diff --git a/backend/mpc-system/deploy.sh b/backend/mpc-system/deploy.sh
index c2dcd57d..f892a34c 100755
--- a/backend/mpc-system/deploy.sh
+++ b/backend/mpc-system/deploy.sh
@@ -86,8 +86,8 @@ load_environment() {
 
 # Service lists
 CORE_SERVICES="postgres"
-DEV_MPC_SERVICES="session-coordinator message-router server-party-1 server-party-2 server-party-3 server-party-api account-service"
-PROD_CENTRAL_SERVICES="postgres message-router session-coordinator account-service server-party-api"
+DEV_MPC_SERVICES="session-coordinator message-router server-party-1 server-party-2 server-party-3 server-party-api server-party-co-managed-1 server-party-co-managed-2 server-party-co-managed-3 account-service"
+PROD_CENTRAL_SERVICES="postgres message-router session-coordinator account-service server-party-api server-party-co-managed-1 server-party-co-managed-2 server-party-co-managed-3"
 
 # ============================================
 # Development Mode Commands (docker-compose.yml)
@@ -582,7 +582,8 @@ show_help() {
     echo ""
     echo "Services (Development):"
     echo "  postgres, session-coordinator, message-router, account-service,"
-    echo "  server-party-api, server-party-1, server-party-2, server-party-3"
+    echo "  server-party-api, server-party-1, server-party-2, server-party-3,"
+    echo "  server-party-co-managed-1, server-party-co-managed-2, server-party-co-managed-3"
     echo ""
     echo "Examples:"
     echo "  # Development (all on one machine)"
diff --git a/backend/mpc-system/docker-compose.yml b/backend/mpc-system/docker-compose.yml
index 3862c571..109b821c 100644
--- a/backend/mpc-system/docker-compose.yml
+++ b/backend/mpc-system/docker-compose.yml
@@ -279,6 +279,123 @@ services:
       - mpc-network
     restart: unless-stopped
 
+  # ============================================
+  # Co-Managed Server Party Services - TSS 参与方 (专用于 co_managed_keygen)
+  # 与普通 server-party 隔离，使用两阶段事件处理
+  # 行为与 service-party-app 100% 兼容
+  # ============================================
+
+  # Co-Managed Server Party 1
+  server-party-co-managed-1:
+    build:
+      context: .
+      dockerfile: services/server-party-co-managed/Dockerfile
+    container_name: mpc-server-party-co-managed-1
+    environment:
+      TZ: Asia/Shanghai
+      MPC_SERVER_HTTP_PORT: 8080
+      MPC_SERVER_ENVIRONMENT: ${ENVIRONMENT:-development}
+      MPC_LOGGER_LEVEL: ${LOG_LEVEL:-debug}
+      MPC_DATABASE_HOST: postgres
+      MPC_DATABASE_PORT: 5432
+      MPC_DATABASE_USER: ${POSTGRES_USER:-mpc_user}
+      MPC_DATABASE_PASSWORD: ${POSTGRES_PASSWORD:?POSTGRES_PASSWORD must be set}
+      MPC_DATABASE_DBNAME: mpc_system
+      MPC_DATABASE_SSLMODE: disable
+      MESSAGE_ROUTER_ADDR: message-router:50051
+      MPC_CRYPTO_MASTER_KEY: ${CRYPTO_MASTER_KEY}
+      PARTY_ID: co-managed-party-1
+    depends_on:
+      postgres:
+        condition: service_healthy
+      session-coordinator:
+        condition: service_healthy
+      message-router:
+        condition: service_healthy
+    healthcheck:
+      test: ["CMD", "curl", "-sf", "http://localhost:8080/health"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 30s
+    networks:
+      - mpc-network
+    restart: unless-stopped
+
+  # Co-Managed Server Party 2
+  server-party-co-managed-2:
+    build:
+      context: .
