Silence a composition video as soon as its item ends

A video in a composition plays on a driven player that the item tells
where to stand every frame. When the item ended, its object was gone
and stopped asking, but the player ran on with its sound until it was
let go for being unused. That took 2 to 4 seconds, and in a pause it
never happened at all. The same held for the composition preview.

- A driven player nobody asked for in 100 ms is now paused and muted.
  When its wearer comes back it carries on where it should be, as
  before. It is still let go after 2 to 4 seconds.
- A player still without its first picture keeps playing, without
  sound, because it only gets that picture by playing.
- Leaving the animation or composition tab now silences their video
  preview at once instead of after 2 to 4 seconds.
- Free videos (Video clock free) keep the old behaviour. A sprite
  destroyed by a behavior is still heard for 2 to 4 seconds.

Tests:
- Unit video-library: 10 green (1 new). Without the new timer the
  new test is red.
- e2e 68: ALL PASSED, 11 checks (68g new). An item of 0.5 s with a
  2 s video plays audibly while it is there, and the player is
  paused and muted in every frame from about 200 ms after it ends.
- Gate on melektaus-atx: green, 305 files, 4737 tests.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/viewport/video-library.test.ts

@@ -213,6 +213,51 @@ describe('VideoLibrary driven players (#404)', () => {
     expect(videos.showsAsked(key)).toBe(true);
   });
 
+  it('holds a driven player quiet as soon as its wearer is gone, as an ended composition item', async () => {
+    vi.useFakeTimers({ toFake: ['setInterval', 'clearInterval', 'performance'] });
+    const events = new Map<string, () => void>();
+    let frames: (() => void)[] = [];
+    const element = {
+      ...fakeVideo(),
+      ended: false,
+      duration: 10,
+      playbackRate: 1,
+      seeking: false,
+      readyState: 4,
+      videoWidth: 320,
+      videoHeight: 180,
+      play() {
+        this.paused = false;
+        return Promise.resolve();
+      },
+      pause() {
+        this.paused = true;
+      },
+      addEventListener: (type: string, listener: () => void) => events.set(type, listener),
+      requestVideoFrameCallback: (callback: () => void) => frames.push(callback),
+    };
+    vi.stubGlobal('document', { hidden: false, addEventListener: () => {}, createElement: () => element });
+    const { soundLibrary } = await import('../../src/viewport/SoundLibrary');
+    vi.spyOn(soundLibrary, 'mediaInput').mockReturnValue(null);
+    const videos = await freshLibrary();
+    const props = { videoClock: 'driven', videoTime: 0 };
+    videos.wear(REF, props, 'view1:a', 'game');
+    events.get('loadeddata')!();
+    [frames] = [[], ...frames.map((frame) => frame())];
+    // Worn at 1x for a second, heard.
+    for (let ms = 0; ms <= 1000; ms += 1000 / 60) {
+      element.currentTime = ms / 1000;
+      videos.wear(REF, { ...props, videoTime: ms / 1000 }, 'view1:a', 'game');
+      vi.advanceTimersByTime(1000 / 60);
+    }
+    expect([element.paused, element.muted]).toEqual([false, false]);
+    // The item ends: nothing wears the player any more. Let go only after 2 s, it played on heard.
+    vi.advanceTimersByTime(200);
+    expect([element.paused, element.muted]).toEqual([true, true]);
+    expect(videos.debugInfo()).toHaveLength(1);
+    vi.useRealTimers();
+  });
+
   it('tells a view whether one of its driven players still waits for its first picture', async () => {
     const videos = await freshLibrary();
     videos.get(KEY);