Pending Response Tracking

The protocol

1. Write session-state.json with pending_response: {message_id, preview, reacted_at}
2. Do the work
3. Send the response
4. Clear pending_response to null

Heartbeat sweep contract

On every heartbeat tick, maintenance reads pending_response. A non-null value older than the heartbeat window means the prior session crashed mid-work; heartbeat reposts the response or sends a state-loss notice, then clears the entry.

Who writes / clears

• default session writes the entry when it begins working on an inbound
• default session clears the entry after the response lands
• maintenance session reads + clears stale entries via the heartbeat sweep