diff --git a/crates/ui-egui/src/frames.rs b/crates/ui-egui/src/frames.rs
index ed00690a..a7023a49 100644
--- a/crates/ui-egui/src/frames.rs
+++ b/crates/ui-egui/src/frames.rs
@@ -1467,933 +1467,4 @@ impl Queue {
 }
 
 #[cfg(test)]
-mod tests {
-    use super::*;
-
-    struct ProbeDisk {
-        keys: Mutex<HashSet<u128>>,
-        probes: std::sync::atomic::AtomicUsize,
-    }
-
-    impl RemoteFrames for ProbeDisk {
-        fn slots(&self) -> usize {
-            0
-        }
-
-        fn disk(&self) -> bool {
-            true
-        }
-
-        fn disk_contains(&self, key: u128) -> bool {
-            self.probes.fetch_add(1, Ordering::Relaxed);
-            self.keys.lock().unwrap().contains(&key)
-        }
-
-        fn start(&self, _: RemoteJob, _: RemoteDone) {}
-    }
-
-    fn disk_fixture(stored_frames: &[i64]) -> (Frames, RenderSource, FrameKey, RenderOpts, Arc<ProbeDisk>, u128) {
-        let mut session = effectcraft_engine::Session::default();
-        session.execute("comp.new", serde_json::json!({"width": 32, "height": 18, "duration": 1})).unwrap();
-        let comp = session.active_comp_id().unwrap();
-        let opts = RenderOpts::default();
-        let content = 1234;
-        let mut base = key(1, 0, opts_hash(&opts));
-        base.revision = 7;
-        base.comp = comp.0;
-        let disk = Arc::new(ProbeDisk { keys: Mutex::new(HashSet::new()), probes: 0.into() });
-        disk.keys.lock().unwrap().extend(stored_frames.iter().map(|frame| disk_cache::frame_key(content, *frame, base.scale, base.view ^ opts_hash(&opts))));
-        let mut frames = Frames::default();
-        frames.set_remote(Some(disk.clone()));
-        frames.content_keys.lock().unwrap().insert((base.revision, base.comp, 0), content);
-        let source = RenderSource {
-            project: session.project.clone(),
-            footage: session.footage.clone(),
-            expr: None,
-            layer_cache: Arc::default(),
-            gpu: None,
-            gpu_display: false,
-            disk: None,
-        };
-        (frames, source, base, opts, disk, content)
-    }
-
-    #[cfg(not(target_arch = "wasm32"))]
-    #[test]
-    fn disk_indicator_does_not_hash_on_ui_thread_and_coalesces_edits() {
-        use std::sync::mpsc;
-        use std::time::{Duration, Instant};
-        struct Disk(u128);
-        impl RemoteFrames for Disk {
-            fn slots(&self) -> usize {
-                1
-            }
-            fn disk(&self) -> bool {
-                true
-            }
-            fn disk_contains(&self, key: u128) -> bool {
-                self.0 == key
-            }
-            fn start(&self, _: RemoteJob, done: RemoteDone) {
-                done(Err("test has no renderer".into()));
-            }
-        }
-        let mut s = effectcraft_engine::Session::default();
-        s.execute("comp.new", serde_json::json!({"width":32,"height":18,"duration":1})).unwrap();
-        let cid = s.active_comp_id().unwrap();
-        let opts = RenderOpts::default();
-        let stored = disk_cache::frame_key(disk_cache::comp_content_key(&s.project, cid), 2, 1000, opts_hash(&opts));
-        let mut frames = Frames { pool: Some(rayon::ThreadPoolBuilder::new().num_threads(1).build().unwrap()), ..Default::default() };
-        frames.set_remote(Some(Arc::new(Disk(stored))));
-        let (entered, started) = mpsc::channel();
-        let (release, wait) = mpsc::channel();
-        frames.pool.as_ref().unwrap().spawn(move || {
-            entered.send(()).unwrap();
-            wait.recv_timeout(Duration::from_secs(5)).unwrap();
-        });
-        started.recv_timeout(Duration::from_secs(3)).unwrap();
-        let src = RenderSource {
-            project: s.project.clone(),
-            footage: s.footage.clone(),
-            expr: None,
-            layer_cache: Arc::default(),
-            gpu: None,
-            gpu_display: false,
-            disk: None,
-        };
-        let mut base = key(1, 0, 0);
-        base.comp = cid.0;
-        for revision in 1..50 {
-            base.revision = revision;
-            assert!(frames.disk_frames(&src, &base, 0..30, &opts).is_empty());
-        }
-        assert!(frames.content_keys.lock().unwrap().is_empty(), "painting computed a content hash while the worker was blocked");
-        assert_eq!(frames.content_key_jobs.lock().unwrap().pending.len(), 1);
-        release.send(()).unwrap();
-        let until = Instant::now() + Duration::from_secs(3);
-        while !frames.content_keys.lock().unwrap().contains_key(&(base.revision, base.comp, 0)) {
-            assert!(Instant::now() < until);
-            std::thread::sleep(Duration::from_millis(1));
-        }
-        assert_eq!(frames.disk_frames(&src, &base, 0..30, &opts), vec![2], "the blue indicator must return once its key is ready");
-        assert_eq!(frames.content_keys.lock().unwrap().len(), 1, "superseded revisions were hashed");
-    }
-
-    #[test]
-    fn disk_indicator_range_tracks_live_membership() {
-        let (frames, src, base, opts, disk, _) = disk_fixture(&[10, 12]);
-        assert_eq!(frames.disk_frames(&src, &base, 10..13, &opts), vec![10, 12]);
-        assert_eq!(disk.probes.load(Ordering::Relaxed), 3);
-
-        disk.keys.lock().unwrap().insert(disk_cache::frame_key(1234, 11, base.scale, base.view ^ opts_hash(&opts)));
-        assert_eq!(frames.disk_frames(&src, &base, 10..13, &opts), vec![10, 11, 12]);
-
-        insert(&frames, FrameKey { frame: 11, ..base });
-        disk.probes.store(0, Ordering::Relaxed);
-        assert_eq!(frames.disk_frames(&src, &base, 10..13, &opts), vec![10, 12]);
-        assert_eq!(disk.probes.load(Ordering::Relaxed), 2);
-
-        disk.keys.lock().unwrap().remove(&disk_cache::frame_key(1234, 12, base.scale, base.view ^ opts_hash(&opts)));
-        assert_eq!(frames.disk_frames(&src, &base, 10..13, &opts), vec![10]);
-
-        let mut revised = base;
-        revised.revision += 1;
-        frames.content_keys.lock().unwrap().insert((revised.revision, revised.comp, 0), 5678);
-        assert!(frames.disk_frames(&src, &revised, 10..13, &opts).is_empty());
-
-        let changed = FrameKey { scale: base.scale + 1, ..base };
-        assert!(frames.disk_frames(&src, &changed, 10..13, &opts).is_empty());
-        let changed = FrameKey { view: base.view + 1, ..base };
-        assert!(frames.disk_frames(&src, &changed, 10..13, &opts).is_empty());
-        assert!(frames.disk_frames(&src, &base, 10..13, &RenderOpts { draft: true, ..opts }).is_empty());
-    }
-
-    #[test]
-    fn disk_indicator_range_is_bounded() {
-        let (frames, src, base, opts, disk, _) = disk_fixture(&[0, 1, 99_999]);
-        assert_eq!(frames.disk_frames(&src, &base, -5..2, &opts), vec![0, 1]);
-        assert_eq!(disk.probes.load(Ordering::Relaxed), 2);
-        disk.probes.store(0, Ordering::Relaxed);
-        assert_eq!(frames.disk_frames(&src, &base, 99_999..i64::MAX, &opts), vec![99_999]);
-        assert_eq!(disk.probes.load(Ordering::Relaxed), 1);
-        disk.probes.store(0, Ordering::Relaxed);
-        assert!(frames.disk_frames(&src, &base, 2..2, &opts).is_empty());
-        // Written as a struct literal: `3..2` trips clippy::reversed_empty_ranges.
-        let reversed = std::ops::Range { start: 3, end: 2 };
-        assert!(frames.disk_frames(&src, &base, reversed, &opts).is_empty());
-        assert_eq!(disk.probes.load(Ordering::Relaxed), 0);
-    }
-
-    /// Frames larger than the texture limit are averaged down by a whole factor (#201: an
-    /// 11000×2200 comp at Full resolution against an 8192 limit).
-    #[test]
-    fn frames_over_the_texture_limit_are_averaged_down() {
-        assert_eq!(fitted_size([11000, 2200], 8192), [5500, 1100]);
-        assert_eq!(fitted_size([8192, 100], 8192), [8192, 100]);
-        assert_eq!(fitted_size([30000, 30000], 16384), [15000, 15000]);
-        assert_eq!(fitted_size([0, 0], 0), [0, 0]);
-        // 5×2 (three columns of white, then black) into 2 px: 3×2 blocks (the last one 2×2).
-        let w = egui::Color32::WHITE;
-        let b = egui::Color32::from_rgba_premultiplied(0, 0, 0, 255);
-        let img = egui::ColorImage::new([5, 2], vec![w, w, w, b, b, w, w, w, b, b]);
-        let out = fit_texture(img.clone(), 2);
-        assert_eq!(out.size, [2, 1]);
-        assert_eq!(out.pixels, vec![w, b]);
-        assert_eq!(fit_texture(img.clone(), 5).pixels, img.pixels);
-        let mixed = fit_texture(egui::ColorImage::new([2, 1], vec![w, b]), 1);
-        assert_eq!(mixed.pixels, vec![egui::Color32::from_rgba_premultiplied(128, 128, 128, 255)]);
-    }
-
-    #[test]
-    fn retirement_reaches_existing_workers_and_keeps_cpu_frames_and_completion_live() {
-        let frames = Frames::default();
-        let worker = frames.worker();
-        let first = key(1, 0, 0);
-        insert(&frames, first);
-        frames.retire_gpu();
-        assert!(worker.gpu_retired.load(Ordering::Acquire), "already queued workers share retirement");
-        assert!(frames.is_cached(&first), "healthy materialized CPU frames survive");
-        let next = key(1, 1, 0);
-        frames.inflight.lock().unwrap().insert(next);
-        frames.queue.lock().unwrap().running.insert(next);
-        worker.finish_key(next, false, img(), web_time::Instant::now());
-        assert!(frames.is_cached(&next), "CPU retry can still publish");
-        assert_eq!(frames.inflight(), 0);
-        assert!(frames.queue.lock().unwrap().running.is_empty());
-    }
-
-    fn key(content: u64, frame: i64, opts: u64) -> FrameKey {
-        FrameKey { revision: content, content, comp: 1, frame, scale: 1000, view: 0, opts }
-    }
-
-    fn img() -> FrameImage {
-        FrameImage::Cpu(Arc::new(egui::ColorImage::new([2, 2], vec![egui::Color32::BLACK; 4])))
-    }
-
-    fn insert(f: &Frames, k: FrameKey) {
-        f.cache.lock().unwrap().insert(k, img());
-    }
-
-    /// A frame whose render panics (a GPU out of memory used to, on every frame thread) is
-    /// released, not left "in progress" forever, so the viewer can ask for it again (#106).
-    #[test]
-    fn a_frame_whose_render_panics_is_released() {
-        use effectcraft_engine::Session;
-        use effectcraft_engine::project::{Footage, FootageKind};
-        use effectcraft_engine::render::Image;
-        use serde_json::json;
-        use std::sync::atomic::{AtomicUsize, Ordering};
-        #[derive(Default)]
-        struct Explodes(AtomicUsize);
-        impl FootageSource for Explodes {
-            fn frame(&self, _: ItemId, _: &Footage, _: Tick) -> Option<Arc<Image>> {
-                self.0.fetch_add(1, Ordering::SeqCst);
-                panic!("a decoder bug");
-            }
-        }
-        let mut s = Session::default();
-        let cid = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 1})).unwrap()["comp"].as_u64().unwrap());
-        let clip = Footage { kind: FootageKind::Still, width: 8, height: 8, has_video: true, ..Default::default() };
-        let item = Arc::make_mut(&mut s.project).add_item("clip.png", Default::default(), None, ItemKind::Footage(clip));
-        s.execute("layer.addItem", json!({"item": item.0})).unwrap();
-        let footage = Arc::new(Explodes::default());
-        let src = RenderSource {
-            project: s.project.clone(),
-            footage: footage.clone(),
-            expr: None,
-            layer_cache: Arc::default(),
-            gpu: None,
-            gpu_display: false,
-            disk: None,
-        };
-        let f = Frames::default();
-        let key = FrameKey { revision: s.revision, content: f.content_of(&s.project, s.revision, cid), ..key(0, 0, 0) };
-        let key = FrameKey { comp: cid.0, ..key };
-        f.request(&src, key, cid, Tick::ZERO, RenderOpts::default());
-        for _ in 0..1000 {
-            if f.inflight() == 0 {
-                break;
-            }
-            std::thread::sleep(std::time::Duration::from_millis(5));
-        }
-        assert!(footage.0.load(Ordering::SeqCst) > 0, "the render reached the footage");
-        assert_eq!(f.inflight(), 0, "released");
-        assert!(!f.is_cached(&key));
-    }
-
-    /// #647: a pool thread waiting inside a render (on a parallel loop) never starts another
-    /// frame render on top of it. Dragging a layer queues a frame every UI frame; renders used to
-    /// nest on every thread, each holding its buffers, until memory ran out.
