine/tests/it/atn_stroke_width.rs
@@ -23,7 +23,7 @@ fn fixture(depth: u32) -> Session {
 
 /// Compare the flattened document, including alpha, rather than only imported JSON.
 fn pixels(s: &Session) -> Vec<[f32; 4]> {
-    photocraft_compose::flatten(&s.active().unwrap().doc).px
+    photocraft_compose::flatten(&s.active().unwrap().doc).into_px()
 }
 
 /// Direct execution, native playback and strict binary ATN playback must agree exactly.
diff --git a/crates/engine/tests/it/photoshop_oracles.rs b/crates/engine/tests/it/photoshop_oracles.rs
index 88e63b67fc..435bab8cc1 100644
--- a/crates/engine/tests/it/photoshop_oracles.rs
+++ b/crates/engine/tests/it/photoshop_oracles.rs
@@ -124,7 +124,7 @@ fn photoshop_oracles_rerendered() {
             }
         };
         let Ok(merged) = photocraft_io::merged_composite(&file) else { continue };
-        let ours = photocraft_compose::flatten(&doc).px;
+        let ours = photocraft_compose::flatten(&doc).into_px();
         let (m, bad) = max_diff(&ours, &merged);
         let group = name.split(['/', '\\']).next().unwrap_or(".").to_string();
         let g = groups.entry(group).or_default();
diff --git a/crates/engine/tests/scratch_release.rs b/crates/engine/tests/scratch_release.rs
new file mode 100644
index 0000000000..6976f0cb7f
--- /dev/null
+++ b/crates/engine/tests/scratch_release.rs
@@ -0,0 +1,114 @@
+//! One integration-test process keeps the process-wide scratch pool isolated from parallel unit
+//! tests (#10479).
+use photocraft_engine::Session;
+use photocraft_engine::jobs::Started;
+use photocraft_raster::scratch;
+use serde_json::json;
+use std::sync::{Mutex, PoisonError};
+
+static SERIAL: Mutex<()> = Mutex::new(());
+
+/// Holds the test lock with the pool's idle release off, so a slow runner can't empty the pool
+/// between a command and the check after it; the release comes back on when dropped.
+struct Quiet {
+    _serial: std::sync::MutexGuard<'static, ()>,
+}
+
+impl Quiet {
+    /// Locks the test process and disables idle pool release for this guard's lifetime.
+    fn new() -> Self {
+        let _serial = SERIAL.lock().unwrap_or_else(PoisonError::into_inner);
+        scratch::set_idle_release(false);
+        Quiet { _serial }
+    }
+}
+
+impl Drop for Quiet {
+    fn drop(&mut self) {
+        scratch::set_idle_release(true);
+    }
+}
+
+#[test]
+/// Verifies closing one or all documents releases their scratch buffers.
+fn closing_a_document_leaves_none_of_its_buffers_in_the_pool() {
+    let _q = Quiet::new();
+    for close in ["file.close", "file.closeAll"] {
+        let mut s = Session::new();
+        s.execute("file.new", json!({"width": 1024, "height": 1024})).unwrap();
+        s.execute("edit.fill", json!({"contents": "color", "color": "#808080"})).unwrap();
+        s.execute("filter.blur.gaussianBlur", json!({"radius": 3})).unwrap();
+        // Dispatch holds the active document across the command; its tiles must not land in
+        // the pool after the release.
+        s.execute(close, json!({})).unwrap();
+        assert_eq!(scratch::retained_bytes(), 0, "{close}");
+    }
+}
+
+#[test]
+/// Verifies a command that keeps its document does not release unrelated pooled buffers.
+fn commands_that_keep_their_documents_keep_the_pool() {
+    let _q = Quiet::new();
+    let mut s = Session::new();
+    s.execute("file.new", json!({"width": 1024, "height": 1024})).unwrap();
+    scratch::give(vec![0u8; scratch::MIN_POOLED_BYTES]);
+    s.execute("edit.fill", json!({"contents": "color", "color": "#808080"})).unwrap();
+    assert!(scratch::retained_bytes() > 0);
+}
+
+#[test]
+/// Verifies a cancelled worker releases its document buffers after it exits.
+fn a_cancelled_job_of_a_closed_document_returns_its_buffers_once_it_exits() {
+    let _q = Quiet::new();
+    let mut s = Session::new();
+    s.execute("file.new", json!({"width": 2048, "height": 2048})).unwrap();
+    s.execute("edit.fill", json!({"contents": "color", "color": "#808080"})).unwrap();
+    let Started::Job(_) = s.start("filter.blur.gaussianBlur", json!({"radius": 60})).unwrap() else {
+        panic!("Gaussian Blur runs as a background job");
+    };
+    // Closing cancels the job, but its worker still holds the document until it exits.
+    s.close(0);
+    scratch::give(vec![0u8; scratch::MIN_POOLED_BYTES]);
+    s.join_cancelled_jobs();
+    assert_eq!(scratch::retained_bytes(), 0);
+}
+
+#[test]
+/// Verifies cancelling a job before document close still releases its buffers.
+fn a_job_cancelled_before_its_document_closes_still_returns_its_buffers() {
+    let _q = Quiet::new();
+    let mut s = Session::new();
+    s.execute("file.new", json!({"width": 2048, "height": 2048})).unwrap();
+    s.execute("edit.fill", json!({"contents": "color", "color": "#808080"})).unwrap();
+    let Started::Job(id) = s.start("filter.blur.gaussianBlur", json!({"radius": 60})).unwrap() else {
+        panic!("Gaussian Blur runs as a background job");
+    };
+    // Cancelled first: the worker is already off the running list when the document closes.
+    assert!(s.cancel_job(id));
+    s.close(0);
+    scratch::give(vec![0u8; scratch::MIN_POOLED_BYTES]);
+    s.join_cancelled_jobs();
+    assert_eq!(scratch::retained_bytes(), 0);
+}
+
+/// Verifies polling alone releases buffers after a closed document's cancelled worker exits.
+#[test]
+fn a_cancelled_job_of_a_closed_document_is_released_by_polling() {
+    let _q = Quiet::new();
+    let mut s = Session::new();
+    s.execute("file.new", json!({"width": 2048, "height": 2048})).unwrap();
+    s.execute("edit.fill", json!({"contents": "color", "color": "#808080"})).unwrap();
+    let Started::Job(_) = s.start("filter.blur.gaussianBlur", json!({"radius": 60})).unwrap() else {
+        panic!("Gaussian Blur runs as a background job");
+    };
+    s.close(0);
+    // Seed after close so the close path cannot satisfy the assertion.
+    scratch::give(vec![0u8; scratch::MIN_POOLED_BYTES]);
+    assert!(scratch::retained_bytes() > 0);
+    let deadline = std::time::Instant::now() + std::time::Duration::from_secs(30);
+    while scratch::retained_bytes() > 0 && std::time::Instant::now() < deadline {
+        s.poll_jobs();
+        std::thread::sleep(std::time::Duration::from_millis(5));
+    }
+    assert_eq!(scratch::retained_bytes(), 0);
+}
diff --git a/crates/format/src/store.rs b/crates/format/src/store.rs
index af6678088b..67bb8df27b 100644
--- a/crates/format/src/store.rs
+++ b/crates/format/src/store.rs
@@ -30,8 +30,87 @@ fn blob_path(h: &str) -> String {
     format!("blobs/{h}.zst")
 }
 
-fn compress(data: &[u8]) -> Vec<u8> {
-    ruzstd::encoding::compress_to_vec(data, ruzstd::encoding::CompressionLevel::Fastest)
+/// The bytes an [`Object`] stores, owned by (or shared with) the compressor's source so one
+/// [`Compressor`] can be reused for objects of any lifetime.
+enum Source {
+    Tile(Arc<Tile>),
+    Blob(Arc<Vec<u8>>),
+    /// A little-endian copy of a tile (big-endian hosts only).
+    Owned(Vec<u8>),
+}
+
+struct SourceReader {
+    source: Source,
+    pos: usize,
+}
+
+impl SourceReader {
+    fn all(&self) -> &[u8] {
+        match &self.source {
+            Source::Tile(t) => t.bytes(),
+            Source::Blob(b) => b.as_slice(),
+            Source::Owned(v) => v.as_slice(),
+        }
+    }
+
+    fn len(&self) -> usize {
+        self.all().len()
+    }
+}
+
+impl Read for SourceReader {
+    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+        let all = self.all();
+        let rest = all.get(self.pos..).unwrap_or(&[]);
+        let n = rest.len().min(buf.len());
+        if let (Some(dst), Some(src)) = (buf.get_mut(..n), rest.get(..n)) {
+            dst.copy_from_slice(src);
+        }
+        self.pos += n;
+        Ok(n)
+    }
+}
+
+/// A reusable zstd compressor. `ruzstd` allocates a block buffer, a ~1 MiB suffix table and a
+/// block output buffer per frame; keeping the [`FrameCompressor`](ruzstd::encoding::FrameCompressor)
+/// between objects reuses the first two (its matcher resets itself on every `compress`).
+/// Output is byte-identical to `compress_to_vec` at the same level.
+struct Compressor {
+    inner: ruzstd::encoding::FrameCompressor<SourceReader, Vec<u8>, ruzstd::encoding::MatchGeneratorDriver>,
+}
+
+impl Compressor {
+    fn new() -> Self {
+        Self { inner: ruzstd::encoding::FrameCompressor::new(ruzstd::encoding::CompressionLevel::Fastest) }
+    }
+
+    fn run(&mut self, source: Source) -> Vec<u8> {
+        let reader = SourceReader { source, pos: 0 };
+        // Room for the worst case (raw blocks: 3 bytes per 128 KiB, plus frame header and
+        // checksum), so the output never regrows; shrunk afterwards to what it used. Untouched
+        // pages cost nothing.
+        let len = reader.len();
+        let mut drain = Vec::new();
+        if drain.try_reserve_exact(len.saturating_add(len / 16384).saturating_add(64)).is_err() {
+            drain = Vec::new();
+        }
+        self.inner.set_source(reader);
+        self.inner.set_drain(drain);
+        self.inner.compress();
+        self.inner.take_source();
+        let mut out = self.inner.take_drain().unwrap_or_default();
+        out.shrink_to_fit();
+        out
+    }
+
+    fn object(&mut self, obj: &Object) -> Vec<u8> {
+        let source = match obj {
+            Object::Tile(tile, _) if cfg!(target_endian = "little") => Source::Tile(Arc::clone(tile)),
+            Object::Tile(tile, sample) => Source::Owned(tile_le(tile, *sample).into_owned()),
+            Object::Blob(blob) => Source::Blob(Arc::clone(blob)),
+        };
+        self.run(source)
+    }
 }
 
 /// Decodes a zstd frame of at most `max` bytes (`LimitExceeded` beyond). With `exact`, the
@@ -528,8 +607,8 @@ enum Object {
 }
 
 impl Object {
-    fn compressed(&self) -> Vec<u8> {
-        compress(&self.content())
+    fn compressed(&self, compressor: &mut Compressor) -> Vec<u8> {
+        compressor.object(self)
     }
 
     /// The bytes this object stores (tiles little-endian).
@@ -860,7 +939,8 @@ type Compressed<'a> = (&'a String, Arc<Vec<u8>>);
 fn par_compress<'a>(objects: &[(&'a String, &'a Object)]) -> Result<Vec<Compressed<'a>>> {
     let threads = if cfg!(target_arch = "wasm32") { 1 } else { std::thread::available_parallelism().map_or(1, |n| n.get()).clamp(1, 32) };
     if threads < 2 || objects.len() < 2 {
-        return Ok(objects.iter().map(|(p, o)| (*p, Arc::new(o.compressed()))).collect());
+        let mut compressor = Compressor::new();
+        return Ok(objects.iter().map(|(p, o)| (*p, Arc::new(o.compressed(&mut compressor)))).collect());
     }
     let next = std::sync::atomic::AtomicUsize::new(0);
     std::thread::scope(|sc| {
@@ -868,10 +948,11 @@ fn par_compress<'a>(objects: &[(&'a String, &'a Object)]) -> Result<Vec<Compress
             .map(|_| {
                 sc.spawn(|| {
                     let mut out = Vec::new();
+                    let mut compressor = Compressor::new();
                     loop {
                         let i = next.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
                         let Some((p, o)) = objects.get(i) else { break };
-                        out.push((*p, Arc::new(o.compressed())));
+                        out.push((*p, Arc::new(o.compressed(&mut compressor))));
                     }
                     out
                 })
@@ -976,6 +1057,7 @@ impl PcraftWriter {
         for (name, data) in &previews {
             z.add(name, data)?;
         }
+        let mut compressor: Option<Compressor> = None;
         for (path, obj) in &p.objects {
             let (key, data) = match self.compressed.remove_entry(path) {
                 Some((key, data)) => {
@@ -989,7 +1071,7 @@ impl PcraftWriter {
                         Object::Tile(..) => stats.tiles_written += 1,
                         Object::Blob(_) => stats.blobs_written += 1,
                     }
-                    (None, fresh.remove(path).unwrap_or_else(|| Arc::new(obj.compressed())))
+                    (None, fresh.remove(path).unwrap_or_else(|| Arc::new(obj.compressed(compressor.get_or_insert_with(Compressor::new)))))
                 }
             };
             z.add(path, &data)?;
@@ -1036,6 +1118,7 @@ impl PcraftWriter {
             None => 0,
         };
         let recheck = self.rolling_recheck(&p.objects);
+        let mut compressor: Option<Compressor> = None;
         for (path, obj) in &p.objects {
             let object_path = dir.join(path);
             // bundle_root and list_objects validated the fixed parent directories once. Check
@@ -1070,7 +1153,7 @@ impl PcraftWriter {
                 Object::Tile(..) => stats.tiles_written += 1,
                 Object::Blob(_) => stats.blobs_written += 1,
             }
-            write_bundle_file(dir, &object_path, &obj.compressed(), fs)?;
+            write_bundle_file(dir, &object_path, &obj.compressed(compressor.get_or_insert_with(Compressor::new)), fs)?;
             let written = path_signature(&object_path)?;
             if let Some(cache) = &mut self.verified_directory {
                 match written {
@@ -1421,6 +1504,38 @@ pub(crate) fn write_atomic(path: &Path, data: &[u8]) -> Result<()> {
 #[cfg(all(test, windows))]
 mod durability_tests;
 