+      dockerfile: services/server-party-co-managed/Dockerfile
+    container_name: mpc-server-party-co-managed-2
+    environment:
+      TZ: Asia/Shanghai
+      MPC_SERVER_HTTP_PORT: 8080
+      MPC_SERVER_ENVIRONMENT: ${ENVIRONMENT:-development}
+      MPC_LOGGER_LEVEL: ${LOG_LEVEL:-debug}
+      MPC_DATABASE_HOST: postgres
+      MPC_DATABASE_PORT: 5432
+      MPC_DATABASE_USER: ${POSTGRES_USER:-mpc_user}
+      MPC_DATABASE_PASSWORD: ${POSTGRES_PASSWORD:?POSTGRES_PASSWORD must be set}
+      MPC_DATABASE_DBNAME: mpc_system
+      MPC_DATABASE_SSLMODE: disable
+      MESSAGE_ROUTER_ADDR: message-router:50051
+      MPC_CRYPTO_MASTER_KEY: ${CRYPTO_MASTER_KEY}
+      PARTY_ID: co-managed-party-2
+    depends_on:
+      postgres:
+        condition: service_healthy
+      session-coordinator:
+        condition: service_healthy
+      message-router:
+        condition: service_healthy
+    healthcheck:
+      test: ["CMD", "curl", "-sf", "http://localhost:8080/health"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 30s
+    networks:
+      - mpc-network
+    restart: unless-stopped
+
+  # Co-Managed Server Party 3
+  server-party-co-managed-3:
+    build:
+      context: .
+      dockerfile: services/server-party-co-managed/Dockerfile
+    container_name: mpc-server-party-co-managed-3
+    environment:
+      TZ: Asia/Shanghai
+      MPC_SERVER_HTTP_PORT: 8080
+      MPC_SERVER_ENVIRONMENT: ${ENVIRONMENT:-development}
+      MPC_LOGGER_LEVEL: ${LOG_LEVEL:-debug}
+      MPC_DATABASE_HOST: postgres
+      MPC_DATABASE_PORT: 5432
+      MPC_DATABASE_USER: ${POSTGRES_USER:-mpc_user}
+      MPC_DATABASE_PASSWORD: ${POSTGRES_PASSWORD:?POSTGRES_PASSWORD must be set}
+      MPC_DATABASE_DBNAME: mpc_system
+      MPC_DATABASE_SSLMODE: disable
+      MESSAGE_ROUTER_ADDR: message-router:50051
+      MPC_CRYPTO_MASTER_KEY: ${CRYPTO_MASTER_KEY}
+      PARTY_ID: co-managed-party-3
+    depends_on:
+      postgres:
+        condition: service_healthy
+      session-coordinator:
+        condition: service_healthy
+      message-router:
+        condition: service_healthy
+    healthcheck:
+      test: ["CMD", "curl", "-sf", "http://localhost:8080/health"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 30s
+    networks:
+      - mpc-network
+    restart: unless-stopped
+
   # ============================================
   # Account Service - External API Entry Point
   # Main HTTP API for backend mpc-service integration
diff --git a/backend/mpc-system/services/server-party-co-managed/Dockerfile b/backend/mpc-system/services/server-party-co-managed/Dockerfile
new file mode 100644
index 00000000..bf0a0fef
--- /dev/null
+++ b/backend/mpc-system/services/server-party-co-managed/Dockerfile
@@ -0,0 +1,38 @@
+# Build stage
+FROM golang:1.24-alpine AS builder
+
+RUN apk add --no-cache git ca-certificates
+
+# Set Go proxy (can be overridden with --build-arg GOPROXY=...)
