User Story 02: One Request, One Response

Implementation-oriented user story for SDK development.

Send a Task Request and Receive a Single Reply

Goal

Agent A sends one request to Agent B and receives exactly one response message on the reply topic.

Preconditions

• Agent B is discoverable on:
  • $a2a/v1/discovery/{org_id}/{unit_id}/{agent_id}
• Agent A has selected Agent B and has a writable request topic plus a subscribed reply topic.

End-to-End Flow

1. Agent A subscribes to reply topic:
   • $a2a/v1/reply/{org_id}/{unit_id}/{agent_id}/{reply_suffix}
2. Agent A publishes one request to:
   • $a2a/v1/request/{org_id}/{unit_id}/{agent_id}
   • QoS: 1 (recommended)
   • MQTT v5 properties:
     • Response Topic: reply topic above
     • Correlation Data: unique request correlation bytes
3. Agent B processes request and publishes one response message to Response Topic:
   • Echoes the same Correlation Data
4. Agent A matches response by Correlation Data and completes the request.

Expected Payload Outcome

• Response payload may contain:
  • message
  • task
• If task is present, task.id echoes the requester-generated UUIDv4 and identifies any follow-up task operations.

SDK Requirements Checklist

• Generate unique Correlation Data per request.
• Route response strictly by Correlation Data.
• Handle one-shot completion without waiting for stream updates.
• Persist returned task.id when present.