+#[cfg(test)]
+#[test]
+fn reused_compressor_matches_compress_to_vec_and_round_trips() {
+    let mut state = 0x9e37_79b9_u32;
+    let mut noise = |n: usize| -> Vec<u8> {
+        (0..n)
+            .map(|_| {
+                state = state.wrapping_mul(1_664_525).wrapping_add(1_013_904_223);
+                (state >> 24) as u8
+            })
+            .collect()
+    };
+    let inputs: Vec<Vec<u8>> = vec![
+        Vec::new(),
+        vec![7],
+        b"hello hello hello hello hello".to_vec(),
+        noise(1000),
+        (0..300_000u32).map(|i| (i / 7 % 251) as u8).collect(),
+        noise(300_000),
+        vec![0; 262_144],
+        // A repeat after a big one proves the matcher state is reset between objects.
+        b"hello hello hello hello hello".to_vec(),
+    ];
+    let mut compressor = Compressor::new();
+    for data in inputs {
+        let expected = ruzstd::encoding::compress_to_vec(data.as_slice(), ruzstd::encoding::CompressionLevel::Fastest);
+        let got = compressor.object(&Object::Blob(Arc::new(data.clone())));
+        assert_eq!(got, expected, "len {}", data.len());
+        assert_eq!(decompress(&got, data.len(), "test").unwrap(), data);
+    }
+}
+
 #[cfg(test)]
 #[test]
 fn an_incompressible_blob_at_its_limit_still_loads() {
@@ -1442,7 +1557,7 @@ fn an_incompressible_blob_at_its_limit_still_loads() {
             x as u8
         })
         .collect();
-    let z = compress(&data);
+    let z = Compressor::new().object(&Object::Blob(Arc::new(data.clone())));
     assert!(z.len() > data.len(), "the fixture must not compress");
     let hash = hash_bytes(&data);
     let src = One(blob_path(&hash), z);
diff --git a/crates/gpu/src/convert.rs b/crates/gpu/src/convert.rs
index 9dbfc81814..19ad194765 100644
--- a/crates/gpu/src/convert.rs
+++ b/crates/gpu/src/convert.rs
@@ -1,6 +1,7 @@
 use super::batch::write_tile;
 use super::textures::{Resident, TexKind};
 use super::{Arc, F, HashMap, I, PixelFormat, Rect, SampleType, Surface, TILE_SIZE, Tile, TileCoord, U, fx};
+use photocraft_raster::scratch;
 
 /// Distinct tiles converted per parallel batch: bounds the converted bytes held at once (64 tiles
 /// of a 16-bit page are 32 MiB).
@@ -141,6 +142,8 @@ pub(crate) fn convert_tiles(
                 _ => put(t, cs, &bytes.concat()),
             }
         }
+        // The texels are on their way to the GPU: the buffers serve the next batch.
+        parts.into_iter().for_each(scratch::give);
     }
     groups.len()
 }
@@ -157,7 +160,9 @@ pub(crate) fn colour_managed(fmt: &PixelFormat, kind: TexKind) -> bool {
 /// Tile pixels in the texture's format. `tile = None` gives the default pixel everywhere.
 pub(crate) fn convert_tile(surface: &Surface, tile: Option<&Arc<Tile>>, kind: TexKind, c: TileCoord) -> Vec<u8> {
     if let (Some(t), TexKind::Rgba8Direct | TexKind::R8Direct) = (tile, kind) {
-        return t.bytes().to_vec();
+        let mut out = scratch::take_cap(t.bytes().len());
+        out.extend_from_slice(t.bytes());
+        return out;
     }
     let fmt = surface.format();
     if let (Some(t), TexKind::Rgba16F) = (tile, kind)
@@ -179,7 +184,7 @@ fn convert_rows(surface: &Surface, tile: Option<&Arc<Tile>>, kind: TexKind, rect
         Some(_) => surface.read_region(rect),
         None => surface.default_pixel().repeat(n),
     };
-    let mut out = Vec::with_capacity(n * kind.bytes_per_pixel());
+    let mut out = scratch::take_cap(n * kind.bytes_per_pixel());
     // The previous pixel and its colour.
     let mut last: Option<(usize, [f32; 4])> = None;
     for (i, px) in raw.chunks_exact(ch).enumerate() {
@@ -209,6 +214,7 @@ fn convert_rows(surface: &Surface, tile: Option<&Arc<Tile>>, kind: TexKind, rect
             TexKind::R32F => out.extend(px[0].to_le_bytes()),
         }
     }
+    scratch::give(raw);
     out
 }
 
@@ -229,7 +235,7 @@ pub(crate) fn rgb_gray16_to_f16(fmt: &PixelFormat, bytes: &[u8]) -> Option<Vec<u
     let half = HALF.get_or_init(|| (0..=u16::MAX).map(|v| f32_to_f16(v as f32 / 65535.0)).collect());
     let one = f32_to_f16(1.0).to_le_bytes();
     let ch = fmt.channels();
-    let mut out = Vec::with_capacity((TILE_SIZE * TILE_SIZE) as usize * 8);
+    let mut out = scratch::take_cap((TILE_SIZE * TILE_SIZE) as usize * 8);
     for px in bytes.chunks_exact(ch * 2) {
         let h = |i: usize| -> [u8; 2] {
             let v = px.get(i * 2..i * 2 + 2).map_or(0, |b| u16::from_ne_bytes([b[0], b[1]]));
@@ -261,7 +267,7 @@ pub(crate) fn rgb_gray32_to_f16(fmt: &PixelFormat, bytes: &[u8]) -> Option<Vec<u
     };
     let one = f32_to_f16(1.0).to_le_bytes();
     let ch = fmt.channels();
-    let mut out = Vec::with_capacity((TILE_SIZE * TILE_SIZE) as usize * 8);
+    let mut out = scratch::take_cap((TILE_SIZE * TILE_SIZE) as usize * 8);
     for px in bytes.chunks_exact(ch * 4) {
         let h = |i: usize| -> [u8; 2] {
             let v = px.get(i * 4..i * 4 + 4).map_or(0.0, |b| f32::from_ne_bytes([b[0], b[1], b[2], b[3]]));
diff --git a/crates/gpu/src/fx.rs b/crates/gpu/src/fx.rs
index ceff607686..972ccadbea 100644
--- a/crates/gpu/src/fx.rs
+++ b/crates/gpu/src/fx.rs
@@ -427,12 +427,20 @@ fn fields_in_windows<const N: usize>(
     })
 }
 
-/// The layer's shape (`compose::layer_shape`) over `r`, in parallel bands.
+/// The layer's shape (`compose::layer_shape`) over `r`, in parallel bands. Callers hand the
+/// result back with `photocraft_raster::scratch::give` once they have read it.
 pub(crate) fn shape(doc: &photocraft_doc::Document, layer: &Layer, r: Rect) -> Vec<f32> {
     if r.is_empty() {
         return Vec::new();
     }
-    par_map(bands(r, BAND), |band| photocraft_compose::layer_shape(doc, layer, band)).concat()
+    let parts = par_map(bands(r, BAND), |band| photocraft_compose::layer_shape(doc, layer, band));
+    let mut shape = photocraft_raster::scratch::take_cap(parts.iter().map(Vec::len).sum());
+    // A band can be a pooled mask (Transparency Shapes Layer off): hand each back once copied.
+    for part in parts {
+        shape.extend_from_slice(&part);
+        photocraft_raster::scratch::give(part);
+    }
+    shape
 }
 
 /// Write `v` (row-major over `r`) into the region-sized `shape`.
diff --git a/crates/gpu/src/fx_passes.rs b/crates/gpu/src/fx_passes.rs
index f3f5ce6da3..9472141066 100644
--- a/crates/gpu/src/fx_passes.rs
+++ b/crates/gpu/src/fx_passes.rs
@@ -60,6 +60,7 @@ impl Compositor {
                 e.region = region;
                 rebuild = false;
             }
+            photocraft_raster::scratch::give(v);
         }
         if rebuild {
             let shape = Tex::map(device, "pc_fx_shape", region, MAP32);
@@ -108,6 +109,7 @@ impl Compositor {
             fx::paste(&mut e.shape_cpu, region, damage, &v);
             e.shape.write_r32(queue, region, damage, &v);
             staged += v.len() as u64 * 4;
+            photocraft_raster::scratch::give(v);
         }
 
         // Programs, and the distance fields they read (max reach per field).
diff --git a/crates/gpu/tests/it/parity.rs b/crates/gpu/tests/it/parity.rs
index d22a4515d1..e8ab0b91c4 100644
--- a/crates/gpu/tests/it/parity.rs
+++ b/crates/gpu/tests/it/parity.rs
@@ -957,7 +957,7 @@ fn hard_stop_gradients_match_cpu_or_fall_back() {
                 Ok(out) => out,
                 Err(e) => {
                     assert!(e.0.contains("coincident gradient stops"), "{e}");
-                    photocraft_compose::render(&d, d.bounds()).px
+                    photocraft_compose::render(&d, d.bounds()).into_px()
                 }
             };
             let worst = worst_diff(&cpu.px, &out);
diff --git a/crates/io/examples/oracle_diff.rs b/crates/io/examples/oracle_diff.rs
index cc4b5aa0de..13977e1a61 100644
--- a/crates/io/examples/oracle_diff.rs
+++ b/crates/io/examples/oracle_diff.rs
@@ -34,7 +34,7 @@ fn run_file(path: &str) {
     println!("mode {:?} depth {:?} layers {} warnings {:?} light {:?}", doc.mode, doc.depth, doc.layer_count(), imp.warnings, doc.global_light);
     print_layer_details(doc);
     dump_filter_effects(&file);
-    let ours = photocraft_compose::flatten(doc).px;
+    let ours = photocraft_compose::flatten(doc).into_px();
     let merged = photocraft_io::merged_composite(&file).unwrap();
     compare_modes(doc, &ours, &merged);
 }
@@ -487,7 +487,7 @@ fn corpus_summary(root: &std::path::Path) {
             return (name, None);
         }
         let Ok(merged) = photocraft_io::merged_composite(&file) else { return (name, None) };
-        let ours = photocraft_compose::flatten(&imp.document).px;
+        let ours = photocraft_compose::flatten(&imp.document).into_px();
         let mut m = 0.0f32;
         let mut bad = 0usize;
         for (a, b) in ours.iter().zip(merged) {
diff --git a/crates/io/src/flat.rs b/crates/io/src/flat.rs
index 8e169bd556..9863bdf9b0 100644
--- a/crates/io/src/flat.rs
+++ b/crates/io/src/flat.rs
@@ -452,9 +452,16 @@ pub(crate) fn image_surface(img: &Image, target_layout: ChannelLayout, csample:
         let band = (BAND_BYTES / row.max(1)).max(1);
         for (i, rows) in img.data().chunks(row.max(1) * band).enumerate() {
             let n = (rows.len() / row.max(1)) as u32;
-            let part = Image::from_raw(w, n, img.layout(), img.sample_type(), rows.to_vec())?.convert(target_layout, csample);
+            // Band buffers cycle through the scratch pool: at this size each fresh one is an
+            // mmap that gets page-faulted in.
+            let mut src = photocraft_raster::scratch::take_cap::<u8>(rows.len());
+            src.extend_from_slice(rows);
+            let src = Image::from_raw(w, n, img.layout(), img.sample_type(), src)?;
+            let part = src.convert(target_layout, csample);
             let y0 = (i * band) as i32;
             s.write_interleaved(Rect::new(0, y0, w as i32, y0 + n as i32), part.data());
+            photocraft_raster::scratch::give(src.into_data());
+            photocraft_raster::scratch::give(part.into_data());
         }
     }
     Ok(s)
diff --git a/crates/io/src/lib.rs b/crates/io/src/lib.rs
index b3135df1ad..d9bb69af2c 100644
--- a/crates/io/src/lib.rs
+++ b/crates/io/src/lib.rs
@@ -765,14 +765,14 @@ pub fn merged_composite(file: &PsdFile) -> Result<Vec<[f32; 4]>, IoError> {
     let (doc, _) = psd_to_document(&PsdFile { layer_info, ..file.clone() });
     // Multichannel documents keep their channels apart (no layer): composite them.
     if doc.layers.is_empty() && doc.mode == photocraft_color::ColorMode::Multichannel {
-        return Ok(photocraft_compose::flatten(&doc).px);
+        return Ok(photocraft_compose::flatten(&doc).into_px());
     }
     let l = doc.layers.first().ok_or_else(|| IoError::Unsupported("no merged image".into()))?;
     let s = l.surface().ok_or_else(|| IoError::Unsupported("no merged image".into()))?;
     // CMYK reads through the file's own profile, as the compositor reads its layers, so a tagged
     // file's merged image and its composite are compared in the same colours.
     let cmyk = photocraft_compose::cmyk_space(&doc);
-    Ok(photocraft_color::convert::with_cmyk_space(cmyk.as_ref(), || photocraft_compose::surface_to_buffer(s, doc.bounds()).px))
+    Ok(photocraft_color::convert::with_cmyk_space(cmyk.as_ref(), || photocraft_compose::surface_to_buffer(s, doc.bounds()).into_px()))
 }
 
