fix(studio): address PR review — restore rollback, fix probe race, harden edit suppression

Restore rollback path: enqueueEdit now returns the queued promise so
Promise.resolve(handler(...)).catch(rollback) in useTimelineClipDrag
fires correctly on save failure. Handlers return the promise chain.

Fix lost-update race in probe enrichment: use zustand's functional
setState so concurrent probe completions each read the latest state
atomically instead of all reading the same stale snapshot.

Harden file-change suppression: pendingTimelineEditPathRef is now a
Set<string> with exact-match lookup instead of single-slot + endsWith.
Multiple concurrent edits on different files are all suppressed correctly.

Remove dead canOffsetTrimClipStart function and its tests — no longer
called after the capability gate simplification.

Document runtime sync mechanism: added comment explaining that the
runtime re-reads data attributes on each sync tick (init.ts:1324-1368).

Fix comment wording in patchIframeDomTiming catch block.

packages/studio/src/App.tsx

@@ -117,7 +117,7 @@ export function StudioApp() {
   });
   const editHistory = usePersistentEditHistory({ projectId });
   const domEditSaveTimestampRef = useRef(0);
-  const pendingTimelineEditPathRef = useRef<string | null>(null);
+  const pendingTimelineEditPathRef = useRef(new Set<string>());
   const reloadPreview = useCallback(() => {
     setRefreshKey((k) => k + 1);
   }, []);

packages/studio/src/hooks/usePreviewPersistence.ts

@@ -30,7 +30,7 @@ interface UsePreviewPersistenceParams {
   domEditSaveTimestampRef: React.MutableRefObject<number>;
   /** Tracks in-flight timeline edits that patch the iframe DOM directly. File-change
    *  events for these paths are always suppressed since the preview is already up-to-date. */
-  pendingTimelineEditPathRef?: React.MutableRefObject<string | null>;
+  pendingTimelineEditPathRef?: React.MutableRefObject<Set<string>>;
   /** Called to reload the preview after undo/redo or external file changes. */
   reloadPreview: () => void;
 }
@@ -167,9 +167,8 @@ export function usePreviewPersistence({
       const changedPath = readStudioFileChangePath(payload);
       if (!changedPath) return;
       const recentDomEditSave = Date.now() - domEditSaveTimestampRef.current < 4000;
-      const pendingPath = pendingTimelineEditPathRef?.current;
-      if (pendingPath && changedPath.endsWith(pendingPath)) {
-        pendingTimelineEditPathRef!.current = null;
+      if (pendingTimelineEditPathRef?.current.has(changedPath)) {
+        pendingTimelineEditPathRef.current.delete(changedPath);
         return;
       }
       if (!recentDomEditSave) {

packages/studio/src/hooks/useTimelineEditing.ts

@@ -39,7 +39,7 @@ interface UseTimelineEditingOptions {
   domEditSaveTimestampRef: React.MutableRefObject<number>;
   reloadPreview: () => void;
   previewIframeRef: React.RefObject<HTMLIFrameElement | null>;
-  pendingTimelineEditPathRef: React.MutableRefObject<string | null>;
+  pendingTimelineEditPathRef: React.MutableRefObject<Set<string>>;
   uploadProjectFiles: (files: Iterable<File>, dir?: string) => Promise<string[]>;
 }
 
@@ -55,6 +55,9 @@ function buildPatchTarget(element: { domId?: string; selector?: string; selector
   return null;
 }
 
+// The runtime re-reads data-start/data-duration from the DOM on each sync tick
+// (packages/core/src/runtime/init.ts:1324-1368), so attribute mutations here are
+// picked up automatically on the next frame without a rebind call.
 function patchIframeDomTiming(
   iframe: HTMLIFrameElement | null,
   element: TimelineElement,
@@ -71,7 +74,7 @@ function patchIframeDomTiming(
     if (!el) return;
     for (const [name, value] of attrs) el.setAttribute(name, value);
   } catch {
-    // Cross-origin or mid-navigation — safe to ignore, file is already saved.
+    // Cross-origin or mid-navigation — file save is enqueued; iframe patch is best-effort.
   }
 }
 
@@ -112,7 +115,7 @@ interface PersistTimelineEditInput {
   writeProjectFile: (path: string, content: string) => Promise<void>;
   recordEdit: (input: RecordEditInput) => Promise<void>;
   domEditSaveTimestampRef: React.MutableRefObject<number>;
-  pendingTimelineEditPathRef: React.MutableRefObject<string | null>;
+  pendingTimelineEditPathRef: React.MutableRefObject<Set<string>>;
 }
 
 async function persistTimelineEdit(input: PersistTimelineEditInput): Promise<void> {
@@ -129,7 +132,7 @@ async function persistTimelineEdit(input: PersistTimelineEditInput): Promise<voi
     throw new Error(`Unable to patch timeline element ${input.element.id} in ${targetPath}`);
   }
 