-    #[test]
-    fn a_waiting_render_never_starts_another_on_its_thread() {
-        use effectcraft_engine::Session;
-        use effectcraft_engine::project::{Footage, FootageKind};
-        use effectcraft_engine::render::Image;
-        use effectcraft_engine::time::FrameRate;
-        use serde_json::json;
-        use std::cell::Cell;
-        use std::sync::atomic::AtomicUsize;
-        thread_local! {
-            static DEPTH: Cell<usize> = const { Cell::new(0) };
-        }
-        /// A decoder that works in parallel, as the renderer does: its thread joins the loop and
-        /// may wait for the parts other threads took.
-        #[derive(Default)]
-        struct Parallel {
-            calls: AtomicUsize,
-            deepest: AtomicUsize,
-        }
-        impl FootageSource for Parallel {
-            fn frame(&self, _: ItemId, _: &Footage, _: Tick) -> Option<Arc<Image>> {
-                let d = DEPTH.get() + 1;
-                DEPTH.set(d);
-                self.deepest.fetch_max(d, Ordering::SeqCst);
-                self.calls.fetch_add(1, Ordering::SeqCst);
-                (0..64).into_par_iter().for_each(|_| std::thread::sleep(std::time::Duration::from_millis(1)));
-                DEPTH.set(d - 1);
-                Some(Arc::new(Image::new(4, 4)))
-            }
-        }
-        let mut s = Session::default();
-        let cid = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 10})).unwrap()["comp"].as_u64().unwrap());
-        let clip = Footage {
-            kind: FootageKind::Video,
-            width: 4,
-            height: 4,
-            has_video: true,
-            frame_rate: FrameRate::FPS_30,
-            duration: Tick::from_seconds_f64(10.0),
-            ..Default::default()
-        };
-        let item = Arc::make_mut(&mut s.project).add_item("clip.mov", Default::default(), None, ItemKind::Footage(clip));
-        s.execute("layer.addItem", json!({"item": item.0})).unwrap();
-        let footage = Arc::new(Parallel::default());
-        let src = RenderSource {
-            project: s.project.clone(),
-            footage: footage.clone(),
-            expr: None,
-            layer_cache: Arc::default(),
-            gpu: None,
-            gpu_display: false,
-            disk: None,
-        };
-        let f = Frames::default();
-        let content = f.content_of(&s.project, s.revision, cid);
-        let frames = 60;
-        for frame in 0..frames {
-            let key = FrameKey { revision: s.revision, content, comp: cid.0, frame, scale: 1000, view: 0, opts: 0 };
-            f.request(&src, key, cid, FrameRate::FPS_30.tick_of(frame), RenderOpts::default());
-        }
-        for _ in 0..4000 {
-            if f.inflight() == 0 {
-                break;
-            }
-            std::thread::sleep(std::time::Duration::from_millis(5));
-        }
-        assert_eq!(f.inflight(), 0, "every queued frame rendered");
-        assert!(footage.calls.load(Ordering::SeqCst) >= frames as usize);
-        assert_eq!(footage.deepest.load(Ordering::SeqCst), 1, "renders nested on a waiting thread");
-    }
-
-    /// #329: scrubbing a long movie, the viewer frame of every step the pointer passed started
-    /// rendering and seeked the movie's decoder in turn; the frame under the pointer waited for
-    /// all of them. A newer viewer frame of another time calls off the one rendering, which is
-    /// not cached (its footage may be missing).
-    #[test]
-    fn a_newer_viewer_frame_calls_off_the_one_rendering() {
-        use effectcraft_engine::Session;
-        use effectcraft_engine::project::{Footage, FootageKind};
-        use effectcraft_engine::render::Image;
-        use effectcraft_engine::time::FrameRate;
-        use serde_json::json;
-        use std::cell::RefCell;
-        thread_local! {
-            static CANCEL: RefCell<Option<Arc<AtomicBool>>> = const { RefCell::new(None) };
-        }
-        /// A movie whose first frames take a long seek, which a called-off read gives up.
-        #[derive(Default)]
-        struct Seeking {
-            seeking: AtomicBool,
-            called_off: AtomicBool,
-        }
-        impl FootageSource for Seeking {
-            fn cancellable(&self, cancel: &Arc<AtomicBool>, f: &mut dyn FnMut()) {
-                let prev = CANCEL.replace(Some(cancel.clone()));
-                f();
-                CANCEL.set(prev);
-            }
-            fn frame(&self, _: ItemId, _: &Footage, t: Tick) -> Option<Arc<Image>> {
-                if t < Tick::from_seconds_f64(0.25) {
-                    self.seeking.store(true, Ordering::SeqCst);
-                    for _ in 0..1000 {
-                        if CANCEL.with_borrow(|c| c.as_ref().is_some_and(|c| c.load(Ordering::SeqCst))) {
-                            self.called_off.store(true, Ordering::SeqCst);
-                            return None;
-                        }
-                        std::thread::sleep(std::time::Duration::from_millis(5));
-                    }
-                }
-                Some(Arc::new(Image::new(4, 4)))
-            }
-        }
-        let mut s = Session::default();
-        let cid = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 10})).unwrap()["comp"].as_u64().unwrap());
-        let clip = Footage {
-            kind: FootageKind::Video,
-            width: 4,
-            height: 4,
-            has_video: true,
-            frame_rate: FrameRate::FPS_30,
-            duration: Tick::from_seconds_f64(10.0),
-            ..Default::default()
-        };
-        let item = Arc::make_mut(&mut s.project).add_item("clip.mov", Default::default(), None, ItemKind::Footage(clip));
-        s.execute("layer.addItem", json!({"item": item.0})).unwrap();
-        let footage = Arc::new(Seeking::default());
-        let src = RenderSource {
-            project: s.project.clone(),
-            footage: footage.clone(),
-            expr: None,
-            layer_cache: Arc::default(),
-            gpu: None,
-            gpu_display: false,
-            disk: None,
-        };
-        let f = Frames::default();
-        let content = f.content_of(&s.project, s.revision, cid);
-        let key = |frame| FrameKey { revision: s.revision, content, comp: cid.0, frame, scale: 1000, view: 0, opts: 0 };
-        f.request_urgent(&src, key(0), cid, Tick::ZERO, RenderOpts::default());
-        for _ in 0..1000 {
-            if footage.seeking.load(Ordering::SeqCst) {
-                break;
-            }
-            std::thread::sleep(std::time::Duration::from_millis(2));
-        }
-        assert!(footage.seeking.load(Ordering::SeqCst), "the first frame's render reached the footage");
-        f.request_urgent(&src, key(150), cid, FrameRate::FPS_30.tick_of(150), RenderOpts::default());
-        for _ in 0..1000 {
-            if f.inflight() == 0 {
-                break;
-            }
-            std::thread::sleep(std::time::Duration::from_millis(5));
-        }
-        assert!(footage.called_off.load(Ordering::SeqCst), "the superseded frame's seek ran on");
-        assert!(f.is_cached(&key(150)), "the newest frame rendered");
-        assert!(!f.is_cached(&key(0)), "a called-off frame is not cached");
-        assert_eq!(f.inflight(), 0, "released");
-    }
-
-    /// #284: scrubbing asks for a viewer frame at every step; a newer one drops the comp's viewer
-    /// frames still waiting (they would all render first), but not prefetch frames or another
-    /// comp's viewer frame.
-    #[test]
-    fn a_newer_viewer_frame_drops_the_ones_still_waiting() {
-        /// Starts nothing, so every request stays queued.
-        struct Idle;
-        impl RemoteFrames for Idle {
-            fn slots(&self) -> usize {
-                0
-            }
-            fn start(&self, _: RemoteJob, _: RemoteDone) {}
-        }
-        let mut f = Frames::default();
-        f.set_remote(Some(Arc::new(Idle)));
-        let src = RenderSource {
-            project: Arc::default(),
-            footage: Arc::new(effectcraft_engine::render::NoFootage),
-            expr: None,
-            layer_cache: Arc::default(),
-            gpu: None,
-            gpu_display: false,
-            disk: None,
-        };
-        let request = |k: FrameKey, urgent: bool| f.request_with(&src, k, ItemId(k.comp), Tick::ZERO, RenderOpts::default(), urgent);
-        let other = FrameKey { comp: 2, ..key(1, 0, 0) };
-        request(other, true);
-        request(key(1, 20, 0), false);
-        for frame in 0..10 {
-            request(key(1, frame, 0), true);
-        }
-        let mut queued: Vec<(u64, i64, bool)> = f.queue.lock().unwrap().jobs.iter().map(|j| (j.key.comp, j.key.frame, j.urgent)).collect();
-        queued.sort();
-        assert_eq!(queued, [(1, 9, true), (1, 20, false), (2, 0, false)]);
-        assert_eq!(f.inflight(), 3, "dropped frames aren't in flight: the viewer can ask again");
-    }
-
-    /// Each time the GPU runs out of memory, half as many GPU frames are kept, down to a floor.
-    #[test]
-    fn running_out_of_video_memory_halves_the_gpu_frame_budget() {
-        let f = Frames::default();
-        let mut c = f.cache.lock().unwrap();
-        assert_eq!(c.gpu_budget, GPU_BUDGET);
-        c.gpu_out_of_memory();
-        assert_eq!(c.gpu_budget, GPU_BUDGET / 2);
-        for _ in 0..20 {
-            c.gpu_out_of_memory();
-        }
-        assert_eq!(c.gpu_budget, MIN_GPU_BUDGET);
-    }
-
-    #[test]
-    fn least_recently_shown_frames_go_first() {
-        let f = Frames::default();
-        f.set_budget(3 * 16);
-        for i in 0..3 {
-            insert(&f, key(1, i, 0));
-        }
-        // Frame 0 is shown again, so frame 1 is now the oldest.
-        assert!(f.get(&key(1, 0, 0)).is_some());
-        insert(&f, key(1, 3, 0));
-        assert!(f.is_cached(&key(1, 0, 0)) && !f.is_cached(&key(1, 1, 0)));
-        assert!(f.is_cached(&key(1, 2, 0)) && f.is_cached(&key(1, 3, 0)));
-    }
-
-    fn playhead(cur: i64, looping: bool) -> Playhead {
-        Playhead { series: key(1, 0, 0), cur, start: 0, end: 99, step: 1, looping }
-    }
-
-    /// #595: a playing preview's cache is full. The frames just ahead of the playhead were
-    /// rendered before the ones just shown, so plain LRU evicted them first and the preview
-    /// played into a gap. Frames the preview no longer reaches go first, then the ones it
-    /// reaches last.
-    #[test]
-    fn a_full_cache_keeps_the_frames_just_ahead_of_the_playhead() {
-        let f = Frames::default();
-        f.set_budget(4 * 16);
-        // Prefetch rendered 11..=13, then 10 was shown (the most recently used).
-        for i in [11, 12, 13, 10] {
-            insert(&f, key(1, i, 0));
-        }
-        let cached = |f: &Frames| f.cached_frames(&key(1, 0, 0));
-        f.set_playhead(Some(playhead(10, false)));
-        // The next frame rendered is the one the preview reaches last: the frames just ahead stay.
-        insert(&f, key(1, 14, 0));
-        assert_eq!(cached(&f), [10, 11, 12, 13]);
-        // Without looping, a frame behind the playhead goes before any frame ahead of it.
-        f.set_playhead(Some(playhead(12, false)));
-        insert(&f, key(1, 14, 0));
-        assert_eq!(cached(&f), [10, 12, 13, 14]);
-        // Looping, the frame just behind is the one reached last.
-        f.set_playhead(Some(playhead(13, true)));
-        insert(&f, key(1, 0, 0));
-        assert_eq!(cached(&f), [0, 10, 13, 14]);
-        // Stopped: least recently shown first again.
