fix(core,player,studio): bound trimmed audio playback to the clip window (#1430)

* fix(player): bound the parent audio proxy to its clip window

When iframe autoplay is blocked, audible playback is promoted to a parent-frame
audio proxy. The proxy read the clip's data-start/data-duration once at adopt
time and mirrorTime() only skipped (never paused) the element outside that
window — so a trimmed/moved music clip kept playing the full source past its
on-timeline end, even though the iframe element was correctly paused.

Fix: the proxy keeps a reference to its source iframe element and re-reads
data-start/data-duration each mirror tick (live trims/moves apply), pauses the
proxy when the playhead leaves [start, start+duration), and resumes it when the
playhead re-enters during parent-owned playback.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Co-authored-by: Miguel Ángel <miguel07alm@protonmail.com>

* fix(core,studio): bound trimmed audio playback to the clip window

Trimmed audio played to the source file's natural end instead of
stopping at the clip edge, on every audio path:

- WebAudio (the audible path in Studio): schedulePlayback now passes
  the clip's data-duration as the third start() arg, so the decoded
  buffer stops at the trimmed edge instead of running to the file end.
- Runtime element gating: the duration resolver caps each clip by its
  own data-duration (min of source length, host window, authored
  duration), so a trimmed <audio>/<video> element pauses at its edge.

Studio trim UX:

- Resize live-patches the media-start/playback-start offset, so a
  start-edge drag trims into the source instead of only repositioning
  the clip.
- AudioWaveform windows the rendered peaks to the trimmed slice so the
  waveform tracks the clip edges.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Co-authored-by: Miguel Ángel <miguel07alm@protonmail.com>

* fix(player,core): gate proxy playback to the live clip window

Review follow-ups on the parent-audio-proxy / WebAudio bound:
- seekAll now re-reads live source bounds (_refreshEntryBounds) before
  gating, so a paused scrub right after a trim/move uses the current clip
  window instead of the adopt-time one.
- playAll and clip adoption only start a proxy when the playhead is inside
  the clip's window (_playEntryIfActive), so bulk starts / promotion no
  longer blip audio for clips outside their window until the next tick.
- The WebAudio buffer is now bounded by the host-composition window too
  (matching resolveDurationSeconds), so a sub-composition-nested clip stops
  at the same edge on the WebAudio and HTMLMedia paths.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Co-authored-by: Miguel Ángel <miguel07alm@protonmail.com>

* fix(core,player): reschedule bounded WebAudio on rate change; guard NaN bounds

A bounded WebAudio source's wall-clock length is baked into start()'s duration
arg (in buffer-sample seconds) at its scheduling rate. Mutating playbackRate in
place on a later rate change does not rescale that bound, so a trimmed clip ends
early (fast) or late (slow). setRate now reports whether the rate changed and
exposes hasBoundedActiveSources(); the runtime stopAll()+reschedules active
clips at the new rate when any bounded source is live. The per-clip schedule
loop is extracted to a shared closure so play() and the rate path agree.

Also guard _refreshEntryBounds against a non-numeric duration attribute parsing
to NaN, which would make every window check false and let the proxy play past
its clip end.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Co-authored-by: Miguel Ángel <miguel07alm@protonmail.com>

---------

Co-authored-by: Miguel Ángel <miguel07alm@protonmail.com>

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

@@ -171,6 +171,43 @@ describe("WebAudioTransport", () => {
     });
   });
 
+  describe("clip duration bound (trim)", () => {
+    it("bounds an in-progress clip to its remaining authored window", async () => {
+      const { transport, mock, gen } = setupTransport(100);
+      // compStart=5, mediaStart=0, compTime=8 → elapsed=3; clipDuration=10 → 7 left
+      await transport.schedulePlayback(mockEl, mockBuffer, 5, 0, 8, 1, gen, 1, 10);
+      expect(mock.startFn).toHaveBeenCalledWith(0, 3, 7);
+    });
+
+    it("bounds a future clip to its full authored window", async () => {
+      const { transport, mock, gen } = setupTransport(100);
+      // compStart=10, mediaStart=1.5, compTime=2 → elapsed=-8 → delay 8; clipDuration=4
+      await transport.schedulePlayback(mockEl, mockBuffer, 10, 1.5, 2, 1, gen, 1, 4);
+      expect(mock.startFn).toHaveBeenCalledWith(108, 1.5, 4);
+    });
+
+    it("does not schedule a clip whose window has already elapsed", async () => {
+      const { transport, mock, gen } = setupTransport(100);
+      // elapsed=15 > clipDuration=10 → nothing to play
+      const result = await transport.schedulePlayback(mockEl, mockBuffer, 5, 0, 20, 1, gen, 1, 10);
+      expect(result).toBeNull();
+      expect(mock.startFn).not.toHaveBeenCalled();
+    });
+
+    it("scales the bound by playback rate (buffer seconds)", async () => {
+      const { transport, mock, gen } = setupTransport(100);
+      // rate=2, clipDuration=10 → clipSourceLen=20; elapsed=3 → 17 buffer seconds left
+      await transport.schedulePlayback(mockEl, mockBuffer, 5, 0, 8, 1, gen, 2, 10);
+      expect(mock.startFn).toHaveBeenCalledWith(0, 3, 17);
+    });
+
+    it("plays unbounded when clipDuration is omitted (legacy behavior)", async () => {
+      const { transport, mock, gen } = setupTransport(100);
+      await transport.schedulePlayback(mockEl, mockBuffer, 5, 0, 8, 1, gen);
+      expect(mock.startFn).toHaveBeenCalledWith(0, 3);
+    });
+  });
+
   describe("playback rate", () => {
     it("sets sourceNode.playbackRate.value when rate is provided", async () => {
       const { transport, mock, gen } = setupTransport(100);