-  input.pendingTimelineEditPathRef.current = targetPath;
+  input.pendingTimelineEditPathRef.current.add(targetPath);
   input.domEditSaveTimestampRef.current = Date.now();
   await saveProjectFilesWithHistory({
     projectId: input.projectId,
@@ -183,26 +186,26 @@ export function useTimelineEditing({
       element: TimelineElement,
       label: string,
       buildPatches: PersistTimelineEditInput["buildPatches"],
-    ) => {
+    ): Promise<void> => {
       const pid = projectIdRef.current;
-      if (!pid) return;
-      editQueueRef.current = editQueueRef.current
-        .then(() =>
-          persistTimelineEdit({
-            projectId: pid,
-            element,
-            activeCompPath,
-            label,
-            buildPatches,
-            writeProjectFile,
-            recordEdit,
-            domEditSaveTimestampRef,
-            pendingTimelineEditPathRef,
-          }),
-        )
-        .catch((error) => {
-          console.error(`[Timeline] Failed to persist: ${label}`, error);
-        });
+      if (!pid) return Promise.resolve();
+      const queued = editQueueRef.current.then(() =>
+        persistTimelineEdit({
+          projectId: pid,
+          element,
+          activeCompPath,
+          label,
+          buildPatches,
+          writeProjectFile,
+          recordEdit,
+          domEditSaveTimestampRef,
+          pendingTimelineEditPathRef,
+        }),
+      );
+      editQueueRef.current = queued.catch((error) => {
+        console.error(`[Timeline] Failed to persist: ${label}`, error);
+      });
+      return queued;
     },
     [
       activeCompPath,
@@ -219,7 +222,7 @@ export function useTimelineEditing({
         ["data-start", formatTimelineAttributeNumber(updates.start)],
         ["data-track-index", String(updates.track)],
       ]);
-      enqueueEdit(element, "Move timeline clip", (original, target) => {
+      return enqueueEdit(element, "Move timeline clip", (original, target) => {
         let patched = applyPatchByTarget(original, target, {
           type: "attribute",
           property: "start",
@@ -244,7 +247,7 @@ export function useTimelineEditing({
         ["data-start", formatTimelineAttributeNumber(updates.start)],
         ["data-duration", formatTimelineAttributeNumber(updates.duration)],
       ]);
-      enqueueEdit(element, "Resize timeline clip", (original, target) => {
+      return enqueueEdit(element, "Resize timeline clip", (original, target) => {
         const pbs = resolveResizePlaybackStart(original, target, element, updates);
         let patched = applyPatchByTarget(original, target, {
           type: "attribute",

packages/studio/src/player/components/timelineEditing.test.ts

@@ -4,7 +4,6 @@ import {
   buildPromptCopyText,
   buildTimelineElementAgentPrompt,
   buildTimelineAgentPrompt,
-  canOffsetTrimClipStart,
   getTimelineEditCapabilities,
   hasPatchableTimelineTarget,
   resolveBlockedTimelineEditIntent,
@@ -158,42 +157,6 @@ describe("resolveTimelineMove", () => {
   });
 });
 
-describe("canOffsetTrimClipStart", () => {
-  it("allows front trim for clips that carry playback offset metadata", () => {
-    expect(
-      canOffsetTrimClipStart({
-        tag: "div",
-        playbackStartAttr: "media-start",
-      }),
-    ).toBe(true);
-  });
-
-  it("allows front trim for media clips with source duration metadata", () => {
-    expect(
-      canOffsetTrimClipStart({
-        tag: "video",
-        sourceDuration: 12,
-      }),
-    ).toBe(true);
-  });
-
-  it("allows front trim for plain audio clips even before media-start exists", () => {
-    expect(
-      canOffsetTrimClipStart({
-        tag: "audio",
-      }),
-    ).toBe(true);
-  });
-
-  it("blocks front trim for generic motion clips", () => {
-    expect(
-      canOffsetTrimClipStart({
-        tag: "section",
-      }),
-    ).toBe(false);
-  });
-});
-
 describe("hasPatchableTimelineTarget", () => {
   it("returns true when the clip has a DOM id", () => {
     expect(hasPatchableTimelineTarget({ domId: "hero-card" })).toBe(true);

packages/studio/src/player/components/timelineEditing.ts

@@ -201,18 +201,6 @@ export function hasPatchableTimelineTarget(input: { domId?: string; selector?: s
   return Boolean(input.domId || input.selector);
 }
 
-export function canOffsetTrimClipStart(input: {
-  tag: string;
-  playbackStart?: number;
-  playbackStartAttr?: "media-start" | "playback-start";
-  sourceDuration?: number;
-}): boolean {
-  if (input.playbackStartAttr != null) return true;
-  if (input.playbackStart != null) return true;
-  const normalizedTag = input.tag.toLowerCase();
-  return ["video", "audio"].includes(normalizedTag);
-}
-
 export function getTimelineEditCapabilities(input: {
   tag: string;
   duration: number;

packages/studio/src/player/hooks/useTimelinePlayer.ts

@@ -122,13 +122,14 @@ export function useTimelinePlayer() {
           needsProbe.map(async (el) => {
             const result = await probeMediaUrl(el.src!);
             if (!result) return;
-            const current = usePlayerStore.getState().elements;
             const key = el.key ?? el.id;
-            const idx = current.findIndex((e) => (e.key ?? e.id) === key);
-            if (idx === -1 || current[idx].sourceDuration != null) return;
-            const patched = current.slice();
-            patched[idx] = { ...current[idx], sourceDuration: result.duration };
-            setElements(patched);
+            usePlayerStore.setState((state) => {
+              const idx = state.elements.findIndex((e) => (e.key ?? e.id) === key);
+              if (idx === -1 || state.elements[idx].sourceDuration != null) return {};
+              const patched = state.elements.slice();
+              patched[idx] = { ...state.elements[idx], sourceDuration: result.duration };
+              return { elements: patched };
+            });
           }),
         );
       }