-        f.set_playhead(None);
-        insert(&f, key(1, 50, 0));
-        assert!(!f.is_cached(&key(1, 13, 0)) && f.is_cached(&key(1, 50, 0)));
-    }
-
-    /// A frame source that queues jobs and never renders them: the tests check the queue.
-    struct Idle;
-    impl RemoteFrames for Idle {
-        fn slots(&self) -> usize {
-            0
-        }
-        fn start(&self, _: RemoteJob, _: RemoteDone) {}
-    }
-
-    fn idle_source() -> RenderSource {
-        RenderSource {
-            project: Arc::default(),
-            footage: Arc::new(effectcraft_engine::render::NoFootage),
-            expr: None,
-            layer_cache: Arc::default(),
-            gpu: None,
-            gpu_display: false,
-            disk: None,
-        }
-    }
-
-    /// #595: prefetch renders the frames the preview reaches first, whatever order they were
-    /// asked for in (a frame evicted and asked for again waited behind every frame further
-    /// ahead); queued frames the preview no longer reaches are dropped and not left in flight.
-    #[test]
-    fn prefetch_renders_the_frames_the_playhead_reaches_first() {
-        let mut f = Frames::default();
-        f.set_remote(Some(Arc::new(Idle)));
-        let src = idle_source();
-        for frame in [40, 30, 20, 5, 12, 11] {
-            f.request(&src, key(1, frame, 0), ItemId(1), Tick::ZERO, RenderOpts::default());
-        }
-        f.request(&src, FrameKey { comp: 2, ..key(1, 1, 0) }, ItemId(2), Tick::ZERO, RenderOpts::default());
-        f.set_playhead(Some(playhead(10, false)));
-        let mut order = vec![];
-        loop {
-            let mut q = f.queue.lock().unwrap();
-            let Some(i) = q.best() else { break };
-            let j = q.jobs.swap_remove(i);
-            order.push((j.key.comp, j.key.frame));
-        }
-        assert_eq!(order, [(1, 11), (1, 12), (1, 20), (1, 30), (1, 40), (2, 1)]);
-        assert_eq!(f.inflight(), 6, "frame 5, behind the playhead, is no longer in flight");
-    }
-
-    /// The cache is full. A zoom (or preview-resolution) change left the frames of the old
-    /// size to the plain least-recently-shown order, so the frames of the zoom the viewer is back
-    /// at went before the ones of the abandoned zoom. The other size's frames go first, then the
-    /// order is as before.
-    #[test]
-    fn a_size_change_evicts_frames_of_other_sizes_first() {
-        let mut f = Frames::default();
-        f.set_remote(Some(Arc::new(Idle)));
-        f.set_budget(4 * 16);
-        let at = |frame, scale| FrameKey { scale, ..key(1, frame, 0) };
-        // 100% (frames 0..=1) is cached, then 50% (2..=3): the 100% frames are the oldest.
-        for (frame, scale) in [(0, 1000), (1, 1000), (2, 500), (3, 500)] {
-            insert(&f, at(frame, scale));
-        }
-        // A passive viewer at 50% asks for a frame: that doesn't change which size is kept.
-        f.request(&idle_source(), at(9, 500), ItemId(1), Tick::ZERO, RenderOpts::default());
-        // Back at 100%: the viewer asks for frame 4.
-        f.request_urgent(&idle_source(), at(4, 1000), ItemId(1), Tick::ZERO, RenderOpts::default());
-        f.request(&idle_source(), at(10, 500), ItemId(1), Tick::ZERO, RenderOpts::default());
-        insert(&f, at(4, 1000));
-        assert!(
-            f.is_cached(&at(0, 1000)) && f.is_cached(&at(1, 1000)) && !f.is_cached(&at(2, 500)) && f.is_cached(&at(3, 500)),
-            "the first frame of the old size goes, not the cached ones of the current size"
-        );
-        insert(&f, at(5, 1000));
-        assert!(!f.is_cached(&at(3, 500)), "then the last frame of the old size");
-        assert_eq!(f.cached_frames(&at(0, 1000)), [0, 1, 4, 5]);
-        // No other size left: least recently shown first again.
-        insert(&f, at(6, 1000));
-        assert_eq!(f.cached_frames(&at(0, 1000)), [1, 4, 5, 6]);
-    }
-
-    #[test]
-    fn frames_are_keyed_by_content_and_series_are_kept_apart() {
-        let f = Frames::default();
-        insert(&f, key(1, 0, 0));
-        insert(&f, key(2, 0, 0));
-        insert(&f, key(2, 1, 7));
-        // Other content or render options (Draft, shadows…) are another series.
-        assert_eq!(f.cached_frames(&key(2, 0, 0)), vec![0]);
-        assert_eq!(f.cached_frames(&key(2, 0, 7)), vec![1]);
-        // A later revision with the same content finds the frame (an edit elsewhere, an undo).
-        assert!(f.is_cached(&FrameKey { revision: 99, ..key(1, 0, 0) }));
-        assert!(!f.is_cached(&key(3, 0, 0)));
-    }
-
-    #[test]
-    fn live_edits_present_the_newest_completed_revision_without_going_backwards() {
-        let f = Frames::default();
-        let shown = key(1, 0, 0);
-        let newest = key(3, 0, 0);
-        let wanted = key(5, 0, 0);
-        insert(&f, shown);
-        insert(&f, newest);
-        insert(&f, key(2, 0, 0)); // Older worker finishes after the newer one.
-        let displayed = f.get_for_viewer(&wanted, Some(&shown)).unwrap().0;
-        assert_eq!(displayed, newest);
-        assert!(f.get_for_viewer(&wanted, Some(&displayed)).is_none(), "never replay an older completion");
-        insert(&f, wanted);
-        assert_eq!(f.get_for_viewer(&wanted, Some(&displayed)).unwrap().0, wanted, "settle on the exact final edit");
-        // Undo reuses the content of an earlier revision immediately.
-        let undo = FrameKey { revision: 6, ..shown };
-        let reused = f.get_for_viewer(&undo, Some(&wanted)).unwrap().0;
-        assert_eq!(reused.content, shown.content);
-        assert_eq!(reused.revision, undo.revision);
-    }
-
-    #[test]
-    fn live_edits_do_not_substitute_other_times_views_or_render_settings() {
-        let f = Frames::default();
-        let shown = key(1, 0, 0);
-        let wanted = key(3, 0, 0);
-        let done = key(2, 0, 0);
-        for mismatch in [
-            FrameKey { comp: 9, ..done },
-            FrameKey { frame: 1, ..done },
-            FrameKey { scale: 500, ..done },
-            FrameKey { view: 1, ..done },
-            FrameKey { opts: 1, ..done },
-            FrameKey { revision: 4, ..done },
-        ] {
-            f.clear();
-            insert(&f, mismatch);
-            assert!(f.get_for_viewer(&wanted, Some(&shown)).is_none(), "wrong candidate: {mismatch:?}");
-        }
-        f.clear();
-        insert(&f, done);
-        assert!(f.get_for_viewer(&wanted, None).is_none(), "no stale content on opening a viewer");
-        assert!(f.get_for_viewer(&wanted, Some(&FrameKey { comp: 9, ..shown })).is_none());
-        assert!(f.get_for_viewer(&wanted, Some(&FrameKey { frame: 1, ..shown })).is_none());
-        assert!(f.get_for_viewer(&wanted, Some(&FrameKey { view: 1, ..shown })).is_none());
-    }
-
-    #[test]
-    fn an_edit_keeps_the_frames_of_comps_it_does_not_touch() {
-        use effectcraft_engine::Session;
-        use serde_json::json;
-        let mut s = Session::default();
-        let a = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 1})).unwrap()["comp"].as_u64().unwrap());
-        let b = ItemId(s.execute("comp.new", json!({"name": "B", "width": 8, "height": 8, "duration": 1})).unwrap()["comp"].as_u64().unwrap());
-        let f = Frames::default();
-        let at = |s: &Session, c: ItemId| f.content_of(&s.project, s.revision, c);
-        let (a0, b0) = (at(&s, a), at(&s, b));
-        // Edit B: A's content (and frames) stay, B's change.
-        s.execute("layer.newSolid", json!({"comp": b.0, "color": "#ff0000"})).unwrap();
-        assert_eq!(at(&s, a), a0);
-        assert_ne!(at(&s, b), b0);
-        // Undo: B is back to the content its old frames were rendered for.
-        s.execute("edit.undo", json!({})).unwrap();
-        assert_eq!(at(&s, b), b0);
-    }
-
-    #[test]
-    fn a_long_drag_keeps_a_bounded_number_of_states() {
-        use effectcraft_engine::Session;
-        use serde_json::json;
-        let mut s = Session::default();
-        let a = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 1})).unwrap()["comp"].as_u64().unwrap());
-        let f = Frames::default();
-        let mut last = None;
-        for i in 0..200 {
-            s.execute("comp.settings", json!({"width": 8 + i, "merge": "drag"})).unwrap();
-            let k = FrameKey { content: f.content_of(&s.project, s.revision, a), ..key(0, 0, 0) };
-            insert(&f, k);
-            last = Some(k);
-        }
-        // The snapshots and the frames kept stay bounded (a dropped identity's frames go with it,
-        // so a later state that reuses its addresses can't be shown an old frame).
-        assert!(f.keepers.lock().unwrap().1.len() <= MAX_KEEPERS);
-        assert!(f.cache.lock().unwrap().map.len() <= MAX_KEEPERS);
-        assert!(f.is_cached(&last.unwrap()), "the current state's frame stays");
-    }
-
-    #[test]
-    fn an_identity_keeps_its_comps_so_an_edit_in_place_still_changes_it() {
-        use effectcraft_engine::Session;
-        use serde_json::json;
-        let mut s = Session::default();
-        let a = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 1})).unwrap()["comp"].as_u64().unwrap());
-        // A project nothing else holds (no undo history): make_mut would edit the comp in place,
-        // at the same address, if the identity hadn't kept a snapshot holding it.
-        let mut p = Arc::new((*s.project).clone());
-        drop(s);
-        let f = Frames::default();
-        let before = f.content_of(&p, 1, a);
-        let comp = Arc::make_mut(&mut p).comp_mut(a).unwrap();
-        comp.width = 16;
-        assert_ne!(f.content_of(&p, 2, a), before);
-    }
-
-    /// Audio, Lock and Shy (and Hide Shy Layers) don't change pixels: toggling them, in the comp
-    /// or a comp it nests, keeps its frames, also when toggled back (#103).
-    #[test]
-    fn audio_lock_and_shy_switches_keep_the_frames() {
-        use effectcraft_engine::Session;
-        use serde_json::json;
-        let mut s = Session::default();
-        let id = |v: serde_json::Value, k: &str| v[k].as_u64().unwrap();
-        let inner = ItemId(id(s.execute("comp.new", json!({"name": "Inner", "width": 8, "height": 8, "duration": 1})).unwrap(), "comp"));
-        let solid = id(s.execute("layer.newSolid", json!({"comp": inner.0, "color": "#ff0000"})).unwrap(), "layer");
-        let outer = ItemId(id(s.execute("comp.new", json!({"name": "Outer", "width": 8, "height": 8, "duration": 1})).unwrap(), "comp"));
-        let nested = id(s.execute("layer.addItem", json!({"comp": outer.0, "item": inner.0})).unwrap(), "layer");
-        let f = Frames::default();
-        let at = |s: &Session| f.content_of(&s.project, s.revision, outer);
-        let o0 = at(&s);
-        let switch = |s: &mut Session, comp: ItemId, layer: u64, sw: &str, v: bool| {
-            s.execute("layer.setSwitch", json!({"comp": comp.0, "layers": [layer], "switch": sw, "value": v})).unwrap();
-        };
-        for (comp, layer, sw) in [(outer, nested, "audio"), (outer, nested, "lock"), (outer, nested, "shy"), (inner, solid, "audio"), (inner, solid, "shy")] {
-            // Audio off; Lock and Shy on.
-            switch(&mut s, comp, layer, sw, sw != "audio");
-            assert_eq!(at(&s), o0, "{sw} on in {comp:?}");
-        }
-        s.execute("comp.setSwitch", json!({"comp": outer.0, "switch": "hideShy", "value": true})).unwrap();
-        assert_eq!(at(&s), o0, "Hide Shy Layers");
-        switch(&mut s, outer, nested, "audio", true);
-        switch(&mut s, outer, nested, "lock", false);
-        assert_eq!(at(&s), o0, "toggled back");
-        // Switches that change pixels still do.
