fix(backend): prevent duplicate key constraint on empty login id when syncing users

backend/internal/handler/auth_handler.go

@@ -496,9 +496,51 @@ func (h *AuthHandler) Signup(c *fiber.Ctx) error {
 				return errorJSON(c, fiber.StatusForbidden, "The specified organization is not active.")
 			}
 		} else {
-			// If companyCode provided but not found, we should probably reject if we want strictness,
-			// or just treat as GENERAL user. Given the risk "존재하지 않는 테넌트도 저장됨", we should reject.
-			return errorJSON(c, fiber.StatusBadRequest, "해당하는 가족사(테넌트)를 찾을 수 없습니다.")
+			// If companyCode provided but not found, we automatically create one
+			// [New Policy] 자동 생성 로직 추가
+			slog.Info("[Signup] CompanyCode not found, creating new tenant automatically", "slug", req.CompanyCode)
+
+			// Determine name from CompanyCode
+			tenantName := req.CompanyCode
+			// Map slug to localized name if possible
+			slugToName := map[string]string{
+				"HANMAC":   "한맥",
+				"SAMAN":    "삼안",
+				"JANGHEON": "장헌",
+				"HALLA":    "한라",
+				"PTC":      "PTC",
+				"BARON":    "바론",
+			}
+			if name, ok := slugToName[strings.ToUpper(req.CompanyCode)]; ok {
+				tenantName = name
+			}
+
+			// Create the tenant
+			// Note: creatorID is unknown at this point, will be set via Read-Model sync later
+			newTenant, err := h.TenantService.RegisterTenant(c.Context(),
+				tenantName,
+				req.CompanyCode,
+				domain.TenantTypeCompany,
+				"Automatically created during signup",
+				nil, // domains
+				nil, // parentID
+				"",  // creatorID (will sync later)
+			)
+			if err != nil {
+				// Handle race condition: if tenant was created by another request just now
+				if strings.Contains(err.Error(), "already exists") {
+					newTenant, err = h.TenantService.GetTenantBySlug(c.Context(), req.CompanyCode)
+				}
+
+				if err != nil || newTenant == nil {
+					slog.Error("[Signup] Failed to create tenant automatically", "slug", req.CompanyCode, "error", err)
+					return errorJSON(c, fiber.StatusInternalServerError, "Failed to initialize organization.")
+				}
+			}
+
+			slog.Info("[Signup] Successfully created missing tenant", "slug", req.CompanyCode, "id", newTenant.ID)
+			tenantID = &newTenant.ID
+			companyCode = newTenant.Slug
 		}
 	}