fix(embedded-mpv): tighten effect signal-tracking to prevent latent re-run bugs

Audit followup to the support-loop and volume-restart fixes. Two more
effects pulled in transitive signal deps that would have caused the same
class of regression the next time the surrounding helpers grew.

1. Component session-fan-out effect: the body called
   scheduleControlsHide(), which reads isPlaying/menus.anyOpen/statusLabel/
   controlsVisible. Those became tracked deps of the effect, so opening a
   popover, pausing, or hovering re-ran the whole body — re-emitting
   timeUpdate. If a parent ever wires timeUpdate back into
   playback.startTime as a "resume where I left off" feature, this would
   have been the next stream-restart bug. Wrap the side-effect block in
   untracked() so the effect only listens to session changes.

2. Controller stalled-tracker effect: tracked the full session signal
   even though only status was needed. The session payload updates ~2 Hz
   during playback (positionSeconds advances), making the effect re-run
   constantly to call a no-op. Add a sessionStatus computed and track
   that instead — fires only on real status transitions.

No behavior change for current users; both fixes are preventative.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Entire-Checkpoint: f957cd9849e0

libs/ui/playback/src/lib/embedded-mpv-player/embedded-mpv-player.component.ts

@@ -295,12 +295,18 @@ export class EmbeddedMpvPlayerComponent implements OnDestroy {
             if (!session) {
                 return;
             }
-            this.volume.set(session.volume);
-            this.timeUpdate.emit({
-                currentTime: session.positionSeconds,
-                duration: session.durationSeconds ?? 0,
+            // Side effects must not pull in transitive signal deps via
+            // scheduleControlsHide — otherwise opening a popover, pausing, or
+            // hovering would re-run this body and re-emit timeUpdate (which
+            // could feed back into playback inputs and restart the stream).
+            untracked(() => {
+                this.volume.set(session.volume);
+                this.timeUpdate.emit({
+                    currentTime: session.positionSeconds,
+                    duration: session.durationSeconds ?? 0,
+                });
+                this.scheduleControlsHide();
             });
-            this.scheduleControlsHide();
         });
     }
 

libs/ui/playback/src/lib/embedded-mpv-player/embedded-mpv-session-controller.ts

@@ -1,6 +1,7 @@
 import {
     DestroyRef,
     Injectable,
+    computed,
     effect,
     inject,
     signal,
@@ -26,6 +27,10 @@ export class EmbeddedMpvSessionController {
     readonly stalled = signal(false);
     readonly retryToken = signal(0);
 
+    private readonly sessionStatus = computed(
+        () => this.session()?.status ?? null
+    );
+
     private readonly destroyRef = inject(DestroyRef);
     private readonly unsubscribeSessionUpdate?: () => void;
 
@@ -54,8 +59,11 @@ export class EmbeddedMpvSessionController {
             });
         }
 
+        // Track the narrowest possible signal — status only — so this effect
+        // does not re-run on every position-poll snapshot (~2 Hz during play)
+        // even though handleStalledTracking would be a no-op for those.
         effect(() => {
-            const status = this.session()?.status ?? null;
+            const status = this.sessionStatus();
             untracked(() => this.handleStalledTracking(status));
         });