-        switch(&mut s, inner, solid, "video", false);
-        let o1 = at(&s);
-        assert_ne!(o1, o0, "Video");
-        switch(&mut s, outer, nested, "audio", false);
-        assert_eq!(at(&s), o1, "a mute after a real edit keeps that edit's frames");
-        switch(&mut s, inner, solid, "video", true);
-        assert_ne!(at(&s), o1);
-    }
-
-    /// A cut or trim recaches only the frames of the layers it touched (#1641), and none are
-    /// kept when the change reaches other layers (here a child of the trimmed layer).
-    #[test]
-    fn an_edit_keeps_the_frames_outside_the_layers_it_changed() {
-        use effectcraft_engine::Session;
-        use serde_json::json;
-        let mut s = Session::default();
-        let id = |v: serde_json::Value, k: &str| v[k].as_u64().unwrap();
-        let comp = ItemId(id(s.execute("comp.new", json!({"name": "Edit", "width": 8, "height": 8, "duration": 10})).unwrap(), "comp"));
-        let a = id(s.execute("layer.newSolid", json!({"comp": comp.0, "color": "#ff0000"})).unwrap(), "layer");
-        let b = id(s.execute("layer.newSolid", json!({"comp": comp.0, "color": "#00ff00"})).unwrap(), "layer");
-        s.execute("layer.timing", json!({"layers": [a], "in": 0, "out": 4})).unwrap();
-        s.execute("layer.timing", json!({"layers": [b], "in": 4, "out": 10})).unwrap();
-        let (fr, out) = s.project.comp(comp).map(|c| (c.frame_rate, c.layers.iter().find(|l| l.id.0 == a).unwrap().out_point)).unwrap();
-        let frames: Vec<i64> = (0..fr.frame_at(Tick::from_seconds_f64(10.0))).collect();
-        let f = Frames::default();
-        let cache_all = |s: &Session| {
-            let c = f.content_of(&s.project, s.revision, comp);
-            frames.iter().for_each(|&n| insert(&f, key(c, n, 0)));
-            c
-        };
-        let cached = |c: u64| frames.iter().filter(|&&n| f.is_cached(&key(c, n, 0))).copied().collect::<Vec<_>>();
-        let before = cache_all(&s);
-        s.execute("time.set", json!({"time": 2.0})).unwrap();
-        s.execute("edit.splitLayer", json!({"layers": [a]})).unwrap();
-        let after = f.content_of(&s.project, s.revision, comp);
-        assert_ne!(after, before);
-        let kept: Vec<i64> = (fr.frame_at(out) + 2..frames.len() as i64).collect();
-        assert_eq!(cached(after), kept, "the cut layer's frames (and one either side) render again; the rest stay");
-
-        s.execute("layer.setParent", json!({"layers": [b], "parent": a})).unwrap();
-        let parented = cache_all(&s);
-        s.execute("layer.timing", json!({"layers": [a], "out": 1})).unwrap();
-        assert_eq!(cached(f.content_of(&s.project, s.revision, comp)), Vec::<i64>::new(), "the trimmed layer's child moves everywhere");
-        assert_eq!(cached(parented).len(), frames.len(), "the earlier frames stay for undo");
-    }
-
-    /// Every frame an edit keeps renders as a fresh render of the edited project does: Solo
-    /// hides the other layers at every frame, and a camera reaches the frames whose shutter
-    /// samples it (#1641 review).
-    #[test]
-    fn the_frames_an_edit_keeps_match_a_fresh_render() {
-        use effectcraft_engine::Session;
-        use effectcraft_engine::render::NoFootage;
-        use serde_json::json;
-        // Cache every frame of `comp`, run `edit`, check the frames kept against fresh renders.
-        fn kept(s: &mut Session, comp: ItemId, edit: serde_json::Value) -> Vec<i64> {
-            let (fr, n) = s.project.comp(comp).map(|c| (c.frame_rate, c.frame_rate.frame_at(c.duration))).unwrap();
-            let f = Frames::default();
-            let before = f.content_of(&s.project, s.revision, comp);
-            (0..n).for_each(|i| insert(&f, key(before, i, 0)));
-            let old = s.project.clone();
-            s.execute(edit["cmd"].as_str().unwrap(), edit["params"].clone()).unwrap();
-            let after = f.content_of(&s.project, s.revision, comp);
-            let kept: Vec<i64> = (0..n).filter(|&i| f.is_cached(&key(after, i, 0))).collect();
-            let render = |p, i| Renderer::new(p, &NoFootage, RenderOpts::default()).comp_frame(comp, fr.tick_of(i));
-            for &i in &kept {
-                assert_eq!(render(&old, i), render(&s.project, i), "kept frame {i} draws other pixels now");
-            }
-            kept
-        }
-        let id = |v: serde_json::Value, k: &str| v[k].as_u64().unwrap();
-        let mut s = Session::default();
-
-        // Solo on a 2–3 s layer hides the 10 s underlay everywhere; turning it off shows it again.
-        let comp = ItemId(id(s.execute("comp.new", json!({"name": "Solo", "width": 8, "height": 8, "duration": 10})).unwrap(), "comp"));
-        s.execute("layer.newSolid", json!({"comp": comp.0, "color": "#ff0000"})).unwrap();
-        let short = id(s.execute("layer.newSolid", json!({"comp": comp.0, "color": "#00ff00"})).unwrap(), "layer");
-        s.execute("layer.timing", json!({"layers": [short], "in": 2, "out": 3})).unwrap();
-        let solo = |on: bool| json!({"cmd": "layer.setSwitch", "params": {"layers": [short], "switch": "solo", "value": on}});
-        assert_eq!(kept(&mut s, comp, solo(true)), Vec::<i64>::new());
-        assert_eq!(kept(&mut s, comp, solo(false)), Vec::<i64>::new());
-
-        // A 2–3 s camera over a 4 s motion-blurred 3D layer, shutter 720° at phase 360°: a frame
-        // samples 1 to 3 frames ahead, so moving the camera reaches the 3 frames before it.
-        let comp = ItemId(id(
-            s.execute("comp.new", json!({"name": "Cam", "width": 16, "height": 16, "duration": 4, "frameRate": 30, "shutterAngle": 720, "shutterPhase": 360}))
-                .unwrap(),
-            "comp",
-        ));
-        let plane = id(s.execute("layer.newSolid", json!({"comp": comp.0, "color": "#ff0000"})).unwrap(), "layer");
-        for sw in ["threeD", "motionBlur"] {
-            s.execute("layer.setSwitch", json!({"layers": [plane], "switch": sw, "value": true})).unwrap();
-        }
-        let cam = id(s.execute("layer.newCamera", json!({"comp": comp.0})).unwrap(), "layer");
-        s.execute("layer.timing", json!({"layers": [cam], "in": 2, "out": 3})).unwrap();
-        let moved =
-            kept(&mut s, comp, json!({"cmd": "prop.set", "params": {"comp": comp.0, "layer": cam, "path": "transform/position", "value": [40, 8, -30]}}));
-        assert!(moved.contains(&0) && moved.contains(&100), "frames far from the camera stay: {moved:?}");
-        assert!(!(56..=91).any(|f| moved.contains(&f)), "frames whose shutter samples the camera render again: {moved:?}");
-    }
-
-    #[test]
-    fn short_solid_additions_and_removals_keep_unaffected_frames() {
-        use effectcraft_engine::Session;
-        use serde_json::json;
-        let mut s = Session::default();
-        let comp = ItemId(s.execute("comp.new", json!({"width": 8, "height": 8, "frameRate": 30, "duration": 20})).unwrap()["comp"].as_u64().unwrap());
-        s.execute("layer.newSolid", json!({"color": "#ff0000"})).unwrap();
-        let f = Frames::default();
-        let cache_all = |s: &Session| {
-            let content = f.content_of(&s.project, s.revision, comp);
-            (0..600).for_each(|n| insert(&f, key(content, n, 0)));
-        };
-        let cached = |s: &Session| f.cached_frames(&key(f.content_of(&s.project, s.revision, comp), 0, 0));
-        // 2–3 s, a quarter frame of the default shutter and a frame of rounding either side.
-        let kept: Vec<i64> = (0..=57).chain(92..600).collect();
-        cache_all(&s);
-        let solid = s.execute("layer.newSolid", json!({"color": "#00ff00"})).unwrap()["layer"].as_u64().unwrap();
-        s.execute("layer.timing", json!({"layers": [solid], "in": 2, "out": 3})).unwrap();
-        assert_eq!(cached(&s), kept, "adding a source invalidates only frames 58..=91");
-        cache_all(&s);
-        s.execute("edit.undo", json!({})).unwrap();
-        s.execute("edit.undo", json!({})).unwrap();
-        assert_eq!(cached(&s), (0..600).collect::<Vec<_>>(), "undoing the addition restores every frame");
-        s.execute("edit.redo", json!({})).unwrap();
-        s.execute("edit.redo", json!({})).unwrap();
-        assert_eq!(cached(&s), (0..600).collect::<Vec<_>>(), "redoing the addition restores every frame");
-        s.execute("edit.clear", json!({"layers": [solid]})).unwrap();
-        assert_eq!(cached(&s), kept, "removing its layer invalidates the same span");
-    }
-
-    #[test]
-    fn adding_a_source_does_not_hide_changes_to_existing_dependencies() {
-        use effectcraft_engine::Session;
-        use serde_json::json;
-        for (command, params) in [
-            ("layer.settings", json!({"comp": "Outer", "layer": "Underlay", "color": "#0000ff"})),
-            ("prop.set", json!({"comp": "Inner", "layer": "Inner solid", "path": "transform/opacity", "value": 40})),
-        ] {
-            let mut s = Session::default();
-            let comp = ItemId(
-                s.execute("comp.new", json!({"name": "Outer", "width": 8, "height": 8, "frameRate": 30, "duration": 20})).unwrap()["comp"].as_u64().unwrap(),
-            );
-            s.execute("layer.newSolid", json!({"name": "Underlay", "color": "#ff0000"})).unwrap();
-            s.execute("comp.new", json!({"name": "Inner", "width": 8, "height": 8, "duration": 20})).unwrap();
-            s.execute("layer.newSolid", json!({"name": "Inner solid", "color": "#00ff00"})).unwrap();
-            s.execute("comp.open", json!({"comp": "Outer"})).unwrap();
-            s.execute("layer.addItem", json!({"item": "Inner"})).unwrap();
-            let f = Frames::default();
-            let before = f.content_of(&s.project, s.revision, comp);
-            (0..600).for_each(|n| insert(&f, key(before, n, 0)));
-            s.execute(command, params).unwrap();
-            let solid = s.execute("layer.newSolid", json!({"color": "#ffffff"})).unwrap()["layer"].as_u64().unwrap();
-            s.execute("layer.timing", json!({"layers": [solid], "in": 2, "out": 3})).unwrap();
-            let after = f.content_of(&s.project, s.revision, comp);
-            assert!(f.cached_frames(&key(after, 0, 0)).is_empty(), "{command} changes pixels outside the added layer");
-        }
-    }
-
-    #[test]
-    fn markers_keep_the_frames() {
-        use effectcraft_engine::Session;
-        use serde_json::json;
-        let mut s = Session::default();
-        let id = |v: serde_json::Value, k: &str| v[k].as_u64().unwrap();
-        let outer = ItemId(id(s.execute("comp.new", json!({"name": "Outer", "width": 8, "height": 8, "duration": 1})).unwrap(), "comp"));
-        let solid = id(s.execute("layer.newSolid", json!({"comp": outer.0, "color": "#ff0000"})).unwrap(), "layer");
-        let f = Frames::default();
-        let at = |s: &Session| f.content_of(&s.project, s.revision, outer);
-        let o0 = at(&s);
-        s.execute("layer.addMarker", json!({"comp": outer.0, "layers": [solid], "time": 0.5, "comment": "beat"})).unwrap();
-        assert_eq!(at(&s), o0, "a marker changes no pixels, so it keeps the frames");
-    }
-
-    #[test]
-    fn markers_count_when_an_expression_can_read_them() {
-        use effectcraft_engine::Session;
-        use serde_json::json;
-        let mut s = Session::default();
-        let id = |v: serde_json::Value, k: &str| v[k].as_u64().unwrap();
-        let outer = ItemId(id(s.execute("comp.new", json!({"name": "Outer", "width": 8, "height": 8, "duration": 1})).unwrap(), "comp"));
-        let solid = id(s.execute("layer.newSolid", json!({"comp": outer.0, "color": "#ff0000"})).unwrap(), "layer");
-        s.execute("prop.setExpression", json!({"comp": outer.0, "layer": solid, "path": "transform/opacity", "expression": "1"})).unwrap();
-        let f = Frames::default();
