fix: 재생 큐 및 오디오 포커스 동시성 문제 수정

app/src/main/java/com/happyseal/zenplayer/features/player/data/AudioFocusManager.kt

@@ -39,8 +39,13 @@ class AudioFocusManager(
 ) {
     private val audioManager = context.getSystemService(Context.AUDIO_SERVICE) as AudioManager
 
+    @Volatile
     private var currentFocusState = FocusState.NO_FOCUS
+
+    @Volatile
     private var wasPlayingBeforeTransientLoss = false
+
+    @Volatile
     private var wasDucked = false
 
     private val audioFocusChangeListener =

app/src/main/java/com/happyseal/zenplayer/features/player/data/PlayQueueManager.kt

@@ -84,8 +84,11 @@ class PlayQueueManager(
      * 다음 곡 재생
      */
     override suspend fun playNext() {
-        check(_playQueue.value != null) { "재생 큐가 설정되지 않은 상태에서 playNext() 호출" }
-        playlistMutex.withLock { playNextInternal() }
+        val action = playlistMutex.withLock {
+            check(_playQueue.value != null) { "재생 큐가 설정되지 않은 상태에서 playNext() 호출" }
+            computeNextAction()
+        }
+        action()
     }
 
     /**
@@ -132,30 +135,33 @@ class PlayQueueManager(
             }
     }
 
-    private suspend fun playNextInternal() {
-        val current = _playQueue.value ?: return
+    // 락 안에서 상태를 변경하고, 락 밖에서 실행할 side effect(emit/play)를 반환한다.
+    private fun computeNextAction(): suspend () -> Unit {
+        val current = _playQueue.value ?: return {}
 
-        when (_repeatMode.value) {
-            RepeatMode.ONE -> {
-                current.currentTrack?.let { audioController.prepareTrack(it) }
+        if (_repeatMode.value == RepeatMode.ONE) {
+            val track = current.currentTrack
+            return {
+                track?.let { audioController.prepareTrack(it) }
                 audioController.play()
-                return
             }
-            // NONE/ALL은 공통 로직(다음 인덱스 계산)으로 fall-through
-            RepeatMode.NONE,
-            RepeatMode.ALL,
-            -> Unit
         }
 
         val nextIndex = getNextIndex(current)
-        if (nextIndex != null) {
+        return if (nextIndex != null) {
             val updated = current.copy(currentIndex = nextIndex)
             _playQueue.value = updated
-            updated.currentTrack?.let { audioController.prepareTrack(it) }
-            audioController.play()
+            val track = updated.currentTrack
+            {
+                track?.let { audioController.prepareTrack(it) }
+                audioController.play()
+            }
         } else {
-            _events.emit(PlaylistEvent.PlaylistEnded)
-            current.currentTrack?.let { audioController.prepareTrack(it) }
+            val track = current.currentTrack
+            {
+                _events.emit(PlaylistEvent.PlaylistEnded)
+                track?.let { audioController.prepareTrack(it) }
+            }
         }
     }