fix(runtime): publish rebound timeline before apply

Author: vanceingalls

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

@@ -2708,13 +2708,18 @@ describe("initSandboxRuntimeModular", () => {
     const replacement = createMockTimeline(10);
     window.__timelines = { main: first };
     const applied: Array<Record<string, unknown>> = [];
+    const deliveryOrder: string[] = [];
     vi.spyOn(window.parent, "postMessage").mockImplementation((message: unknown) => {
       if (typeof message !== "object" || message === null) return;
       const payload = message as Record<string, unknown>;
+      if (payload.type === "timeline" || payload.type === "runtime-data-applied") {
+        deliveryOrder.push(String(payload.type));
+      }
       if (payload.type === "runtime-data-applied") applied.push(payload);
     });
 
     initSandboxRuntimeModular();
+    deliveryOrder.length = 0;
     window.__player?.seek(0.25);
     registerRuntimeDataHandler("captions", async () => {
       await Promise.resolve();
@@ -2733,6 +2738,7 @@ describe("initSandboxRuntimeModular", () => {
     expect(first.time()).toBeCloseTo(7 / 30, 5);
     expect(replacement.time()).toBeCloseTo(37 / 30, 5);
     expect(applied[0]).toMatchObject({ channel: "captions", requestId: 7 });
+    expect(deliveryOrder.slice(0, 2)).toEqual(["timeline", "runtime-data-applied"]);
   });
 
   it("does not seek a removed timeline after runtime data is cleared", async () => {

packages/core/src/runtime/init.ts

@@ -1582,7 +1582,14 @@ export function initSandboxRuntimeModular(): void {
     }
     syncTimedElementVisibility(state.currentTime);
   };
-  reconcileTimelineAfterRuntimeData = reconcileTimeline;
+  reconcileTimelineAfterRuntimeData = () => {
+    reconcileTimeline();
+    // The parent treats runtime-data-applied as permission to re-seek immediately. Publish the
+    // replacement duration first; otherwise that seek is clamped by the bootstrap timeline (often
+    // one second) and a style switch appears frozen on the first caption segment until some later
+    // polling tick happens to post the rebuilt timeline.
+    postTimeline();
+  };
   (window as Window & { __hfForceTimelineRebind?: () => void }).__hfForceTimelineRebind =
     reconcileTimeline;