-        let at = |s: &Session| f.content_of(&s.project, s.revision, outer);
-        let o0 = at(&s);
-        s.execute("layer.addMarker", json!({"comp": outer.0, "layers": [solid], "time": 0.5, "comment": "beat"})).unwrap();
-        assert_ne!(at(&s), o0, "an expression can read the marker, so the frames change");
-    }
-}
+mod tests;
diff --git a/crates/ui-egui/src/frames/tests.rs b/crates/ui-egui/src/frames/tests.rs
new file mode 100644
index 00000000..eae81419
--- /dev/null
+++ b/crates/ui-egui/src/frames/tests.rs
@@ -0,0 +1,928 @@
+use super::*;
+
+struct ProbeDisk {
+    keys: Mutex<HashSet<u128>>,
+    probes: std::sync::atomic::AtomicUsize,
+}
+
+impl RemoteFrames for ProbeDisk {
+    fn slots(&self) -> usize {
+        0
+    }
+
+    fn disk(&self) -> bool {
+        true
+    }
+
+    fn disk_contains(&self, key: u128) -> bool {
+        self.probes.fetch_add(1, Ordering::Relaxed);
+        self.keys.lock().unwrap().contains(&key)
+    }
+
+    fn start(&self, _: RemoteJob, _: RemoteDone) {}
+}
+
+fn disk_fixture(stored_frames: &[i64]) -> (Frames, RenderSource, FrameKey, RenderOpts, Arc<ProbeDisk>, u128) {
+    let mut session = effectcraft_engine::Session::default();
+    session.execute("comp.new", serde_json::json!({"width": 32, "height": 18, "duration": 1})).unwrap();
+    let comp = session.active_comp_id().unwrap();
+    let opts = RenderOpts::default();
+    let content = 1234;
+    let mut base = key(1, 0, opts_hash(&opts));
+    base.revision = 7;
+    base.comp = comp.0;
+    let disk = Arc::new(ProbeDisk { keys: Mutex::new(HashSet::new()), probes: 0.into() });
+    disk.keys.lock().unwrap().extend(stored_frames.iter().map(|frame| disk_cache::frame_key(content, *frame, base.scale, base.view ^ opts_hash(&opts))));
+    let mut frames = Frames::default();
+    frames.set_remote(Some(disk.clone()));
+    frames.content_keys.lock().unwrap().insert((base.revision, base.comp, 0), content);
+    let source = RenderSource {
+        project: session.project.clone(),
+        footage: session.footage.clone(),
+        expr: None,
+        layer_cache: Arc::default(),
+        gpu: None,
+        gpu_display: false,
+        disk: None,
+    };
+    (frames, source, base, opts, disk, content)
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+#[test]
+fn disk_indicator_does_not_hash_on_ui_thread_and_coalesces_edits() {
+    use std::sync::mpsc;
+    use std::time::{Duration, Instant};
+    struct Disk(u128);
+    impl RemoteFrames for Disk {
+        fn slots(&self) -> usize {
+            1
+        }
+        fn disk(&self) -> bool {
+            true
+        }
+        fn disk_contains(&self, key: u128) -> bool {
+            self.0 == key
+        }
+        fn start(&self, _: RemoteJob, done: RemoteDone) {
+            done(Err("test has no renderer".into()));
+        }
+    }
+    let mut s = effectcraft_engine::Session::default();
+    s.execute("comp.new", serde_json::json!({"width":32,"height":18,"duration":1})).unwrap();
+    let cid = s.active_comp_id().unwrap();
+    let opts = RenderOpts::default();
+    let stored = disk_cache::frame_key(disk_cache::comp_content_key(&s.project, cid), 2, 1000, opts_hash(&opts));
+    let mut frames = Frames { pool: Some(rayon::ThreadPoolBuilder::new().num_threads(1).build().unwrap()), ..Default::default() };
+    frames.set_remote(Some(Arc::new(Disk(stored))));
+    let (entered, started) = mpsc::channel();
+    let (release, wait) = mpsc::channel();
+    frames.pool.as_ref().unwrap().spawn(move || {
+        entered.send(()).unwrap();
+        wait.recv_timeout(Duration::from_secs(5)).unwrap();
+    });
+    started.recv_timeout(Duration::from_secs(3)).unwrap();
+    let src = RenderSource {
+        project: s.project.clone(),
+        footage: s.footage.clone(),
+        expr: None,
+        layer_cache: Arc::default(),
+        gpu: None,
+        gpu_display: false,
+        disk: None,
+    };
+    let mut base = key(1, 0, 0);
+    base.comp = cid.0;
+    for revision in 1..50 {
+        base.revision = revision;
+        assert!(frames.disk_frames(&src, &base, 0..30, &opts).is_empty());
+    }
+    assert!(frames.content_keys.lock().unwrap().is_empty(), "painting computed a content hash while the worker was blocked");
+    assert_eq!(frames.content_key_jobs.lock().unwrap().pending.len(), 1);
+    release.send(()).unwrap();
+    let until = Instant::now() + Duration::from_secs(3);
+    while !frames.content_keys.lock().unwrap().contains_key(&(base.revision, base.comp, 0)) {
+        assert!(Instant::now() < until);
+        std::thread::sleep(Duration::from_millis(1));
+    }
+    assert_eq!(frames.disk_frames(&src, &base, 0..30, &opts), vec![2], "the blue indicator must return once its key is ready");
+    assert_eq!(frames.content_keys.lock().unwrap().len(), 1, "superseded revisions were hashed");
+}
+
+#[test]
+fn disk_indicator_range_tracks_live_membership() {
+    let (frames, src, base, opts, disk, _) = disk_fixture(&[10, 12]);
+    assert_eq!(frames.disk_frames(&src, &base, 10..13, &opts), vec![10, 12]);
+    assert_eq!(disk.probes.load(Ordering::Relaxed), 3);
+
+    disk.keys.lock().unwrap().insert(disk_cache::frame_key(1234, 11, base.scale, base.view ^ opts_hash(&opts)));
+    assert_eq!(frames.disk_frames(&src, &base, 10..13, &opts), vec![10, 11, 12]);
+
+    insert(&frames, FrameKey { frame: 11, ..base });
+    disk.probes.store(0, Ordering::Relaxed);
+    assert_eq!(frames.disk_frames(&src, &base, 10..13, &opts), vec![10, 12]);
+    assert_eq!(disk.probes.load(Ordering::Relaxed), 2);
+
+    disk.keys.lock().unwrap().remove(&disk_cache::frame_key(1234, 12, base.scale, base.view ^ opts_hash(&opts)));
+    assert_eq!(frames.disk_frames(&src, &base, 10..13, &opts), vec![10]);
+
+    let mut revised = base;
+    revised.revision += 1;
+    frames.content_keys.lock().unwrap().insert((revised.revision, revised.comp, 0), 5678);
+    assert!(frames.disk_frames(&src, &revised, 10..13, &opts).is_empty());
+
+    let changed = FrameKey { scale: base.scale + 1, ..base };
+    assert!(frames.disk_frames(&src, &changed, 10..13, &opts).is_empty());
+    let changed = FrameKey { view: base.view + 1, ..base };
+    assert!(frames.disk_frames(&src, &changed, 10..13, &opts).is_empty());
+    assert!(frames.disk_frames(&src, &base, 10..13, &RenderOpts { draft: true, ..opts }).is_empty());
+}
+
+#[test]
+fn disk_indicator_range_is_bounded() {
+    let (frames, src, base, opts, disk, _) = disk_fixture(&[0, 1, 99_999]);
+    assert_eq!(frames.disk_frames(&src, &base, -5..2, &opts), vec![0, 1]);
+    assert_eq!(disk.probes.load(Ordering::Relaxed), 2);
+    disk.probes.store(0, Ordering::Relaxed);
+    assert_eq!(frames.disk_frames(&src, &base, 99_999..i64::MAX, &opts), vec![99_999]);
+    assert_eq!(disk.probes.load(Ordering::Relaxed), 1);
+    disk.probes.store(0, Ordering::Relaxed);
+    assert!(frames.disk_frames(&src, &base, 2..2, &opts).is_empty());
+    // Written as a struct literal: `3..2` trips clippy::reversed_empty_ranges.
+    let reversed = std::ops::Range { start: 3, end: 2 };
+    assert!(frames.disk_frames(&src, &base, reversed, &opts).is_empty());
+    assert_eq!(disk.probes.load(Ordering::Relaxed), 0);
+}
+
+/// Frames larger than the texture limit are averaged down by a whole factor (#201: an
+/// 11000×2200 comp at Full resolution against an 8192 limit).
+#[test]
+fn frames_over_the_texture_limit_are_averaged_down() {
+    assert_eq!(fitted_size([11000, 2200], 8192), [5500, 1100]);
+    assert_eq!(fitted_size([8192, 100], 8192), [8192, 100]);
+    assert_eq!(fitted_size([30000, 30000], 16384), [15000, 15000]);
+    assert_eq!(fitted_size([0, 0], 0), [0, 0]);
+    // 5×2 (three columns of white, then black) into 2 px: 3×2 blocks (the last one 2×2).
+    let w = egui::Color32::WHITE;
+    let b = egui::Color32::from_rgba_premultiplied(0, 0, 0, 255);
+    let img = egui::ColorImage::new([5, 2], vec![w, w, w, b, b, w, w, w, b, b]);
+    let out = fit_texture(img.clone(), 2);
+    assert_eq!(out.size, [2, 1]);
+    assert_eq!(out.pixels, vec![w, b]);
+    assert_eq!(fit_texture(img.clone(), 5).pixels, img.pixels);
+    let mixed = fit_texture(egui::ColorImage::new([2, 1], vec![w, b]), 1);
+    assert_eq!(mixed.pixels, vec![egui::Color32::from_rgba_premultiplied(128, 128, 128, 255)]);
+}
+
+#[test]
+fn retirement_reaches_existing_workers_and_keeps_cpu_frames_and_completion_live() {
+    let frames = Frames::default();
+    let worker = frames.worker();
+    let first = key(1, 0, 0);
+    insert(&frames, first);
+    frames.retire_gpu();
+    assert!(worker.gpu_retired.load(Ordering::Acquire), "already queued workers share retirement");
+    assert!(frames.is_cached(&first), "healthy materialized CPU frames survive");
+    let next = key(1, 1, 0);
+    frames.inflight.lock().unwrap().insert(next);
+    frames.queue.lock().unwrap().running.insert(next);
+    worker.finish_key(next, false, img(), web_time::Instant::now());
+    assert!(frames.is_cached(&next), "CPU retry can still publish");
+    assert_eq!(frames.inflight(), 0);
+    assert!(frames.queue.lock().unwrap().running.is_empty());
+}
+
+fn key(content: u64, frame: i64, opts: u64) -> FrameKey {
+    FrameKey { revision: content, content, comp: 1, frame, scale: 1000, view: 0, opts }
+}
+
+fn img() -> FrameImage {
+    FrameImage::Cpu(Arc::new(egui::ColorImage::new([2, 2], vec![egui::Color32::BLACK; 4])))
+}
+
+fn insert(f: &Frames, k: FrameKey) {
+    f.cache.lock().unwrap().insert(k, img());
+}
+
+/// A frame whose render panics (a GPU out of memory used to, on every frame thread) is
+/// released, not left "in progress" forever, so the viewer can ask for it again (#106).
+#[test]
+fn a_frame_whose_render_panics_is_released() {
+    use effectcraft_engine::Session;
+    use effectcraft_engine::project::{Footage, FootageKind};
+    use effectcraft_engine::render::Image;
+    use serde_json::json;
+    use std::sync::atomic::{AtomicUsize, Ordering};
+    #[derive(Default)]
+    struct Explodes(AtomicUsize);
+    impl FootageSource for Explodes {
+        fn frame(&self, _: ItemId, _: &Footage, _: Tick) -> Option<Arc<Image>> {
+            self.0.fetch_add(1, Ordering::SeqCst);
+            panic!("a decoder bug");
+        }
+    }
+    let mut s = Session::default();
+    let cid = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 1})).unwrap()["comp"].as_u64().unwrap());
+    let clip = Footage { kind: FootageKind::Still, width: 8, height: 8, has_video: true, ..Default::default() };
+    let item = Arc::make_mut(&mut s.project).add_item("clip.png", Default::default(), None, ItemKind::Footage(clip));
+    s.execute("layer.addItem", json!({"item": item.0})).unwrap();
+    let footage = Arc::new(Explodes::default());
+    let src = RenderSource {
+        project: s.project.clone(),
+        footage: footage.clone(),
+        expr: None,
+        layer_cache: Arc::default(),
+        gpu: None,
+        gpu_display: false,
+        disk: None,
+    };
+    let f = Frames::default();
+    let key = FrameKey { revision: s.revision, content: f.content_of(&s.project, s.revision, cid), ..key(0, 0, 0) };
+    let key = FrameKey { comp: cid.0, ..key };
+    f.request(&src, key, cid, Tick::ZERO, RenderOpts::default());
+    for _ in 0..1000 {
+        if f.inflight() == 0 {
+            break;
+        }
+        std::thread::sleep(std::time::Duration::from_millis(5));
+    }
+    assert!(footage.0.load(Ordering::SeqCst) > 0, "the render reached the footage");
+    assert_eq!(f.inflight(), 0, "released");
+    assert!(!f.is_cached(&key));
+}
+
+/// #647: a pool thread waiting inside a render (on a parallel loop) never starts another
+/// frame render on top of it. Dragging a layer queues a frame every UI frame; renders used to
+/// nest on every thread, each holding its buffers, until memory ran out.
