diff --git a/crates/engine/src/cmd/watch_folder.rs b/crates/engine/src/cmd/watch_folder.rs
index fd41071ed..6e480a9e6 100644
--- a/crates/engine/src/cmd/watch_folder.rs
+++ b/crates/engine/src/cmd/watch_folder.rs
@@ -88,6 +88,9 @@ fn render_project(host: &Session, path: &Path) -> Value {
         let failed = s.project.render_queue.iter().any(|i| matches!(i.status, RenderStatus::Failed(_)));
         Ok(json!({"state": if failed { "failed" } else { "done" }, "items": items}))
     })();
+    // The project shared `host`'s footage source and gave it its own set of footage effects read
+    // the channels of (#474): give back the host's.
+    host.footage.set_aux_footage(host.aux_footage.as_deref().unwrap_or(&[]));
     let mut v = match result {
         Ok(v) => v,
         Err(e) => json!({"state": "failed", "error": e, "items": []}),
diff --git a/crates/engine/src/tests/aux_footage.rs b/crates/engine/src/tests/aux_footage.rs
index 5a74d3b77..01c3c1c96 100644
--- a/crates/engine/src/tests/aux_footage.rs
+++ b/crates/engine/src/tests/aux_footage.rs
@@ -83,9 +83,9 @@ fn effect_edits_undo_and_redo_update_the_set() {
     let mut s = session(&rec);
     let item = import(&mut s, "/renders/a.exr");
     let l = add_layer(&mut s, &item);
-    assert_eq!(rec.last().unwrap_or_default(), Vec::<String>::new(), "no effect reads it yet");
+    assert_eq!(rec.last(), paths(&[]), "no effect reads it yet");
     s.execute_checked("effect.apply", json!({"effect": "Gaussian Blur", "layers": [l]})).unwrap();
-    assert_eq!(rec.last().unwrap_or_default(), Vec::<String>::new(), "a blur doesn't read channels");
+    assert_eq!(rec.last(), paths(&[]), "a blur doesn't read channels");
     s.execute_checked("effect.apply", json!({"effect": "EXtractoR", "layers": [l]})).unwrap();
     assert_eq!(rec.last(), paths(&["/renders/a.exr"]));
     assert!(s.undo());
@@ -173,3 +173,28 @@ fn source_and_footage_replacement_follow() {
     s.execute_checked("file.replaceFootage", json!({"item": b, "path": "/renders/c.exr"})).unwrap();
     assert_eq!(rec.last(), paths(&["/renders/c.exr"]), "the item's new file");
 }
+
+/// A watch-folder render opens its project in a session sharing the host's footage source: the
+/// host's set is given back afterwards.
+#[test]
+fn a_watch_folder_render_gives_the_host_set_back() {
+    let dir = std::env::temp_dir().join(format!("ec-aux-footage-watch-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    let mut other = Session::default();
+    other.execute("comp.new", json!({"name": "Idle", "width": 8, "height": 8, "duration": 1})).unwrap();
+    other.execute("file.saveAs", json!({"path": dir.join("idle.ecproj").to_string_lossy()})).unwrap();
+
+    let rec = Arc::new(Recorder::default());
+    let mut s = session(&rec);
+    let item = import(&mut s, "/renders/a.exr");
+    let l = add_layer(&mut s, &item);
+    s.execute_checked("effect.apply", json!({"effect": "EXtractoR", "layers": [l]})).unwrap();
+    let calls = rec.calls();
+    let r = s.execute("file.watchFolder", json!({"folder": dir.to_string_lossy()})).unwrap();
+    assert_eq!(r["rendered"].as_array().map(Vec::len), Some(1), "{r}");
+    assert!(rec.calls() > calls + 1, "the watched project gave its own set");
+    assert_eq!(rec.last(), paths(&["/renders/a.exr"]), "the host's set is back");
+    s.execute("file.watchFolder", json!({"stop": true})).unwrap();
+    let _ = std::fs::remove_dir_all(&dir);
+}
diff --git a/crates/gpu/src/tests/fx_depth.rs b/crates/gpu/src/tests/fx_depth.rs
index 8a6665655..ebc75919d 100644
--- a/crates/gpu/src/tests/fx_depth.rs
+++ b/crates/gpu/src/tests/fx_depth.rs
@@ -208,6 +208,13 @@ fn on() -> Value {
     Value::Bool(true)
 }
 
