feat(assets): protect referenced stickers from deletion

backend/service/app.py

@@ -1399,6 +1399,26 @@ def _zip_asset_entry(zf: zipfile.ZipFile, pkg_id: str) -> str:
     return sorted(candidates)[0]
 
 
+def _asset_reference_names(asset_id: str) -> list[str]:
+    usages: list[str] = []
+    data_sources = (
+        (DESIGN_TEMPLATES_DIR, "template.json"),
+        (PROJECTS_DIR, "project.json"),
+    )
+    for root, filename in data_sources:
+        for item in _list_dirs(root):
+            path = item / filename
+            if not path.exists():
+                continue
+            try:
+                data = json.loads(path.read_text(encoding="utf-8"))
+            except Exception:
+                continue
+            if asset_id in json.dumps(data, ensure_ascii=False):
+                usages.append(str(data.get("name") or item.name))
+    return usages
+
+
 def _remap_import_asset_ids(document: dict, asset_map: dict[str, str]) -> None:
     elements = document.get("elements")
     if not isinstance(elements, list):
@@ -1796,6 +1816,10 @@ def delete_asset(asset_id: str) -> None:
     meta = _read_asset_meta(d)
     if not meta:
         raise HTTPException(status_code=404, detail="asset not found")
+    usages = _asset_reference_names(asset_id)
+    if usages:
+        names = "、".join(dict.fromkeys(usages))
+        raise HTTPException(status_code=409, detail=f"素材仍被以下设计引用，无法删除：{names}")
     shutil.rmtree(d, ignore_errors=True)