Fix persistent low volume after uninstalling Background Music

BGMApp/BGMApp/BGMAppDelegate.mm

@@ -369,12 +369,18 @@ - (void) initVolumesMenuSection {
 
 - (void) applicationWillTerminate:(NSNotification*)aNotification {
     #pragma unused (aNotification)
-    
+
     DebugMsg("BGMAppDelegate::applicationWillTerminate");
 
+    // Deactivate control sync and playthrough before changing the default device back. This
+    // prevents the default device change from triggering volume sync listeners that could leave
+    // the output device at the wrong volume. See
+    // https://github.com/kyleneideck/BackgroundMusic/issues/841
+    [audioDevices prepareForTermination];
+
     // Change the user's default output device back.
     NSError* error = [audioDevices unsetBGMDeviceAsOSDefault];
-    
+
     if (error) {
         [self showSetDeviceAsDefaultError:error
                                   message:@"Failed to reset your system's audio output device."

BGMApp/BGMApp/BGMAudioDeviceManager.h

@@ -63,6 +63,11 @@ static const int kBGMErrorCode_ReturningEarly       = 2;
 // Replace BGMDevice as the default device with the output device
 - (NSError* __nullable) unsetBGMDeviceAsOSDefault;
 
+// Prepare for app termination by deactivating control sync and playthrough before the default
+// device is changed back. This prevents stale volume state from being left on the output device.
+// Must be called before unsetBGMDeviceAsOSDefault.
+- (void) prepareForTermination;
+
 #ifdef __cplusplus
 // The virtual device published by BGMDriver.
 - (BGMBackgroundMusicDevice) bgmDevice;

BGMApp/BGMApp/BGMAudioDeviceManager.mm

@@ -128,6 +128,33 @@ - (NSError* __nullable) setBGMDeviceAsOSDefault {
     return nil;
 }
 
+- (void) prepareForTermination {
+    DebugMsg("BGMAudioDeviceManager::prepareForTermination: Deactivating control sync and "
+             "playthrough before termination");
+
+    @try {
+        [stateLock lock];
+
+        // Deactivate control sync BEFORE changing the default device. This removes the volume/mute
+        // listeners so that the default device change doesn't trigger any stale volume sync that
+        // could leave the output device at the wrong volume.
+        // See https://github.com/kyleneideck/BackgroundMusic/issues/841
+        BGMLogAndSwallowExceptions("BGMAudioDeviceManager::prepareForTermination", [&] {
+            deviceControlSync.Deactivate();
+        });
+
+        // Stop playthrough so we don't try to pass audio during shutdown.
+        BGMLogAndSwallowExceptions("BGMAudioDeviceManager::prepareForTermination", [&] {
+            playThrough.Deactivate();
+        });
+        BGMLogAndSwallowExceptions("BGMAudioDeviceManager::prepareForTermination", [&] {
+            playThrough_UISounds.Deactivate();
+        });
+    } @finally {
+        [stateLock unlock];
+    }
+}
+
 - (NSError* __nullable) unsetBGMDeviceAsOSDefault {
     // Copy the devices so we can call the HAL without holding stateLock. See startPlayThroughSync.
     BGMBackgroundMusicDevice* bgmDeviceCopy;

BGMApp/BGMApp/BGMTermination.mm

@@ -122,6 +122,10 @@
     // it's better for things to work even if BGMXPCHelper isn't installed.
     if(sAudioDevices)
     {
+        // Deactivate control sync and playthrough before changing the default device back.
+        // This prevents the default device change from triggering volume sync that could leave
+        // the output device at the wrong volume.
+        [sAudioDevices prepareForTermination];
         [sAudioDevices unsetBGMDeviceAsOSDefault];
     }
 }

BGMApp/BGMApp/_uninstall-non-interactive.sh

@@ -133,6 +133,29 @@ osascript -e 'tell application id "com.apple.finder"
   || rm -rf "${trash_dir}" \
   || true
 
+# Clean up BGMDevice entries from macOS audio preferences to prevent persistent low volume
+# after uninstall. See https://github.com/kyleneideck/BackgroundMusic/issues/841
+echo "Cleaning up audio device preferences."
+for plist_dir in "$HOME/Library/Preferences" "/Library/Preferences/Audio"; do
+  for plist in "com.apple.audio.DeviceSettings.plist" "com.apple.audio.SystemSettings.plist"; do
+    plist_path="${plist_dir}/${plist}"
+    if [ -f "${plist_path}" ]; then
+      # Remove entries keyed by BGMDevice UIDs
+      for uid in "BGMDevice" "BGMDevice_UISounds"; do
+        defaults delete "${plist_path}" "${uid}" &>/dev/null || true
+      done
+    fi
+  done
+done
+# Also clean up ByHost audio preferences
+for byhost_plist in "$HOME/Library/Preferences/ByHost"/com.apple.audio.*.plist; do
+  if [ -f "${byhost_plist}" ]; then
+    for uid in "BGMDevice" "BGMDevice_UISounds"; do
+      defaults delete "${byhost_plist}" "${uid}" &>/dev/null || true
+    done
+  fi
+done
+
 echo "Restarting Core Audio."
 # Wait a little because moving files to the trash plays a short sound.
 sleep 2