Step 12：后端轻量优化（API 稳定性 & 前端友好）

backend/app/core/exceptions.py

@@ -0,0 +1,19 @@
+from fastapi import FastAPI, Request, status
+from fastapi.responses import JSONResponse
+
+
+class AppException(Exception):
+    def __init__(self, code: str, message: str, status_code: int = status.HTTP_400_BAD_REQUEST):
+        self.code = code
+        self.message = message
+        self.status_code = status_code
+        super().__init__(message)
+
+
+def register_exception_handlers(app: FastAPI) -> None:
+    @app.exception_handler(AppException)
+    async def app_exception_handler(_: Request, exc: AppException) -> JSONResponse:
+        return JSONResponse(
+            status_code=exc.status_code,
+            content={"code": exc.code, "message": exc.message},
+        )