fix(issue-18): default ack timeout T = 180 s

In the v4.5.0 review round grok read the brief and published `started`
70 s after the injection; with T = 60 the wrapper had already closed the
job as agent_blocked and refused its later PASS. T bounds delivery, not
work, so a generous default costs nothing when the agent answers fast.
Code, docs and the CLI snapshot updated together.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

MESSAGING.md

@@ -198,7 +198,7 @@ orchestrator's disk, take part on equal terms.
 |---|---|---|
 | **Heartbeat obligation** | While working, the agent publishes `progress` at least every **N** s (`heartbeat_sec`, default 30). `publish_event.py --event started --heartbeat N` starts a detached timer that publishes `progress` (`detail: heartbeat`) every N s with the same `dispatch_token`/`attempt_id`, so the agent does not have to remember. The timer stops itself at the terminal event (which also kills it through `<registry>/<job>.heartbeat.pid`), on re-dispatch, after `timeout_sec`, and within one period of the agent process it watches going away (`--watch-pid`, default the nearest agent-CLI ancestor of the publishing command; a remote runner watches itself) - a crashed agent stops heartbeating, an alive-but-stuck one does not. | `lib_py/delegation/heartbeat.py`, `publish_event.py --heartbeat` |
 | **Unresponsive** | The orchestrator treats a job as unresponsive after **K x N** s without any event (`heartbeat_misses`, default 4 → 120 s; `--idle-timeout` overrides). The subscriber's idle clock counts every accepted message (`progress` and retained state included); the wrapper's post-idle grace re-reads only the job's events.log (`_recent_disk_heartbeat`, written before every wire publish). herdr status and the pane are logged once as a *diagnostic* (`liveness: ... herdr/pane says busy=yes/no (diagnostic only)`) and never decide. | `multi-agent-mux-delegate-job` (`finalize_unfinished`), `job_subscriber.py` |
-| **Delivery** | After the prompt is handed over (herdr accepted the submission, or the remote dispatch was published), the agent's `started` must arrive within **T** s (`ack_timeout_sec`, default 60): the registry leaves `pending`, a `started` line lands in events.log, or the subscriber prints one. No `started` within T → the inject fails closed: rc 1, registry `error` (`agent_blocked`), and the prompt is **never re-injected**. `send_keys_safe` confirms an accepted-but-unconfirmed submission only by `agent_status == working` or the job's `started`; pane changes and busy tokens are no longer signals. | `_wait_started`, `lib.sh: _sks_job_started` |
+| **Delivery** | After the prompt is handed over (herdr accepted the submission, or the remote dispatch was published), the agent's `started` must arrive within **T** s (`ack_timeout_sec`, default 180; a real agent reads the brief before it runs the start command): the registry leaves `pending`, a `started` line lands in events.log, or the subscriber prints one. No `started` within T → the inject fails closed: rc 1, registry `error` (`agent_blocked`), and the prompt is **never re-injected**. `send_keys_safe` confirms an accepted-but-unconfirmed submission only by `agent_status == working` or the job's `started`; pane changes and busy tokens are no longer signals. | `_wait_started`, `lib.sh: _sks_job_started` |
 | **Termination** | Only `completed` / `error` (and an operator `cancelled`) end a job. Terminal immutability (Issue #6 CAS) refuses anything that arrives after `deadline_timeout` closed the job. | `engine.py` |
 | **Wire durability** | Every event (QoS 1) is followed, on the same connection, by a **retained** `<topic_prefix>/state` message (`event: state`, `status`, `last_event`, `seq`, signed like an event). A subscriber that connects or reconnects receives it at once: a terminal status ends the wait, any state resets the idle window, and a `seq` beyond the last one seen is recorded as `seq_gap` in the audit log (also for gaps between events). paho reconnects on its own; `on_connect` re-subscribes both topics and logs `reconnected`. | `publish_event.py: build_state_payload`, `job_subscriber.py: _on_state` |
 | **Credentials** | Each host connects with its own `.mam.env` (Issue #12: the password is never in a record). Every event and state message carries the job's HMAC (`auth_token`). A remote dispatch is signed with the pre-shared `MAM_DISPATCH_SECRET`. | `mqtt_common.py`, `remote.py` |