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A run belongs to the agent server, not to the request that started it. It goes on when the client disconnects, and the task stores its outcome either way. A client follows the task through one of the A2A methods below.

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Durable and ephemeral updates

An ephemeral update reaches only the streams open on the server running the task, as it happens. Everything durable can be read again later.

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Delivery methods

SendMessage always answers with a Task, never a bare Message, and every stream closes with the stored Task. How a subscription is served when several servers share one database is described in Multiple Instances.

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When a stream ends early

A stream that closes on a Task that is still SUBMITTED or WORKING, and a SendMessage answered with one, did not see the run end. Two things cause it:
  • a2a-sdk drops a subscriber that falls 1024 events behind, and logs Evicting event queue sink.
  • A stopping server closes its connections.
The run itself is not affected. Resubscribe with SubscribeToTask, or poll GetTask, for the outcome. To stop a run, call CancelTask; disconnecting does not stop it.

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Push notifications

A webhook receives exactly what the task stores, and never an ephemeral update. That includes every outcome the task stores, also those the run did not write itself:
  • a cancel written by another server of the agent;
  • the FAILED of an agent that raised;
  • a task settled FAILED when its server shut down, with aion:settledReason set to server_shutdown;
  • a task settled FAILED as abandoned after AION_STALE_TASK_TIMEOUT, with aion:settledReason set to task_abandoned.
See Multiple Instances for when the server settles a task. Each delivery carries the configuration’s token as X-A2A-Notification-Token, and its authentication as Authorization: <scheme> <credentials>; credentials without a scheme are sent as Bearer. CreateTaskPushNotificationConfig answers with the configuration as stored: an id the request left empty is the task’s id. Deliveries are made one at a time from the task’s event loop, each after its change is stored. A webhook that answers slowly therefore holds back the delivery of the run’s later events, on every channel, for up to PUSH_NOTIFICATION_TIMEOUT_SECONDS (default 5 seconds) per delivery. Connecting to the webhook is limited to 5 seconds. On a server the Aion platform hosts, a webhook URL must be http or https and resolve to public addresses only; see Environment Variables.