fix(agent): map closed database worker to 503

app/factory.py

@@ -14,7 +14,10 @@ from app.adapters.observability.otel import build_observation_port
 from app.adapters.web.plugin.routes import FastAPIDynamicRouteRegistry
 from app.adapters.web.health import install_health_routes
 from app.application.plugin.routes import configure_plugin_routes
-from app.application.database import DatabaseWorkerOverloadedError
+from app.application.database import (
+    DatabaseWorkerClosedError,
+    DatabaseWorkerOverloadedError,
+)
 from app.adapters.web.security.access import (
     configure_token_codec,
     verify_apikey,
@@ -234,9 +237,9 @@ async def localized_http_exception_handler(
 
 async def database_worker_overloaded_handler(
         request: Request,
-        _exc: DatabaseWorkerOverloadedError,
+        _exc: DatabaseWorkerClosedError | DatabaseWorkerOverloadedError,
 ) -> JSONResponse:
-    """将数据库短事务背压映射为可重试的 503 响应。"""
+    """将数据库 worker 暂不可用映射为可重试的 503 响应。"""
     return await localized_http_exception_handler(
         request,
         HTTPException(
@@ -335,6 +338,10 @@ def create_app() -> FastAPI:
         DatabaseWorkerOverloadedError,
         database_worker_overloaded_handler,
     )
+    _app.add_exception_handler(
+        DatabaseWorkerClosedError,
+        database_worker_overloaded_handler,
+    )
     _app.add_exception_handler(
         RequestValidationError,
         localized_validation_exception_handler,