> ## Documentation Index
> Fetch the complete documentation index at: https://docs.usefused.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Agent2Agent (A2A)

> Expose a Harnest agent through A2A and call remote A2A agents through a bounded client.

Harnest supports both sides of the A2A 1.0 protocol. An authored Agent Card can expose the compiled agent, while `A2AClient` and `RemoteAgent` let trusted application code call another agent.

| Goal                                                 | Harnest boundary                                                |
| ---------------------------------------------------- | --------------------------------------------------------------- |
| Make this agent discoverable and callable            | Declare an HTTP+JSON or JSON-RPC interface in `agent-card.yaml` |
| Make a direct outbound request                       | Use `A2AClient` from trusted Python                             |
| Add a remote agent to a portable graph               | Use `RemoteAgent` as a graph node                               |
| Expose a remote agent as a model-selected capability | Convert `RemoteAgent` to an Agent Tool                          |

Harnest keeps the default path small. A completed blocking interaction returns an A2A `Message`; it does not create a Task merely because the protocol supports Tasks. Streaming, asynchronous execution, approvals, client tools, and durable external waits use an A2A `Task` when task identity is required.

Task lookup, listing, cancellation, and subscription happen only when the client asks for them. The outbound client does not list or monitor unrelated Tasks in the background.

<CardGroup cols={2}>
  <Card title="Serve an agent through A2A" icon="tower-broadcast" href="/harnest/runtime/a2a/serve">
    Publish an Agent Card, mount a binding, and choose durable Task storage.
  </Card>

  <Card title="Call a remote agent" icon="arrow-right-arrow-left" href="/harnest/runtime/a2a/client">
    Send, stream, poll, cancel, subscribe, or compose a remote agent.
  </Card>
</CardGroup>

<Note>
  Harnest A2A uses the same agent, tools, durable Tasks, sessions, authentication, lifecycle, and telemetry as the neutral API. It is a transport adapter, not a second agent runtime.
</Note>