Agent Mail — optional coordination adapter

Agent Mail carries messages, acknowledgements, identities, and temporary file reservations. It is not a task tracker, queue, proof ledger, or lifecycle controller.

Reservations are advisory: they prevent collisions only because every cooperating writer checks them against the same absolute project path, and one writer registered against a different path resolution makes the whole ledger advisory fiction. Agent Mail enforces nothing on a writer that does not check.

Named failure mode — silence-as-status: reading an unanswered thread as "work stalled" or "work done"; mail silence proves only that no mail arrived.

Anti-pattern: widening or renewing a reservation unprompted when a conflict appears. Corrective: report the conflict to the caller as-is; scope and TTL changes are the caller's call.

Boundary