Agent2Agent (A2A) - Fused

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

Completed blocking requests return a Message. Streaming, asynchronous execution, and suspended interactions use an A2A Task. 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.

Serve an agent through A2A

Publish an Agent Card, mount a binding, and choose durable Task storage.

Call a remote agent

Send, stream, poll, cancel, subscribe, or compose a remote agent.

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.