 #[cfg(test)]
diff --git a/crates/io/src/ora.rs b/crates/io/src/ora.rs
index fb7968fbcc..36ebbc7b0a 100644
--- a/crates/io/src/ora.rs
+++ b/crates/io/src/ora.rs
@@ -629,7 +629,7 @@ impl Writer<'_> {
             LayerContent::Raster(s) => {
                 let r = s.content_bounds();
                 admit_layer(r)?;
-                (r, photocraft_compose::surface_to_buffer(s, r).px)
+                (r, photocraft_compose::surface_to_buffer(s, r).into_px())
             }
             _ => {
                 // Rendered as it shows on its own, before the layer's blending options.
@@ -643,7 +643,7 @@ impl Writer<'_> {
                 solo.effects = Default::default();
                 let r = photocraft_compose::composite_bounds(&solo, canvas).unwrap_or(canvas).intersect(&canvas);
                 admit_layer(r)?;
-                (r, photocraft_compose::render_layer(&solo, r).px)
+                (r, photocraft_compose::render_layer(&solo, r).into_px())
             }
         };
         if let Some(mask) = layer.mask.as_ref().filter(|m| m.enabled) {
diff --git a/crates/io/src/pattern_map.rs b/crates/io/src/pattern_map.rs
index 97417b7cc7..0b949a4bdf 100644
--- a/crates/io/src/pattern_map.rs
+++ b/crates/io/src/pattern_map.rs
@@ -120,7 +120,9 @@ fn pattern_from_psd(p: &PsdPattern, oom: &mut Option<String>) -> Option<Pattern>
         crate::pixels::lab16_chroma(&mut bytes, refs.len(), true);
     }
     let mut surface = Surface::new(fmt);
-    if let Err(error) = surface.try_write_interleaved(Rect::new(0, 0, w as i32, h as i32), &bytes) {
+    let result = surface.try_write_interleaved(Rect::new(0, 0, w as i32, h as i32), &bytes);
+    photocraft_raster::scratch::give(bytes);
+    if let Err(error) = result {
         *oom = Some(error.to_string());
         return None;
     }
diff --git a/crates/io/src/pixels.rs b/crates/io/src/pixels.rs
index 1ac715984f..63c6742a1c 100644
--- a/crates/io/src/pixels.rs
+++ b/crates/io/src/pixels.rs
@@ -47,7 +47,8 @@ fn invert_sample(bytes: &mut [u8], s: SampleType) {
 /// are filled with `fill[c]` (a native-endian encoded sample). Channels whose
 /// `invert[c]` is set are inverted (PSD stores CMYK as `max - ink`).
 pub fn interleave(planes: &[Option<&[u8]>], fill: &[Vec<u8>], n: usize, s: SampleType, invert: &[bool]) -> Vec<u8> {
-    let mut out = vec![0u8; n * planes.len() * s.bytes()];
+    // Large results come from (and callers may return them to) the scratch pool.
+    let mut out = photocraft_raster::scratch::take(n * planes.len() * s.bytes(), 0u8);
     interleave_into(planes, fill, n, s, invert, &mut out);
     out
 }
@@ -69,9 +70,7 @@ pub fn try_interleave(planes: &[Option<&[u8]>], fill: &[Vec<u8>], n: usize, s: S
             return Err(PsdError::Invalid("interleave fill has the wrong sample size".into()));
         }
     }
-    let mut out = Vec::new();
-    out.try_reserve_exact(len).map_err(|_| PsdError::OutOfMemory("not enough memory to interleave PSD pixels"))?;
-    out.resize(len, 0);
+    let mut out = photocraft_raster::scratch::try_take_exact(len, 0u8).ok_or(PsdError::OutOfMemory("not enough memory to interleave PSD pixels"))?;
     interleave_into(planes, fill, n, s, invert, &mut out);
     Ok(out)
 }
diff --git a/crates/io/src/psd_export.rs b/crates/io/src/psd_export.rs
index 315744b354..6086aaf644 100644
--- a/crates/io/src/psd_export.rs
+++ b/crates/io/src/psd_export.rs
@@ -223,6 +223,8 @@ impl Ex {
         let mut bytes = Vec::with_capacity(row_len * h_of(r) * s.format().bytes_per_pixel());
         for part in parts {
             bytes.extend_from_slice(&part);
+            // Free gathered bands before allocating channel planes below; pooling them here
+            // retains another layer-sized allocation throughout deinterleave.
         }
         if self.fmt.mode == ColorMode::Lab && self.fmt.sample == SampleType::U16 {
             crate::pixels::lab16_chroma(&mut bytes, self.cc + 1, false);
diff --git a/crates/io/src/psd_import.rs b/crates/io/src/psd_import.rs
index 6989941d31..a70577fb6f 100644
--- a/crates/io/src/psd_import.rs
+++ b/crates/io/src/psd_import.rs
@@ -328,6 +328,12 @@ impl Ctx<'_> {
                 self.allocation_failed(format!("layer \"{name}\": {error}"));
                 return Surface::new(self.fmt);
             }
+            // The interleaved band goes back to the scratch pool for the next band (and the next
+            // import): it is a fresh page-faulted mmap otherwise. The decoded planes don't: the
+            // decoder allocates its own, so pooled ones would only sit there.
+            drop(refs);
+            photocraft_raster::scratch::give(bytes);
+            drop(planes);
         }
         surf.prune();
         // A white background, a solid fill's cache: one tile per value, shared across layers.
@@ -1408,6 +1414,7 @@ fn import_layered(import: DecodedImport<'_>, doc: &mut Document, cx: &mut Ctx<'_
     if let Err(error) = surface.try_write_interleaved(canvas, &bytes) {
         return cx.allocation_failed(format!("merged image: {error}"));
     }
+    photocraft_raster::scratch::give(bytes);
     if alpha_idx.is_some() {
         let white = photocraft_raster::from_rgba(&fmt, [1.0, 1.0, 1.0, 1.0]);
         let mut vals = Vec::new();
@@ -1547,6 +1554,7 @@ fn import_extra_channels(import: DecodedImport<'_>, doc: &mut Document, cx: &mut
         if let Err(error) = s.try_write_interleaved(canvas, &raw) {
             return cx.allocation_failed(format!("extra channel {idx}: {error}"));
         }
+        photocraft_raster::scratch::give(raw);
         s.prune();
         let name = names.get(k).cloned().unwrap_or_else(|| format!("Alpha {}", k + 1));
         doc.channels.push(AlphaChannel::new(name, s));
diff --git a/crates/io/src/smart_map.rs b/crates/io/src/smart_map.rs
index 72adbe1291..cacce2b7cb 100644
--- a/crates/io/src/smart_map.rs
+++ b/crates/io/src/smart_map.rs
@@ -173,6 +173,7 @@ pub fn mask_from_item(item: &FilterEffectsItem, sample: SampleType, stack: &Filt
     let n = w.checked_mul(h).ok_or("the smart filter mask is too large")?;
     let bytes = crate::pixels::interleave(&[Some(&plane)], &[crate::pixels::zero_sample(sample)], n, sample, &[false]);
     surface.write_interleaved(GeomRect::new(rect.left, rect.top, rect.right, rect.bottom), &bytes);
+    photocraft_raster::scratch::give(bytes);
     surface.prune();
     if surface.content_bounds().is_empty() {
         return Ok(None);
@@ -215,6 +216,7 @@ pub fn unfiltered_from_item(item: &FilterEffectsItem, fmt: PixelFormat) -> Optio
     }
     let mut surface = Surface::new(fmt);
     surface.write_interleaved(GeomRect::new(item.rect.left, item.rect.top, item.rect.right, item.rect.bottom), &bytes);
+    photocraft_raster::scratch::give(bytes);
     surface.prune();
     Some(surface)
 }
diff --git a/crates/io/tests/it/banded.rs b/crates/io/tests/it/banded.rs
index eb8e97d6b5..c526b79fdb 100644
--- a/crates/io/tests/it/banded.rs
+++ b/crates/io/tests/it/banded.rs
@@ -82,7 +82,7 @@ fn psd_merged_image_matches_composite_and_drops_near_opaque_alpha() {
         let file = document_to_psd(&d);
         assert_eq!(file.merged_has_alpha(), alpha < 0.99, "alpha {alpha}");
         let merged = merged_composite(&file).unwrap();
-        let want = photocraft_compose::flatten(&d).px;
+        let want = photocraft_compose::flatten(&d).into_px();
         let m = merged.iter().zip(&want).flat_map(|(a, b)| (0..4).map(move |i| (a[i] - b[i]).abs())).fold(0.0f32, f32::max);
         // Un-matting divides the 8-bit rounding error by alpha.
         assert!(m <= 1.0 / (255.0 * alpha) + 1e-4, "alpha {alpha}: max diff {m}");
diff --git a/crates/io/tests/it/blend_modes_corpus.rs b/crates/io/tests/it/blend_modes_corpus.rs
index 296e2e2a50..72980bed5b 100644
--- a/crates/io/tests/it/blend_modes_corpus.rs
+++ b/crates/io/tests/it/blend_modes_corpus.rs
@@ -18,7 +18,7 @@ fn cell_error(mode: BlendMode) -> (f32, f32) {
     let doc = import("rgb-blend-modes.psd", &bytes).expect("opens").document;
     let file = PsdFile::from_bytes(&bytes).expect("parses");
     let merged = merged_composite(&file).expect("merged image");
-    let ours = photocraft_compose::flatten(&doc).px;
+    let ours = photocraft_compose::flatten(&doc).into_px();
     let width = doc.size.width as i32;
     let duck = doc.walk().into_iter().map(|(_, _, l)| l).find(|l| l.name == "rubber_duck_PNG1" && l.blend == mode).expect("the mode's duck");
     let surface = duck.surface().expect("duck pixels");
diff --git a/crates/io/tests/it/cmyk_composite_export.rs b/crates/io/tests/it/cmyk_composite_export.rs
index 0fea33695d..77f35a62d2 100644
--- a/crates/io/tests/it/cmyk_composite_export.rs
+++ b/crates/io/tests/it/cmyk_composite_export.rs
@@ -313,7 +313,8 @@ fn rgb_only_export_uses_direct_composite_not_reseparated_cmyk() {
     let doc = document(SampleType::U16, 0.5);
     let rgb = photocraft_compose::flatten(&doc);
     let expected =
-        photocraft_codecs::Image::from_normalized(8, 8, ChannelLayout::Rgba, CodecSample::U16, &rgb.px.into_iter().flatten().collect::<Vec<_>>()).unwrap();
+        photocraft_codecs::Image::from_normalized(8, 8, ChannelLayout::Rgba, CodecSample::U16, &rgb.into_px().into_iter().flatten().collect::<Vec<_>>())
+            .unwrap();
 
     let result = export(&doc, "png", &ExportOptions::default()).unwrap();
 