+ARG GOPROXY=https://proxy.golang.org,direct
+ENV GOPROXY=${GOPROXY}
+
+WORKDIR /app
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+
+RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build \
+    -ldflags="-w -s" \
+    -o /bin/server-party-co-managed \
+    ./services/server-party-co-managed/cmd/server
+
+# Final stage
+FROM alpine:3.18
+
+RUN apk --no-cache add ca-certificates curl
+RUN adduser -D -s /bin/sh mpc
+
+COPY --from=builder /bin/server-party-co-managed /bin/server-party-co-managed
+
+USER mpc
+
+EXPOSE 8080
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
+    CMD curl -sf http://localhost:8080/health || exit 1
+
+ENTRYPOINT ["/bin/server-party-co-managed"]
diff --git a/backend/mpc-system/services/server-party-co-managed/cmd/server/main.go b/backend/mpc-system/services/server-party-co-managed/cmd/server/main.go
new file mode 100644
index 00000000..aed62243
--- /dev/null
+++ b/backend/mpc-system/services/server-party-co-managed/cmd/server/main.go
@@ -0,0 +1,422 @@
+package main
+
+import (
+	"context"
+	"database/sql"
+	"encoding/hex"
+	"flag"
+	"fmt"
+	"net/http"
+	"os"
+	"os/signal"
+	"sync"
+	"syscall"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+	_ "github.com/lib/pq"
+
+	router "github.com/rwadurian/mpc-system/api/grpc/router/v1"
+	"github.com/rwadurian/mpc-system/pkg/config"
+	"github.com/rwadurian/mpc-system/pkg/crypto"
+	"github.com/rwadurian/mpc-system/pkg/logger"
+	grpcclient "github.com/rwadurian/mpc-system/services/server-party/adapters/output/grpc"
+	"github.com/rwadurian/mpc-system/services/server-party/adapters/output/postgres"
+	"github.com/rwadurian/mpc-system/services/server-party/application/use_cases"
+	"go.uber.org/zap"
+)
+
+// PendingSession stores session info between session_created and session_started events
+type PendingSession struct {
+	SessionID   uuid.UUID
+	JoinToken   string
+	MessageHash []byte
+	CreatedAt   time.Time
+}
+
+// PendingSessionCache stores pending sessions waiting for session_started
+type PendingSessionCache struct {
+	mu       sync.RWMutex
+	sessions map[string]*PendingSession // sessionID -> PendingSession
+}
+
+// Global pending session cache
+var pendingSessionCache = &PendingSessionCache{
+	sessions: make(map[string]*PendingSession),
+}
+
+// Store stores a pending session
+func (c *PendingSessionCache) Store(sessionID string, session *PendingSession) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.sessions[sessionID] = session
+	logger.Info("Pending session stored",
+		zap.String("session_id", sessionID))
+}
+
+// Get retrieves and deletes a pending session
+func (c *PendingSessionCache) Get(sessionID string) (*PendingSession, bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	session, exists := c.sessions[sessionID]
+	if exists {
+		delete(c.sessions, sessionID)
+		logger.Info("Pending session retrieved and deleted",
+			zap.String("session_id", sessionID))
+	}
+	return session, exists
+}
+
+// Delete removes a pending session without returning it
+func (c *PendingSessionCache) Delete(sessionID string) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	delete(c.sessions, sessionID)
+}
+
+func main() {
+	// Parse flags
+	configPath := flag.String("config", "", "Path to config file")
+	flag.Parse()
+
+	// Load configuration
+	cfg, err := config.Load(*configPath)
+	if err != nil {
+		fmt.Printf("Failed to load config: %v\n", err)
+		os.Exit(1)
+	}
+
+	// Initialize logger
+	if err := logger.Init(&logger.Config{
+		Level:    cfg.Logger.Level,
+		Encoding: cfg.Logger.Encoding,
+	}); err != nil {
+		fmt.Printf("Failed to initialize logger: %v\n", err)
+		os.Exit(1)
+	}
+	defer logger.Sync()
+
+	logger.Info("Starting Server Party Co-Managed Service",
+		zap.String("environment", cfg.Server.Environment),
+		zap.Int("http_port", cfg.Server.HTTPPort))
+
+	// Initialize database connection
+	db, err := initDatabase(cfg.Database)
+	if err != nil {
+		logger.Fatal("Failed to connect to database", zap.Error(err))
+	}
+	defer db.Close()
+
+	// Initialize crypto service with master key from environment
+	masterKeyHex := os.Getenv("MPC_CRYPTO_MASTER_KEY")
+	if masterKeyHex == "" {
+		masterKeyHex = "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef" // 64 hex chars = 32 bytes
