diff --git a/crates/ui-egui/src/frames.rs b/crates/ui-egui/src/frames.rs
index a157359f..866bf021 100644
--- a/crates/ui-egui/src/frames.rs
+++ b/crates/ui-egui/src/frames.rs
@@ -521,6 +521,42 @@ impl Frames {
         Some(img)
     }
 
+    /// Prefer the exact requested frame. While an edit renders, advance to the newest completed
+    /// revision of the same comp, time, scale, view and render options instead of freezing on the
+    /// image from before the drag. Input may arrive before the viewer draws on every UI frame,
+    /// so even a fast worker cannot always finish the *latest* revision in time.
+    ///
+    /// Never move backwards when workers finish out of order, and never substitute another time
+    /// or view while scrubbing or switching comps. The exact content lookup above also means an
+    /// undo can immediately reuse an old cache entry, regardless of its original revision.
+    pub fn get_for_viewer(&self, wanted: &FrameKey, shown: Option<&FrameKey>) -> Option<(FrameKey, FrameImage)> {
+        if let Some(img) = self.get(wanted) {
+            return Some((*wanted, img));
+        }
+        let shown = shown?;
+        if shown.comp != wanted.comp || shown.frame != wanted.frame || shown.view != wanted.view || shown.revision >= wanted.revision {
+            return None;
+        }
+        let mut c = self.cache.lock().ok()?;
+        let newest = c
+            .map
+            .keys()
+            .filter(|k| {
+                k.revision > shown.revision
+                    && k.revision < wanted.revision
+                    && k.comp == wanted.comp
+                    && k.frame == wanted.frame
+                    && k.scale == wanted.scale
+                    && k.view == wanted.view
+                    && k.opts == wanted.opts
+            })
+            .max_by_key(|k| k.revision)
+            .copied()?;
+        let img = c.map.get(&newest).cloned()?;
+        c.touch(&newest);
+        Some((newest, img))
+    }
+
     /// The [`comp_content`] identity of `comp` in `project` at `revision` (taken once per
     /// revision). The project is kept while frames of that identity are cached or rendering, so
     /// the comp addresses it hashes can't be reused by other comps meanwhile.
@@ -678,8 +714,9 @@ impl Frames {
             // Only the newest viewer frame is urgent. The comp's earlier viewer frames that
             // haven't started are dropped (scrubbing: rendering every frame the pointer passed
             // would hold the workers the frame under it needs); frames already rendering finish
-            // into the cache, and the viewer shows its last frame until the new one is in
-            // (#284). Other comps' viewer frames become prefetch.
+            // into the cache. During edits the viewer advances through compatible completed
+            // revisions; scrubbing holds its last frame until the requested time is in (#284).
+            // Other comps' viewer frames become prefetch.
             q.jobs.retain(|j| {
                 let superseded = j.urgent && j.key != key && j.key.comp == key.comp;
                 if superseded {
@@ -1247,6 +1284,53 @@ mod tests {
         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;
diff --git a/crates/ui-egui/src/panels/viewer.rs b/crates/ui-egui/src/panels/viewer.rs
index e63d9c7f..8998236e 100644
--- a/crates/ui-egui/src/panels/viewer.rs
+++ b/crates/ui-egui/src/panels/viewer.rs
@@ -641,7 +641,7 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, rect: Rect) {
     let frame = comp.frame_rate.frame_at(time);
     let key = app.frame_key(cid, frame, scale);
     app.request_frame_urgent(cid, frame, scale);
-    if let Some(img) = app.frames.get(&key) {
+    if let Some((key, img)) = app.frames.get_for_viewer(&key, app.viewer_shown.as_ref().map(|(_, k)| k)) {
         let stale = app.viewer_shown.as_ref().is_none_or(|(_, k)| *k != key);
         if stale {
             show_frame(app, &ctx, key, img);
diff --git a/crates/ui-egui/src/panels/viewers.rs b/crates/ui-egui/src/panels/viewers.rs
index 57a3511f..cb314fed 100644
--- a/crates/ui-egui/src/panels/viewers.rs
+++ b/crates/ui-egui/src/panels/viewers.rs
@@ -101,7 +101,7 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, id: u32, rect: Rect) {
             let frame = c.frame_rate.frame_at(app.session.time_of(cid));
             app.request_frame(cid, frame, scale);
             let key = app.frame_key(cid, frame, scale);
-            if let Some(img) = app.frames.get(&key) {
+            if let Some((key, img)) = app.frames.get_for_viewer(&key, app.passive_tex.get(&id).map(|(k, _)| k)) {
                 set_texture(app, &ctx, id, key, img);
             }
             match app.passive_tex.get(&id).filter(|(k, _)| k.comp == cid.0) {
@@ -127,7 +127,12 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, id: u32, rect: Rect) {
 
 /// Keep the frame viewer `id` shows in its texture.
