Don't queue display events while backgrounded

When we are backgrounded, don't queue display events.  This prevents
a hang and sluggish replay of display events once we are re-foregrounded
later

android/app/src/main/java/com/audiobookshelf/app/managers/SleepTimerManager.kt

@@ -527,4 +527,18 @@ constructor(private val playerNotificationService: PlayerNotificationService) {
 
     checkAutoSleepTimer()
   }
+
+  /**
+   * Sends the current sleep timer state to the client.
+   * Called when app resumes from background to sync UI state.
+   */
+  fun sendCurrentSleepTimerState() {
+    if (sleepTimerRunning) {
+      val timeRemaining = getSleepTimerTimeRemainingSeconds(getPlaybackSpeed())
+      playerNotificationService.clientEventEmitter?.onSleepTimerSet(timeRemaining, isAutoSleepTimer)
+    } else {
+      // No timer running - send 0 to clear any stale UI state
+      playerNotificationService.clientEventEmitter?.onSleepTimerSet(0, false)
+    }
+  }
 }

android/app/src/main/java/com/audiobookshelf/app/plugins/AbsAudioPlayer.kt

@@ -33,6 +33,9 @@ class AbsAudioPlayer : Plugin() {
 
   private var isCastAvailable:Boolean = false
 
+  // Track foreground state to avoid flooding WebView with events while backgrounded
+  private var isInForeground: Boolean = true
+
   override fun load() {
     mainActivity = (activity as MainActivity)
     apiHandler = ApiHandler(mainActivity)
@@ -60,6 +63,8 @@ class AbsAudioPlayer : Plugin() {
         }
 
         override fun onMetadata(metadata: PlaybackMetadata) {
+          // Skip frequent metadata updates when app is backgrounded to prevent event queue buildup
+          if (!isInForeground) return
           notifyListeners("onMetadata", JSObject(jacksonMapper.writeValueAsString(metadata)))
         }
 
@@ -68,6 +73,8 @@ class AbsAudioPlayer : Plugin() {
         }
 
         override fun onSleepTimerSet(sleepTimeRemaining: Int, isAutoSleepTimer:Boolean) {
+          // Skip sleep timer updates when app is backgrounded to prevent event queue buildup
+          if (!isInForeground) return
           val ret = JSObject()
           ret.put("value", sleepTimeRemaining)
           ret.put("isAuto", isAutoSleepTimer)
@@ -118,6 +125,26 @@ class AbsAudioPlayer : Plugin() {
     notifyListeners(evtName, ret)
   }
 
+  override fun handleOnPause() {
+    super.handleOnPause()
+    isInForeground = false
+    Log.d(tag, "App paused - disabling frequent event emission")
+  }
+
+  override fun handleOnResume() {
+    super.handleOnResume()
+    isInForeground = true
+    Log.d(tag, "App resumed - enabling event emission and sending current state")
+
+    // Send current state to UI after resume to sync up
+    if (::playerNotificationService.isInitialized && playerNotificationService.currentPlaybackSession != null) {
+      Handler(Looper.getMainLooper()).post {
+        playerNotificationService.sendClientMetadata(PlayerState.READY)
+        playerNotificationService.sleepTimerManager.sendCurrentSleepTimerState()
+      }
+    }
+  }
+
   private fun initCastManager() {
     val googleApi = GoogleApiAvailability.getInstance()
     val statusCode = googleApi.isGooglePlayServicesAvailable(mainActivity)