+	}
+	masterKey, err := hex.DecodeString(masterKeyHex)
+	if err != nil {
+		logger.Fatal("Invalid master key format", zap.Error(err))
+	}
+	cryptoService, err := crypto.NewCryptoService(masterKey)
+	if err != nil {
+		logger.Fatal("Failed to create crypto service", zap.Error(err))
+	}
+
+	// Get Message Router address from environment
+	routerAddr := os.Getenv("MESSAGE_ROUTER_ADDR")
+	if routerAddr == "" {
+		routerAddr = "localhost:9092"
+	}
+
+	// Initialize Message Router client
+	messageRouter, err := grpcclient.NewMessageRouterClient(routerAddr)
+	if err != nil {
+		logger.Fatal("Failed to connect to message router", zap.Error(err))
+	}
+	defer messageRouter.Close()
+
+	// Initialize repositories
+	keyShareRepo := postgres.NewKeySharePostgresRepo(db)
+
+	// Initialize use cases
+	participateKeygenUC := use_cases.NewParticipateKeygenUseCase(
+		keyShareRepo,
+		messageRouter,
+		messageRouter,
+		cryptoService,
+	)
+
+	// Create shutdown context
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	// Get party ID from environment
+	partyID := os.Getenv("PARTY_ID")
+	if partyID == "" {
+		partyID, _ = os.Hostname()
+		if partyID == "" {
+			partyID = "co-managed-party-" + uuid.New().String()[:8]
+		}
+	}
+
+	// Party role is co_managed_persistent - different from normal persistent
+	// This ensures co_managed_keygen sessions only select these parties
+	partyRole := "co_managed_persistent"
+
+	// Register this party with Message Router
+	logger.Info("Registering co-managed party with Message Router",
+		zap.String("party_id", partyID),
+		zap.String("role", partyRole))
+
+	if err := messageRouter.RegisterPartyWithNotification(ctx, partyID, partyRole, "1.0.0", nil); err != nil {
+		logger.Fatal("Failed to register party", zap.Error(err))
+	}
+
+	// Start heartbeat
+	heartbeatCancel := messageRouter.StartHeartbeat(ctx, partyID, 30*time.Second, func(pendingCount int32) {
+		if pendingCount > 0 {
+			logger.Info("Pending messages detected via heartbeat",
+				zap.String("party_id", partyID),
+				zap.Int32("pending_count", pendingCount))
+		}
+	})
+	defer heartbeatCancel()
+	logger.Info("Heartbeat started", zap.String("party_id", partyID), zap.Duration("interval", 30*time.Second))
+
+	// Subscribe to session events with two-phase handling for co_managed_keygen
+	logger.Info("Subscribing to session events (co_managed_keygen only)", zap.String("party_id", partyID))
+
+	eventHandler := createCoManagedSessionEventHandler(
+		ctx,
+		partyID,
+		participateKeygenUC,
+	)
+
+	if err := messageRouter.SubscribeSessionEvents(ctx, partyID, eventHandler); err != nil {
+		logger.Fatal("Failed to subscribe to session events", zap.Error(err))
+	}
+
+	logger.Info("Co-managed party initialized successfully",
+		zap.String("party_id", partyID),
+		zap.String("role", partyRole))
+
+	// Start HTTP server
+	errChan := make(chan error, 1)
+	go func() {
+		if err := startHTTPServer(cfg); err != nil {
+			errChan <- fmt.Errorf("HTTP server error: %w", err)
+		}
+	}()
+
+	// Wait for shutdown signal
+	sigChan := make(chan os.Signal, 1)
+	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)
+
+	select {
+	case sig := <-sigChan:
+		logger.Info("Received shutdown signal", zap.String("signal", sig.String()))
+	case err := <-errChan:
+		logger.Error("Server error", zap.Error(err))
+	}
+
+	// Graceful shutdown
+	logger.Info("Shutting down...")
+	cancel()
+
+	time.Sleep(5 * time.Second)
+	logger.Info("Shutdown complete")
+}
+
+func initDatabase(cfg config.DatabaseConfig) (*sql.DB, error) {
+	const maxRetries = 10
+	const retryDelay = 2 * time.Second
+
+	var db *sql.DB
+	var err error
+
+	for i := 0; i < maxRetries; i++ {
+		db, err = sql.Open("postgres", cfg.DSN())
+		if err != nil {
+			logger.Warn("Failed to open database connection, retrying...",
+				zap.Int("attempt", i+1),
+				zap.Int("max_retries", maxRetries),
+				zap.Error(err))
+			time.Sleep(retryDelay * time.Duration(i+1))
+			continue
+		}
+
+		db.SetMaxOpenConns(cfg.MaxOpenConns)
+		db.SetMaxIdleConns(cfg.MaxIdleConns)
+		db.SetConnMaxLifetime(cfg.ConnMaxLife)
+
+		if err = db.Ping(); err != nil {
+			logger.Warn("Failed to ping database, retrying...",