diff --git a/crates/io/tests/it/color.rs b/crates/io/tests/it/color.rs
index 15453a2518..5da5df1c7e 100644
--- a/crates/io/tests/it/color.rs
+++ b/crates/io/tests/it/color.rs
@@ -116,11 +116,11 @@ fn cmyk_fills_survive_psd_roundtrip_at_every_depth() {
                 let mut doc = Document::new("CMYK fill", photocraft_geom::Size::new(9, 6), ColorMode::Cmyk, depth);
                 doc.icc_profile = profile.clone();
                 doc.layers.push(Layer::new("Fill", LayerContent::Fill(fill)));
-                let expected = photocraft_compose::flatten(&doc).px;
+                let expected = photocraft_compose::flatten(&doc).into_px();
                 assert!(max_diff(&expected, &photocraft_compose::render_tiled(&doc, doc.bounds(), 3).px) <= 1e-6);
                 let bytes = export(&doc, "x.psd", &ExportOptions::default()).unwrap().bytes;
                 let back = import("x.psd", &bytes).unwrap().document;
-                let actual = photocraft_compose::flatten(&back).px;
+                let actual = photocraft_compose::flatten(&back).into_px();
                 let diff = max_diff(&expected, &actual);
                 assert!(diff <= 1e-6, "{depth:?} {style:?}: round-trip error {diff}");
                 assert_eq!(back.icc_profile, doc.icc_profile);
@@ -144,7 +144,7 @@ fn uncached_cmyk_gradient_corpus_roundtrip() {
     let bytes = std::fs::read(path).expect("run cargo xtask corpus --all");
     let doc = import("x.psd", &bytes).unwrap().document;
     assert!(doc.layers.iter().any(|l| matches!(l.content, photocraft_doc::LayerContent::Fill(_)) && l.fill_cache.is_none()));
-    let expected = photocraft_compose::flatten(&doc).px;
+    let expected = photocraft_compose::flatten(&doc).into_px();
     let saved = export(&doc, "x.psd", &ExportOptions::default()).unwrap().bytes;
     let back = import("x.psd", &saved).unwrap().document;
     let diff = max_diff(&expected, &photocraft_compose::flatten(&back).px);
@@ -305,7 +305,7 @@ fn gradient_maps_with_cmyk_lab_gray_stops_import_and_keep_their_space() {
                 _ => assert_eq!((first, last), ([1.0; 3], [0.0; 3])),
             }
             // The layer now renders: the composite differs from the background alone.
-            let with_map = photocraft_compose::flatten(&back).px;
+            let with_map = photocraft_compose::flatten(&back).into_px();
             let mut hidden = back.clone();
             hidden.layers[1].visible = false;
             assert!(max_diff(&with_map, &photocraft_compose::flatten(&hidden).px) > 0.01, "{mode:?} {depth:?}");
diff --git a/crates/io/tests/it/composite.rs b/crates/io/tests/it/composite.rs
index cef80e6a08..74eb0c95f1 100644
--- a/crates/io/tests/it/composite.rs
+++ b/crates/io/tests/it/composite.rs
@@ -15,7 +15,7 @@ fn check_export_oracle(d: &photocraft_doc::Document, tol: f32) {
     let f = PsdFile::from_bytes(&r.bytes).unwrap();
     let merged = merged_composite(&f).unwrap();
     let d2 = import("x.psd", &r.bytes).unwrap().document;
-    let mut ours = photocraft_compose::flatten(&d2).px;
+    let mut ours = photocraft_compose::flatten(&d2).into_px();
     if d.mode == ColorMode::Cmyk {
         // The merged CMYK image is the RGB composite separated through the CMYK profile, which
         // gamut-maps colours that blend modes push outside CMYK: project ours the same way.
@@ -107,7 +107,7 @@ fn builder_oracle(depth: u16, mode: ColorMode) {
     let f = PsdFile::from_bytes(&bytes).unwrap();
     let merged = merged_composite(&f).unwrap();
     let d2 = import("b.psd", &bytes).unwrap().document;
-    let ours = photocraft_compose::flatten(&d2).px;
+    let ours = photocraft_compose::flatten(&d2).into_px();
     let m = max_diff(&ours, &merged);
     // Density/feather of masks are not written by the builder; the generated
     // doc uses them only on a disabled mask, so results must match.
@@ -157,7 +157,7 @@ fn hidden_and_clipped_affect_composite() {
     for l in &mut d2.layers {
         l.visible = true;
     }
-    let other = photocraft_compose::flatten(&d2).px;
+    let other = photocraft_compose::flatten(&d2).into_px();
     assert!(max_diff(&other, &merged) > 0.0, "unhiding a layer must change the composite");
 }
 
diff --git a/crates/io/tests/it/corpus.rs b/crates/io/tests/it/corpus.rs
index 182d60095a..3c8ca3288a 100644
--- a/crates/io/tests/it/corpus.rs
+++ b/crates/io/tests/it/corpus.rs
@@ -316,9 +316,9 @@ fn check_file(name: &str, bytes: &[u8]) -> (Outcome, Option<f32>) {
             return (Outcome::Error, None);
         }
     };
-    let ours = photocraft_compose::flatten(doc).px;
+    let ours = photocraft_compose::flatten(doc).into_px();
     // Our own export must not change how the document renders.
-    let again = photocraft_compose::flatten(&reimported).px;
+    let again = photocraft_compose::flatten(&reimported).into_px();
     let rt = if again.len() == ours.len() { common::max_diff(&ours, &again) } else { f32::INFINITY };
     let layers = doc.layer_count();
     // Oracle choice: the merged image (Photoshop's composite; for files without layers it is the
diff --git a/crates/io/tests/it/effects_multi.rs b/crates/io/tests/it/effects_multi.rs
index 637e926085..7cabb04b4c 100644
--- a/crates/io/tests/it/effects_multi.rs
+++ b/crates/io/tests/it/effects_multi.rs
@@ -17,7 +17,7 @@ fn roundtrip(doc: &Document) -> Document {
 }
 
 fn max_diff(a: &Document, b: &Document) -> f32 {
-    let (x, y) = (photocraft_compose::flatten(a).px, photocraft_compose::flatten(b).px);
+    let (x, y) = (photocraft_compose::flatten(a).into_px(), photocraft_compose::flatten(b).into_px());
     assert_eq!(x.len(), y.len());
     x.iter().zip(&y).flat_map(|(p, q)| (0..4).map(move |c| (p[c] * p[3] - q[c] * q[3]).abs())).fold(0.0, f32::max)
 }
diff --git a/crates/io/tests/it/flat.rs b/crates/io/tests/it/flat.rs
index f6e888eb06..c40c76a12b 100644
--- a/crates/io/tests/it/flat.rs
+++ b/crates/io/tests/it/flat.rs
@@ -350,7 +350,7 @@ fn layered_to_png_warns_flatten() {
     assert!(r.warnings.iter().any(|w| w.contains("flattened")), "{:?}", r.warnings);
     let back = import("out.png", &r.bytes).unwrap().document;
     // Composite equals our flatten.
-    let flat = photocraft_compose::flatten(&d).px;
+    let flat = photocraft_compose::flatten(&d).into_px();
     let s = back.layers[0].surface().unwrap();
     let px: Vec<[f32; 4]> = s.read_region(back.bounds()).as_chunks::<4>().0.iter().map(|p| [p[0], p[1], p[2], p[3]]).collect();
     assert!(max_diff(&px, &flat) <= 1.0 / 255.0 + 1e-4);
diff --git a/crates/io/tests/it/lab16.rs b/crates/io/tests/it/lab16.rs
index 0aee251861..ff0707c11b 100644
--- a/crates/io/tests/it/lab16.rs
+++ b/crates/io/tests/it/lab16.rs
@@ -60,8 +60,8 @@ fn lab_round_trips_at_every_depth() {
         let p = back.layers[0].surface().unwrap().pixel(2, 0);
         let tol = if depth == SampleType::U8 { 0.5 / 255.0 + 1e-6 } else { 2e-5 };
         assert!((p[1] - A).abs() <= tol && (p[2] - B).abs() <= tol, "{depth:?}: {p:?}");
-        let a = photocraft_compose::flatten(&doc).px;
-        let b = photocraft_compose::flatten(&back).px;
+        let a = photocraft_compose::flatten(&doc).into_px();
+        let b = photocraft_compose::flatten(&back).into_px();
         for (x, y) in a.iter().zip(&b) {
             for c in 0..4 {
                 assert!((x[c] - y[c]).abs() <= 1.0 / 255.0, "{depth:?}: {x:?} vs {y:?}");
diff --git a/crates/io/tests/it/large_files.rs b/crates/io/tests/it/large_files.rs
index b0a2669480..be4d5eeab7 100644
--- a/crates/io/tests/it/large_files.rs
+++ b/crates/io/tests/it/large_files.rs
@@ -42,7 +42,7 @@ fn check_grid(g: &Grid, doc: &Document, what: &str) {
     ];
     assert_eq!(census(doc), want, "{what}: [raster, groups, masked, with effects, hidden]");
     for (x, y) in g.sample_points() {
-        let px = photocraft_compose::render(doc, Rect::from_xywh(x as i32, y as i32, 1, 1)).px;
+        let px = photocraft_compose::render(doc, Rect::from_xywh(x as i32, y as i32, 1, 1)).into_px();
         let got = px.first().copied().unwrap_or_default();
         let want = g.expected(x, y);
         for c in 0..3 {
diff --git a/crates/io/tests/it/multichannel.rs b/crates/io/tests/it/multichannel.rs
index 4e7ffeeb2e..f4f7154d41 100644
--- a/crates/io/tests/it/multichannel.rs
+++ b/crates/io/tests/it/multichannel.rs
@@ -56,7 +56,7 @@ fn alpha_type_channels_import_as_alpha_and_round_trip() {
         as_ink.channels[1].surface = s;
         as_ink.channels[1].spot = Some((photocraft_color::Color::BLACK, 0.0));
         // Within f32 rounding: the inverted copy is re-quantised to the channel depth.
-        let (shown, inked) = (photocraft_compose::flatten(&d).px, photocraft_compose::flatten(&as_ink).px);
+        let (shown, inked) = (photocraft_compose::flatten(&d).into_px(), photocraft_compose::flatten(&as_ink).into_px());
         assert_eq!(shown.len(), inked.len());
         for (a, b) in shown.iter().zip(&inked) {
             assert!(a.iter().zip(b).all(|(x, y)| (x - y).abs() < 1e-5), "{a:?} vs {b:?} ({depth}-bit)");
@@ -115,7 +115,7 @@ fn alpha_type_channels_are_stored_as_is_not_as_ink() {
         assert_eq!(values(&d.channels[0]), [1.0, 0.0, 1.0, 0.0], "spot channel ({depth}-bit)");
 
         // The composite is what Photoshop shows: the alpha prints as black ink where unselected.
-        let px = photocraft_compose::flatten(&d).px;
+        let px = photocraft_compose::flatten(&d).into_px();
         assert_eq!(px.iter().map(|p| [p[0], p[1], p[2]]).collect::<Vec<_>>(), [[0.0, 1.0, 1.0], [1.0, 1.0, 1.0], [0.0, 0.0, 0.0], [0.0, 0.0, 0.0]]);
 
         // Saved back byte for byte.
diff --git a/crates/io/tests/it/psd32_export.rs b/crates/io/tests/it/psd32_export.rs
index f9a297a7f6..428fb7903e 100644
--- a/crates/io/tests/it/psd32_export.rs
+++ b/crates/io/tests/it/psd32_export.rs
@@ -118,7 +118,7 @@ fn layered_32bit_export_reimports_render_equal() {
     for mode in [ColorMode::Rgb, ColorMode::Grayscale] {
         let doc = common::gen_doc(mode, SampleType::F32, Features::ALL);
         let back = import("t.psd", &export_psd(&doc)).unwrap().document;
-        let (a, b) = (photocraft_compose::flatten(&doc).px, photocraft_compose::flatten(&back).px);
+        let (a, b) = (photocraft_compose::flatten(&doc).into_px(), photocraft_compose::flatten(&back).into_px());
         assert_eq!(a.len(), b.len());
         let d = common::max_diff(&a, &b);
         assert!(d <= 1e-4, "{mode:?}: render differs by {d}");
@@ -154,7 +154,7 @@ fn photoshop_32bit_corpus_round_trip() {
         assert_32bit_layout(&name, &out);
         let back = import(&name, &out).unwrap().document;
         assert_eq!(doc.layer_count(), back.layer_count(), "{name}: layer count");
-        let (a, b) = (photocraft_compose::flatten(&doc).px, photocraft_compose::flatten(&back).px);
+        let (a, b) = (photocraft_compose::flatten(&doc).into_px(), photocraft_compose::flatten(&back).into_px());
         assert_eq!(a.len(), b.len(), "{name}");
         let d = common::max_diff(&a, &b);
         assert!(d <= 1e-4, "{name}: render differs by {d}");
diff --git a/crates/io/tests/it/psd_damaged_merged.rs b/crates/io/tests/it/psd_damaged_merged.rs
index 8e20687bb5..51121d59b7 100644
--- a/crates/io/tests/it/psd_damaged_merged.rs
+++ b/crates/io/tests/it/psd_damaged_merged.rs
@@ -32,7 +32,7 @@ fn truncated_merged_image_keeps_layer_pixels_at_every_depth_and_compression() {
             for compression in Compression::ALL {
                 let mut file = layered_in_mode(mode, depth, extension);
                 let intact = import(extension, &file.to_bytes().unwrap()).unwrap();
-                let expected = photocraft_compose::flatten(&intact.document).px;
+                let expected = photocraft_compose::flatten(&intact.document).into_px();
                 let pixels = file.decode_merged().unwrap();
                 file.image_data = photocraft_psd::ImageData::encode(compression, &pixels, &file.header).unwrap();
                 file.image_data.data.truncate(file.image_data.data.len() / 2);
diff --git a/crates/io/tests/it/psd_type_bounds.rs b/crates/io/tests/it/psd_type_bounds.rs
index b87d4f4a3a..43ce38c674 100644
--- a/crates/io/tests/it/psd_type_bounds.rs
+++ b/crates/io/tests/it/psd_type_bounds.rs
@@ -283,7 +283,7 @@ fn imported_type_layers_keep_their_full_bounds() {
         let o = iou(&ours.surface, cache);
         assert!(o > 0.97, "{}: re-render overlap {o}", c.name);
         // And the document composite is the file's merged composite.
-        let px = photocraft_compose::flatten(&doc).px;
+        let px = photocraft_compose::flatten(&doc).into_px();
         let worst = common::max_diff(&px, &merged);
         assert!(worst <= 2.0 / 255.0, "{}: composite differs from the merged image by {worst}", c.name);
     }
diff --git a/crates/io/tests/it/tiff_corpus.rs b/crates/io/tests/it/tiff_corpus.rs
index 697eab6d32..1b3c36a05d 100644
--- a/crates/io/tests/it/tiff_corpus.rs
+++ b/crates/io/tests/it/tiff_corpus.rs
@@ -124,8 +124,8 @@ fn corpus_round_trips_through_layered_tiff() {
                 }
                 d
             };
-            let x = photocraft_compose::flatten(&expected).px;
-            let y = photocraft_compose::flatten(&back).px;
+            let x = photocraft_compose::flatten(&expected).into_px();
+            let y = photocraft_compose::flatten(&back).into_px();
             let diff = max_diff(&x, &y);
             if diff > 1.0 / 255.0 + 1e-5 {
                 return Err(format!("render differs by {diff}"));
diff --git a/crates/io/tests/it/tiff_layers.rs b/crates/io/tests/it/tiff_layers.rs
index f2ccddc92e..3c7815a37a 100644
--- a/crates/io/tests/it/tiff_layers.rs
+++ b/crates/io/tests/it/tiff_layers.rs
@@ -87,8 +87,8 @@ fn tiff_and_psd_open_as_the_same_document() {
         )
         .unwrap()
         .document;
-        let a = photocraft_compose::flatten(&d).px;
-        let b = photocraft_compose::flatten(&flat).px;
+        let a = photocraft_compose::flatten(&d).into_px();
+        let b = photocraft_compose::flatten(&flat).into_px();
         assert!(max_diff(&a, &b) <= 2.0 / 255.0, "{mode:?} {depth:?}: composite differs by {}", max_diff(&a, &b));
     }
 }
diff --git a/crates/raster/src/lib.rs b/crates/raster/src/lib.rs
index 5d0f6fe257..d949445bcc 100644
--- a/crates/raster/src/lib.rs
+++ b/crates/raster/src/lib.rs
@@ -9,6 +9,7 @@
 
