fix(player): drive composition ticks from widget-frame rAF via postMessage (#805)

Chromium throttles requestAnimationFrame in deeply nested cross-origin
iframes. In Claude desktop (Electron), the composition iframe's own rAF
loop stalls, so GSAP is never seeked and animation freezes even when
TransportClock.isPlaying() is true.

The correct fix is to drive ticks from the widget-frame rAF, which lives
one level up and is not subject to the same throttling. When play() takes
the runtime bridge path (no direct timeline adapter), the player now starts
a parent-frame rAF loop that sends "tick" postMessages to the composition
iframe on every frame. The runtime's control bridge handles "tick" by calling
seekTimelineAndAdapters(clock.now()) if the clock is playing — identical to
what transportTick does on each rAF, just driven from outside.

The composition iframe's own rAF loop is unchanged and keeps running
normally in standard browsers. Seeking GSAP twice per frame is idempotent,
so there is no regression on claude.ai or any other non-throttled environment.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core/src/runtime/bridge.test.ts

@@ -6,6 +6,7 @@ function createMockDeps() {
     onPlay: vi.fn(),
     onPause: vi.fn(),
     onSeek: vi.fn(),
+    onTick: vi.fn(),
     onSetMuted: vi.fn(),
     onSetVolume: vi.fn(),
     onSetMediaOutputMuted: vi.fn(),
@@ -110,6 +111,13 @@ describe("installRuntimeControlBridge", () => {
     expect(deps.onSetPlaybackRate).toHaveBeenCalledWith(1);
   });
 
+  it("dispatches tick command", () => {
+    const deps = createMockDeps();
+    const handler = installRuntimeControlBridge(deps);
+    handler(makeControlMessage("tick"));
+    expect(deps.onTick).toHaveBeenCalledOnce();
+  });
+
   it("dispatches enable-pick-mode", () => {
     const deps = createMockDeps();
     const handler = installRuntimeControlBridge(deps);

packages/core/src/runtime/bridge.ts

@@ -5,6 +5,7 @@ type BridgeDeps = {
   onPlay: () => void;
   onPause: () => void;
   onSeek: (frame: number, seekMode: "drag" | "commit") => void;
+  onTick: () => void;
   onSetMuted: (muted: boolean) => void;
   onSetVolume: (volume: number) => void;
   onSetMediaOutputMuted: (muted: boolean) => void;
@@ -39,6 +40,10 @@ export function installRuntimeControlBridge(deps: BridgeDeps): (event: MessageEv
       deps.onSeek(Number(data.frame ?? 0), data.seekMode ?? "commit");
       return;
     }
+    if (action === "tick") {
+      deps.onTick();
+      return;
+    }
     if (action === "set-muted") {
       deps.onSetMuted(Boolean(data.muted));
       return;

packages/core/src/runtime/init.ts

@@ -1602,6 +1602,27 @@ export function initSandboxRuntimeModular(): void {
       applyPlaybackRate(rate);
       if (state.transportClock) state.transportClock.setRate(state.playbackRate);
     },
+    onTick: () => {
+      if (state.tornDown || !clock.isPlaying()) return;
+      const t = clock.now();
+      state.currentTime = t;
+      seekTimelineAndAdapters(t);
+      if (clock.reachedEnd()) {
+        webAudio.stopAll();
+        clock.detachAudioSource();
+        clock.pause();
+        state.isPlaying = false;
+        const dur = clock.getDuration();
+        if (Number.isFinite(dur)) {
+          clock.seek(dur);
+          state.currentTime = dur;
+          seekTimelineAndAdapters(dur);
+        }
+        runAdapters("pause");
+        syncMediaForCurrentState();
+        postState(true);
+      }
+    },
     onEnablePickMode: () => picker.enablePickMode(),
     onDisablePickMode: () => picker.disablePickMode(),
   });

packages/core/src/runtime/types.ts

@@ -10,6 +10,7 @@ export type RuntimeBridgeControlAction =
   | "play"
   | "pause"
   | "seek"
+  | "tick"
   | "set-muted"
   | "set-volume"
   | "set-media-output-muted"

packages/player/src/hyperframes-player.ts

@@ -55,6 +55,7 @@ class HyperframesPlayer extends HTMLElement {
   private _compositionHeight = 1080;
   private _directTimelineAdapter: DirectTimelineAdapter | null = null;
   private _directTimelineClock: DirectTimelineClock;
+  private _parentTickRaf: number | null = null;
   private _media: ParentMediaManager;
 
