debug: add logging for participant information in gRPC handlers

Added debug logging to track participant details including party_index in:
- account service MPC keygen handler
- session coordinator gRPC client
- session coordinator gRPC handler

This helps debug the party index assignment issue where all parties
were receiving index 0 instead of unique indices (0, 1, 2).

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

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

backend/mpc-system/services/account/adapters/input/http/account_handler.go

@@ -8,10 +8,12 @@ import (
 
 	"github.com/gin-gonic/gin"
 	"github.com/google/uuid"
+	"github.com/rwadurian/mpc-system/pkg/logger"
 	"github.com/rwadurian/mpc-system/services/account/adapters/output/grpc"
 	"github.com/rwadurian/mpc-system/services/account/application/ports"
 	"github.com/rwadurian/mpc-system/services/account/application/use_cases"
 	"github.com/rwadurian/mpc-system/services/account/domain/value_objects"
+	"go.uber.org/zap"
 )
 
 // AccountHTTPHandler handles HTTP requests for accounts
@@ -579,6 +581,11 @@ func (h *AccountHTTPHandler) CreateKeygenSession(c *gin.Context) {
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
 
+	logger.Info("Calling CreateKeygenSession via gRPC",
+		zap.Int("threshold_n", req.ThresholdN),
+		zap.Int("threshold_t", req.ThresholdT),
+		zap.Int("num_participants", len(participants)))
+
 	resp, err := h.sessionCoordinatorClient.CreateKeygenSession(
 		ctx,
 		int32(req.ThresholdN),
@@ -588,10 +595,15 @@ func (h *AccountHTTPHandler) CreateKeygenSession(c *gin.Context) {
 	)
 
 	if err != nil {
+		logger.Error("gRPC CreateKeygenSession failed", zap.Error(err))
 		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 		return
 	}
 
+	logger.Info("gRPC CreateKeygenSession succeeded",
+		zap.String("session_id", resp.SessionID),
+		zap.Int("num_join_tokens", len(resp.JoinTokens)))
+
 	c.JSON(http.StatusCreated, gin.H{
 		"session_id":  resp.SessionID,
 		"session_type": "keygen",

backend/mpc-system/services/account/adapters/output/grpc/session_coordinator_client.go

@@ -91,11 +91,21 @@ func (c *SessionCoordinatorClient) CreateKeygenSession(
 		ExpiresInSeconds: expiresInSeconds,
 	}
 
+	logger.Info("Sending CreateSession gRPC request",
+		zap.String("session_type", "keygen"),
+		zap.Int32("threshold_n", thresholdN),
+		zap.Int32("threshold_t", thresholdT))
+
 	resp, err := c.client.CreateSession(ctx, req)
 	if err != nil {
+		logger.Error("CreateSession gRPC call failed", zap.Error(err))
 		return nil, fmt.Errorf("failed to create keygen session: %w", err)
 	}
 
+	logger.Info("CreateSession gRPC call succeeded",
+		zap.String("session_id", resp.SessionId),
+		zap.Int("num_join_tokens", len(resp.JoinTokens)))
+
 	return &CreateSessionResponse{
 		SessionID:  resp.SessionId,
 		JoinTokens: resp.JoinTokens,

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

@@ -6,11 +6,13 @@ import (
 
 	"github.com/google/uuid"
 	pb "github.com/rwadurian/mpc-system/api/grpc/coordinator/v1"
+	"github.com/rwadurian/mpc-system/pkg/logger"
 	"github.com/rwadurian/mpc-system/services/session-coordinator/application/ports/input"
 	"github.com/rwadurian/mpc-system/services/session-coordinator/application/use_cases"
 	"github.com/rwadurian/mpc-system/services/session-coordinator/domain/entities"
 	"github.com/rwadurian/mpc-system/services/session-coordinator/domain/repositories"
 	"github.com/rwadurian/mpc-system/services/session-coordinator/domain/value_objects"
+	"go.uber.org/zap"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
 )
@@ -50,6 +52,12 @@ func (s *SessionCoordinatorServer) CreateSession(
 	ctx context.Context,
 	req *pb.CreateSessionRequest,
 ) (*pb.CreateSessionResponse, error) {
+	logger.Info("gRPC CreateSession received",
+		zap.String("session_type", req.SessionType),
+		zap.Int32("threshold_n", req.ThresholdN),
+		zap.Int32("threshold_t", req.ThresholdT),
+		zap.Int("num_participants", len(req.Participants)))
+
 	// Convert request to input
 	participants := make([]input.ParticipantInfo, len(req.Participants))
 	for i, p := range req.Participants {
@@ -81,9 +89,14 @@ func (s *SessionCoordinatorServer) CreateSession(
 	// Execute use case
 	output, err := s.createSessionUC.Execute(ctx, inputData)
 	if err != nil {
+		logger.Error("gRPC CreateSession use case failed", zap.Error(err))
 		return nil, toGRPCError(err)
 	}
 
+	logger.Info("gRPC CreateSession completed successfully",
+		zap.String("session_id", output.SessionID.String()),
+		zap.Int("num_join_tokens", len(output.JoinTokens)))
+
 	// Convert output to response
 	return &pb.CreateSessionResponse{
 		SessionId:  output.SessionID.String(),