fix(player): return from background audio onto the episode it advanced to

An episode that ends while backgrounded in audio-only mode advances in the
backend, but player_exit_background_audio returned only a position, so the
video page reloaded the episode it was mounted with -- the previous one, at
the new episode's timestamp.

The command now returns BackgroundAudioResume { itemId, positionSeconds }.
planHandoffReturn yields "other-item" when the id differs from the mounted
one, and the player page navigates to that episode with resumeAt=<seconds>,
marking the outgoing episode watched and suppressing its stale stop report.

TRACES: UR-040, UR-023 | DR-296 | UT-265, UT-266

src-tauri/src/commands/player/mod.rs

@@ -939,12 +939,17 @@ pub async fn player_background_action(
     Ok(action)
 }
 
-/// TRACES: UR-040 | DR-052 | UT-061, IT-013
+/// Returns the item the native player is on and its absolute position. The
+/// item matters: an episode that ended while backgrounded has already advanced
+/// in the backend, so reloading the video the webview was mounted with would
+/// bring back the previous episode. (DR-296)
+///
+/// TRACES: UR-040, UR-023 | DR-052, DR-296 | UT-061, IT-013
 #[tauri::command]
 #[specta::specta]
 pub async fn player_exit_background_audio(
     player: State<'_, PlayerStateWrapper>,
-) -> Result<f64, String> {
+) -> Result<crate::player::BackgroundAudioResume, String> {
     let controller = player.0.lock().await;
 
     // Read the position BEFORE clearing either base. The position tick applies the
@@ -954,23 +959,23 @@ pub async fn player_exit_background_audio(
     // lock discipline from CLAUDE.md: never hold work across a re-entrant call.
     // (DR-159)
     //
-    // `absolute_position` rather than `position`, because a tick that has not
+    // `background_audio_resume` reads `absolute_position` rather than `position`, because a tick that has not
     // landed *yet* is the same hazard from the other side: returning to the
     // foreground while the audio-only transcode is still opening read 0.0, and
     // the video reloaded at StartTimeTicks=0 — the episode restarting from the
     // beginning. Flooring at the handoff base cannot overshoot: the stream is
     // physically incapable of being behind its own starting point. (DR-178)
-    let absolute = controller.absolute_position();
+    let resume = controller.background_audio_resume();
 
     // Now safe to tear the handoff down, native side first.
     let _ = crate::player::set_lockscreen_position_offset(0.0);
     controller.exit_background_audio();
     controller.stop().map_err(|e| e.to_string())?;
     info!(
-        "player_exit_background_audio: resuming the video at {:.1}s",
-        absolute
+        "player_exit_background_audio: resuming {:?} at {:.1}s",
+        resume.item_id, resume.position_seconds
     );
-    Ok(absolute)
+    Ok(resume)
 }
 
 /// Play a queue of media items