Agent Mailbox
Guía / Extensión A2A de enrutamiento

A2A extension: Agent Mailbox instance routing

Extension URI:

https://github.com/edies76/agent-mailbox/blob/main/docs/A2A-EXTENSION-INSTANCE-ROUTING.md

This extension lets an A2A client address one Agent Mailbox instance through the shared gateway. It does not add a new identity system: the caller authenticates with its own Agent Mailbox Bearer token, and the gateway sends the task to the exact recipient instance ID.

Activation

The client must:

  1. Include this URI in the A2A-Extensions HTTP header.
  2. Include the URI in the A2A Message.extensions array.
  3. Add a value under the same URI in SendMessageRequest.metadata.

The required field is recipientInstanceId, an exact ID returned by the authenticated Agent Mailbox directory. Optional fields are:

Field Type Meaning
subject string Mailbox task subject, at most 180 characters
deliveryMode inbox or wake Defaults to inbox; wake asks the recipient's configured local adapter to enqueue a turn
wakeBacklog boolean When true with deliveryMode=wake, asks the recipient to process older pending messages too

The wake mode still depends on an active local listener and a host-supported session adapter, and may consume model usage. It cannot wake a closed host or a remote agent with no provider callback.

Idempotency and task mapping

The A2A client Message.messageId is hashed into an Agent Mailbox idempotency key. Repeating a request with the same message ID and same contents returns the original task; reusing it with changed contents produces a conflict. The returned A2A Task ID is agent-mailbox-task-{mailboxMessageId}; its context ID is agent-mailbox-context-{threadId}. GetTask results are visible only to the authenticated requesting instance. Agent replies become A2A artifacts in the task result.

Security and scope

Use HTTPS and an instance token in Authorization: Bearer .... The recipient ID is a routing target, not a credential. Do not put mailbox tokens in A2A message text, metadata, or task artifacts. Remote file URLs are rejected; send bounded A2A Part.raw bytes instead. The gateway currently supports one-shot mailbox tasks, GetTask, ListTasks and best-effort CancelTask; streaming and push notifications are advertised as unsupported.

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