+#[test]
+fn a_waiting_render_never_starts_another_on_its_thread() {
+    use effectcraft_engine::Session;
+    use effectcraft_engine::project::{Footage, FootageKind};
+    use effectcraft_engine::render::Image;
+    use effectcraft_engine::time::FrameRate;
+    use serde_json::json;
+    use std::cell::Cell;
+    use std::sync::atomic::AtomicUsize;
+    thread_local! {
+        static DEPTH: Cell<usize> = const { Cell::new(0) };
+    }
+    /// A decoder that works in parallel, as the renderer does: its thread joins the loop and
+    /// may wait for the parts other threads took.
+    #[derive(Default)]
+    struct Parallel {
+        calls: AtomicUsize,
+        deepest: AtomicUsize,
+    }
+    impl FootageSource for Parallel {
+        fn frame(&self, _: ItemId, _: &Footage, _: Tick) -> Option<Arc<Image>> {
+            let d = DEPTH.get() + 1;
+            DEPTH.set(d);
+            self.deepest.fetch_max(d, Ordering::SeqCst);
+            self.calls.fetch_add(1, Ordering::SeqCst);
+            (0..64).into_par_iter().for_each(|_| std::thread::sleep(std::time::Duration::from_millis(1)));
+            DEPTH.set(d - 1);
+            Some(Arc::new(Image::new(4, 4)))
+        }
+    }
+    let mut s = Session::default();
+    let cid = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 10})).unwrap()["comp"].as_u64().unwrap());
+    let clip = Footage {
+        kind: FootageKind::Video,
+        width: 4,
+        height: 4,
+        has_video: true,
+        frame_rate: FrameRate::FPS_30,
+        duration: Tick::from_seconds_f64(10.0),
+        ..Default::default()
+    };
+    let item = Arc::make_mut(&mut s.project).add_item("clip.mov", Default::default(), None, ItemKind::Footage(clip));
+    s.execute("layer.addItem", json!({"item": item.0})).unwrap();
+    let footage = Arc::new(Parallel::default());
+    let src = RenderSource {
+        project: s.project.clone(),
+        footage: footage.clone(),
+        expr: None,
+        layer_cache: Arc::default(),
+        gpu: None,
+        gpu_display: false,
+        disk: None,
+    };
+    let f = Frames::default();
+    let content = f.content_of(&s.project, s.revision, cid);
+    let frames = 60;
+    for frame in 0..frames {
+        let key = FrameKey { revision: s.revision, content, comp: cid.0, frame, scale: 1000, view: 0, opts: 0 };
+        f.request(&src, key, cid, FrameRate::FPS_30.tick_of(frame), RenderOpts::default());
+    }
+    for _ in 0..4000 {
+        if f.inflight() == 0 {
+            break;
+        }
+        std::thread::sleep(std::time::Duration::from_millis(5));
+    }
+    assert_eq!(f.inflight(), 0, "every queued frame rendered");
+    assert!(footage.calls.load(Ordering::SeqCst) >= frames as usize);
+    assert_eq!(footage.deepest.load(Ordering::SeqCst), 1, "renders nested on a waiting thread");
+}
+
+/// #329: scrubbing a long movie, the viewer frame of every step the pointer passed started
+/// rendering and seeked the movie's decoder in turn; the frame under the pointer waited for
+/// all of them. A newer viewer frame of another time calls off the one rendering, which is
+/// not cached (its footage may be missing).
+#[test]
+fn a_newer_viewer_frame_calls_off_the_one_rendering() {
+    use effectcraft_engine::Session;
+    use effectcraft_engine::project::{Footage, FootageKind};
+    use effectcraft_engine::render::Image;
+    use effectcraft_engine::time::FrameRate;
+    use serde_json::json;
+    use std::cell::RefCell;
+    thread_local! {
+        static CANCEL: RefCell<Option<Arc<AtomicBool>>> = const { RefCell::new(None) };
+    }
+    /// A movie whose first frames take a long seek, which a called-off read gives up.
+    #[derive(Default)]
+    struct Seeking {
+        seeking: AtomicBool,
+        called_off: AtomicBool,
+    }
+    impl FootageSource for Seeking {
+        fn cancellable(&self, cancel: &Arc<AtomicBool>, f: &mut dyn FnMut()) {
+            let prev = CANCEL.replace(Some(cancel.clone()));
+            f();
+            CANCEL.set(prev);
+        }
+        fn frame(&self, _: ItemId, _: &Footage, t: Tick) -> Option<Arc<Image>> {
+            if t < Tick::from_seconds_f64(0.25) {
+                self.seeking.store(true, Ordering::SeqCst);
+                for _ in 0..1000 {
+                    if CANCEL.with_borrow(|c| c.as_ref().is_some_and(|c| c.load(Ordering::SeqCst))) {
+                        self.called_off.store(true, Ordering::SeqCst);
+                        return None;
+                    }
+                    std::thread::sleep(std::time::Duration::from_millis(5));
+                }
+            }
+            Some(Arc::new(Image::new(4, 4)))
+        }
+    }
+    let mut s = Session::default();
+    let cid = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 10})).unwrap()["comp"].as_u64().unwrap());
+    let clip = Footage {
+        kind: FootageKind::Video,
+        width: 4,
+        height: 4,
+        has_video: true,
+        frame_rate: FrameRate::FPS_30,
+        duration: Tick::from_seconds_f64(10.0),
+        ..Default::default()
+    };
+    let item = Arc::make_mut(&mut s.project).add_item("clip.mov", Default::default(), None, ItemKind::Footage(clip));
+    s.execute("layer.addItem", json!({"item": item.0})).unwrap();
+    let footage = Arc::new(Seeking::default());
+    let src = RenderSource {
+        project: s.project.clone(),
+        footage: footage.clone(),
+        expr: None,
+        layer_cache: Arc::default(),
+        gpu: None,
+        gpu_display: false,
+        disk: None,
+    };
+    let f = Frames::default();
+    let content = f.content_of(&s.project, s.revision, cid);
+    let key = |frame| FrameKey { revision: s.revision, content, comp: cid.0, frame, scale: 1000, view: 0, opts: 0 };
+    f.request_urgent(&src, key(0), cid, Tick::ZERO, RenderOpts::default());
+    for _ in 0..1000 {
+        if footage.seeking.load(Ordering::SeqCst) {
+            break;
+        }
+        std::thread::sleep(std::time::Duration::from_millis(2));
+    }
+    assert!(footage.seeking.load(Ordering::SeqCst), "the first frame's render reached the footage");
+    f.request_urgent(&src, key(150), cid, FrameRate::FPS_30.tick_of(150), RenderOpts::default());
+    for _ in 0..1000 {
+        if f.inflight() == 0 {
+            break;
+        }
+        std::thread::sleep(std::time::Duration::from_millis(5));
+    }
+    assert!(footage.called_off.load(Ordering::SeqCst), "the superseded frame's seek ran on");
+    assert!(f.is_cached(&key(150)), "the newest frame rendered");
+    assert!(!f.is_cached(&key(0)), "a called-off frame is not cached");
+    assert_eq!(f.inflight(), 0, "released");
+}
+
+/// #284: scrubbing asks for a viewer frame at every step; a newer one drops the comp's viewer
+/// frames still waiting (they would all render first), but not prefetch frames or another
+/// comp's viewer frame.
+#[test]
+fn a_newer_viewer_frame_drops_the_ones_still_waiting() {
+    /// Starts nothing, so every request stays queued.
+    struct Idle;
+    impl RemoteFrames for Idle {
+        fn slots(&self) -> usize {
+            0
+        }
+        fn start(&self, _: RemoteJob, _: RemoteDone) {}
+    }
+    let mut f = Frames::default();
+    f.set_remote(Some(Arc::new(Idle)));
+    let src = RenderSource {
+        project: Arc::default(),
+        footage: Arc::new(effectcraft_engine::render::NoFootage),
+        expr: None,
+        layer_cache: Arc::default(),
+        gpu: None,
+        gpu_display: false,
+        disk: None,
+    };
+    let request = |k: FrameKey, urgent: bool| f.request_with(&src, k, ItemId(k.comp), Tick::ZERO, RenderOpts::default(), urgent);
+    let other = FrameKey { comp: 2, ..key(1, 0, 0) };
+    request(other, true);
+    request(key(1, 20, 0), false);
+    for frame in 0..10 {
+        request(key(1, frame, 0), true);
+    }
+    let mut queued: Vec<(u64, i64, bool)> = f.queue.lock().unwrap().jobs.iter().map(|j| (j.key.comp, j.key.frame, j.urgent)).collect();
+    queued.sort();
+    assert_eq!(queued, [(1, 9, true), (1, 20, false), (2, 0, false)]);
+    assert_eq!(f.inflight(), 3, "dropped frames aren't in flight: the viewer can ask again");
+}
+
+/// Each time the GPU runs out of memory, half as many GPU frames are kept, down to a floor.
+#[test]
+fn running_out_of_video_memory_halves_the_gpu_frame_budget() {
+    let f = Frames::default();
+    let mut c = f.cache.lock().unwrap();
+    assert_eq!(c.gpu_budget, GPU_BUDGET);
+    c.gpu_out_of_memory();
+    assert_eq!(c.gpu_budget, GPU_BUDGET / 2);
+    for _ in 0..20 {
+        c.gpu_out_of_memory();
+    }
+    assert_eq!(c.gpu_budget, MIN_GPU_BUDGET);
+}
+
+#[test]
+fn least_recently_shown_frames_go_first() {
+    let f = Frames::default();
+    f.set_budget(3 * 16);
+    for i in 0..3 {
+        insert(&f, key(1, i, 0));
+    }
+    // Frame 0 is shown again, so frame 1 is now the oldest.
+    assert!(f.get(&key(1, 0, 0)).is_some());
+    insert(&f, key(1, 3, 0));
+    assert!(f.is_cached(&key(1, 0, 0)) && !f.is_cached(&key(1, 1, 0)));
+    assert!(f.is_cached(&key(1, 2, 0)) && f.is_cached(&key(1, 3, 0)));
+}
+
+fn playhead(cur: i64, looping: bool) -> Playhead {
+    Playhead { series: key(1, 0, 0), cur, start: 0, end: 99, step: 1, looping }
+}
+
+/// #595: a playing preview's cache is full. The frames just ahead of the playhead were
+/// rendered before the ones just shown, so plain LRU evicted them first and the preview
+/// played into a gap. Frames the preview no longer reaches go first, then the ones it
+/// reaches last.
+#[test]
+fn a_full_cache_keeps_the_frames_just_ahead_of_the_playhead() {
+    let f = Frames::default();
+    f.set_budget(4 * 16);
+    // Prefetch rendered 11..=13, then 10 was shown (the most recently used).
+    for i in [11, 12, 13, 10] {
+        insert(&f, key(1, i, 0));
+    }
+    let cached = |f: &Frames| f.cached_frames(&key(1, 0, 0));
+    f.set_playhead(Some(playhead(10, false)));
+    // The next frame rendered is the one the preview reaches last: the frames just ahead stay.
+    insert(&f, key(1, 14, 0));
+    assert_eq!(cached(&f), [10, 11, 12, 13]);
+    // Without looping, a frame behind the playhead goes before any frame ahead of it.
+    f.set_playhead(Some(playhead(12, false)));
+    insert(&f, key(1, 14, 0));
+    assert_eq!(cached(&f), [10, 12, 13, 14]);
+    // Looping, the frame just behind is the one reached last.
+    f.set_playhead(Some(playhead(13, true)));
+    insert(&f, key(1, 0, 0));
+    assert_eq!(cached(&f), [0, 10, 13, 14]);
+    // Stopped: least recently shown first again.
+    f.set_playhead(None);
+    insert(&f, key(1, 50, 0));
+    assert!(!f.is_cached(&key(1, 13, 0)) && f.is_cached(&key(1, 50, 0)));
+}
+
+/// A frame source that queues jobs and never renders them: the tests check the queue.
