Answers the A2A JSON-RPC methods message/send and message/stream for an agent that writes A2UI.

case A2UIAgent.A2A.Server.handle(body, &MyAgent.run/1, generator: generator) do
  {:reply, response, extensions} -> # send the response as JSON
  {:stream, events, extensions} -> # send each event as a server-sent event
end

extensions lists the extension URIs activated for the request, for the X-A2A-Extensions response header. A2UIAgent.A2A.Plug does all of this over HTTP.

The agent

The agent is a function of an A2UIAgent.A2A.Request, or a module implementing A2UIAgent.A2A.Agent. It returns:

• {:ok, output} or {:ok, output, state} — the model's response, as a string or an enumerable of streamed chunks, and the state the task ends in ("input-required" unless the :final_state option says otherwise);
• {:error, reason} — the task fails, with reason as its status message.

Requests and answers

The server reads the message into an A2UIAgent.A2A.Request and negotiates catalogs for the renderer. Given a generator and renderer capabilities (from the message metadata, else the :default_capabilities option), the request carries an A2UIAgent.RequestProcessor: the agent gives its prompt to the model, and its parser reads the model's output into a text part for each run of text and an A2UI data part for each message. Without a processor the output is answered as text. Capabilities that name none of the agent's catalogs fail the task.

message/send answers with the finished task, whose status message holds every part. A response that does not parse is answered as text. message/stream answers with a stream of JSON-RPC responses: the task (submitted), a working status update for each chunk that completes parts, and a final status update. A stream that stops parsing fails the task. A format that reads a response only once it is complete (A2UIAgent.Express) answers with one working update at the end of the stream, holding every part.

Options

• :generator — an A2UIAgent.Generator, or a list of them (one per protocol version, in order of preference; the first that negotiates wins).
• :default_capabilities — the capabilities to negotiate when the message carries none.
• :extensions — the extension URIs the client requested in the X-A2A-Extensions header.
• :advertised — the A2UI extension URIs the agent advertises (A2UIAgent.A2A.advertised_extensions/1 of its agent card).
• :final_state — the state a task ends in (default "input-required").
• :id_generator — a zero-arity function that returns new task, context and message ids (default: random UUIDs).
• :clock — a zero-arity function that returns the ISO 8601 timestamp of a task status (default: the current time).