test(playlist): pin the volume re-read across same-id channel entries

`createChannel` falls back to the URL for a missing id, so one stream listed
in two groups yields two entries sharing an id. The volume re-read must not
depend on ids being distinct; the linkedSignal now sources the channel itself
and the guarantee is pinned by a test.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

libs/playlist/m3u/feature-player/src/lib/video-player/video-player-movie-gate.spec.ts

@@ -357,5 +357,22 @@ describe('VideoPlayerComponent — M3U movie recognition gate', () => {
 
             expect(component.volume()).toBe(0);
         });
+
+        it('re-reads even when the next entry shares the previous id', () => {
+            // `createChannel` falls back to the URL for the id, so one stream
+            // listed under two groups yields two entries with the same id.
+            // Pins the user-visible guarantee independently of what the
+            // linkedSignal source happens to derive.
+            localStorage.setItem('volume', '0.8');
+            syncStoreState(movieChannel);
+            fixture.detectChanges();
+            expect(component.volume()).toBe(0.8);
+
+            localStorage.setItem('volume', '0.2');
+            syncStoreState({ ...movieChannel, group: { title: 'New' } });
+            fixture.detectChanges();
+
+            expect(component.volume()).toBe(0.2);
+        });
     });
 });

libs/playlist/m3u/feature-player/src/lib/video-player/video-player.component.ts

@@ -486,9 +486,18 @@ export class VideoPlayerComponent implements OnInit, OnDestroy {
      * with as soon as the user zapped after adjusting it in the player.
      * Remote-control writes still `set()` this signal directly and store the
      * same value, so re-reading the bus per channel agrees with them.
+     *
+     * The source is the whole channel, not a derived key: `linkedSignal`
+     * re-runs its computation whenever the source EXPRESSION invalidates —
+     * the derived value's equality does not gate it (`producerRecomputeValue`
+     * calls `computation()` right after re-evaluating `source()`). Selecting
+     * the channel is therefore the trigger, which is exactly the intent, and
+     * nothing here depends on ids being distinct — `createChannel` falls back
+     * to the URL, so one stream listed in two groups shares an id. A re-read
+     * is one idempotent localStorage hit, so an extra one costs nothing.
      */
     readonly volume = linkedSignal({
-        source: () => this.activeChannel()?.id ?? null,
+        source: () => this.activeChannel(),
         computation: () => readStoredVolume(),
     });