fix(core): a GSAP call added after the first seek fires once, not twice (#4948)

The seek path skips its silent re-render on timelines with a zero-duration callback, because that
re-render re-arms the callback and the next forward seek fires it again. The answer was cached per
timeline on the first seek, so a tl.call added later was never seen: the re-render ran and the call
fired twice. The check now reads the timeline's current children on every seek.

Author: miguel-heygen

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

@@ -2897,6 +2897,29 @@ describe("initSandboxRuntimeModular", () => {
     expect(seekCalls).toEqual([{ time: 2, suppressEvents: false }]);
   });
 
+  it("fires a call added after the first seek exactly once", () => {
+    const root = document.createElement("div");
+    root.setAttribute("data-composition-id", "main");
+    root.setAttribute("data-root", "true");
+    root.setAttribute("data-start", "0");
+    root.setAttribute("data-duration", "10");
+    root.setAttribute("data-width", "1920");
+    root.setAttribute("data-height", "1080");
+    document.body.appendChild(root);
+
+    const main = gsap.timeline({ paused: true }).to({ x: 0 }, { x: 1, duration: 10 });
+    window.__timelines = { main };
+    initSandboxRuntimeModular();
+    window.__player?.renderSeek(1);
+
+    const fired = vi.fn();
+    main.call(fired, [], 2);
+    window.__player?.renderSeek(2);
+    window.__player?.renderSeek(3);
+
+    expect(fired).toHaveBeenCalledTimes(1);
+  });
+
   it("shows pip video at global start time even when host composition starts late", () => {
     // Regression: resolveStartForElement used to add the host composition's start on top of
     // the video's own data-start, causing double-offset. A pip video with data-start="45.40"

packages/core/src/runtime/init.ts

@@ -4249,7 +4249,6 @@ export function initSandboxRuntimeModular(): void {
   const isObjectRecord = (value: unknown): value is Record<string, unknown> =>
     typeof value === "object" && value !== null;
 
-  const gsapCallbackTweenCache = new WeakMap<RuntimeTimelineLike, boolean>();
   const GSAP_CALLBACK_NAMES = [
     "onStart",
     "onUpdate",
@@ -4271,9 +4270,6 @@ export function initSandboxRuntimeModular(): void {
   };
 
   const hasZeroDurationCallbackTween = (timeline: RuntimeTimelineLike): boolean => {
-    const cached = gsapCallbackTweenCache.get(timeline);
-    if (cached != null) return cached;
-
     if (!("getChildren" in timeline) || typeof timeline.getChildren !== "function") {
       return false;
     }
@@ -4283,13 +4279,9 @@ export function initSandboxRuntimeModular(): void {
       children = timeline.getChildren(true, true, true);
     } catch (err) {
       swallow("runtime.init.gsapCallbackChildren", err);
-      gsapCallbackTweenCache.set(timeline, false);
-      return false;
-    }
-    if (!Array.isArray(children)) {
-      gsapCallbackTweenCache.set(timeline, false);
       return false;
     }
+    if (!Array.isArray(children)) return false;
 
     for (const child of children) {
       if (!isObjectRecord(child)) continue;
@@ -4300,13 +4292,8 @@ export function initSandboxRuntimeModular(): void {
 
       const totalDuration = readGsapDuration(child, "totalDuration");
       const duration = totalDuration ?? readGsapDuration(child, "duration");
-      if (duration != null && duration <= 0.000001) {
-        gsapCallbackTweenCache.set(timeline, true);
-        return true;
-      }
+      if (duration != null && duration <= 0.000001) return true;
     }
-
-    gsapCallbackTweenCache.set(timeline, false);
     return false;
   };