fix(core): enforce strict runtime safety

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

@@ -0,0 +1,57 @@
+import { describe, expect, it } from "vitest";
+import {
+  PLAY_REBIND_HOLD_SECONDS,
+  TIMELINE_REBIND_INTERVAL_FRAMES,
+  shouldAttemptPeriodicTimelineBind,
+} from "./timelineRebindPolicy";
+
+describe("shouldAttemptPeriodicTimelineBind", () => {
+  it("only checks for replacements at the periodic boundary", () => {
+    expect(
+      shouldAttemptPeriodicTimelineBind({
+        tick: TIMELINE_REBIND_INTERVAL_FRAMES - 1,
+        isPlaying: false,
+        hasCapturedTimeline: true,
+        currentTimeSeconds: 0,
+      }),
+    ).toBe(false);
+    expect(
+      shouldAttemptPeriodicTimelineBind({
+        tick: TIMELINE_REBIND_INTERVAL_FRAMES,
+        isPlaying: false,
+        hasCapturedTimeline: true,
+        currentTimeSeconds: 0,
+      }),
+    ).toBe(true);
+  });
+
+  it("holds a captured timeline during the first playback seconds", () => {
+    expect(
+      shouldAttemptPeriodicTimelineBind({
+        tick: TIMELINE_REBIND_INTERVAL_FRAMES,
+        isPlaying: true,
+        hasCapturedTimeline: true,
+        currentTimeSeconds: PLAY_REBIND_HOLD_SECONDS - 0.001,
+      }),
+    ).toBe(false);
+    expect(
+      shouldAttemptPeriodicTimelineBind({
+        tick: TIMELINE_REBIND_INTERVAL_FRAMES,
+        isPlaying: true,
+        hasCapturedTimeline: true,
+        currentTimeSeconds: PLAY_REBIND_HOLD_SECONDS,
+      }),
+    ).toBe(true);
+  });
+
+  it("does not hold when no timeline has bound yet", () => {
+    expect(
+      shouldAttemptPeriodicTimelineBind({
+        tick: TIMELINE_REBIND_INTERVAL_FRAMES,
+        isPlaying: true,
+        hasCapturedTimeline: false,
+        currentTimeSeconds: 0,
+      }),
+    ).toBe(true);
+  });
+});