fix(android): add logging for session event subscription debugging

- Add warning log when parties miss session event broadcast (message-router)
- Add logging for subscribeSessionEvents to detect null asyncStub
- Add sessionStatusPollingJob field for future fallback polling mechanism

This helps diagnose why Android parties are not receiving session_started events.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/mpc-system/services/message-router/domain/session_event_broadcaster.go

@@ -4,6 +4,8 @@ import (
 	"sync"
 
 	pb "github.com/rwadurian/mpc-system/api/grpc/router/v1"
+	"github.com/rwadurian/mpc-system/pkg/logger"
+	"go.uber.org/zap"
 )
 
 // SessionEventBroadcaster manages session event subscriptions and broadcasting
@@ -69,16 +71,34 @@ func (b *SessionEventBroadcaster) BroadcastToParties(event *pb.SessionEvent, par
 	b.mu.RLock()
 	defer b.mu.RUnlock()
 
+	sentCount := 0
+	missedParties := []string{}
+
 	for _, partyID := range partyIDs {
 		if ch, exists := b.subscribers[partyID]; exists {
 			// Non-blocking send
 			select {
 			case ch <- event:
+				sentCount++
 			default:
 				// Channel full, skip this subscriber
+				missedParties = append(missedParties, partyID+" (channel full)")
 			}
+		} else {
+			// Party not subscribed - this is a problem for session_started events!
+			missedParties = append(missedParties, partyID+" (not subscribed)")
 		}
 	}
+
+	// Log if any parties were missed (helps debug event delivery issues)
+	if len(missedParties) > 0 {
+		logger.Warn("Some parties missed session event broadcast",
+			zap.String("event_type", event.EventType),
+			zap.String("session_id", event.SessionId),
+			zap.Int("sent_count", sentCount),
+			zap.Int("missed_count", len(missedParties)),
+			zap.Strings("missed_parties", missedParties))
+	}
 }
 
 // SubscriberCount returns the number of active subscribers

backend/mpc-system/services/service-party-android/app/src/main/java/com/durian/tssparty/data/remote/GrpcClient.kt

@@ -854,9 +854,19 @@ class GrpcClient @Inject constructor() {
             }
         }
 
-        asyncStub?.subscribeSessionEvents(request, observer)
+        val currentAsyncStub = asyncStub
+        if (currentAsyncStub == null) {
+            Log.e(TAG, "subscribeSessionEvents: asyncStub is null! Cannot subscribe.")
+            close(Exception("gRPC not connected - asyncStub is null"))
+            return@callbackFlow
+        }
+
+        Log.d(TAG, "subscribeSessionEvents: Starting subscription for partyId=$partyId")
+        currentAsyncStub.subscribeSessionEvents(request, observer)
+        Log.d(TAG, "subscribeSessionEvents: Subscription request sent")
 
         awaitClose {
+            Log.d(TAG, "subscribeSessionEvents: Flow closed for partyId=$partyId")
             eventStreamSubscribed.set(false)
             eventStreamPartyId = null
         }

backend/mpc-system/services/service-party-android/app/src/main/java/com/durian/tssparty/data/repository/TssRepository.kt

@@ -50,6 +50,10 @@ class TssRepository @Inject constructor(
     // This allows session_started events to be matched even if _currentSession is not yet set
     private var pendingSessionId: String? = null
 
+    // Fallback polling job for session status (handles gRPC stream disconnection on Android)
+    // Android gRPC streams can disconnect when app goes to background, so we poll as backup
+    private var sessionStatusPollingJob: Job? = null
+
     /**
      * Get the current party ID
      */