 fn set_texture(app: &mut EffectcraftApp, ctx: &egui::Context, id: u32, key: FrameKey, img: FrameImage) {
-    if app.passive_tex.get(&id).is_some_and(|(k, _)| *k == key) {
+    if let Some((k, _)) = app.passive_tex.get_mut(&id)
+        && *k == key
+    {
+        // An undo or an edit elsewhere can reuse this content at a newer revision. Keep that
+        // revision as the lower bound for subsequent intermediate edit frames.
+        k.revision = key.revision;
         return;
     }
     let opts = super::viewer::zoom_texture_options(app.session.prefs.viewer_zoom_smooth());
diff --git a/crates/ui-egui/tests/ui_live_preview.rs b/crates/ui-egui/tests/ui_live_preview.rs
new file mode 100644
index 00000000..e72856bf
--- /dev/null
+++ b/crates/ui-egui/tests/ui_live_preview.rs
@@ -0,0 +1,158 @@
+//! Completed edits must reach the viewer even when a newer edit is still rendering.
+
+use std::sync::{Arc, Mutex};
+
+use effectcraft_engine::{
+    Session,
+    project::LayerId,
+    render::{NoFootage, Renderer},
+};
+use effectcraft_ui_egui::{
+    EffectcraftApp,
+    frames::{RemoteDone, RemoteFrame, RemoteFrames, RemoteJob, to_color_image},
+};
+use egui_kittest::Harness;
+use serde_json::json;
+
+/// Hold completions explicitly: input/render ordering is deterministic, without timing sleeps.
+#[derive(Default)]
+struct HeldRenderer(Mutex<Vec<(RemoteJob, RemoteDone)>>);
+
+impl RemoteFrames for HeldRenderer {
+    fn slots(&self) -> usize {
+        1
+    }
+    fn start(&self, job: RemoteJob, done: RemoteDone) {
+        self.0.lock().unwrap().push((job, done));
+    }
+}
+
+impl HeldRenderer {
+    fn finish(&self) -> egui::ColorImage {
+        let (job, done) = self.0.lock().unwrap().remove(0);
+        let image = Renderer::new(&job.project, &NoFootage, job.opts).comp_frame(job.comp, job.t);
+        let pixels = to_color_image(&image);
+        done(Ok(RemoteFrame { width: image.width, height: image.height, rgba: pixels.pixels.iter().flat_map(|c| c.to_array()).collect(), ms: 20.0 }));
+        pixels
+    }
+}
+
+#[test]
+fn opacity_edits_show_completed_intermediate_frames_before_the_drag_stops() {
+    let mut session = Session::default();
+    session.execute("comp.new", json!({"name":"Live opacity", "width":64, "height":36, "duration":1})).unwrap();
+    let layer = session.execute("layer.newSolid", json!({"color":"#ffffff"})).unwrap()["layer"].as_u64().unwrap();
+    let renderer = Arc::new(HeldRenderer::default());
+    let mut app = EffectcraftApp::new(session);
+    app.frames.set_remote(Some(renderer.clone()));
+    let mut h = Harness::builder().with_size(egui::vec2(1400.0, 900.0)).with_step_dt(0.016).build_eframe(|_| app);
+    h.run_steps(3);
+    assert_eq!(h.state().frames.dispatch_remote(), 1);
+    renderer.finish();
+    h.step();
+    let alpha = |h: &mut Harness<'_, EffectcraftApp>| h.state_mut().viewer_pixels().unwrap().pixels[32 + 18 * 64].a();
+    assert_eq!(alpha(&mut h), 255);
+    for opacity in [80, 60, 40, 20] {
+        h.state_mut().session.execute("prop.set", json!({"layer":layer, "path":"transform/opacity", "value":opacity, "merge":"scrub"})).unwrap();
+        h.step();
+        assert_eq!(h.state().frames.dispatch_remote(), 1);
+        // Another input arrives before that frame completes, as in a fast slider drag.
