fix(android): fix session_started event race condition with pendingSessionId

Problem:
- Android initiator/joiner could miss session_started events due to race condition
- Events arriving between joinSession() and _currentSession.value assignment were ignored
- This caused keygen timeout because parties never started the TSS protocol

Solution:
- Add pendingSessionId field set BEFORE joinSession() call
- Modify startSessionEventSubscription() to match events against both activeSession and pendingSessionId
- Clear pendingSessionId on session completion, failure, or cancellation

This ensures session_started events are correctly processed even if they arrive
before _currentSession is fully initialized.

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

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

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

@@ -46,6 +46,10 @@ class TssRepository @Inject constructor(
     private var messageCollectionJob: Job? = null
     private var sessionEventJob: Job? = null
 
+    // Pre-registered session ID for event matching (set before joinSession to avoid race condition)
+    // This allows session_started events to be matched even if _currentSession is not yet set
+    private var pendingSessionId: String? = null
+
     /**
      * Get the current party ID
      */
@@ -161,12 +165,18 @@ class TssRepository @Inject constructor(
                 android.util.Log.d("TssRepository", "  sessionId: ${event.sessionId}")
                 android.util.Log.d("TssRepository", "  selectedParties: ${event.selectedParties}")
 
-                // Check if this event is for our active session
+                // Check if this event is for our active session OR pending session
+                // (pendingSessionId handles race condition where session_started arrives before _currentSession is set)
                 val activeSession = _currentSession.value
+                val pendingId = pendingSessionId
                 android.util.Log.d("TssRepository", "  activeSession: ${activeSession?.sessionId ?: "null"}")
+                android.util.Log.d("TssRepository", "  pendingSessionId: ${pendingId ?: "null"}")
 
-                if (activeSession != null && event.sessionId == activeSession.sessionId) {
+                val matchesActiveSession = activeSession != null && event.sessionId == activeSession.sessionId
-                    android.util.Log.d("TssRepository", "  → Event matches active session!")
+                val matchesPendingSession = pendingId != null && event.sessionId == pendingId
+
+                if (matchesActiveSession || matchesPendingSession) {
+                    android.util.Log.d("TssRepository", "  → Event matches session! (active=$matchesActiveSession, pending=$matchesPendingSession)")
                     when (event.eventType) {
                         "session_started" -> {
                             android.util.Log.d("TssRepository", "  → Processing session_started event")
@@ -186,10 +196,10 @@ class TssRepository @Inject constructor(
                         }
                     }
                 } else {
-                    android.util.Log.d("TssRepository", "  → Event does NOT match active session (ignored)")
+                    android.util.Log.d("TssRepository", "  → Event does NOT match any session (ignored)")
-                    if (activeSession == null) {
+                    if (activeSession == null && pendingId == null) {
-                        android.util.Log.d("TssRepository", "    Reason: activeSession is null")
+                        android.util.Log.d("TssRepository", "    Reason: both activeSession and pendingSessionId are null")
-                    } else {
+                    } else if (activeSession != null) {
                         android.util.Log.d("TssRepository", "    Reason: sessionId mismatch (event: ${event.sessionId}, active: ${activeSession.sessionId})")
                     }
                 }
@@ -290,6 +300,12 @@ class TssRepository @Inject constructor(
 
                 android.util.Log.d("TssRepository", "Session created: sessionId=$sessionId, inviteCode=$inviteCode, joinToken length=${joinToken.length}")
 
+                // CRITICAL: Set pendingSessionId BEFORE joinSession to avoid race condition
+                // This ensures session_started events can be matched even if they arrive
+                // before _currentSession is set
+                pendingSessionId = sessionId
+                android.util.Log.d("TssRepository", "Set pendingSessionId=$sessionId for event matching")
+
                 // Auto-join session via gRPC (matching Electron behavior)
                 var partyIndex = 0
                 var sessionAlreadyInProgress = false
@@ -585,6 +601,12 @@ class TssRepository @Inject constructor(
             try {
                 android.util.Log.d("TssRepository", "Joining keygen session via gRPC: sessionId=$sessionId, joinToken length=${joinToken.length}")
 