+/// #474: every effect done here reads aux channels, so the session gives the media layer its
+/// footage ([`effectcraft_effects::reads_aux`]).
+#[test]
+fn every_effect_here_reads_aux() {
+    assert!(crate::fx_depth::IDS.iter().all(|i| effectcraft_effects::reads_aux(i)));
+}
+
 #[test]
 fn channel_extract() {
     case("ec.3d.channelextract", &[("blackPoint", n(0.0)), ("whitePoint", n(1200.0))]);
diff --git a/crates/media/src/exr_channels.rs b/crates/media/src/exr_channels.rs
index 3b5ee6084..c3e7cfc3d 100644
--- a/crates/media/src/exr_channels.rs
+++ b/crates/media/src/exr_channels.rs
@@ -653,7 +653,7 @@ impl ChannelCache {
                 decoded_here = true;
                 self.decodes.fetch_add(1, Ordering::Relaxed);
                 #[cfg(test)]
-                count_decode();
+                count_decode(true);
                 let _abandon = Abandon { cache: self, slot: &slot };
                 let bytes = read()?;
                 // The planes it will allocate count against the budget while it decodes.
@@ -742,21 +742,27 @@ pub(crate) fn cached(path: &str, read: impl FnOnce() -> Option<Arc<[u8]>>) -> Op
 
 #[cfg(test)]
 thread_local! {
-    /// Decodes of a still's pixels on this thread: the channel cache's and the `image` crate's
-    /// ([`count_decode`]).
-    static DECODES: std::cell::Cell<u64> = const { std::cell::Cell::new(0) };
+    /// Decodes of a still's pixels on this thread ([`count_decode`]): the `image` crate's, then
+    /// the channel cache's.
+    static DECODES: std::cell::Cell<[u64; 2]> = const { std::cell::Cell::new([0; 2]) };
 }
 
-/// Count a decode of a file's pixels on this thread (tests).
+/// Count a decode of a file's pixels on this thread (tests): by the channel cache (`channels`)
+/// or by the `image` crate.
 #[cfg(test)]
-pub(crate) fn count_decode() {
-    DECODES.with(|d| d.set(d.get() + 1));
+pub(crate) fn count_decode(channels: bool) {
+    DECODES.with(|d| {
+        let mut n = d.get();
+        n[usize::from(channels)] += 1;
+        d.set(n);
+    });
 }
 
-/// The decodes [`count_decode`] counted on this thread since the last call.
+/// The decodes [`count_decode`] counted on this thread since the last call: by the `image` crate
+/// and by the channel cache.
 #[cfg(test)]
-pub(crate) fn take_decodes() -> u64 {
-    DECODES.with(|d| d.replace(0))
+pub(crate) fn take_decodes() -> [u64; 2] {
+    DECODES.with(|d| d.replace([0; 2]))
 }
 
 #[cfg(test)]
@@ -1088,11 +1094,11 @@ mod tests {
         pool.frame_at(&f[given], t).unwrap();
         let aux = pool.aux(effectcraft_project::ItemId(1), &f[given], t).unwrap();
         assert_eq!(aux.get("GlossDir.R").and_then(|p| p.first()).copied(), Some(0.25));
-        assert_eq!(take_decodes(), 1, "the picture and the channels share one decode");
+        assert_eq!(take_decodes(), [0, 1], "the picture and the channels share one decode");
         // Learned only at the first `aux()`: the picture was decoded on its own before.
         pool.frame_at(&f[learned], t).unwrap();
         pool.aux(effectcraft_project::ItemId(2), &f[learned], t).unwrap();
-        assert_eq!(take_decodes(), 2);
+        assert_eq!(take_decodes(), [1, 1]);
     }
 