+        h.state_mut().session.execute("prop.set", json!({"layer":layer, "path":"transform/opacity", "value":opacity - 1, "merge":"scrub"})).unwrap();
+        renderer.finish();
+        h.step();
+        assert_eq!(alpha(&mut h), (opacity as f32 * 2.55).round() as u8, "completed {opacity}% opacity must display while the next edit renders");
+    }
+    // Releasing the slider still converges to the exact final state.
+    assert_eq!(h.state().frames.dispatch_remote(), 1);
+    renderer.finish();
+    h.step();
+    assert_eq!(alpha(&mut h), (19.0_f32 * 2.55).round() as u8);
+    let series = h.state().shown_series(h.state().session.active_comp_id().unwrap());
+    assert!(h.state().frames.is_cached(&series));
+}
+
+#[test]
+fn position_anchor_and_effect_edits_present_intermediate_pixels() {
+    for (effect, path, first, second) in [
+        (None, "transform/position", json!([22, 18, 0]), json!([18, 18, 0])),
+        (None, "transform/anchor", json!([9, 8, 0]), json!([6, 8, 0])),
+        (Some("Gaussian Blur"), "blurriness", json!(3), json!(6)),
+        (Some("CC Radial Fast Blur"), "center", json!([4, 4]), json!([18, 12])),
+    ] {
+        let mut session = Session::default();
+        session.execute("comp.new", json!({"width":64,"height":36,"duration":1})).unwrap();
+        let layer = session.execute("layer.newSolid", json!({"color":"#ffffff","width":24,"height":16})).unwrap()["layer"].as_u64().unwrap();
+        if effect == Some("CC Radial Fast Blur") {
+            // A uniform solid is invariant under a radial blur; give the point edit visible detail.
+            session.execute("effect.apply", json!({"layers":[layer],"effect":"Gradient Ramp"})).unwrap();
+        }
+        let property = if let Some(effect) = effect {
+            session.execute("effect.apply", json!({"layers":[layer],"effect":effect})).unwrap();
+            session.active_comp().unwrap().layer(LayerId(layer)).unwrap().effects().unwrap().groups().last().unwrap().get(path).unwrap().uid
+        } else {
+            session.active_comp().unwrap().layer(LayerId(layer)).unwrap().props.prop(path).unwrap().uid
+        };
+        let renderer = Arc::new(HeldRenderer::default());
+        let mut app = EffectcraftApp::new(session);
+        app.frames.set_remote(Some(renderer.clone()));
+        let mut h = Harness::builder().with_size(egui::vec2(1400.0, 900.0)).with_step_dt(0.016).build_eframe(|_| app);
+        h.run_steps(3);
+        h.state().frames.dispatch_remote();
+        let initial = renderer.finish();
+        h.step();
+        h.state_mut().session.execute("prop.set", json!({"layer":layer,"prop":property,"value":first,"merge":"drag"})).unwrap();
+        h.step();
+        assert_eq!(h.state().frames.dispatch_remote(), 1);
+        h.state_mut().session.execute("prop.set", json!({"layer":layer,"prop":property,"value":second,"merge":"drag"})).unwrap();
+        let intermediate = renderer.finish();
+        assert!(initial.pixels != intermediate.pixels, "{effect:?} {path}: fixture must change rendered pixels");
+        h.step();
+        assert_eq!(h.state_mut().viewer_pixels().unwrap().pixels, intermediate.pixels, "{effect:?} {path}: display finished edit while next edit renders");
+        assert_eq!(h.state().frames.dispatch_remote(), 1);
+        let final_image = renderer.finish();
+        h.step();
+        assert_eq!(h.state_mut().viewer_pixels().unwrap().pixels, final_image.pixels, "{effect:?} {path}: converge to exact final edit");
+    }
+}
+
+/// Manual throughput probe: no timing threshold in CI. Includes egui layout and native workers,
+/// but no window compositor or GPU upload; it measures presentation progress during edits.
