fix(mpc-system): GetSessionStatus 返回实际的 threshold_n 和 threshold_t

问题：
- Message Router 的 GetSessionStatus 把 TotalParties 当作 ThresholdN 返回
- 导致 server-party 收到错误的 threshold_n=2 而不是 3
- TSS 协议无法正确启动（参与者数量验证失败）

修复：
- 在 session_coordinator.proto 添加 threshold_n 和 threshold_t 字段
- Session Coordinator 返回实际的 threshold 值
- Message Router 透传 threshold 值而不是参与者数量

Generated with Claude Code

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

backend/mpc-system/api/grpc/coordinator/v1/session_coordinator.pb.go

@@ -851,6 +851,10 @@ type GetSessionStatusResponse struct {
 	// participants contains detailed participant information including party_index
 	// Used by service-party-app for co_managed_keygen sessions
 	Participants []*ParticipantStatus `protobuf:"bytes,9,rep,name=participants,proto3" json:"participants,omitempty"`
+	// threshold_n and threshold_t - actual threshold values from session config
+	// Used for co_managed_keygen sessions where total_parties may differ from threshold_n during joining
+	ThresholdN    int32 `protobuf:"varint,10,opt,name=threshold_n,json=thresholdN,proto3" json:"threshold_n,omitempty"` // Total number of parties required (e.g., 3 in 2-of-3)
+	ThresholdT    int32 `protobuf:"varint,11,opt,name=threshold_t,json=thresholdT,proto3" json:"threshold_t,omitempty"` // Minimum parties needed to sign (e.g., 2 in 2-of-3)
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
 }
@@ -948,6 +952,20 @@ func (x *GetSessionStatusResponse) GetParticipants() []*ParticipantStatus {
 	return nil
 }
 
+func (x *GetSessionStatusResponse) GetThresholdN() int32 {
+	if x != nil {
+		return x.ThresholdN
+	}
+	return 0
+}
+
+func (x *GetSessionStatusResponse) GetThresholdT() int32 {
+	if x != nil {
+		return x.ThresholdT
+	}
+	return 0
+}
+
 // ParticipantStatus contains participant status information
 type ParticipantStatus struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
@@ -1718,7 +1736,7 @@ const file_session_coordinator_proto_rawDesc = "" +
 	"deviceInfo\"8\n" +
 	"\x17GetSessionStatusRequest\x12\x1d\n" +
 	"\n" +
-	"session_id\x18\x01 \x01(\tR\tsessionId\"\xa0\x03\n" +
+	"session_id\x18\x01 \x01(\tR\tsessionId\"\xe2\x03\n" +
 	"\x18GetSessionStatusResponse\x12\x16\n" +
 	"\x06status\x18\x01 \x01(\tR\x06status\x12+\n" +
 	"\x11completed_parties\x18\x02 \x01(\x05R\x10completedParties\x12#\n" +
@@ -1729,7 +1747,12 @@ const file_session_coordinator_proto_rawDesc = "" +
 	"\tsignature\x18\x06 \x01(\fR\tsignature\x12!\n" +
 	"\fhas_delegate\x18\a \x01(\bR\vhasDelegate\x12L\n" +
 	"\x0edelegate_share\x18\b \x01(\v2%.mpc.coordinator.v1.DelegateShareInfoR\rdelegateShare\x12I\n" +
-	"\fparticipants\x18\t \x03(\v2%.mpc.coordinator.v1.ParticipantStatusR\fparticipants\"g\n" +
+	"\fparticipants\x18\t \x03(\v2%.mpc.coordinator.v1.ParticipantStatusR\fparticipants\x12\x1f\n" +
+	"\vthreshold_n\x18\n" +
+	" \x01(\x05R\n" +
+	"thresholdN\x12\x1f\n" +
+	"\vthreshold_t\x18\v \x01(\x05R\n" +
+	"thresholdT\"g\n" +
 	"\x11ParticipantStatus\x12\x19\n" +
 	"\bparty_id\x18\x01 \x01(\tR\apartyId\x12\x1f\n" +
 	"\vparty_index\x18\x02 \x01(\x05R\n" +

backend/mpc-system/api/proto/session_coordinator.proto

@@ -135,6 +135,10 @@ message GetSessionStatusResponse {
   // participants contains detailed participant information including party_index
   // Used by service-party-app for co_managed_keygen sessions
   repeated ParticipantStatus participants = 9;
+  // threshold_n and threshold_t - actual threshold values from session config
+  // Used for co_managed_keygen sessions where total_parties may differ from threshold_n during joining
+  int32 threshold_n = 10;                // Total number of parties required (e.g., 3 in 2-of-3)
+  int32 threshold_t = 11;                // Minimum parties needed to sign (e.g., 2 in 2-of-3)
 }
 
 // ParticipantStatus contains participant status information

backend/mpc-system/services/message-router/adapters/input/grpc/message_grpc_handler.go

@@ -694,8 +694,8 @@ func (s *MessageRouterServer) GetSessionStatus(
 	return &pb.GetSessionStatusResponse{
 		SessionId:    req.SessionId,
 		Status:       coordResp.Status,
-		ThresholdN:   coordResp.TotalParties,    // Use TotalParties as N
-		ThresholdT:   coordResp.CompletedParties, // Return completed count in ThresholdT for info
+		ThresholdN:   coordResp.ThresholdN,   // Actual threshold N from session config
+		ThresholdT:   coordResp.ThresholdT,   // Actual threshold T from session config
 		Participants: participants,           // Include participants for co_managed_keygen
 	}, nil
 }

backend/mpc-system/services/session-coordinator/adapters/input/grpc/session_grpc_handler.go

@@ -360,6 +360,8 @@ func (s *SessionCoordinatorServer) GetSessionStatus(
 		Signature:        output.Signature,
 		HasDelegate:      output.HasDelegate, // Only meaningful for keygen sessions
 		Participants:     protoParticipants,  // Include participant details with party_index
+		ThresholdN:       int32(output.ThresholdN),
+		ThresholdT:       int32(output.ThresholdT),
 	}
 
 	// Try to get delegate share from cache