 mod interrupt;
 pub use interrupt::{Cancelled, Interrupt};
+pub mod scratch;
 
 use std::collections::BTreeMap;
 use std::fmt;
@@ -62,18 +63,30 @@ impl TileInterner {
 }
 
 /// Pixel storage for one tile: `TILE_SIZE² × bytes_per_pixel`, row-major, interleaved channels.
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Debug, PartialEq, Eq)]
 pub struct Tile {
     data: Box<[u8]>,
 }
 
+impl Clone for Tile {
+    fn clone(&self) -> Self {
+        let mut data = scratch::take_exact(self.data.len(), 0u8);
+        data.copy_from_slice(&self.data);
+        Tile { data: data.into_boxed_slice() }
+    }
+}
+
+impl Drop for Tile {
+    fn drop(&mut self) {
+        scratch::give(std::mem::take(&mut self.data).into_vec());
+    }
+}
+
 impl Tile {
     fn try_filled(format: &PixelFormat, pixel: &[u8]) -> Result<Self, AllocationError> {
         let n = (TILE_SIZE * TILE_SIZE) as usize;
         let bytes = n.checked_mul(format.bytes_per_pixel()).ok_or(AllocationError::SizeOverflow)?;
-        let mut data = Vec::new();
-        data.try_reserve_exact(bytes).map_err(|_| AllocationError::NotEnoughMemory { bytes })?;
-        data.resize(bytes, 0);
+        let mut data = scratch::try_take_exact(bytes, 0u8).ok_or(AllocationError::NotEnoughMemory { bytes })?;
         if pixel.iter().any(|&b| b != 0) {
             for px in data.chunks_exact_mut(pixel.len()) {
                 px.copy_from_slice(pixel);
@@ -85,15 +98,14 @@ impl Tile {
     /// Clone this tile's pixel buffer with a fallible reservation.
     pub fn try_clone(&self) -> Result<Self, AllocationError> {
         let bytes = self.data.len();
-        let mut data = Vec::new();
-        data.try_reserve_exact(bytes).map_err(|_| AllocationError::NotEnoughMemory { bytes })?;
-        data.extend_from_slice(&self.data);
+        let mut data = scratch::try_take_exact(bytes, 0u8).ok_or(AllocationError::NotEnoughMemory { bytes })?;
+        data.copy_from_slice(&self.data);
         Ok(Tile { data: data.into_boxed_slice() })
     }
 
     fn filled(format: &PixelFormat, pixel: &[u8]) -> Self {
         let row_len = TILE_SIZE as usize * format.bytes_per_pixel();
-        let mut data = vec![0u8; row_len * TILE_SIZE as usize];
+        let mut data = scratch::take_exact(row_len * TILE_SIZE as usize, 0u8);
         if pixel.iter().any(|&b| b != 0) {
             // One prebuilt row copied per tile row: 256 bulk copies instead of one
             // copy_from_slice per pixel.
@@ -358,9 +370,7 @@ impl Surface {
     pub fn try_read_region(&self, r: Rect) -> Result<Vec<f32>, AllocationError> {
         let len = (r.width() as usize).checked_mul(r.height() as usize).and_then(|n| n.checked_mul(self.channels())).ok_or(AllocationError::SizeOverflow)?;
         let bytes = len.checked_mul(std::mem::size_of::<f32>()).ok_or(AllocationError::SizeOverflow)?;
-        let mut out = Vec::new();
-        out.try_reserve_exact(len).map_err(|_| AllocationError::NotEnoughMemory { bytes })?;
-        out.resize(len, 0.0);
+        let mut out = scratch::try_take_exact(len, 0.0f32).ok_or(AllocationError::NotEnoughMemory { bytes })?;
         self.read_region_into(r, &mut out);
         Ok(out)
     }
@@ -761,7 +771,7 @@ impl Surface {
     pub fn read_region(&self, r: Rect) -> Vec<f32> {
         let n = self.channels();
         let w = r.width() as usize;
-        let mut out = vec![0.0f32; w * r.height() as usize * n];
+        let mut out = scratch::take(w * r.height() as usize * n, 0.0f32);
         self.read_samples_into(r, &mut out);
         out
     }
@@ -935,7 +945,7 @@ impl Surface {
     pub fn to_interleaved(&self, r: Rect) -> Vec<u8> {
         let bpp = self.format.bytes_per_pixel();
         let w = r.width() as usize;
-        let mut out = vec![0u8; w * r.height() as usize * bpp];
+        let mut out = scratch::take(w * r.height() as usize * bpp, 0u8);
         for tc in r.tiles() {
             let tr = tc.rect().intersect(&r);
             let span = tr.width() as usize * bpp;
@@ -1022,7 +1032,7 @@ impl Surface {
                 return hit.clone().map(|t| (dc, t));
             }
 
