fix: guard reserved sessions and bounded response state

recognization/code/app.py

@@ -270,7 +270,8 @@ def create_app(
     async def lifespan(_app: FastAPI):
         yield
         for session in list(sessions.values()):
-            session.close()
+            if session is not None:
+                session.close()
         engine.shutdown()
 
     app = FastAPI(
@@ -1111,6 +1112,11 @@ def main() -> None:
     LOGGER.info("Loading model and catalog (device=%s, imgsz=%s)...",
                 engine_settings.device or "auto", engine_settings.imgsz)
     engine = build_default_engine(engine_settings)
+    if (engine_settings.identity_backend or "").lower() == "gallery":
+        if engine.identity_gallery() is None:
+            raise RuntimeError(
+                "gallery identity backend requires local DINOv2 weights; refusing to start"
+            )
     warm_ms = engine.warm_up()
     LOGGER.info(
         "Ready: %d SKUs, catalog %s, warmup %.0f ms, classify workers %d",