fix: harden adaptive audio resume and release

tests/unit/adaptive-mixer.test.ts

@@ -74,6 +74,32 @@ describe('adaptive mixer', () => {
       .toContainEqual(expect.objectContaining({ kind: 'linear', value: 0 }));
   });
 
+  it('finishes an audible lift entry smoothly before scheduling its exit', () => {
+    const harness = createFakeAudioHarness();
+    const mixer = createAdaptiveMixer(harness.context, harness.destination);
+    const liftGate = harness.gainNodes[3]!.gain;
+    const liftEvents = recordFor(harness, liftGate).events;
+    mixer.setTransportAnchor(0);
+    mixer.setDriveLiftAvailableAt(0);
+    harness.setCurrentTime(1);
+    mixer.setDriveEnergy({ energy: 0.7, source: 'physical' });
+    const eventsBeforeDrop = liftEvents.length;
+
+    const entryMidpoint = 3.5 * MUSIC_BEAT_SECONDS;
+    harness.setCurrentTime(entryMidpoint);
+    mixer.setDriveEnergy({ energy: 0.2, source: 'physical' });
+
+    expect(liftEvents).toContainEqual({
+      kind: 'linear',
+      value: 1,
+      at: 4 * MUSIC_BEAT_SECONDS,
+    });
+    expect(liftEvents.slice(eventsBeforeDrop)).toEqual([
+      { kind: 'set', value: 1, at: 5 * MUSIC_BEAT_SECONDS },
+      { kind: 'linear', value: 0, at: 6 * MUSIC_BEAT_SECONDS },
+    ]);
+  });
+
   it('replays cached strong drive only after a late loop source is ready', () => {
     const harness = createFakeAudioHarness();
     const mixer = createAdaptiveMixer(harness.context, harness.destination);

tests/unit/soundtrack-engine.test.ts

@@ -298,6 +298,20 @@ describe('soundtrack engine', () => {
     expect(test.mixer.setDriveLiftAvailableAt).toHaveBeenCalledWith(drive.starts[0]!.at);
   });
 
+  it('does not reload the attached drive lift after resuming established main playback', async () => {
+    const test = createEngineHarness({
+      chapter: resolveChapterIntent('experience'),
+      drive: { energy: 0.8, source: 'physical' },
+    });
+    await test.graph.resume();
+    await test.flushOptionalLoads();
+
+    await test.graph.suspend();
+    await test.graph.resume();
+
+    expect(test.loadCalls.filter((url) => url === '/drive-lift.opus')).toHaveLength(1);
+  });
+
   it('routes drive commands immediately to texture and mixer', () => {
     const test = createEngineHarness();
     const sample = { energy: 0.72, source: 'physical' } as const;