feat(account): add GET /sign/:sessionId endpoint for co-sign session status

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

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

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

@@ -60,6 +60,7 @@ func (h *CoManagedHTTPHandler) RegisterRoutes(router *gin.RouterGroup) {
 
 		// Sign session routes (new - does not affect existing functionality)
 		coManaged.POST("/sign", h.CreateSignSession)
+		coManaged.GET("/sign/:sessionId", h.GetSignSessionStatus)
 		coManaged.GET("/sign/by-invite-code/:inviteCode", h.GetSignSessionByInviteCode)
 	}
 }
@@ -588,6 +589,62 @@ func (h *CoManagedHTTPHandler) CreateSignSession(c *gin.Context) {
 	})
 }
 
+// GetSignSessionStatus handles getting the status of a co-managed sign session
+func (h *CoManagedHTTPHandler) GetSignSessionStatus(c *gin.Context) {
+	sessionID := c.Param("sessionId")
+	if sessionID == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "session_id is required"})
+		return
+	}
+
+	// Validate session ID format
+	if _, err := uuid.Parse(sessionID); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid session_id format"})
+		return
+	}
+
+	// Call session coordinator via gRPC
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	resp, err := h.sessionCoordinatorClient.GetSessionStatus(ctx, sessionID)
+	if err != nil {
+		logger.Error("Failed to get sign session status", zap.Error(err))
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	result := gin.H{
+		"session_id":        sessionID,
+		"status":            resp.Status,
+		"session_type":      resp.SessionType,
+		"threshold_t":       resp.ThresholdT,
+		"threshold_n":       resp.ThresholdN,
+		"completed_parties": resp.CompletedParties,
+		"total_parties":     resp.TotalParties,
+	}
+
+	// Add signature if sign completed
+	if resp.SessionType == "sign" && len(resp.Signature) > 0 {
+		result["signature"] = hex.EncodeToString(resp.Signature)
+	}
+
+	// Include participants with party_index
+	if len(resp.Participants) > 0 {
+		participants := make([]gin.H, len(resp.Participants))
+		for i, p := range resp.Participants {
+			participants[i] = gin.H{
+				"party_id":    p.PartyID,
+				"party_index": p.PartyIndex,
+				"status":      p.Status,
+			}
+		}
+		result["participants"] = participants
+	}
+
+	c.JSON(http.StatusOK, result)
+}
+
 // GetSignSessionByInviteCode handles looking up a sign session by its invite code
 // This is a completely new endpoint that does not affect existing functionality
 func (h *CoManagedHTTPHandler) GetSignSessionByInviteCode(c *gin.Context) {