Log multi-agent communication lifecycle

[bolinfest]

Why

#30867 makes submit_inter_agent_communication the common outbound sink for multi-agent v2 communications. This follow-up uses that single point to log every communication lifecycle without requiring new hooks as spawn, messaging, follow-up, or result paths evolve.

For each communication, the logs need to identify its type, sender and receiver threads, and content, while correlating the successful send with receipt by the destination mailbox. The logging path must not query externally supplied time providers because those calls can be expensive for app-server clients.

What changed

• Added structured INFO events on the OpenTelemetry-exported codex_otel.agent_communication target for spawn, message, followup, and result communications.
• Logged successful sends from submit_inter_agent_communication with the communication kind, sender and receiver thread IDs, content, and submission ID.
• Logged receives after the communication has been enqueued in the receiver mailbox, using the same submission ID.
• Avoided time-provider calls and other asynchronous work in the logging path.
• Narrowed ordinary spawn and send-input APIs to Vec<UserInput> so Op::InterAgentCommunication cannot bypass the context-bearing centralized path.

The refactor does not change submission IDs, capacity checks, last-task bookkeeping, mailbox ordering, protocol types, rollout data, or model-visible context.

Event shape

Illustrative JSON representation of the two independently emitted records:

[
  {
    "event.name": "codex.agent_communication",
    "communication_id": "019f20e1-40d1-7890-a123-456789abcdef",
    "kind": "spawn",
    "state": "send",
    "sender_thread_id": "019f20df-fbe1-7890-a123-456789abcdef",
    "receiver_thread_id": "019f20e1-3f79-7890-a123-456789abcdef",
    "content": "inspect the repository"
  },
  {
    "event.name": "codex.agent_communication",
    "communication_id": "019f20e1-40d1-7890-a123-456789abcdef",
    "state": "receive"
  }
]

Consumers join the receive record to the send record by communication_id for the immutable communication metadata.

Testing

• Extended the existing end-to-end multi-agent v2 spawn test to verify content, both thread IDs, and a correlated send/receive submission ID.
• Re-ran focused control and handler coverage for direct messages, follow-up tasks, and completion results.

[rka-oai]

The events are emitted as INFO right? Maybe we should set INFO instead of TRACE here?

[rka-oai]

OOC, do we need sender_thread_id to be set to pub(crate)? should other modules be able to access/view it (looks like it’s only accessed within this module, so could it remain private)