fix: watch together guest losing sync when host switches episodes

close #431

lib/watch_together/models/sync_message.dart

@@ -45,6 +45,9 @@ enum SyncMessageType {
 
   /// Player is ready (attached and loaded)
   playerReady,
+
+  /// Request session config from host (guest recovery)
+  requestSessionConfig,
 }
 
 /// A message sent over the WebRTC data channel for synchronization
@@ -181,12 +184,18 @@ class SyncMessage {
   }
 
   /// Create a SESSION_CONFIG message (sent by host to new guests)
+  ///
+  /// Optionally includes current media info so guests can catch up
+  /// if they missed a mediaSwitch broadcast.
   factory SyncMessage.sessionConfig({
     required ControlMode controlMode,
     required Duration currentPosition,
     required bool isPlaying,
     required double playbackRate,
     String? peerId,
+    String? ratingKey,
+    String? serverId,
+    String? mediaTitle,
   }) {
     return SyncMessage(
       type: SyncMessageType.sessionConfig,
@@ -196,6 +205,18 @@ class SyncMessage {
       bufferingState: !isPlaying, // Reuse field: false = playing, true = paused
       rate: playbackRate,
       peerId: peerId,
+      ratingKey: ratingKey,
+      serverId: serverId,
+      mediaTitle: mediaTitle,
+    );
+  }
+
+  /// Create a REQUEST_SESSION_CONFIG message (sent by guest to request current config from host)
+  factory SyncMessage.requestSessionConfig({String? peerId}) {
+    return SyncMessage(
+      type: SyncMessageType.requestSessionConfig,
+      timestamp: DateTime.now().millisecondsSinceEpoch,
+      peerId: peerId,
     );
   }
 

lib/watch_together/providers/watch_together_provider.dart

@@ -356,6 +356,10 @@ class WatchTogetherProvider with ChangeNotifier {
         _handleSessionConfig(message);
         break;
 
+      case SyncMessageType.requestSessionConfig:
+        // Handled at sync manager level (host responds with config)
+        break;
+
       default:
         break;
     }
@@ -372,6 +376,18 @@ class WatchTogetherProvider with ChangeNotifier {
       _syncManager?.updateSession(_session!); // Update sync manager if it exists
       notifyListeners();
     }
+
+    // If config contains media info that differs from our current state,
+    // trigger a media switch so the guest navigates to the correct content.
+    // This handles the case where a guest missed a mediaSwitch broadcast
+    // (e.g., host switched episodes while guest was popping out of the player).
+    if (message.ratingKey != null &&
+        message.serverId != null &&
+        message.mediaTitle != null &&
+        message.ratingKey != _session?.mediaRatingKey) {
+      appLogger.d('WatchTogether: Session config contains different media, triggering switch');
+      _handleMediaSwitch(message);
+    }
   }
 
   /// Called when user seeks locally (to broadcast to peers)
@@ -431,7 +447,17 @@ class WatchTogetherProvider with ChangeNotifier {
 
     appLogger.d('WatchTogether: Received media switch: ${message.mediaTitle}');
 
-    // Update local session state
+    // Dispatch callback BEFORE updating session state.
+    // If the callback fails silently (e.g., player disposed mid-animation),
+    // the ratingKey stays unchanged so the next positionSync or re-sent
+    // message can retry instead of being treated as a duplicate.
+    if (onPlayerMediaSwitched != null) {
+      onPlayerMediaSwitched!(message.ratingKey!, message.serverId!, message.mediaTitle!);
+    } else {
+      onMediaSwitched?.call(message.ratingKey!, message.serverId!, message.mediaTitle!);
+    }
+
+    // Update local session state after successful dispatch
     _session = _session?.copyWith(
       mediaRatingKey: message.ratingKey,
       mediaServerId: message.serverId,
@@ -439,15 +465,6 @@ class WatchTogetherProvider with ChangeNotifier {
     );
 
     notifyListeners();
-
-    // If player handler is set (VideoPlayerScreen is active), use that for proper navigation context
-    if (onPlayerMediaSwitched != null) {
-      onPlayerMediaSwitched!(message.ratingKey!, message.serverId!, message.mediaTitle!);
-      return;
-    }
-
-    // Otherwise, trigger app-level navigation callback (MainScreen handles it)
-    onMediaSwitched?.call(message.ratingKey!, message.serverId!, message.mediaTitle!);
   }
 
   /// Notify guests that host is exiting the video player
@@ -469,6 +486,11 @@ class WatchTogetherProvider with ChangeNotifier {
 
     appLogger.d('WatchTogether: Host exited player, callback set: ${onHostExitedPlayer != null}');
 
+    // Clear the player callback BEFORE popping so that any mediaSwitch message
+    // arriving during the pop animation routes to MainScreen's handler instead
+    // of the dying VideoPlayerScreen.
+    onPlayerMediaSwitched = null;
+
     // Trigger callback for the app to navigate guest out of player
     if (onHostExitedPlayer != null) {
       onHostExitedPlayer!.call();

lib/watch_together/services/watch_together_sync_manager.dart

@@ -136,6 +136,15 @@ class WatchTogetherSyncManager {
 
     // Note: playerReady will be announced when video loads (first buffering: false)
 
+    // If guest, request current session config from host in case we missed
+    // a mediaSwitch broadcast (e.g., host switched episodes while we were
+    // popping out of the previous player).
+    if (!_session.isHost) {
+      _peerService.broadcast(
+        SyncMessage.requestSessionConfig(peerId: _peerService.myPeerId),
+      );
+    }
+
     appLogger.d('WatchTogether: Player attached, isHost: ${_session.isHost}');
   }
 
@@ -504,6 +513,14 @@ class WatchTogetherSyncManager {
           await _checkAutoResume();
         }
         break;
+
+      case SyncMessageType.requestSessionConfig:
+        // Guest is requesting current session config (recovery after missed mediaSwitch)
+        if (_session.isHost && _hasAnnouncedReady && message.peerId != null) {
+          appLogger.d('WatchTogether: Guest ${message.peerId} requested session config, sending');
+          _sendSessionConfig(toPeerId: message.peerId);
+        }
+        break;
     }
   }
 
@@ -776,6 +793,9 @@ class WatchTogetherSyncManager {
       isPlaying: isPlaying,
       playbackRate: rate,
       peerId: _peerService.myPeerId,
+      ratingKey: _session.mediaRatingKey,
+      serverId: _session.mediaServerId,
+      mediaTitle: _session.mediaTitle,
     );
 
     if (toPeerId != null) {