+                // CRITICAL: Set pendingSessionId BEFORE joinSession to avoid race condition
+                // This ensures session_started events can be matched even if they arrive
+                // before _currentSession is set
+                pendingSessionId = sessionId
+                android.util.Log.d("TssRepository", "Set pendingSessionId=$sessionId for event matching (joiner)")
+
                 // Join session via gRPC (matching Electron's grpcClient.joinSession)
                 val joinResult = grpcClient.joinSession(sessionId, partyId, joinToken)
                 if (joinResult.isFailure) {
@@ -738,6 +760,7 @@ class TssRepository @Inject constructor(
             grpcClient.reportCompletion(sessionId, partyId, publicKeyBytes)
 
             _sessionStatus.value = SessionStatus.COMPLETED
+            pendingSessionId = null  // Clear pending session ID on completion
 
             android.util.Log.d("TssRepository", "Keygen as joiner completed: address=$address, partyIndex=$actualPartyIndex")
 
@@ -746,6 +769,7 @@ class TssRepository @Inject constructor(
         } catch (e: Exception) {
             android.util.Log.e("TssRepository", "Execute keygen as joiner failed", e)
             _sessionStatus.value = SessionStatus.FAILED
+            pendingSessionId = null  // Clear pending session ID on failure
             Result.failure(e)
         }
     }
@@ -783,6 +807,12 @@ class TssRepository @Inject constructor(
 
                 // Note: Password is verified during actual sign execution, same as Electron
 
+                // CRITICAL: Set pendingSessionId BEFORE joinSession to avoid race condition
+                // This ensures session_started events can be matched even if they arrive
+                // before _currentSession is set
+                pendingSessionId = sessionId
+                android.util.Log.d("TssRepository", "Set pendingSessionId=$sessionId for event matching (sign joiner)")
+
                 // Join session via gRPC (matching Electron's grpcClient.joinSession)
                 val joinResult = grpcClient.joinSession(sessionId, partyId, joinToken)
                 if (joinResult.isFailure) {
@@ -906,6 +936,7 @@ class TssRepository @Inject constructor(
             grpcClient.reportCompletion(sessionId, partyId, signature = signatureBytes)
 
             _sessionStatus.value = SessionStatus.COMPLETED
+            pendingSessionId = null  // Clear pending session ID on completion
             messageCollectionJob?.cancel()
 
             android.util.Log.d("TssRepository", "Sign as joiner completed: signature=${result.signature.take(20)}...")
@@ -915,6 +946,7 @@ class TssRepository @Inject constructor(
         } catch (e: Exception) {
             android.util.Log.e("TssRepository", "Execute sign as joiner failed", e)
             _sessionStatus.value = SessionStatus.FAILED
+            pendingSessionId = null  // Clear pending session ID on failure
             Result.failure(e)
         }
     }
@@ -1437,6 +1469,7 @@ class TssRepository @Inject constructor(
             grpcClient.reportCompletion(sessionId, partyId, publicKeyBytes)
 
             _sessionStatus.value = SessionStatus.COMPLETED
+            pendingSessionId = null  // Clear pending session ID on completion
             sessionEventJob?.cancel()
 
             Result.success(shareEntity.copy(id = id).toShareRecord())
@@ -1444,6 +1477,7 @@ class TssRepository @Inject constructor(
         } catch (e: Exception) {
             android.util.Log.e("TssRepository", "Start keygen as initiator failed", e)
             _sessionStatus.value = SessionStatus.FAILED
+            pendingSessionId = null  // Clear pending session ID on failure
             Result.failure(e)
         }
     }
@@ -1458,6 +1492,9 @@ class TssRepository @Inject constructor(
         _currentSession.value = null
         _sessionStatus.value = SessionStatus.WAITING
 
+        // Clear pending session ID (race condition prevention)
+        pendingSessionId = null
+
         // Clear reconnection recovery params
         currentMessageRoutingSessionId = null
         currentMessageRoutingPartyIndex = null