User Story 05: Shared Pool Dispatch

Implementation-oriented user story for SDK development.

One Request to Unit Pool, One Responder Selected by Shared Subscription

Goal

Agent A sends a request to a unit-level shared pool topic. Multiple compatible agents are subscribed through a shared subscription group, and exactly one responder agent handles the request.

Preconditions

• Compatible responder agents are registered under the same unit and support the same service contract.
• Responders subscribe with the same shared group:
  • $share/{group_id}/$a2a/v1/request/{org_id}/{unit_id}/pool/{pool_id}
• Agent A has a subscribed reply topic and can publish to the pool request topic.

End-to-End Flow

1. Agent A publishes request to:
   • $a2a/v1/request/{org_id}/{unit_id}/pool/{pool_id}
   • QoS: 1 (recommended)
   • MQTT v5 properties:
     • Response Topic: $a2a/v1/reply/{org_id}/{unit_id}/{client_agent_id}/{reply_suffix}
     • Correlation Data: unique request correlation bytes
2. Broker delivers the request to one responder in the shared group.
3. Selected responder processes request and publishes reply to Response Topic:
   • echoes same Correlation Data
   • includes User Property:
     • key: a2a-responder-agent-id
     • value: concrete responder agent_id
4. If a task is created, reply includes server-generated Task.id.
5. Agent A records tuple:
   • Task.id
   • a2a-responder-agent-id
6. Agent A sends follow-up task operations to the concrete responder direct topic:
   • $a2a/v1/request/{org_id}/{unit_id}/{a2a-responder-agent-id}

SDK Requirements Checklist

• Support pool request topic publishing.
• Keep Correlation Data-based reply correlation.
• Require and parse a2a-responder-agent-id on pooled responses.
• Persist responder identity with Task.id for follow-up routing.
• Keep responder-specific follow-up traffic off pooled topic.

Failure Cases to Test

• Missing a2a-responder-agent-id in pooled reply: requester treats as protocol error.
• Responder unavailable after initial assignment: requester retries with task-aware policy.
• Mixed-capability pool members: requester receives unsupported-operation errors and should apply pool compatibility checks.