     /// #474: once the project no longer names footage (its effect removed), later frames decode
@@ -1109,21 +1115,22 @@ mod tests {
         f.kind = effectcraft_project::FootageKind::Sequence;
         f.sequence = paths.clone();
         let at = |i: i64| f.frame_rate.tick_of(i);
-        let in_cache = |p: &str| cache().cached().iter().any(|c| c == p);
+        // (counted on this thread, so other tests sharing the channel cache don't change them)
+        let frame = |i: i64| {
+            take_decodes();
+            pool.frame_at(&f, at(i)).unwrap();
+            take_decodes()
+        };
         pool.set_aux_footage(std::slice::from_ref(&f.path));
-        pool.frame_at(&f, at(0)).unwrap();
-        assert!(in_cache(&paths[0]), "given: the picture comes from the channel decode");
+        assert_eq!(frame(0), [0, 1], "given: the picture comes from the channel decode");
         pool.set_aux_footage(&[]);
         assert!(!cache().lock().held.iter().any(|(p, _)| *p == paths[0]), "no longer kept once no effect reads it");
-        pool.frame_at(&f, at(1)).unwrap();
-        assert!(!in_cache(&paths[1]), "no longer given: the picture alone");
+        assert_eq!(frame(1), [1, 0], "no longer given: the picture alone");
         // Learned by `aux()`, then a new set without it: picture only again.
         pool.aux(effectcraft_project::ItemId(1), &f, at(1)).unwrap();
-        pool.frame_at(&f, at(2)).unwrap();
-        assert!(in_cache(&paths[2]), "learned");
+        assert_eq!(frame(2), [0, 1], "learned");
         pool.set_aux_footage(&[]);
-        pool.frame_at(&f, at(3)).unwrap();
-        assert!(!in_cache(&paths[3]), "a new set drops what was learned");
+        assert_eq!(frame(3), [1, 0], "a new set drops what was learned");
     }
 
     /// #474: the picture made of the cached planes of a file with exact R, G, B channels is the
diff --git a/crates/media/src/pool.rs b/crates/media/src/pool.rs
index e9157a5ca..b0b2f2539 100644
--- a/crates/media/src/pool.rs
+++ b/crates/media/src/pool.rs
@@ -885,7 +885,7 @@ impl Inner {
             return Ok(img);
         }
         #[cfg(test)]
-        crate::exr_channels::count_decode();
+        crate::exr_channels::count_decode(false);
         match crate::probe::load_oriented(&bytes, crate::still_format(path, &bytes)) {
             Ok(img) => Ok(dynamic_to_image(&img, op)),
             // A multi-layer OpenEXR file without an unnamed RGB layer: its colour layer.
diff --git a/docs/file-format-parity.md b/docs/file-format-parity.md
index f56a57319..ba8c1db7a 100644
--- a/docs/file-format-parity.md
+++ b/docs/file-format-parity.md
@@ -41,7 +41,7 @@ trips and renders, checked by tests, not against After Effects), **partial** (na
 | PNG | R/W | yes | yes (sequence) | good |
 | JPEG | R/W | yes | yes (sequence) | good |
 | TIFF | R/W | yes | yes (sequence) | good |
-| OpenEXR (multi-layer, Cryptomatte) | R/W | yes | yes (32-bit sequence) | good; HTJ2K compression fails (#482); a multi-layer frame decodes once for its picture and EXtractoR / Cryptomatte from the first frame on, except files whose picture the `image` crate still decodes (#474); footage alone keeps only its picture's channels, though a single-part file still decompresses every channel's pixels; decoded channels are held as f32 |
+| OpenEXR (multi-layer, Cryptomatte) | R/W | yes | yes (32-bit sequence) | good; HTJ2K compression fails (#482); a multi-layer frame decodes once for its picture and EXtractoR / Cryptomatte from the first frame on, except Media Replacement items, which are learned at their first frame, and files whose picture the `image` crate still decodes (#474); footage alone keeps only its picture's channels, though a single-part file still decompresses every channel's pixels; decoded channels are held as f32 |
 | Photoshop PSD / PSB | R (footage, composition) / W (layers, sequence) | yes (layers, groups, masks, styles, smart objects) | Save Frame As ▸ Photoshop Layers; no Photoshop sequence output | good, from Adobe's published spec |
 | Illustrator `.ai`, PDF, EPS | R | yes (vector, Continuously Rasterize, Create Shapes; Composition and Composition - Retain Layer Sizes, #1536) | — | partial: no JPX / JBIG2 images, no Illustrator procset EPS |
 | SVG | R | yes | — | good; SVG markup on the clipboard pastes as a shape layer (26.3, #738); Illustrator's own clipboard data (PDF/AI) doesn't |