+struct Idle;
+impl RemoteFrames for Idle {
+    fn slots(&self) -> usize {
+        0
+    }
+    fn start(&self, _: RemoteJob, _: RemoteDone) {}
+}
+
+fn idle_source() -> RenderSource {
+    RenderSource {
+        project: Arc::default(),
+        footage: Arc::new(effectcraft_engine::render::NoFootage),
+        expr: None,
+        layer_cache: Arc::default(),
+        gpu: None,
+        gpu_display: false,
+        disk: None,
+    }
+}
+
+/// #595: prefetch renders the frames the preview reaches first, whatever order they were
+/// asked for in (a frame evicted and asked for again waited behind every frame further
+/// ahead); queued frames the preview no longer reaches are dropped and not left in flight.
+#[test]
+fn prefetch_renders_the_frames_the_playhead_reaches_first() {
+    let mut f = Frames::default();
+    f.set_remote(Some(Arc::new(Idle)));
+    let src = idle_source();
+    for frame in [40, 30, 20, 5, 12, 11] {
+        f.request(&src, key(1, frame, 0), ItemId(1), Tick::ZERO, RenderOpts::default());
+    }
+    f.request(&src, FrameKey { comp: 2, ..key(1, 1, 0) }, ItemId(2), Tick::ZERO, RenderOpts::default());
+    f.set_playhead(Some(playhead(10, false)));
+    let mut order = vec![];
+    loop {
+        let mut q = f.queue.lock().unwrap();
+        let Some(i) = q.best() else { break };
+        let j = q.jobs.swap_remove(i);
+        order.push((j.key.comp, j.key.frame));
+    }
+    assert_eq!(order, [(1, 11), (1, 12), (1, 20), (1, 30), (1, 40), (2, 1)]);
+    assert_eq!(f.inflight(), 6, "frame 5, behind the playhead, is no longer in flight");
+}
+
+/// The cache is full. A zoom (or preview-resolution) change left the frames of the old
+/// size to the plain least-recently-shown order, so the frames of the zoom the viewer is back
+/// at went before the ones of the abandoned zoom. The other size's frames go first, then the
+/// order is as before.
+#[test]
+fn a_size_change_evicts_frames_of_other_sizes_first() {
+    let mut f = Frames::default();
+    f.set_remote(Some(Arc::new(Idle)));
+    f.set_budget(4 * 16);
+    let at = |frame, scale| FrameKey { scale, ..key(1, frame, 0) };
+    // 100% (frames 0..=1) is cached, then 50% (2..=3): the 100% frames are the oldest.
+    for (frame, scale) in [(0, 1000), (1, 1000), (2, 500), (3, 500)] {
+        insert(&f, at(frame, scale));
+    }
+    // A passive viewer at 50% asks for a frame: that doesn't change which size is kept.
+    f.request(&idle_source(), at(9, 500), ItemId(1), Tick::ZERO, RenderOpts::default());
+    // Back at 100%: the viewer asks for frame 4.
+    f.request_urgent(&idle_source(), at(4, 1000), ItemId(1), Tick::ZERO, RenderOpts::default());
+    f.request(&idle_source(), at(10, 500), ItemId(1), Tick::ZERO, RenderOpts::default());
+    insert(&f, at(4, 1000));
+    assert!(
+        f.is_cached(&at(0, 1000)) && f.is_cached(&at(1, 1000)) && !f.is_cached(&at(2, 500)) && f.is_cached(&at(3, 500)),
+        "the first frame of the old size goes, not the cached ones of the current size"
+    );
+    insert(&f, at(5, 1000));
+    assert!(!f.is_cached(&at(3, 500)), "then the last frame of the old size");
+    assert_eq!(f.cached_frames(&at(0, 1000)), [0, 1, 4, 5]);
+    // No other size left: least recently shown first again.
+    insert(&f, at(6, 1000));
+    assert_eq!(f.cached_frames(&at(0, 1000)), [1, 4, 5, 6]);
+}
+
+#[test]
+fn frames_are_keyed_by_content_and_series_are_kept_apart() {
+    let f = Frames::default();
+    insert(&f, key(1, 0, 0));
+    insert(&f, key(2, 0, 0));
+    insert(&f, key(2, 1, 7));
+    // Other content or render options (Draft, shadows…) are another series.
+    assert_eq!(f.cached_frames(&key(2, 0, 0)), vec![0]);
+    assert_eq!(f.cached_frames(&key(2, 0, 7)), vec![1]);
+    // A later revision with the same content finds the frame (an edit elsewhere, an undo).
+    assert!(f.is_cached(&FrameKey { revision: 99, ..key(1, 0, 0) }));
+    assert!(!f.is_cached(&key(3, 0, 0)));
+}
+
+#[test]
+fn live_edits_present_the_newest_completed_revision_without_going_backwards() {
+    let f = Frames::default();
+    let shown = key(1, 0, 0);
+    let newest = key(3, 0, 0);
+    let wanted = key(5, 0, 0);
+    insert(&f, shown);
+    insert(&f, newest);
+    insert(&f, key(2, 0, 0)); // Older worker finishes after the newer one.
+    let displayed = f.get_for_viewer(&wanted, Some(&shown)).unwrap().0;
+    assert_eq!(displayed, newest);
+    assert!(f.get_for_viewer(&wanted, Some(&displayed)).is_none(), "never replay an older completion");
+    insert(&f, wanted);
+    assert_eq!(f.get_for_viewer(&wanted, Some(&displayed)).unwrap().0, wanted, "settle on the exact final edit");
+    // Undo reuses the content of an earlier revision immediately.
+    let undo = FrameKey { revision: 6, ..shown };
+    let reused = f.get_for_viewer(&undo, Some(&wanted)).unwrap().0;
+    assert_eq!(reused.content, shown.content);
+    assert_eq!(reused.revision, undo.revision);
+}
+
+#[test]
+fn live_edits_do_not_substitute_other_times_views_or_render_settings() {
+    let f = Frames::default();
+    let shown = key(1, 0, 0);
+    let wanted = key(3, 0, 0);
+    let done = key(2, 0, 0);
+    for mismatch in [
+        FrameKey { comp: 9, ..done },
+        FrameKey { frame: 1, ..done },
+        FrameKey { scale: 500, ..done },
+        FrameKey { view: 1, ..done },
+        FrameKey { opts: 1, ..done },
+        FrameKey { revision: 4, ..done },
+    ] {
+        f.clear();
+        insert(&f, mismatch);
+        assert!(f.get_for_viewer(&wanted, Some(&shown)).is_none(), "wrong candidate: {mismatch:?}");
+    }
+    f.clear();
+    insert(&f, done);
+    assert!(f.get_for_viewer(&wanted, None).is_none(), "no stale content on opening a viewer");
+    assert!(f.get_for_viewer(&wanted, Some(&FrameKey { comp: 9, ..shown })).is_none());
+    assert!(f.get_for_viewer(&wanted, Some(&FrameKey { frame: 1, ..shown })).is_none());
+    assert!(f.get_for_viewer(&wanted, Some(&FrameKey { view: 1, ..shown })).is_none());
+}
+
+#[test]
+fn an_edit_keeps_the_frames_of_comps_it_does_not_touch() {
+    use effectcraft_engine::Session;
+    use serde_json::json;
+    let mut s = Session::default();
+    let a = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 1})).unwrap()["comp"].as_u64().unwrap());
+    let b = ItemId(s.execute("comp.new", json!({"name": "B", "width": 8, "height": 8, "duration": 1})).unwrap()["comp"].as_u64().unwrap());
+    let f = Frames::default();
+    let at = |s: &Session, c: ItemId| f.content_of(&s.project, s.revision, c);
+    let (a0, b0) = (at(&s, a), at(&s, b));
+    // Edit B: A's content (and frames) stay, B's change.
+    s.execute("layer.newSolid", json!({"comp": b.0, "color": "#ff0000"})).unwrap();
+    assert_eq!(at(&s, a), a0);
+    assert_ne!(at(&s, b), b0);
+    // Undo: B is back to the content its old frames were rendered for.
+    s.execute("edit.undo", json!({})).unwrap();
+    assert_eq!(at(&s, b), b0);
+}
+
+#[test]
+fn a_long_drag_keeps_a_bounded_number_of_states() {
+    use effectcraft_engine::Session;
+    use serde_json::json;
+    let mut s = Session::default();
+    let a = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 1})).unwrap()["comp"].as_u64().unwrap());
+    let f = Frames::default();
+    let mut last = None;
+    for i in 0..200 {
+        s.execute("comp.settings", json!({"width": 8 + i, "merge": "drag"})).unwrap();
+        let k = FrameKey { content: f.content_of(&s.project, s.revision, a), ..key(0, 0, 0) };
+        insert(&f, k);
+        last = Some(k);
+    }
+    // The snapshots and the frames kept stay bounded (a dropped identity's frames go with it,
+    // so a later state that reuses its addresses can't be shown an old frame).
+    assert!(f.keepers.lock().unwrap().1.len() <= MAX_KEEPERS);
+    assert!(f.cache.lock().unwrap().map.len() <= MAX_KEEPERS);
+    assert!(f.is_cached(&last.unwrap()), "the current state's frame stays");
+}
+
+#[test]
+fn an_identity_keeps_its_comps_so_an_edit_in_place_still_changes_it() {
+    use effectcraft_engine::Session;
+    use serde_json::json;
+    let mut s = Session::default();
+    let a = ItemId(s.execute("comp.new", json!({"name": "A", "width": 8, "height": 8, "duration": 1})).unwrap()["comp"].as_u64().unwrap());
+    // A project nothing else holds (no undo history): make_mut would edit the comp in place,
+    // at the same address, if the identity hadn't kept a snapshot holding it.
+    let mut p = Arc::new((*s.project).clone());
+    drop(s);
+    let f = Frames::default();
+    let before = f.content_of(&p, 1, a);
+    let comp = Arc::make_mut(&mut p).comp_mut(a).unwrap();
+    comp.width = 16;
+    assert_ne!(f.content_of(&p, 2, a), before);
+}
+
+/// Audio, Lock and Shy (and Hide Shy Layers) don't change pixels: toggling them, in the comp
+/// or a comp it nests, keeps its frames, also when toggled back (#103).
+#[test]
+fn audio_lock_and_shy_switches_keep_the_frames() {
+    use effectcraft_engine::Session;
+    use serde_json::json;
+    let mut s = Session::default();
+    let id = |v: serde_json::Value, k: &str| v[k].as_u64().unwrap();
+    let inner = ItemId(id(s.execute("comp.new", json!({"name": "Inner", "width": 8, "height": 8, "duration": 1})).unwrap(), "comp"));
+    let solid = id(s.execute("layer.newSolid", json!({"comp": inner.0, "color": "#ff0000"})).unwrap(), "layer");
+    let outer = ItemId(id(s.execute("comp.new", json!({"name": "Outer", "width": 8, "height": 8, "duration": 1})).unwrap(), "comp"));
+    let nested = id(s.execute("layer.addItem", json!({"comp": outer.0, "item": inner.0})).unwrap(), "layer");
+    let f = Frames::default();
+    let at = |s: &Session| f.content_of(&s.project, s.revision, outer);
+    let o0 = at(&s);
+    let switch = |s: &mut Session, comp: ItemId, layer: u64, sw: &str, v: bool| {
+        s.execute("layer.setSwitch", json!({"comp": comp.0, "layers": [layer], "switch": sw, "value": v})).unwrap();
+    };
+    for (comp, layer, sw) in [(outer, nested, "audio"), (outer, nested, "lock"), (outer, nested, "shy"), (inner, solid, "audio"), (inner, solid, "shy")] {
+        // Audio off; Lock and Shy on.
+        switch(&mut s, comp, layer, sw, sw != "audio");
+        assert_eq!(at(&s), o0, "{sw} on in {comp:?}");
+    }
+    s.execute("comp.setSwitch", json!({"comp": outer.0, "switch": "hideShy", "value": true})).unwrap();
+    assert_eq!(at(&s), o0, "Hide Shy Layers");
+    switch(&mut s, outer, nested, "audio", true);
+    switch(&mut s, outer, nested, "lock", false);
+    assert_eq!(at(&s), o0, "toggled back");
+    // Switches that change pixels still do.
+    switch(&mut s, inner, solid, "video", false);
+    let o1 = at(&s);
+    assert_ne!(o1, o0, "Video");
+    switch(&mut s, outer, nested, "audio", false);
+    assert_eq!(at(&s), o1, "a mute after a real edit keeps that edit's frames");
+    switch(&mut s, inner, solid, "video", true);
+    assert_ne!(at(&s), o1);
+}
+
+/// A cut or trim recaches only the frames of the layers it touched (#1641), and none are
+/// kept when the change reaches other layers (here a child of the trimmed layer).
