Behaviour for delivering push notification payloads to a client's webhook.

An agent that stores push notification configs (see A2A.PushNotificationConfig) POSTs a payload to each registered URL every time one of its tasks changes state. This behaviour is the seam where that POST happens, so a host can route deliveries through its own queue, retry policy or egress proxy instead of the bundled HTTP sender.

A2A.PushNotificationSender.HTTP is the default and is used automatically when :req is available. Pass your own with :push_sender:

MyAgent.start_link(push_sender: {MyApp.Webhooks, queue: :webhooks})

Payload

payload is a decoded StreamResponse map carrying exactly one of task, message, statusUpdate or artifactUpdate — the same shape the streaming transport emits, per the spec's Push Notification Payload section. Encode it with Jason.encode/1; do not wrap it in a JSON-RPC envelope.

Contract

Implementations MUST NOT block: the callback is invoked from a short-lived process spawned by the agent, and a slow webhook must not stall task processing for other callers. Returning {:error, reason} is reported through telemetry and otherwise ignored — delivery is best-effort, which is what the spec requires (at least one attempt, retries optional).

Implementations MUST send the credentials from config.authentication as an HTTP Authorization header. That is the one hard requirement the spec places on the caller.