fix: Admin UI에서 전송한 커스텀 필드(metadata)가 백엔드 Kratos 트레이츠에 빈 배열로 깨져서 저장되는 문제 해결 (#440)

backend/internal/handler/user_handler.go

@@ -1194,15 +1194,28 @@ func (h *UserHandler) UpdateUser(c *fiber.Ctx) error {
 	}
 
 	// For namespaced metadata, we don't delete everything, we merge.
-	// But we should remove legacy flat traits that are not in the new req.Metadata if we want strict sync.
-	// For now, let's just merge.
 	for k, v := range req.Metadata {
 		if !coreTraits[k] {
-			traits[k] = v
+			// Ensure we are merging maps (tenant namespaces) correctly, not overwriting with slices
+			if incomingMap, ok := v.(map[string]any); ok {
+				if existingMap, ok := traits[k].(map[string]interface{}); ok {
+					for subK, subV := range incomingMap {
+						existingMap[subK] = subV
+					}
+					traits[k] = existingMap
+				} else {
+					traits[k] = incomingMap // New namespace
+				}
+			} else {
+				traits[k] = v // Fallback for flat metadata
+			}
 		}
 	}
 
 	state := normalizeKratosState(req.Status)
+
+	slog.Info("[UpdateUser] Calling Kratos UpdateIdentity", "userID", userID, "traits", traits, "state", state)
+
 	updated, err := h.KratosAdmin.UpdateIdentity(c.Context(), userID, traits, state)
 	if err != nil {
 		return errorJSON(c, fiber.StatusInternalServerError, err.Error())