+#[test]
+fn an_edit_keeps_the_frames_outside_the_layers_it_changed() {
+    use effectcraft_engine::Session;
+    use serde_json::json;
+    let mut s = Session::default();
+    let id = |v: serde_json::Value, k: &str| v[k].as_u64().unwrap();
+    let comp = ItemId(id(s.execute("comp.new", json!({"name": "Edit", "width": 8, "height": 8, "duration": 10})).unwrap(), "comp"));
+    let a = id(s.execute("layer.newSolid", json!({"comp": comp.0, "color": "#ff0000"})).unwrap(), "layer");
+    let b = id(s.execute("layer.newSolid", json!({"comp": comp.0, "color": "#00ff00"})).unwrap(), "layer");
+    s.execute("layer.timing", json!({"layers": [a], "in": 0, "out": 4})).unwrap();
+    s.execute("layer.timing", json!({"layers": [b], "in": 4, "out": 10})).unwrap();
+    let (fr, out) = s.project.comp(comp).map(|c| (c.frame_rate, c.layers.iter().find(|l| l.id.0 == a).unwrap().out_point)).unwrap();
+    let frames: Vec<i64> = (0..fr.frame_at(Tick::from_seconds_f64(10.0))).collect();
+    let f = Frames::default();
+    let cache_all = |s: &Session| {
+        let c = f.content_of(&s.project, s.revision, comp);
+        frames.iter().for_each(|&n| insert(&f, key(c, n, 0)));
+        c
+    };
+    let cached = |c: u64| frames.iter().filter(|&&n| f.is_cached(&key(c, n, 0))).copied().collect::<Vec<_>>();
+    let before = cache_all(&s);
+    s.execute("time.set", json!({"time": 2.0})).unwrap();
+    s.execute("edit.splitLayer", json!({"layers": [a]})).unwrap();
+    let after = f.content_of(&s.project, s.revision, comp);
+    assert_ne!(after, before);
+    let kept: Vec<i64> = (fr.frame_at(out) + 2..frames.len() as i64).collect();
+    assert_eq!(cached(after), kept, "the cut layer's frames (and one either side) render again; the rest stay");
+
+    s.execute("layer.setParent", json!({"layers": [b], "parent": a})).unwrap();
+    let parented = cache_all(&s);
+    s.execute("layer.timing", json!({"layers": [a], "out": 1})).unwrap();
+    assert_eq!(cached(f.content_of(&s.project, s.revision, comp)), Vec::<i64>::new(), "the trimmed layer's child moves everywhere");
+    assert_eq!(cached(parented).len(), frames.len(), "the earlier frames stay for undo");
+}
+
+/// Every frame an edit keeps renders as a fresh render of the edited project does: Solo
+/// hides the other layers at every frame, and a camera reaches the frames whose shutter
+/// samples it (#1641 review).
+#[test]
+fn the_frames_an_edit_keeps_match_a_fresh_render() {
+    use effectcraft_engine::Session;
+    use effectcraft_engine::render::NoFootage;
+    use serde_json::json;
+    // Cache every frame of `comp`, run `edit`, check the frames kept against fresh renders.
+    fn kept(s: &mut Session, comp: ItemId, edit: serde_json::Value) -> Vec<i64> {
+        let (fr, n) = s.project.comp(comp).map(|c| (c.frame_rate, c.frame_rate.frame_at(c.duration))).unwrap();
+        let f = Frames::default();
+        let before = f.content_of(&s.project, s.revision, comp);
+        (0..n).for_each(|i| insert(&f, key(before, i, 0)));
+        let old = s.project.clone();
+        s.execute(edit["cmd"].as_str().unwrap(), edit["params"].clone()).unwrap();
+        let after = f.content_of(&s.project, s.revision, comp);
+        let kept: Vec<i64> = (0..n).filter(|&i| f.is_cached(&key(after, i, 0))).collect();
+        let render = |p, i| Renderer::new(p, &NoFootage, RenderOpts::default()).comp_frame(comp, fr.tick_of(i));
+        for &i in &kept {
+            assert_eq!(render(&old, i), render(&s.project, i), "kept frame {i} draws other pixels now");
+        }
+        kept
+    }
+    let id = |v: serde_json::Value, k: &str| v[k].as_u64().unwrap();
+    let mut s = Session::default();
+
+    // Solo on a 2–3 s layer hides the 10 s underlay everywhere; turning it off shows it again.
+    let comp = ItemId(id(s.execute("comp.new", json!({"name": "Solo", "width": 8, "height": 8, "duration": 10})).unwrap(), "comp"));
+    s.execute("layer.newSolid", json!({"comp": comp.0, "color": "#ff0000"})).unwrap();
+    let short = id(s.execute("layer.newSolid", json!({"comp": comp.0, "color": "#00ff00"})).unwrap(), "layer");
+    s.execute("layer.timing", json!({"layers": [short], "in": 2, "out": 3})).unwrap();
+    let solo = |on: bool| json!({"cmd": "layer.setSwitch", "params": {"layers": [short], "switch": "solo", "value": on}});
+    assert_eq!(kept(&mut s, comp, solo(true)), Vec::<i64>::new());
+    assert_eq!(kept(&mut s, comp, solo(false)), Vec::<i64>::new());
+
+    // A 2–3 s camera over a 4 s motion-blurred 3D layer, shutter 720° at phase 360°: a frame
+    // samples 1 to 3 frames ahead, so moving the camera reaches the 3 frames before it.
+    let comp = ItemId(id(
+        s.execute("comp.new", json!({"name": "Cam", "width": 16, "height": 16, "duration": 4, "frameRate": 30, "shutterAngle": 720, "shutterPhase": 360}))
+            .unwrap(),
+        "comp",
+    ));
+    let plane = id(s.execute("layer.newSolid", json!({"comp": comp.0, "color": "#ff0000"})).unwrap(), "layer");
+    for sw in ["threeD", "motionBlur"] {
+        s.execute("layer.setSwitch", json!({"layers": [plane], "switch": sw, "value": true})).unwrap();
+    }
+    let cam = id(s.execute("layer.newCamera", json!({"comp": comp.0})).unwrap(), "layer");
+    s.execute("layer.timing", json!({"layers": [cam], "in": 2, "out": 3})).unwrap();
+    let moved =
+        kept(&mut s, comp, json!({"cmd": "prop.set", "params": {"comp": comp.0, "layer": cam, "path": "transform/position", "value": [40, 8, -30]}}));
+    assert!(moved.contains(&0) && moved.contains(&100), "frames far from the camera stay: {moved:?}");
+    assert!(!(56..=91).any(|f| moved.contains(&f)), "frames whose shutter samples the camera render again: {moved:?}");
+}
+
+#[test]
+fn short_solid_additions_and_removals_keep_unaffected_frames() {
+    use effectcraft_engine::Session;
+    use serde_json::json;
+    let mut s = Session::default();
+    let comp = ItemId(s.execute("comp.new", json!({"width": 8, "height": 8, "frameRate": 30, "duration": 20})).unwrap()["comp"].as_u64().unwrap());
+    s.execute("layer.newSolid", json!({"color": "#ff0000"})).unwrap();
+    let f = Frames::default();
+    let cache_all = |s: &Session| {
+        let content = f.content_of(&s.project, s.revision, comp);
+        (0..600).for_each(|n| insert(&f, key(content, n, 0)));
+    };
+    let cached = |s: &Session| f.cached_frames(&key(f.content_of(&s.project, s.revision, comp), 0, 0));
+    // 2–3 s, a quarter frame of the default shutter and a frame of rounding either side.
+    let kept: Vec<i64> = (0..=57).chain(92..600).collect();
+    cache_all(&s);
+    let solid = s.execute("layer.newSolid", json!({"color": "#00ff00"})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("layer.timing", json!({"layers": [solid], "in": 2, "out": 3})).unwrap();
+    assert_eq!(cached(&s), kept, "adding a source invalidates only frames 58..=91");
+    cache_all(&s);
+    s.execute("edit.undo", json!({})).unwrap();
+    s.execute("edit.undo", json!({})).unwrap();
+    assert_eq!(cached(&s), (0..600).collect::<Vec<_>>(), "undoing the addition restores every frame");
+    s.execute("edit.redo", json!({})).unwrap();
+    s.execute("edit.redo", json!({})).unwrap();
+    assert_eq!(cached(&s), (0..600).collect::<Vec<_>>(), "redoing the addition restores every frame");
+    s.execute("edit.clear", json!({"layers": [solid]})).unwrap();
+    assert_eq!(cached(&s), kept, "removing its layer invalidates the same span");
+}
+
+#[test]
+fn adding_a_source_does_not_hide_changes_to_existing_dependencies() {
+    use effectcraft_engine::Session;
+    use serde_json::json;
+    for (command, params) in [
+        ("layer.settings", json!({"comp": "Outer", "layer": "Underlay", "color": "#0000ff"})),
+        ("prop.set", json!({"comp": "Inner", "layer": "Inner solid", "path": "transform/opacity", "value": 40})),
+    ] {
+        let mut s = Session::default();
+        let comp = ItemId(
+            s.execute("comp.new", json!({"name": "Outer", "width": 8, "height": 8, "frameRate": 30, "duration": 20})).unwrap()["comp"].as_u64().unwrap(),
+        );
+        s.execute("layer.newSolid", json!({"name": "Underlay", "color": "#ff0000"})).unwrap();
+        s.execute("comp.new", json!({"name": "Inner", "width": 8, "height": 8, "duration": 20})).unwrap();
+        s.execute("layer.newSolid", json!({"name": "Inner solid", "color": "#00ff00"})).unwrap();
+        s.execute("comp.open", json!({"comp": "Outer"})).unwrap();
+        s.execute("layer.addItem", json!({"item": "Inner"})).unwrap();
+        let f = Frames::default();
+        let before = f.content_of(&s.project, s.revision, comp);
+        (0..600).for_each(|n| insert(&f, key(before, n, 0)));
+        s.execute(command, params).unwrap();
+        let solid = s.execute("layer.newSolid", json!({"color": "#ffffff"})).unwrap()["layer"].as_u64().unwrap();
+        s.execute("layer.timing", json!({"layers": [solid], "in": 2, "out": 3})).unwrap();
+        let after = f.content_of(&s.project, s.revision, comp);
+        assert!(f.cached_frames(&key(after, 0, 0)).is_empty(), "{command} changes pixels outside the added layer");
+    }
+}
+
+#[test]
+fn markers_keep_the_frames() {
+    use effectcraft_engine::Session;
+    use serde_json::json;
+    let mut s = Session::default();
+    let id = |v: serde_json::Value, k: &str| v[k].as_u64().unwrap();
+    let outer = ItemId(id(s.execute("comp.new", json!({"name": "Outer", "width": 8, "height": 8, "duration": 1})).unwrap(), "comp"));
+    let solid = id(s.execute("layer.newSolid", json!({"comp": outer.0, "color": "#ff0000"})).unwrap(), "layer");
+    let f = Frames::default();
+    let at = |s: &Session| f.content_of(&s.project, s.revision, outer);
+    let o0 = at(&s);
+    s.execute("layer.addMarker", json!({"comp": outer.0, "layers": [solid], "time": 0.5, "comment": "beat"})).unwrap();
+    assert_eq!(at(&s), o0, "a marker changes no pixels, so it keeps the frames");
+}
+
+#[test]
+fn markers_count_when_an_expression_can_read_them() {
+    use effectcraft_engine::Session;
+    use serde_json::json;
+    let mut s = Session::default();
+    let id = |v: serde_json::Value, k: &str| v[k].as_u64().unwrap();
+    let outer = ItemId(id(s.execute("comp.new", json!({"name": "Outer", "width": 8, "height": 8, "duration": 1})).unwrap(), "comp"));
+    let solid = id(s.execute("layer.newSolid", json!({"comp": outer.0, "color": "#ff0000"})).unwrap(), "layer");
+    s.execute("prop.setExpression", json!({"comp": outer.0, "layer": solid, "path": "transform/opacity", "expression": "1"})).unwrap();
+    let f = Frames::default();
+    let at = |s: &Session| f.content_of(&s.project, s.revision, outer);
+    let o0 = at(&s);
+    s.execute("layer.addMarker", json!({"comp": outer.0, "layers": [solid], "time": 0.5, "comment": "beat"})).unwrap();
+    assert_ne!(at(&s), o0, "an expression can read the marker, so the frames change");
+}