fix(gateway): log agent task failures instead of silently losing usage data

gateway/platforms/api_server.py

@@ -1326,8 +1326,8 @@ class APIServerAdapter(BasePlatformAdapter):
             try:
                 result, agent_usage = await agent_task
                 usage = agent_usage or usage
-            except Exception:
-                pass
+            except Exception as exc:
+                logger.warning("Agent task %s failed, usage data lost: %s", completion_id, exc)
 
             # Finish chunk
             finish_chunk = {