-            let mut tile = Tile { data: vec![0u8; (TILE_SIZE * TILE_SIZE) as usize * bpp].into_boxed_slice() };
+            let mut tile = Tile { data: scratch::take_exact((TILE_SIZE * TILE_SIZE) as usize * bpp, 0u8).into_boxed_slice() };
             let (tx0, ty0) = (i64::from(dc.tx) * i64::from(TILE_SIZE), i64::from(dc.ty) * i64::from(TILE_SIZE));
             let row_len = TILE_SIZE as usize * bpp;
             // Per stored row: copy the source span that falls inside the content in as few
diff --git a/crates/raster/src/scratch.rs b/crates/raster/src/scratch.rs
new file mode 100644
index 0000000000..cb0f898306
--- /dev/null
+++ b/crates/raster/src/scratch.rs
@@ -0,0 +1,384 @@
+//! Process-wide, capped pool of large scratch buffers.
+//!
+//! With glibc's mmap threshold pinned (`MALLOC_TRIM_THRESHOLD_`, which is how PhotoCraft returns
+//! memory to the OS), every allocation over 128 KiB is a fresh `mmap` that is page-faulted in and
+//! `munmap`ed on free. Tiles, compositor bands and filter scratch are all that size, so a single
+//! viewport render took 350× the page faults. This pool keeps freed buffers (at least
+//! [`MIN_POOLED_BYTES`] of capacity) on per-type free lists and hands them back out, so the
+//! steady state allocates nothing.
+//!
+//! Retention is capped by [`set_budget`] (default [`DEFAULT_BUDGET`]); [`release`] drops
+//! everything, which is what returns the memory to the OS. The engine releases when a document
+//! closes; off wasm a background thread also releases once the pool has gone unused for
+//! [`IDLE_RELEASE_SECS`], so every host (app, CLI, tests) gives memory back the same way.
+
+use std::collections::{BTreeMap, VecDeque};
+use std::sync::atomic::{AtomicBool, AtomicU64, AtomicUsize, Ordering};
+use std::sync::{Mutex, PoisonError};
+
+/// Buffers with less capacity than this are cheap from the heap and are never retained.
+pub const MIN_POOLED_BYTES: usize = 64 * 1024;
+/// Default cap on the bytes the pool retains: about the working set of a 36 MP filter (tiles,
+/// halo images and result bands); a browser's wasm heap never shrinks, so there it is small.
+pub const DEFAULT_BUDGET: usize = if cfg!(target_arch = "wasm32") { 256 << 20 } else { 2 << 30 };
+
+/// Pooled bytes a miss never evicts. A filter's output tiles are all misses (the old tiles stay
+/// in the undo history); evicting every byte they need also dropped the scratch planes the next
+/// tile reuses. On a 36 MP Gaussian Blur with the trim threshold set, 256 MiB keeps the timings
+/// at glibc's defaults (128 MiB: r 40 ~17% slower) for ~10% more peak memory (0: ~20% slower).
+pub const DEFAULT_MISS_FLOOR: usize = if cfg!(target_arch = "wasm32") { 64 << 20 } else { 256 << 20 };
+
+static BUDGET: AtomicUsize = AtomicUsize::new(DEFAULT_BUDGET);
+static MISS_FLOOR: AtomicUsize = AtomicUsize::new(DEFAULT_MISS_FLOOR);
+static RETAINED: AtomicUsize = AtomicUsize::new(0);
+static USES: AtomicU64 = AtomicU64::new(0);
+static IDLE_RELEASE: AtomicBool = AtomicBool::new(true);
+
+/// Seconds without a [`take`] or [`give`] after which the idle thread releases the pool.
+pub const IDLE_RELEASE_SECS: u64 = 2;
+
+/// Starts the idle-release thread once (off wasm, where there are threads). If the thread
+/// can't be spawned the pool still works; it is then released only by [`release`].
+fn start_idle_release() {
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        static STARTED: std::sync::Once = std::sync::Once::new();
+        STARTED.call_once(|| {
+            let _ = std::thread::Builder::new().name("scratch-idle".into()).spawn(|| {
+                let mut seen = uses();
+                loop {
+                    std::thread::sleep(std::time::Duration::from_secs(IDLE_RELEASE_SECS));
+                    let now = uses();
+                    if now == seen {
+                        // Decided under the lock, so `set_idle_release(false)` can't return
+                        // while a release it should have stopped is about to start.
+                        let old = {
+                            let mut pool = lock();
+                            // A `give` or `take` since `now` was read means the pool is in use.
+                            (uses() == now && retained_bytes() > 0 && IDLE_RELEASE.load(Ordering::Relaxed)).then(|| empty(&mut pool))
+                        };
+                        drop(old);
+                    }
+                    seen = now;
+                }
+            });
+        });
+    }
+}
+
+/// One free list: buffers keyed by capacity (in elements), each with the sequence number it
+/// was returned at (oldest first within a capacity).
+#[doc(hidden)]
+pub type FreeList<T> = BTreeMap<usize, VecDeque<(u64, Vec<T>)>>;
+
+/// All the free lists behind one lock, so the oldest buffer of any type can be evicted.
+/// `order` maps every pooled buffer's sequence number to its type and capacity, so the oldest
+/// is found in O(log n); best-fit lookups are a range query on the capacity key.
+#[doc(hidden)]
+pub struct Pool {
+    seq: u64,
+    order: BTreeMap<u64, (Tag, usize)>,
+    u8s: FreeList<u8>,
+    u16s: FreeList<u16>,
+    f32s: FreeList<f32>,
+    px4: FreeList<[f32; 4]>,
+}
+
+static POOL: Mutex<Pool> =
+    Mutex::new(Pool { seq: 0, order: BTreeMap::new(), u8s: BTreeMap::new(), u16s: BTreeMap::new(), f32s: BTreeMap::new(), px4: BTreeMap::new() });
+
+/// Which free list a buffer lives on.
+#[doc(hidden)]
+#[derive(Clone, Copy)]
+pub enum Tag {
+    U8,
+    U16,
+    F32,
+    Px4,
+}
+
+/// A buffer evicted from the pool, dropped by the caller once the lock is released.
+#[allow(dead_code)]
+enum Evicted {
+    U8(Vec<u8>),
+    U16(Vec<u16>),
+    F32(Vec<f32>),
+    Px4(Vec<[f32; 4]>),
+}
+
+/// Element types that have a free list. Implemented for the buffers the hot paths use.
+pub trait Pooled: Copy + Send + 'static {
+    #[doc(hidden)]
+    const TAG: Tag;
+    #[doc(hidden)]
+    fn list(pool: &mut Pool) -> &mut FreeList<Self>;
+}
+
+macro_rules! pooled {
+    ($($t:ty => $field:ident, $tag:ident),*) => {$(
+        impl Pooled for $t {
+            const TAG: Tag = Tag::$tag;
+            fn list(pool: &mut Pool) -> &mut FreeList<Self> {
+                &mut pool.$field
+            }
+        }
+    )*};
+}
+pooled!(u8 => u8s, U8, u16 => u16s, U16, f32 => f32s, F32, [f32; 4] => px4, Px4);
+
+fn bytes_of<T>(v: &Vec<T>) -> usize {
+    v.capacity().saturating_mul(std::mem::size_of::<T>())
+}
+
+fn lock() -> std::sync::MutexGuard<'static, Pool> {
+    POOL.lock().unwrap_or_else(PoisonError::into_inner)
+}
+
+/// Remove the oldest buffer of capacity `cap` from `list`.
+fn drop_oldest<T>(list: &mut FreeList<T>, cap: usize) -> Option<Vec<T>> {
+    let queue = list.get_mut(&cap)?;
+    let v = queue.pop_front()?.1;
+    if queue.is_empty() {
+        list.remove(&cap);
+    }
+    Some(v)
+}
+
+impl Pool {
+    /// Remove the buffer returned longest ago, of any type. `None` when the pool is empty.
+    fn evict_oldest(&mut self) -> Option<Evicted> {
+        let (_, (tag, cap)) = self.order.pop_first()?;
+        let evicted = match tag {
+            Tag::U8 => drop_oldest(&mut self.u8s, cap).map(Evicted::U8),
+            Tag::U16 => drop_oldest(&mut self.u16s, cap).map(Evicted::U16),
+            Tag::F32 => drop_oldest(&mut self.f32s, cap).map(Evicted::F32),
+            Tag::Px4 => drop_oldest(&mut self.px4, cap).map(Evicted::Px4),
+        };
+        if let Some(e) = &evicted {
+            let freed = match e {
+                Evicted::U8(v) => bytes_of(v),
+                Evicted::U16(v) => bytes_of(v),
+                Evicted::F32(v) => bytes_of(v),
+                Evicted::Px4(v) => bytes_of(v),
+            };
+            RETAINED.fetch_sub(freed, Ordering::Relaxed);
+        }
+        evicted
+    }
+}
+
+/// A `Vec` of `len` copies of `fill`, reusing a pooled buffer when one fits: the one whose
+/// capacity equals `len`, else the smallest with capacity in `len..=2*len`.
+pub fn take<T: Pooled>(len: usize, fill: T) -> Vec<T> {
+    take_with(len, fill, 2)
+}
+
+/// An empty `Vec` with room for at least `cap` elements, reusing a pooled buffer when one fits.
+pub fn take_cap<T: Pooled>(cap: usize) -> Vec<T> {
+    USES.fetch_add(1, Ordering::Relaxed);
+    match pop::<T>(cap, 2) {
+        Some(mut v) => {
+            v.clear();
+            v
+        }
+        None => Vec::with_capacity(cap),
+    }
+}
+
+/// Like [`take`] but only reuses a buffer whose capacity is exactly `len`, so
+/// `into_boxed_slice` never reallocates.
+pub fn take_exact<T: Pooled>(len: usize, fill: T) -> Vec<T> {
+    take_with(len, fill, 1)
+}
+
+/// Pop the best-fitting free buffer: capacity `len`, else the smallest up to `len * slack`.
+///
+/// On a miss the caller allocates `len` fresh, so the oldest free buffers of at least that many
+/// bytes are dropped first, down to [`set_miss_floor`]: memory the pool can't reuse for this request
+/// goes back instead of piling up beside the new buffer, so pool plus live buffers exceed what
+/// the program would hold without the pool by at most the floor (#10479).
+fn pop<T: Pooled>(len: usize, slack: usize) -> Option<Vec<T>> {
+    let need = len.saturating_mul(std::mem::size_of::<T>());
+    if need < MIN_POOLED_BYTES {
+        return None;
+    }
+    let mut evicted = Vec::new();
+    let hit = {
+        let mut pool = lock();
+        let max = len.saturating_mul(slack);
+        let list = T::list(&mut pool);
+        let cap = list.range(len..=max).next().map(|(&cap, _)| cap);
+        // The newest buffer of that capacity is the one most likely still in cache.
+        let found = cap.and_then(|cap| {
+            let queue = list.get_mut(&cap)?;
+            let entry = queue.pop_back();
+            if queue.is_empty() {
+                list.remove(&cap);
+            }
+            entry
+        });
+        match found {
+            Some((seq, v)) => {
+                pool.order.remove(&seq);
+                RETAINED.fetch_sub(bytes_of(&v), Ordering::Relaxed);
+                Some(v)
+            }
+            None => {
+                let target = RETAINED.load(Ordering::Relaxed).saturating_sub(need).max(MISS_FLOOR.load(Ordering::Relaxed));
+                while RETAINED.load(Ordering::Relaxed) > target {
+                    match pool.evict_oldest() {
+                        Some(e) => evicted.push(e),
+                        None => break,
+                    }
+                }
+                None
+            }
+        }
+    };
+    // Freed outside the lock.
+    drop(evicted);
+    hit
+}
+
+fn take_with<T: Pooled>(len: usize, fill: T, slack: usize) -> Vec<T> {
+    USES.fetch_add(1, Ordering::Relaxed);
+    if len == 0 {
+        return Vec::new();
+    }
+    match pop::<T>(len, slack) {
+        Some(mut v) => {
+            v.clear();
+            v.resize(len, fill);
+            v
+        }
+        None => vec![fill; len],
+    }
+}
+
+/// Fallible [`take_exact`]: on a pool miss the heap allocation is `try_reserve_exact`, so
+/// `None` means the allocation failed rather than aborting.
+pub fn try_take_exact<T: Pooled>(len: usize, fill: T) -> Option<Vec<T>> {
+    USES.fetch_add(1, Ordering::Relaxed);
+    let mut v = match pop::<T>(len, 1) {
+        Some(v) => v,
+        None => {
+            let mut v = Vec::new();
+            if v.try_reserve_exact(len).is_err() {
+                // The pool may hold up to the miss floor of buffers this request couldn't use:
+                // give them back, then try once more before failing the caller.
+                release();
+                v.try_reserve_exact(len).ok()?;
+            }
+            v
+        }
+    };
+    v.clear();
+    v.resize(len, fill);
+    Some(v)
+}
+
+/// Return a buffer to the pool. Small buffers, and buffers bigger than the whole budget, are
+/// dropped; otherwise the buffers returned longest ago (of any type) make room for it.
+pub fn give<T: Pooled>(v: Vec<T>) {
+    USES.fetch_add(1, Ordering::Relaxed);
+    let bytes = bytes_of(&v);
+    if bytes < MIN_POOLED_BYTES {
+        return;
+    }
+    let mut evicted = Vec::new();
+    {
+        let mut pool = lock();
+        // Read under the lock, which `set_budget` also takes, so no insert uses a stale budget.
+        let budget = BUDGET.load(Ordering::Relaxed);
+        if bytes > budget {
+            return;
+        }
+        start_idle_release();
+        while RETAINED.load(Ordering::Relaxed).saturating_add(bytes) > budget {
+            match pool.evict_oldest() {
+                Some(e) => evicted.push(e),
+                None => break,
+            }
+        }
+        RETAINED.fetch_add(bytes, Ordering::Relaxed);
+        pool.seq += 1;
+        let seq = pool.seq;
+        let cap = v.capacity();
+        pool.order.insert(seq, (T::TAG, cap));
+        T::list(&mut pool).entry(cap).or_default().push_back((seq, v));
+    }
+    // Freed outside the lock.
+    drop(evicted);
+}
+
+/// Set the cap on retained bytes (existing entries beyond it go on the next [`give`]).
+pub fn set_budget(bytes: usize) {
+    let _pool = lock();
+    BUDGET.store(bytes, Ordering::Relaxed);
+}
+
+/// Set the pooled bytes a miss never evicts (default [`DEFAULT_MISS_FLOOR`]).
+pub fn set_miss_floor(bytes: usize) {
+    MISS_FLOOR.store(bytes, Ordering::Relaxed);
+}
+
+/// Let the idle thread release the pool (the default) or not. Tests that check
+/// [`retained_bytes`] turn it off, so a slow runner can't have the pool emptied under them.
+pub fn set_idle_release(on: bool) {
+    // Under the lock: once this returns, the idle thread can't be midway into a release.
+    let _pool = lock();
+    IDLE_RELEASE.store(on, Ordering::Relaxed);
+}
+
+/// Bytes currently held by the pool.
+pub fn retained_bytes() -> usize {
+    RETAINED.load(Ordering::Relaxed)
+}
+
+/// Number of [`take`]/[`give`] calls so far; a changing value means the pool is in use.
+pub fn uses() -> u64 {
+    USES.load(Ordering::Relaxed)
+}
+
+/// Drop every pooled buffer, handing the memory back to the OS.
+pub fn release() {
+    let old = empty(&mut lock());
