fix: guard _handleRenegotiationNeeded against non-stable signaling state

Check RTCSignalingStateStable before creating offer and re-check after
the async createOffer gap to prevent TOCTOU race. Remove outdated TODO.

Author: SERDUN

lib/features/call/bloc/call_bloc.dart

@@ -2788,29 +2788,20 @@ class CallBloc extends Bloc<CallEvent, CallState> with WidgetsBindingObserver im
   }
 
   Future<void> _handleRenegotiationNeeded(String callId, int? lineId, RTCPeerConnection peerConnection) async {
-    // TODO(Serdun): Handle renegotiation needed
-    // This implementation does not handle all possible signaling states.
-    // Specifically, if the current state is `have-remote-offer`, calling
-    // setLocalDescription with an offer will throw:
-    //   WEBRTC_SET_LOCAL_DESCRIPTION_ERROR: Failed to set local offer sdp: Called in wrong state: have-remote-offer
-    //
-    // Known case: when CalleeVideoOfferPolicy.includeInactiveTrack is used,
-    // the callee may trigger onRenegotiationNeeded before the current remote offer is processed.
-    // This causes a race where the local peer is still in 'have-remote-offer' state,
-    // leading to the above error. Currently this does not severely affect behavior,
-    // since the offer includes only an inactive track, but it should still be handled correctly.
-    //
-    // Proper handling should include:
-    // - Waiting until the signaling state becomes 'stable' before creating and setting a new offer
-    // - Avoiding renegotiation if a remote offer is currently being processed
-    // - Ensuring renegotiation is coordinated and state-aware
-
     final pcState = peerConnection.signalingState;
     _logger.fine(() => 'onRenegotiationNeeded signalingState: $pcState');
-    if (pcState != null) {
+    if (pcState == RTCSignalingState.RTCSignalingStateStable) {
       final localDescription = await peerConnection.createOffer({});
       sdpMunger?.apply(localDescription);
 
+      final currentState = peerConnection.signalingState;
+      if (currentState != RTCSignalingState.RTCSignalingStateStable) {
+        _logger.fine(
+          () => 'onRenegotiationNeeded: state changed to $currentState after createOffer, skipping setLocalDescription',
+        );
+        return;
+      }
+
       // According to RFC 8829 5.6 (https://datatracker.ietf.org/doc/html/rfc8829#section-5.6),
       // localDescription should be set before sending the offer to transition into have-local-offer state.
       await peerConnection.setLocalDescription(localDescription);