fix: gracefully handle missing avatar SQLite database

- Return empty list instead of crashing when avatar.db doesn't exist
- Add is_available() check before each endpoint
- 503 status when trying to access unavailable database

backend/app/api/endpoints/avatars.py

@@ -2,7 +2,7 @@
 from fastapi import APIRouter, Query, HTTPException
 
 from app.schemas import ApiResponse
-from app.services.avatar_service import avatar_service, get_session
+from app.services.avatar_service import avatar_service, get_session, is_available
 
 router = APIRouter()
 
@@ -15,6 +15,8 @@ def list_avatars(
     status: str = Query(default=None),
 ):
     """分页查询所有数字分身"""
+    if not is_available():
+        return ApiResponse(data={"total": 0, "page": page, "page_size": page_size, "items": []})
     db = get_session()
     try:
         total, items = avatar_service.list_avatars(
@@ -35,6 +37,8 @@ def list_avatars(
 @router.get("/{avatar_id}")
 def get_avatar(avatar_id: str):
     """获取单个数字分身详情"""
+    if not is_available():
+        raise HTTPException(status_code=503, detail="数字分身数据库尚未初始化")
     db = get_session()
     try:
         data = avatar_service.get_avatar(db, avatar_id)
@@ -54,6 +58,8 @@ def update_avatar_status(avatar_id: str, body: dict):
             status_code=400,
             detail="status 必须是 active、inactive 或 training",
         )
+    if not is_available():
+        raise HTTPException(status_code=503, detail="数字分身数据库尚未初始化")
     db = get_session()
     try:
         data = avatar_service.update_status(db, avatar_id, status)

backend/app/services/avatar_service.py

@@ -23,7 +23,8 @@ def _get_engine_and_session():
         if not os.path.isabs(db_path):
             db_path = os.path.abspath(db_path)
         if not os.path.exists(db_path):
-            raise FileNotFoundError(f"数字分身数据库不存在: {db_path}")
+            # 数据库不存在时返回 None，由调用方处理
+            return None, None
         _engine = create_engine(
             f"sqlite:///{db_path}",
             connect_args={"check_same_thread": False},
@@ -32,11 +33,17 @@ def _get_engine_and_session():
     return _engine, _SessionLocal()
 
 
-def get_session() -> Session:
+def get_session() -> Optional[Session]:
     _, session = _get_engine_and_session()
     return session
 
 
+def is_available() -> bool:
+    """检查数字分身数据库是否可用"""
+    engine, _ = _get_engine_and_session()
+    return engine is not None
+
+
 class AvatarService:
 
     @staticmethod