+#[test]
+#[ignore = "manual native-worker preview throughput probe"]
+fn continuous_opacity_preview_probe() {
+    use std::time::{Duration, Instant};
+    let mut session = Session::default();
+    session.execute("comp.new", json!({"width":1920,"height":1080,"duration":1})).unwrap();
+    let layer = session.execute("layer.newSolid", json!({"color":"#ffffff"})).unwrap()["layer"].as_u64().unwrap();
+    let mut h = Harness::builder().with_size(egui::vec2(1400.0, 900.0)).with_step_dt(1.0 / 60.0).build_eframe(|_| EffectcraftApp::new(session));
+    let ready = Instant::now();
+    while h.state_mut().viewer_pixels().is_none() && ready.elapsed() < Duration::from_secs(5) {
+        h.step();
+        std::thread::sleep(Duration::from_millis(5));
+    }
+    let mut last = h.state_mut().viewer_pixels().expect("initial viewer frame");
+    let start = Instant::now();
+    let mut updates = 0;
+    let mut longest_hold = Duration::ZERO;
+    let mut last_update = start;
+    for i in 0..120 {
+        h.state_mut().session.execute("prop.set", json!({"layer":layer,"path":"transform/opacity","value":99-i%90,"merge":"scrub"})).unwrap();
+        h.step();
+        let now = h.state_mut().viewer_pixels().unwrap();
+        if !Arc::ptr_eq(&now, &last) {
+            updates += 1;
+            longest_hold = longest_hold.max(last_update.elapsed());
+            last_update = Instant::now();
+            last = now;
+        }
+        let deadline = start + Duration::from_secs_f64((i + 1) as f64 / 60.0);
+        std::thread::sleep(deadline.saturating_duration_since(Instant::now()));
+    }
+    longest_hold = longest_hold.max(last_update.elapsed());
+    println!(
+        "LIVE_PREVIEW_PROBE updates={updates}/120 elapsed_ms={:.1} longest_hold_ms={:.1} last_render_ms={:.3}",
+        start.elapsed().as_secs_f64() * 1000.0,
+        longest_hold.as_secs_f64() * 1000.0,
+        *h.state().frames.last_ms.lock().unwrap()
+    );
+}
diff --git a/docs/architecture.md b/docs/architecture.md
index c8c8a4e5..053ed82e 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -164,12 +164,16 @@ its evaluated inputs, excluding the transform. Static and transform-only layers
 editing one layer re-renders only that layer. Effects that read the clock directly are declared in
 `effects::TIME_DEPENDENT`, and a test checks every registered effect against that list.
 
-The viewer's **RAM preview** (`ui-egui/src/frames.rs`) keeps finished frames keyed by project
-revision, comp, frame, scale, 3D view / region of interest and a hash of the other render
-options (Draft / Fast Previews, shadows, nested switches), so frames rendered under other
-options are never shown. When the budget (Settings ▸ Memory & CPU) is full the least recently
-shown frames go first, and frames of an older revision are dropped as soon as the project
-changes. The timeline's green bar counts the frames of exactly what the viewer shows.
+The viewer's **RAM preview** (`ui-egui/src/frames.rs`) keeps finished frames keyed by comp
+content, frame, scale, 3D view / region of interest and a hash of the other render options
+(Draft / Fast Previews, shadows, nested switches). Edits preserve unaffected comps' frames,
+and undo can reuse earlier content. During rapid edits at the same time and view, the viewer
+shows the newest completed revision while the exact requested revision renders; out-of-order
+completions cannot move it backwards. This avoids freezing until a slider or layer drag stops.
+Frames at other times or with other render options are never substituted. Obsolete queued jobs
+are dropped; running jobs finish into the cache. When the budget (Settings ▸ Memory & CPU) is
+full the least recently shown frames go first. The timeline's green bar counts cached frames
+of the current content and viewer settings.
 
 A persistent **disk cache** (`render::disk_cache`, Settings ▸ Media & Disk Cache) backs both
 the layer cache and the viewer's RAM preview: layer buffers that were slow to render and every