fix: eliminate notification/playerbar song desync on Android

Two-pronged fix for the state drift between the system notification
(ground truth) and the WebView player bar:

JS (player.js): onTrackChanged now reconciles the incoming index with a
synchronous NSBridge.getState() call before applying it. Stale callbacks
from earlier rapid skips immediately correct themselves to the live
settled index instead of overwriting the correct state.

Kotlin (MusicService.kt): debounce JS-initiated transitions (seek /
setQueue) by 120 ms so rapid skip sequences produce one onTrackChanged
notification at the final index rather than one per skip step. Auto-advance
transitions are still fired immediately since JS doesn't initiate those.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

android/app/src/main/kotlin/com/novasonic/app/MusicService.kt

@@ -155,6 +155,10 @@ class MusicService : MediaSessionService() {
 
     private inner class PlayerListener : Player.Listener {
 
+        // Debounce JS-initiated transitions (seek / queue-replace) so rapid skips
+        // produce one onTrackChanged notification with the final settled state.
+        private var _pendingTrackChanged: Runnable? = null
+
         override fun onIsPlayingChanged(isPlaying: Boolean) {
             val state = player.playbackState
             stateListener?.onPlaybackStateChanged(
@@ -184,14 +188,31 @@ class MusicService : MediaSessionService() {
                 Player.MEDIA_ITEM_TRANSITION_REASON_PLAYLIST_CHANGED -> "queue"
                 else                                                  -> "seek"
             }
+            // Always warm artwork immediately so the notification never shows a blank cover.
+            warmArtworkCache()
+
+            // Cancel any pending debounced dispatch from a previous transition.
+            _pendingTrackChanged?.let { handler.removeCallbacks(it) }
+            _pendingTrackChanged = null
+
+            val dispatch = Runnable {
+                _pendingTrackChanged = null
                 stateListener?.onTrackChanged(
                     player.currentMediaItemIndex,
-                mediaItem?.mediaId ?: "",
+                    player.currentMediaItem?.mediaId ?: "",
                     reasonStr
                 )
-            // Pre-warm artwork for current + next tracks so notification
-            // never shows a blank cover on auto-advance.
-            warmArtworkCache()
+            }
+
+            if (reason == Player.MEDIA_ITEM_TRANSITION_REASON_AUTO) {
+                // Native auto-advance: JS didn't initiate this, notify immediately.
+                dispatch.run()
+            } else {
+                // JS-initiated (seek or setQueue): debounce 120 ms so rapid skips
+                // coalesce into one callback with the final settled index.
+                _pendingTrackChanged = dispatch
+                handler.postDelayed(dispatch, 120)
+            }
         }
 
         override fun onTimelineChanged(timeline: Timeline, reason: Int) {

src/player.js

@@ -143,9 +143,16 @@ window.NSPlayer = {
     try {
       const p = JSON.parse(payloadJson);
       if (typeof p.index !== 'number') return;
-      if (p.index < 0 || p.index >= S.queue.length) return;
-      const indexChanged = (p.index !== S.qIdx);
-      S.qIdx = p.index;
+      // Reconcile with the live native state so stale out-of-order callbacks
+      // (e.g. from rapid skips) don't overwrite the already-correct index.
+      let idx = p.index;
+      try {
+        const live = JSON.parse(window.NSBridge.getState() || '{}');
+        if (typeof live.currentIndex === 'number') idx = live.currentIndex;
+      } catch {}
+      if (idx < 0 || idx >= S.queue.length) return;
+      const indexChanged = (idx !== S.qIdx);
+      S.qIdx = idx;
       const s = S.queue[S.qIdx];
       if (!s) return;
       updatePlayerUI(s, true);