+				zap.Int("attempt", i+1),
+				zap.Int("max_retries", maxRetries),
+				zap.Error(err))
+			db.Close()
+			time.Sleep(retryDelay * time.Duration(i+1))
+			continue
+		}
+
+		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		var result int
+		err = db.QueryRowContext(ctx, "SELECT 1").Scan(&result)
+		cancel()
+		if err != nil {
+			logger.Warn("Database ping succeeded but query failed, retrying...",
+				zap.Int("attempt", i+1),
+				zap.Int("max_retries", maxRetries),
+				zap.Error(err))
+			db.Close()
+			time.Sleep(retryDelay * time.Duration(i+1))
+			continue
+		}
+
+		logger.Info("Connected to PostgreSQL and verified connectivity",
+			zap.Int("attempt", i+1))
+		return db, nil
+	}
+
+	return nil, fmt.Errorf("failed to connect to database after %d retries: %w", maxRetries, err)
+}
+
+func startHTTPServer(cfg *config.Config) error {
+	if cfg.Server.Environment == "production" {
+		gin.SetMode(gin.ReleaseMode)
+	}
+
+	r := gin.New()
+	r.Use(gin.Recovery())
+	r.Use(gin.Logger())
+
+	// Health check
+	r.GET("/health", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{
+			"status":  "healthy",
+			"service": "server-party-co-managed",
+		})
+	})
+
+	logger.Info("Starting HTTP server", zap.Int("port", cfg.Server.HTTPPort))
+	return r.Run(fmt.Sprintf(":%d", cfg.Server.HTTPPort))
+}
+
+// createCoManagedSessionEventHandler creates a handler specifically for co_managed_keygen sessions
+// Two-phase event handling:
+// Phase 1 (session_created): Store join token and wait
+// Phase 2 (session_started): Execute TSS protocol (same timing as user clients receiving all_joined)
+func createCoManagedSessionEventHandler(
+	ctx context.Context,
+	partyID string,
+	participateKeygenUC *use_cases.ParticipateKeygenUseCase,
+) func(*router.SessionEvent) {
+	return func(event *router.SessionEvent) {
+		// Check if this party is selected for the session
+		isSelected := false
+		for _, selectedParty := range event.SelectedParties {
+			if selectedParty == partyID {
+				isSelected = true
+				break
+			}
+		}
+
+		if !isSelected {
+			logger.Debug("Party not selected for this session",
+				zap.String("session_id", event.SessionId),
+				zap.String("party_id", partyID))
+			return
+		}
+
+		logger.Info("Received session event",
+			zap.String("session_id", event.SessionId),
+			zap.String("party_id", partyID),
+			zap.String("event_type", event.EventType))
+
+		// Parse session ID
+		sessionID, err := uuid.Parse(event.SessionId)
+		if err != nil {
+			logger.Error("Invalid session ID", zap.Error(err))
+			return
+		}
+
+		// Handle different event types
+		switch event.EventType {
+		case "session_created":
+			// Only handle keygen sessions (no message_hash)
+			if len(event.MessageHash) > 0 {
+				logger.Debug("Ignoring sign session (co-managed only handles keygen)",
+					zap.String("session_id", event.SessionId))
+				return
+			}
+
+			// Phase 1: Store session info and wait for session_started
+			joinToken, exists := event.JoinTokens[partyID]
+			if !exists {
+				logger.Error("No join token found for party in session_created",
+					zap.String("session_id", event.SessionId),
+					zap.String("party_id", partyID))
+				return
+			}
+
+			// Store pending session for later use when session_started arrives
+			pendingSessionCache.Store(event.SessionId, &PendingSession{
+				SessionID:   sessionID,
+				JoinToken:   joinToken,
+				MessageHash: event.MessageHash,
+				CreatedAt:   time.Now(),
+			})
+
+			logger.Info("Session created event received, waiting for session_started",
+				zap.String("session_id", event.SessionId),
+				zap.String("party_id", partyID))
+
+		case "session_started":
+			// Phase 2: All participants have joined, now execute TSS protocol
+			pendingSession, exists := pendingSessionCache.Get(event.SessionId)
+			if !exists {
+				logger.Warn("No pending session found for session_started event",
+					zap.String("session_id", event.SessionId),
+					zap.String("party_id", partyID))
+				return
+			}
+
+			logger.Info("Session started event received, beginning TSS keygen protocol",
+				zap.String("session_id", event.SessionId),
+				zap.String("party_id", partyID))
+
+			// Execute TSS keygen protocol in goroutine
