fix(api): enforce project identifier uniqueness

backend/internal/logic/projects/handlers_test.go

@@ -142,6 +142,38 @@ func TestUpdateProject(t *testing.T) {
 		require.Equal(t, "更新后的项目说明", updated.Description)
 	})
 
+	t.Run("clears optional metadata while preserving omitted name and identifier", func(t *testing.T) {
+		router, project, _ := newProjectsHandlerTestRouter(t)
+		require.NoError(t, models.DBService.Model(project).Updates(map[string]any{
+			"icon":        "tree",
+			"background":  "#165DFF",
+			"description": "原项目说明",
+		}).Error)
+		originalName := project.Name
+		originalIdentifier := project.Identifier
+		body, err := json.Marshal(gin.H{
+			"icon":        "",
+			"background":  "",
+			"description": "",
+		})
+		require.NoError(t, err)
+		req := httptest.NewRequest(http.MethodPatch, "/api/v1/projects/"+project.Identity, bytes.NewReader(body))
+		req.Header.Set("Content-Type", "application/json")
+		req.Header.Set("Authorization", "Bearer test-token")
+		rec := httptest.NewRecorder()
+
+		router.ServeHTTP(rec, req)
+
+		require.Equal(t, http.StatusNoContent, rec.Code)
+		var updated models.SenlinAgentProject
+		require.NoError(t, models.DBService.First(&updated, project.ID).Error)
+		require.Equal(t, originalName, updated.Name)
+		require.Equal(t, originalIdentifier, updated.Identifier)
+		require.Empty(t, updated.Icon)
+		require.Empty(t, updated.Background)
+		require.Empty(t, updated.Description)
+	})
+
 	t.Run("returns not found when the identity is not owned by the current user", func(t *testing.T) {
 		router, _, _ := newProjectsHandlerTestRouter(t)
 		other, err := NewService().CreateProject(2, "Other", "")