diff --git a/backend/package/yuxi/agents/backends/sandbox/paths.py b/backend/package/yuxi/agents/backends/sandbox/paths.py
index 598d7fde..8233b4a4 100644
--- a/backend/package/yuxi/agents/backends/sandbox/paths.py
+++ b/backend/package/yuxi/agents/backends/sandbox/paths.py
@@ -21,7 +21,7 @@ def get_virtual_path_prefix() -> str:
     return "/" + VIRTUAL_PATH_PREFIX.strip("/")
 
 
-def _validate_thread_id(thread_id: str) -> str:
+def validate_thread_id(thread_id: str) -> str:
     value = str(thread_id or "").strip()
     if not value:
         raise ValueError("thread_id is required")
@@ -31,7 +31,7 @@ def _validate_thread_id(thread_id: str) -> str:
 
 
 def _thread_root_dir(thread_id: str) -> Path:
-    safe_thread_id = _validate_thread_id(thread_id)
+    safe_thread_id = validate_thread_id(thread_id)
     return Path(conf.save_dir) / "threads" / safe_thread_id / "user-data"
 
 
@@ -55,7 +55,7 @@ def sandbox_user_data_dir(thread_id: str) -> Path:
 
 
 def sandbox_workspace_dir(thread_id: str, user_id: str) -> Path:
-    _validate_thread_id(thread_id)
+    validate_thread_id(thread_id)
     return _global_user_data_dir(user_id) / WORKSPACE_DIR_NAME
 
 
diff --git a/backend/server/routers/mention_router.py b/backend/server/routers/mention_router.py
index b25ed42b..3cfc3b57 100644
--- a/backend/server/routers/mention_router.py
+++ b/backend/server/routers/mention_router.py
@@ -43,9 +43,9 @@ async def search_mention_files(
         # 此时该 thread 专属的 uploads/outputs 目录还没创建或为空，
         # 用户仅能安全地搜索到自己全局的工作区 (workspace) 文件。
         try:
-            from yuxi.agents.backends.sandbox.paths import _validate_thread_id
+            from yuxi.agents.backends.sandbox.paths import validate_thread_id
 
-            _validate_thread_id(thread_id)
+            validate_thread_id(thread_id)
         except ValueError:
             raise HTTPException(status_code=400, detail="非法的 thread_id 格式")