   constructor() {
@@ -134,6 +135,7 @@ class HyperframesPlayer extends HTMLElement {
     this.iframe.removeEventListener("load", this._onIframeLoad);
     this.probe.stop();
     this._directTimelineClock.stop();
+    this._stopParentTickClock();
     this._directTimelineAdapter = null;
     this.shaderLoader.destroy();
     this._media.destroy();
@@ -217,10 +219,21 @@ class HyperframesPlayer extends HTMLElement {
     this.posterEl?.remove();
     this.posterEl = null;
     if (this._duration > 0 && this._currentTime >= this._duration) this.seek(0);
-    const directTimelineStarted = this._tryDirectTimelinePlay();
+    // Must be set before _startParentTickClock so the RAF loop's `_paused`
-    if (!directTimelineStarted) this._sendControl("play");
+    // check doesn't immediately self-terminate on the first callback.
-    if (this._media.audioOwner === "parent") this._media.playAll();
     this._paused = false;
+    const directTimelineStarted = this._tryDirectTimelinePlay();
+    if (!directTimelineStarted) {
+      this._sendControl("play");
+      // Only start the parent tick clock once the composition is ready and
+      // confirmed on the runtime bridge path (not the direct-timeline path).
+      // Guards against firing ticks into an uninitialized iframe when play()
+      // is called before the probe has resolved.
+      if (this._ready && !this._directTimelineAdapter) {
+        this._startParentTickClock();
+      }
+    }
+    if (this._media.audioOwner === "parent") this._media.playAll();
     this.controlsApi?.updatePlaying(true);
     this.dispatchEvent(new Event("play"));
     if (directTimelineStarted && this._directTimelineAdapter) {
@@ -236,6 +249,7 @@ class HyperframesPlayer extends HTMLElement {
   pause() {
     if (!this._tryDirectTimelinePause()) this._sendControl("pause");
     this._directTimelineClock.stop();
+    this._stopParentTickClock();
     if (this._media.audioOwner === "parent") this._media.pauseAll();
     this._paused = true;
     this.controlsApi?.updatePlaying(false);
@@ -247,6 +261,7 @@ class HyperframesPlayer extends HTMLElement {
       this._sendControl("seek", { frame: Math.round(timeInSeconds * 30) });
     }
     this._directTimelineClock.stop();
+    this._stopParentTickClock();
     this._currentTime = timeInSeconds;
     if (this._media.audioOwner === "parent") this._media.seekAll(timeInSeconds);
     this._paused = true;
@@ -378,6 +393,33 @@ class HyperframesPlayer extends HTMLElement {
     return this._withDirectTimeline((tl) => void tl.pause());
   }
 
+  /**
+   * Widget-frame RAF loop that sends "tick" postMessages to the composition
+   * iframe on every frame. Used for the runtime bridge path so that animation
+   * advances even when the composition iframe's own rAF is throttled by
+   * Chromium (e.g. deeply nested cross-origin iframes in Electron / Claude desktop).
+   * The runtime's own rAF loop still runs — ticking GSAP twice per frame is
+   * harmless because seekTimelineAndAdapters is idempotent.
+   */
+  private _startParentTickClock(): void {
+    this._stopParentTickClock();
+    const tick = () => {
+      if (this._paused) {
+        this._parentTickRaf = null;
+        return;
+      }
+      this._sendControl("tick");
+      this._parentTickRaf = requestAnimationFrame(tick);
+    };
+    this._parentTickRaf = requestAnimationFrame(tick);
+  }
+
+  private _stopParentTickClock(): void {
+    if (this._parentTickRaf === null) return;
+    cancelAnimationFrame(this._parentTickRaf);
+    this._parentTickRaf = null;
+  }
+
   private _onMessage(e: MessageEvent) {
     handleRuntimeMessage(e, this.iframe.contentWindow, {
       getPlaybackState: () => ({
@@ -438,6 +480,7 @@ class HyperframesPlayer extends HTMLElement {
   private _onIframeLoad() {
     this._directTimelineAdapter = null;
     this._directTimelineClock.stop();
+    this._stopParentTickClock();
     this.shaderLoader.reset();
     this._media.resetForIframeLoad();
     this.probe.start();