fix(core): keep rebound root timelines clock-driven (#5165)

* fix(core): keep rebound root timelines clock-driven

* test(core): verify transport advances the rebound root

Author: miguel-heygen

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

@@ -3669,6 +3669,61 @@ describe("initSandboxRuntimeModular", () => {
     }
   });
 
+  it("keeps a root rebound during playback paused on GSAP's ticker", () => {
+    vi.useFakeTimers({ toFake: ["setTimeout", "clearTimeout", "Date"] });
+    let nowMs = 1000;
+    vi.spyOn(performance, "now").mockImplementation(() => nowMs);
+    const raf = createManualRaf();
+    window.requestAnimationFrame = raf.requestAnimationFrame;
+    window.cancelAnimationFrame = raf.cancelAnimationFrame;
+    document.body.innerHTML =
+      '<div data-composition-id="main" data-root="true" data-start="0" data-duration="1">' +
+      '<video data-start="0"></video></div>';
+    const video = document.querySelector("video")!;
+    vi.spyOn(video, "play").mockResolvedValue(undefined);
+    vi.spyOn(video, "pause").mockImplementation(() => {});
+    const authored = gsap.timeline({ paused: true });
+    window.gsap = gsap;
+    window.__timelines = { main: authored };
+    const timelines = vi.spyOn(gsap, "timeline");
+    const messages = vi.spyOn(window.parent, "postMessage");
+
+    try {
+      initSandboxRuntimeModular();
+      vi.advanceTimersByTime(0);
+      window.__player!.play();
+      nowMs = 1250;
+      raf.step(250);
+      Object.defineProperty(video, "duration", { value: 12, configurable: true });
+      video.dispatchEvent(new Event("loadedmetadata"));
+      vi.advanceTimersByTime(100);
+
+      expect(
+        messages.mock.calls.some(
+          ([message]) =>
+            (message as { code?: string }).code === "timeline_rebind_after_media_metadata",
+        ),
+      ).toBe(true);
+      const rebound = timelines.mock.results.at(-1)?.value as gsap.core.Timeline;
+      expect(authored.parent).toBe(rebound);
+      expect(window.__player!.isPlaying()).toBe(true);
+      expect(rebound.paused()).toBe(true);
+      const time = rebound.time();
+      gsap.updateRoot(gsap.globalTimeline.time() + 0.5);
+      expect(rebound.time()).toBe(time);
+      expect(window.__player!.getTime()).toBe(0.25);
+      nowMs = 1350;
+      raf.step(100);
+      expect(rebound.time()).toBeCloseTo(0.35, 5);
+    } finally {
+      window.__hfRuntimeTeardown?.();
+      for (const result of timelines.mock.results) {
+        if (result.type === "return") (result.value as gsap.core.Timeline).kill();
+      }
+      authored.kill();
+    }
+  });
+
   it("sets __renderReady only after timeline is bound, not at __playerReady time", async () => {
     const root = document.createElement("div");
     root.setAttribute("data-composition-id", "main");

packages/core/src/runtime/init.ts

@@ -2294,21 +2294,17 @@ export function initSandboxRuntimeModular(): void {
       return false;
     }
     const previousTime = Math.max(0, state.currentTime || 0);
-    const wasPlaying = state.isPlaying;
     state.capturedTimeline = resolution.timeline;
     if (typeof state.capturedTimeline.timeScale === "function") {
       state.capturedTimeline.timeScale(state.playbackRate);
     }
     try {
       // pause guarded separately: a PARTIAL timeline without pause() must not
-      // abort the seek/play restore below (the catch would swallow them too).
+      // abort restoring the transport time below (the catch would swallow it too).
       pauseTimelineIfPossible(state.capturedTimeline);
       if (typeof state.capturedTimeline.seek === "function") {
         state.capturedTimeline.seek(previousTime, false);
       }
-      if (wasPlaying && typeof state.capturedTimeline.play === "function") {
-        state.capturedTimeline.play();
-      }
     } catch (err) {
       // keep runtime resilient even if a timeline implementation throws
       swallow("runtime.init.site7", err);