+    // Freed outside the lock.
+    drop(old);
+}
+
+/// Everything `pool` holds, swapped out of it (to be freed once the lock is dropped).
+fn empty(pool: &mut Pool) -> Pool {
+    RETAINED.store(0, Ordering::Relaxed);
+    let seq = pool.seq;
+    std::mem::replace(pool, Pool { seq, order: BTreeMap::new(), u8s: BTreeMap::new(), u16s: BTreeMap::new(), f32s: BTreeMap::new(), px4: BTreeMap::new() })
+}
+
+/// A pooled buffer that derefs to a slice and returns itself to the pool on drop.
+pub struct Buf<T: Pooled>(Vec<T>);
+
+impl<T: Pooled> Buf<T> {
+    /// `len` copies of `fill` from the pool.
+    pub fn new(len: usize, fill: T) -> Self {
+        Buf(take(len, fill))
+    }
+}
+
+impl<T: Pooled> std::ops::Deref for Buf<T> {
+    type Target = [T];
+    fn deref(&self) -> &[T] {
+        &self.0
+    }
+}
+
+impl<T: Pooled> std::ops::DerefMut for Buf<T> {
+    fn deref_mut(&mut self) -> &mut [T] {
+        &mut self.0
+    }
+}
+
+impl<T: Pooled> Drop for Buf<T> {
+    fn drop(&mut self) {
+        give(std::mem::take(&mut self.0));
+    }
+}
diff --git a/crates/raster/tests/scratch.rs b/crates/raster/tests/scratch.rs
new file mode 100644
index 0000000000..a0f532f174
--- /dev/null
+++ b/crates/raster/tests/scratch.rs
@@ -0,0 +1,361 @@
+//! The scratch pool is process-wide, so these tests live in their own binary (nothing else
+//! allocates tiles here) and take a lock to run one at a time.
+
+use photocraft_raster::scratch::*;
+use std::sync::{Mutex, PoisonError};
+
+static SERIAL: Mutex<()> = Mutex::new(());
+
+/// Lets a miss evict every pooled byte for the test's lifetime, so sizes can be counted.
+struct NoFloor;
+impl NoFloor {
+    /// Sets the miss floor to zero for this guard's lifetime.
+    fn new() -> Self {
+        set_miss_floor(0);
+        NoFloor
+    }
+}
+impl Drop for NoFloor {
+    fn drop(&mut self) {
+        set_miss_floor(DEFAULT_MISS_FLOOR);
+    }
+}
+/// Locks the process-wide pool tests against concurrent access.
+fn lock_serial() -> std::sync::MutexGuard<'static, ()> {
+    SERIAL.lock().unwrap_or_else(PoisonError::into_inner)
+}
+
+/// Runs a test alone with idle release off, so the idle thread can't empty the pool between a
+/// `give` and the checks after it; idle release comes back on when dropped.
+struct Serial {
+    _lock: std::sync::MutexGuard<'static, ()>,
+}
+impl Drop for Serial {
+    fn drop(&mut self) {
+        set_idle_release(true);
+    }
+}
+/// Serializes a test and disables idle release until the guard is dropped.
+fn serial() -> Serial {
+    let _lock = lock_serial();
+    set_idle_release(false);
+    Serial { _lock }
+}
+
+#[test]
+/// Verifies pooled buffers are reused by pointer, retain capacity, and are refilled to the requested length.
+fn reuse_returns_same_capacity_and_refills() {
+    let _g = serial();
+    release();
+    let mut v = take(100_000, 0.0f32);
+    v.iter_mut().for_each(|x| *x = 7.0);
+    let ptr = v.as_ptr();
+    give(v);
+    assert_eq!(retained_bytes(), 400_000);
+    let w = take(100_000, 1.5f32);
+    assert_eq!(w.as_ptr(), ptr);
+    assert_eq!(w.len(), 100_000);
+    assert!(w.iter().all(|&x| x == 1.5));
+    assert_eq!(retained_bytes(), 0);
+    // A smaller request within 2x reuses it too, and is sized exactly.
+    give(w);
+    let s = take(60_000, 0.0f32);
+    assert_eq!(s.as_ptr(), ptr);
+    assert_eq!(s.len(), 60_000);
+    release();
+}
+
+#[test]
+/// Verifies oversized or non-exact buffers are discarded instead of reused.
+fn too_big_a_buffer_is_not_reused() {
+    let _g = serial();
+    release();
+    let _floor = NoFloor::new();
+    give(vec![0u8; 1_000_000]);
+    assert_eq!(take_exact(1_000_000, 0u8).len(), 1_000_000);
+    assert_eq!(retained_bytes(), 0);
+    give(vec![0u8; 1_000_000]);
+    // More than 2x (or not exact): allocated fresh, and the miss drops the unusable buffer.
+    assert_eq!(take(100_000, 0u8).capacity(), 100_000);
+    assert_eq!(retained_bytes(), 0);
+    give(vec![0u8; 1_000_000]);
+    assert_eq!(take_exact(999_999, 0u8).capacity(), 999_999);
+    assert_eq!(retained_bytes(), 0);
+    release();
+}
+
+#[test]
+/// Verifies exact try-takes reuse a matching buffer and succeed on a miss.
+fn try_take_exact_reuses_and_allocates() {
+    let _g = serial();
+    release();
+    let buf = vec![0u8; 200_000];
+    let ptr = buf.as_ptr();
+    give(buf);
+    let v = try_take_exact(200_000, 9u8);
+    assert!(v.as_ref().is_some_and(|v| v.len() == 200_000 && v.iter().all(|&b| b == 9)));
+    assert_eq!(v.as_ref().map(|v| v.as_ptr()), Some(ptr));
+    assert_eq!(retained_bytes(), 0);
+    assert!(try_take_exact(300_000, 0u8).is_some());
+    release();
+}
+
+#[test]
+/// Verifies buffers below the pooling threshold are not retained.
+fn small_buffers_are_not_retained() {
+    let _g = serial();
+    release();
+    give(vec![0u8; MIN_POOLED_BYTES - 1]);
+    give(vec![0.0f32; 100]);
+    assert_eq!(retained_bytes(), 0);
+    assert_eq!(take(10, 3u8), vec![3u8; 10]);
+}
+
+#[test]
+/// Verifies zero-length take and give operations remain empty.
+fn zero_length() {
+    let _g = serial();
+    assert!(take(0, 0u8).is_empty());
+    give(Vec::<u8>::new());
+    assert!(take_exact(0, [0.0f32; 4]).is_empty());
+}
+
+#[test]
+/// Verifies the byte budget evicts oldest buffers and rejects buffers larger than the budget.
+fn budget_evicts_oldest() {
+    let _g = serial();
+    release();
+    set_budget(250_000);
+    let (a, b) = (vec![0u8; 100_000], vec![0u8; 100_000]);
+    let pb = b.as_ptr();
+    give(a);
+    give(b);
+    give(vec![0u8; 100_000]);
+    assert_eq!(retained_bytes(), 200_000);
+    // The oldest was evicted; the survivors include b.
+    let first = take_exact(100_000, 0u8);
+    let second = take_exact(100_000, 0u8);
+    assert!(first.as_ptr() == pb || second.as_ptr() == pb);
+    // Larger than the whole budget: dropped.
+    give(vec![0u8; 300_000]);
+    assert_eq!(retained_bytes(), 0);
+    set_budget(DEFAULT_BUDGET);
+    release();
+}
+
+#[test]
+/// Verifies release empties pooled buffers of several element types.
+fn release_empties() {
+    let _g = serial();
+    give(vec![0u8; 200_000]);
+    give(vec![0.0f32; 200_000]);
+    give(vec![[0.0f32; 4]; 100_000]);
+    assert!(retained_bytes() > 0);
+    release();
+    assert_eq!(retained_bytes(), 0);
+}
+
+#[test]
+/// Verifies the usage counter advances for both take and give.
+fn uses_counts_calls() {
+    let _g = serial();
+    let before = uses();
+    give(take(10, 0u8));
+    assert_eq!(uses(), before + 2);
+}
+
+#[test]
+/// Verifies dropping a `Buf` returns its storage to the pool.
+fn buf_returns_on_drop() {
+    let _g = serial();
+    release();
+    {
+        let mut b = Buf::new(150_000, 0.0f32);
+        b[3] = 1.0;
+        assert_eq!(b.len(), 150_000);
+    }
+    assert_eq!(retained_bytes(), 600_000);
+    release();
+}
+
+#[test]
+/// Verifies concurrent take and give operations preserve initialized values and finish cleanly.
+fn concurrent_smoke() {
+    let _g = serial();
+    release();
+    let handles: Vec<_> = (0..8u8)
+        .map(|t| {
+            std::thread::spawn(move || {
+                for i in 0..200 {
+                    let v = take(70_000 + i % 5, t);
+                    assert!(v.iter().all(|&x| x == t));
+                    give(v);
+                }
+            })
+        })
+        .collect();
+    for h in handles {
+        assert!(h.join().is_ok());
+    }
+    release();
+    assert_eq!(retained_bytes(), 0);
+}
+
+#[test]
+/// Verifies budget eviction uses insertion age across different element types.
+fn eviction_is_oldest_first_across_types() {
+    let _g = serial();
+    release();
+    set_budget(500_000);
+    give(vec![0u8; 300_000]);
+    give(vec![0.0f32; 50_000]);
+    assert_eq!(retained_bytes(), 500_000);
+    // Needs 200 000 more: the older u8 buffer goes, the f32 one stays.
+    give(vec![[0.0f32; 4]; 12_500]);
+    assert_eq!(retained_bytes(), 400_000);
+    assert_eq!(take_exact(50_000, 1.0f32).len(), 50_000);
+    assert_eq!(retained_bytes(), 200_000);
+    set_budget(DEFAULT_BUDGET);
+    release();
+}
+
+#[test]
+/// Verifies reuse chooses the smallest eligible capacity and exact takes require an exact match.
+fn best_fit_picks_the_smallest_fitting_capacity() {
+    let _g = serial();
+    release();
+    let _floor = NoFloor::new();
+    for n in [180_000usize, 120_000, 150_000, 300_000] {
+        give(vec![0u8; n]);
+    }
+    // Within 2x of 100 000: 120 000 is the tightest fit, then 150 000, then 180 000.
+    assert_eq!(take(100_000, 0u8).capacity(), 120_000);
+    assert_eq!(take(100_000, 0u8).capacity(), 150_000);
+    assert_eq!(take(100_000, 0u8).capacity(), 180_000);
+    // 300 000 is more than 2x: allocated fresh, and the miss drops the pooled one.
+    assert_eq!(take(100_000, 0u8).capacity(), 100_000);
+    assert_eq!(retained_bytes(), 0);
+    // An exact capacity beats a smaller-slack scan.
+    give(vec![0u8; 100_000]);
+    assert_eq!(take_exact(100_000, 0u8).capacity(), 100_000);
+    assert_eq!(take_exact(250_000, 0u8).capacity(), 250_000);
+    release();
+}
+
+#[test]
+/// Verifies repeated budget overflow evicts oldest entries across mixed types and capacities.
+fn eviction_walks_oldest_first_through_mixed_types_and_capacities() {
+    let _g = serial();
+    release();
+    let _floor = NoFloor::new();
+    set_budget(700_000);
+    // Oldest to newest, 100 000 bytes each, interleaved types and two u8 capacities.
+    give(vec![0u8; 100_000]);
+    let f = vec![0.0f32; 25_000];
+    give(f);
+    give(vec![0u8; 100_000]);
+    give(vec![0u16; 50_000]);
+    let newest = vec![0u8; 150_000];
+    let np = newest.as_ptr();
+    give(newest);
+    assert_eq!(retained_bytes(), 550_000);
+    // 200 000 more overflows by 50 000: the oldest (u8) goes.
+    give(vec![[0.0f32; 4]; 12_500]);
+    assert_eq!(retained_bytes(), 650_000);
+    // 100 000 more: the next oldest (the f32 buffer) goes.
+    give(vec![0u8; 100_000]);
+    assert_eq!(retained_bytes(), 650_000);
+    // 200 000 more: the u8 then the u16 buffer go.
+    give(vec![0u8; 200_000]);
+    assert_eq!(retained_bytes(), 650_000);
+    // The newest u8 buffer of the old batch is still pooled; the f32 one was evicted.
+    let again = take_exact(150_000, 0u8);
+    assert_eq!(again.as_ptr(), np);
+    assert_eq!(retained_bytes(), 500_000);
+    // The evicted f32 buffer is a miss: the oldest buffers, at least its 100 000 bytes, leave
+    // (the 200 000-byte [f32; 4] one).
+    assert_eq!(take_exact(25_000, 0.0f32).len(), 25_000);
+    assert_eq!(retained_bytes(), 300_000);
+    set_budget(DEFAULT_BUDGET);
+    release();
+}
+
+#[test]
+/// Verifies the idle-release worker clears an unused pooled buffer.
+fn idle_pool_is_released_by_the_background_thread() {
+    // Idle release stays on here: it is what this test checks.
+    let _g = lock_serial();
+    release();
+    give(vec![0u8; MIN_POOLED_BYTES]);
+    assert_eq!(retained_bytes(), MIN_POOLED_BYTES);
+    // Released after one full idle interval without use (at most two from the give).
+    let deadline = std::time::Instant::now() + std::time::Duration::from_secs(3 * IDLE_RELEASE_SECS + 1);
+    while retained_bytes() > 0 && std::time::Instant::now() < deadline {
+        std::thread::sleep(std::time::Duration::from_millis(100));
+    }
+    assert_eq!(retained_bytes(), 0);
+}
+
+#[test]
+/// Verifies a miss discards pooled bytes in proportion to its allocation and a hit preserves the pool.
+fn a_miss_drops_as_many_pooled_bytes_as_it_allocates() {
+    let _g = serial();
+    release();
+    let _floor = NoFloor::new();
+    // Three 64 KiB f32 buffers a byte request can't use.
+    for _ in 0..3 {
+        give(vec![0.0f32; MIN_POOLED_BYTES / 4]);
+    }
+    assert_eq!(retained_bytes(), 3 * MIN_POOLED_BYTES);
+    // A 128 KiB miss drops the two oldest, so pool plus live buffers stay at 192 KiB.
+    let v = take(2 * MIN_POOLED_BYTES, 0u8);
+    assert_eq!(retained_bytes(), MIN_POOLED_BYTES);
+    give(v);
+    // A hit drops nothing.
+    let w = take(MIN_POOLED_BYTES / 4, 0.0f32);
+    assert_eq!(retained_bytes(), 2 * MIN_POOLED_BYTES);
+    drop(w);
+    release();
+}
+
+#[test]
+/// Verifies miss eviction stops when the configured retained-byte floor is reached.
+fn a_miss_keeps_the_floor() {
+    let _g = serial();
+    release();
+    set_miss_floor(2 * MIN_POOLED_BYTES);
+    for _ in 0..3 {
+        give(vec![0.0f32; MIN_POOLED_BYTES / 4]);
+    }
+    // A 192 KiB miss would drop all three; only one goes, down to the floor.
+    assert_eq!(take(3 * MIN_POOLED_BYTES, 0u8).len(), 3 * MIN_POOLED_BYTES);
+    assert_eq!(retained_bytes(), 2 * MIN_POOLED_BYTES);
+    set_miss_floor(DEFAULT_MISS_FLOOR);
+    release();
+}
+
+#[test]
+/// Verifies a failed oversized reservation leaves the pool empty.
+fn a_failed_reservation_releases_the_pool() {
+    let _g = serial();
+    release();
+    // Unmatched buffers under the miss floor stay pooled on a miss.
+    give(vec![0u8; 4 * MIN_POOLED_BYTES]);
+    assert!(retained_bytes() > 0);
+    // No allocator can reserve this: the call fails, but not before the pool was emptied. (The
+    // retry after the release isn't observable here: it needs an allocator that fails once.)
+    assert!(try_take_exact(isize::MAX as usize, 0u8).is_none());
+    assert_eq!(retained_bytes(), 0);
+}
+
+#[test]
+/// Verifies a successful miss preserves unmatched buffers within the miss floor.
+fn a_successful_miss_keeps_unmatched_pooled_buffers() {
+    let _g = serial();
+    release();
+    give(vec![0u8; 4 * MIN_POOLED_BYTES]);
+    let v = try_take_exact(2 * MIN_POOLED_BYTES, 0u8);
+    assert!(v.as_ref().is_some_and(|v| v.len() == 2 * MIN_POOLED_BYTES && v.iter().all(|&b| b == 0)));
+    assert_eq!(retained_bytes(), 4 * MIN_POOLED_BYTES, "within the miss floor, nothing is dropped");
+    release();
+}
diff --git a/crates/testkit/src/perf.rs b/crates/testkit/src/perf.rs
index 6bdf68ab0a..38e6a14cb9 100644
--- a/crates/testkit/src/perf.rs
+++ b/crates/testkit/src/perf.rs
@@ -27,6 +27,19 @@ pub fn process_peak_rss_bytes() -> Option<u64> {
     parse_vm_hwm(&status)
 }
 