+			go func() {
+				// 10 minute timeout for TSS protocol execution
+				participateCtx, cancel := context.WithTimeout(ctx, 10*time.Minute)
+				defer cancel()
+
+				logger.Info("Auto-participating in co_managed_keygen session",
+					zap.String("session_id", event.SessionId),
+					zap.String("party_id", partyID))
+
+				input := use_cases.ParticipateKeygenInput{
+					SessionID: pendingSession.SessionID,
+					PartyID:   partyID,
+					JoinToken: pendingSession.JoinToken,
+				}
+
+				result, err := participateKeygenUC.Execute(participateCtx, input)
+				if err != nil {
+					logger.Error("Co-managed keygen participation failed",
+						zap.Error(err),
+						zap.String("session_id", event.SessionId))
+				} else {
+					logger.Info("Co-managed keygen participation completed",
+						zap.String("session_id", event.SessionId),
+						zap.String("public_key", hex.EncodeToString(result.PublicKey)))
+				}
+			}()
+
+		default:
+			logger.Debug("Ignoring unhandled event type",
+				zap.String("session_id", event.SessionId),
+				zap.String("event_type", event.EventType))
+		}
+	}
+}
diff --git a/backend/mpc-system/services/session-coordinator/application/ports/output/party_pool_port.go b/backend/mpc-system/services/session-coordinator/application/ports/output/party_pool_port.go
index 7ce2f11e..6311e7b7 100644
--- a/backend/mpc-system/services/session-coordinator/application/ports/output/party_pool_port.go
+++ b/backend/mpc-system/services/session-coordinator/application/ports/output/party_pool_port.go
@@ -5,8 +5,14 @@ type PartyRole string
 
 const (
 	// PartyRolePersistent represents a persistent party that stores key shares in database
+	// Used for normal keygen and sign sessions
 	PartyRolePersistent PartyRole = "persistent"
 
+	// PartyRoleCoManagedPersistent represents a persistent party for co_managed_keygen sessions
+	// These parties use two-phase event handling (session_created -> session_started)
+	// and are 100% compatible with service-party-app behavior
+	PartyRoleCoManagedPersistent PartyRole = "co_managed_persistent"
+
 	// PartyRoleDelegate represents a temporary party that generates user shares and returns them
 	PartyRoleDelegate PartyRole = "delegate"
 
diff --git a/backend/mpc-system/services/session-coordinator/application/use_cases/create_session.go b/backend/mpc-system/services/session-coordinator/application/use_cases/create_session.go
index 26c87eab..c9a9031a 100644
--- a/backend/mpc-system/services/session-coordinator/application/use_cases/create_session.go
+++ b/backend/mpc-system/services/session-coordinator/application/use_cases/create_session.go
@@ -381,6 +381,7 @@ func (uc *CreateSessionUseCase) Execute(
 // selectPartiesByCompositionForCoManaged selects parties for co_managed_keygen sessions
 // For co_managed_keygen, TemporaryCount represents external participants who will join
 // dynamically via invite code - we don't select them from pool, only select persistent parties
+// IMPORTANT: Uses PartyRoleCoManagedPersistent to select parties that use two-phase event handling
 func (uc *CreateSessionUseCase) selectPartiesByCompositionForCoManaged(composition *input.PartyComposition) ([]output.PartyEndpoint, error) {
 	if uc.partyPool == nil {
 		return nil, fmt.Errorf("party pool not configured")
@@ -388,14 +389,15 @@ func (uc *CreateSessionUseCase) selectPartiesByCompositionForCoManaged(compositi
 
 	var allSelected []output.PartyEndpoint
 
-	// Select persistent parties (server-side parties)
+	// Select co-managed persistent parties (server-side parties with two-phase event handling)
+	// These are different from normal persistent parties to avoid mixing with regular keygen/sign
 	if composition.PersistentCount > 0 {
 		persistent, err := uc.partyPool.SelectPartiesWithFilter(output.PartySelectionFilter{
 			Count: composition.PersistentCount,
-			Role:  output.PartyRolePersistent,
+			Role:  output.PartyRoleCoManagedPersistent,
 		})
 		if err != nil {
-			return nil, fmt.Errorf("failed to select persistent parties: %w", err)
+			return nil, fmt.Errorf("failed to select co-managed persistent parties: %w", err)
 		}
 		allSelected = append(allSelected, persistent...)
 	}