+/// Minor page faults this process has taken so far (`/proc/self/stat` field 10), `None` off
+/// Linux. A scenario that maps fresh memory on every run shows up here (#10479).
+pub fn minor_faults() -> Option<u64> {
+    let stat = std::fs::read_to_string("/proc/self/stat").ok()?;
+    parse_minflt(&stat)
+}
+
+fn parse_minflt(stat: &str) -> Option<u64> {
+    // `comm` (field 2) may contain spaces; the fields after its closing `)` start at field 3.
+    let rest = stat.get(stat.rfind(')')?.checked_add(1)?..)?;
+    rest.split_whitespace().nth(7)?.parse().ok()
+}
+
 fn parse_vm_hwm(status: &str) -> Option<u64> {
     let line = status.lines().find(|l| l.starts_with("VmHWM:"))?;
     let kb: u64 = line.split_whitespace().nth(1)?.parse().ok()?;
@@ -149,6 +162,14 @@ pub fn write_report(path: &str, report: &Value) -> Result<(), String> {
 mod tests {
     use super::*;
 
+    #[test]
+    fn minflt_is_field_ten_even_with_spaces_in_comm() {
+        assert_eq!(parse_minflt("42 (cat) R 1 2 3 0 -1 4194304 122 0 0 0"), Some(122));
+        assert_eq!(parse_minflt("42 (a b) c) S 1 2 3 0 -1 0 7 0"), Some(7));
+        assert_eq!(parse_minflt("42 (cat) R 1"), None);
+        assert_eq!(parse_minflt("garbage"), None);
+    }
+
     #[test]
     fn summary_nearest_rank() {
         let v: Vec<f64> = (1..=20).map(f64::from).collect();
diff --git a/crates/ui-egui/examples/interactive_bench.rs b/crates/ui-egui/examples/interactive_bench.rs
index efeff0927d..0b4cc5c952 100644
--- a/crates/ui-egui/examples/interactive_bench.rs
+++ b/crates/ui-egui/examples/interactive_bench.rs
@@ -83,9 +83,9 @@ struct Bench {
     /// state later rows need).
     only: Option<String>,
     rows: Vec<(String, f64, f64, f64, f64)>,
-    /// Per row (same order as `rows`): the timed samples and the peak RSS while they ran, for
-    /// `--json` (`cargo xtask perf`).
-    extra: Vec<(Vec<f64>, Option<u64>)>,
+    /// Per row (same order as `rows`): the timed samples, the peak RSS while they ran and the
+    /// minor page faults per warm run (all of it, untimed setup included), for `--json` (`cargo xtask perf`).
+    extra: Vec<(Vec<f64>, Option<u64>, Option<u64>)>,
     rss: photocraft_testkit::perf::RssSampler,
 }
 
@@ -127,11 +127,17 @@ impl Bench {
         }
         self.rss.reset();
         let cold = f(self);
+        let faults0 = photocraft_testkit::perf::minor_faults();
         let mut v: Vec<f64> = (0..self.reps).map(|_| f(self)).collect();
-        self.extra.push((v.clone(), self.rss.peak()));
+        // Minor page faults per warm run: memory mapped fresh from the kernel each time (#10479).
+        // Counted over the whole of `f`, so it includes untimed setup and cleanup (an undo, an
+        // extra refresh), not only the work the milliseconds measure.
+        let faults = faults0.zip(photocraft_testkit::perf::minor_faults()).map(|(a, b)| b.saturating_sub(a) / self.reps as u64);
+        self.extra.push((v.clone(), self.rss.peak(), faults));
         v.sort_by(f64::total_cmp);
         let med = v[v.len() / 2];
-        println!("{name:<44} {med:>9.1} ms   (min {:>8.1}, max {:>8.1}, cold {:>8.1})", v[0], v[v.len() - 1], cold);
+        let fl = faults.map_or(String::new(), |f| format!(", {f} faults/run incl. setup"));
+        println!("{name:<44} {med:>9.1} ms   (min {:>8.1}, max {:>8.1}, cold {:>8.1}{fl})", v[0], v[v.len() - 1], cold);
         self.rows.push((name.to_string(), med, v[0], v[v.len() - 1], cold));
     }
 }
@@ -473,11 +479,12 @@ fn main() {
             .rows
             .iter()
             .zip(&b.extra)
-            .map(|((n, med, min, max, cold), (samples, rss))| {
+            .map(|((n, med, min, max, cold), (samples, rss, faults))| {
                 let mut r = json!({"name": n, "median_ms": med, "min_ms": min, "max_ms": max, "cold_ms": cold});
                 // For `cargo xtask perf`: raw samples (it computes p50 / p95) and peak RSS.
                 r["samples_ms"] = json!(samples);
                 r["peak_rss_bytes"] = json!(rss);
+                r["minor_faults_per_run"] = json!(faults);
                 r
             })
             .collect();
diff --git a/crates/ui-egui/src/dialogs/color_range_ui.rs b/crates/ui-egui/src/dialogs/color_range_ui.rs
index 75fe3c67b9..3b02806d3a 100644
--- a/crates/ui-egui/src/dialogs/color_range_ui.rs
+++ b/crates/ui-egui/src/dialogs/color_range_ui.rs
@@ -236,7 +236,7 @@ fn proxy_mask(app: &PhotocraftApp, proxy: &Document, k: u32, params: &Value) ->
                 surf.read_rgba_into(area, &mut px);
                 px
             }
-            _ => photocraft_compose::render(proxy, area).px,
+            _ => photocraft_compose::render(proxy, area).into_px(),
         };
         let invert = params.get("invert").and_then(Value::as_bool).unwrap_or(false);
         let mut mask: Vec<f32> = query
diff --git a/crates/ui-egui/src/dialogs/file_ui/web.rs b/crates/ui-egui/src/dialogs/file_ui/web.rs
index 0b5ef3cf58..865215d4b5 100644
--- a/crates/ui-egui/src/dialogs/file_ui/web.rs
+++ b/crates/ui-egui/src/dialogs/file_ui/web.rs
@@ -119,7 +119,7 @@ fn web_pane(app: &PhotocraftApp, ui: &mut egui::Ui, size: egui::Vec2, p: Option<
             };
             let buf = photocraft_compose::flatten(&wd);
             let v = (
-                Arc::new(buf.px),
+                Arc::new(buf.into_px()),
                 wd.size.width,
                 wd.size.height,
                 (fw * fh) / (f64::from(wd.size.width) * f64::from(wd.size.height)).max(1.0),
diff --git a/crates/ui-egui/src/dialogs/filter_dialog/tests.rs b/crates/ui-egui/src/dialogs/filter_dialog/tests.rs
index 92daea2528..8c0ba385e6 100644
--- a/crates/ui-egui/src/dialogs/filter_dialog/tests.rs
+++ b/crates/ui-egui/src/dialogs/filter_dialog/tests.rs
@@ -628,7 +628,7 @@ fn smart_displace_preview_uses_the_map_document() {
             applied.add_document((**d).clone(), None);
         }
         applied.execute(SMART_FILTER_SET_PARAMS, p.clone()).unwrap();
-        let want = photocraft_compose::render(&applied.active().unwrap().doc, doc.bounds()).px;
+        let want = photocraft_compose::render(&applied.active().unwrap().doc, doc.bounds()).into_px();
         let preview = preview_document_for_target(
             &doc,
             layer,
diff --git a/crates/ui-egui/src/dialogs/vp_ui/tests.rs b/crates/ui-egui/src/dialogs/vp_ui/tests.rs
index 19f7786e33..f45063d35c 100644
--- a/crates/ui-egui/src/dialogs/vp_ui/tests.rs
+++ b/crates/ui-egui/src/dialogs/vp_ui/tests.rs
@@ -180,7 +180,7 @@ fn overlapping_stamp_preview_matches_commit_across_batches() {
         s.strokes[0].points.extend_from_slice(&points[2..]);
         assert!(s.paint_preview(|| 2));
         let (shown, _) = s.shown().unwrap();
-        let expected = photocraft_compose::flatten(&shown).px;
+        let expected = photocraft_compose::flatten(&shown).into_px();
         assert_ne!(expected, photocraft_compose::flatten(&app.session.active().unwrap().doc).px);
         commit(&mut app).unwrap();
         assert_eq!(photocraft_compose::flatten(&app.session.active().unwrap().doc).px, expected, "newLayer={new_layer}");
@@ -217,7 +217,7 @@ fn stamp_preview_paints_over_the_paste_like_ok() {
         let s = app.distort.vanishing.as_ref().unwrap();
         assert!(s.preview_has_paste(), "the preview shows the paste, so the overlay isn't drawn over the strokes");
         let (shown, _) = s.shown().unwrap();
-        let expected = photocraft_compose::flatten(&shown).px;
+        let expected = photocraft_compose::flatten(&shown).into_px();
         commit(&mut app).unwrap();
         assert_eq!(photocraft_compose::flatten(&app.session.active().unwrap().doc).px, expected, "newLayer={new_layer}");
     }
@@ -349,7 +349,7 @@ fn ok_paints_the_layer_the_mode_was_opened_on() {
         app.session.execute("layer.new.layer", json!({"name": "other"})).unwrap();
         let other = app.session.active().unwrap().active_layer.unwrap();
         sync_preview(&mut app);
-        let expected = photocraft_compose::flatten(&crate::distort_ui::display_doc(&app, 0).unwrap().0).px;
+        let expected = photocraft_compose::flatten(&crate::distort_ui::display_doc(&app, 0).unwrap().0).into_px();
         commit(&mut app).unwrap();
         let d = &app.session.active().unwrap().doc;
         assert!(d.layer(other).unwrap().surface().unwrap().content_bounds().is_empty(), "newLayer={new_layer}");
@@ -389,7 +389,7 @@ fn an_edit_under_the_mode_shows_on_the_canvas() {
     let px = shown.layer(layer).unwrap().surface().unwrap();
     assert!(px.rgba(210, 30)[1] > 0.9, "the edit shows: {:?}", px.rgba(210, 30));
     assert!(px.rgba(120, 80) != st.doc.layer(layer).unwrap().surface().unwrap().rgba(120, 80), "and so does the stroke");
-    let expected = photocraft_compose::flatten(&shown).px;
+    let expected = photocraft_compose::flatten(&shown).into_px();
     commit(&mut app).unwrap();
     assert_eq!(photocraft_compose::flatten(&app.session.active().unwrap().doc).px, expected);
 }
diff --git a/crates/ui-egui/src/tools/transform_fx.rs b/crates/ui-egui/src/tools/transform_fx.rs
index 60fc45d993..0ad888536d 100644
--- a/crates/ui-egui/src/tools/transform_fx.rs
+++ b/crates/ui-egui/src/tools/transform_fx.rs
@@ -256,7 +256,8 @@ pub fn compose(doc: &Document, work: &Layer, plan: &Plan, source: &Source) -> Op
         let band = Rect::new(shown.x0, y0, shown.x1, y0.saturating_add((px.len() / width.max(1)) as i32));
         let mut over = Buffer::transparent(band);
         effects::composite_with_effects(work, &crop(&content, band), &mut over, &maps, plan.bounds, &doc.patterns);
-        for (o, p) in px.iter_mut().zip(over.px) {
+        // Copied, not moved out, so `over` hands its band back to the scratch pool on drop.
+        for (o, p) in px.iter_mut().zip(over.px.iter().copied()) {
             *o = p;
         }
     });
diff --git a/crates/ui-egui/tests/it/adjust_preview_gpu.rs b/crates/ui-egui/tests/it/adjust_preview_gpu.rs
index 2fdae54cbe..4e8aa8552c 100644
--- a/crates/ui-egui/tests/it/adjust_preview_gpu.rs
+++ b/crates/ui-egui/tests/it/adjust_preview_gpu.rs
@@ -152,14 +152,14 @@ fn preview_layer_composites_on_the_gpu_like_the_command() {
                     // may flip a few pixels sitting right at a step (1 % allowed).
                     let skip = if matches!(kind, "threshold" | "posterize") && depth != SampleType::U8 { (b.width() * b.height()) as usize / 100 } else { 0 };
                     let on_gpu = render_to_vec(&mut comp, &device, &queue, &preview, b).unwrap_or_else(|e| panic!("{what}: {e:?}"));
-                    let on_cpu = photocraft_compose::render(&preview, b).px;
+                    let on_cpu = photocraft_compose::render(&preview, b).into_px();
                     let d = max_diff(&on_gpu, &on_cpu, skip);
                     assert!(d <= tol_gpu, "{what}: GPU vs CPU {:.2}/255", d * 255.0);
                     let mut s = photocraft_engine::Session::new();
                     s.add_document(doc.clone(), None);
                     s.select_layer(target).unwrap();
                     s.execute(&format!("image.adjustments.{kind}"), params.clone()).unwrap();
-                    let cmd = photocraft_compose::render(&s.active().unwrap().doc, b).px;
+                    let cmd = photocraft_compose::render(&s.active().unwrap().doc, b).into_px();
                     let d = max_diff(&on_gpu, &cmd, skip);
                     worst = worst.max(d);
                     assert!(d <= tol_cmd, "{what}: GPU preview vs command {:.2}/255", d * 255.0);
@@ -184,7 +184,7 @@ fn proxy_preview_composites_on_the_gpu() {
         for kind in photocraft_ui_egui::adjust_editors::KINDS {
             let p = proxy_with_settings(&proxy, kind, &sample(kind)).unwrap();
             let on_gpu = render_to_vec(&mut comp, &device, &queue, &p, p.bounds()).unwrap();
-            let on_cpu = photocraft_compose::render(&p, p.bounds()).px;
+            let on_cpu = photocraft_compose::render(&p, p.bounds()).into_px();
             let d = max_diff(&on_gpu, &on_cpu, 0);
             assert!(d <= 2.0 / 255.0, "{kind} selection {selection}: {:.2}/255", d * 255.0);
         }