feat(issue-18): decide liveness and delivery by the event protocol, not the screen

Contract (no new event types): heartbeat every N s (automatic timer),
unresponsive after K x N s without an event, `started` within T s of the
injection, retained per-job state, and a remote transport.

- registry: heartbeat_sec / heartbeat_misses / ack_timeout_sec / transport
  fields; idle_timeout_sec derives K x N unless explicit (defaults 30/4/60
  keep the historical 120 s idle window).
- heartbeat.py + publish_event --heartbeat N: detached fixed-cadence timer
  publishing signed `progress` heartbeats (threaded wire publish, local
  record first); stopped by the terminal event via pidfile, by re-dispatch
  and by lifetime. Terminal events refuse --heartbeat.
- publish_event: retained `<prefix>/state` (status, last_event, seq, HMAC)
  sent on the same connection after every event (--no-state to skip);
  publisher.publish_raw takes extra messages.
- job_subscriber: subscribes the state topic, recovers terminal status from
  retained state, resets idle on any accepted message, records seq_gap and
  reconnected in the audit log, idle budget before the first event is
  T + K x N (--ack-timeout), --remote mirrors started/terminal events into
  the registry through the transition boundary.
- lib.sh send_keys_safe: an accepted-but-unconfirmed submission is confirmed
  by agent_status working or the job's own `started` (_sks_job_started);
  pane change and busy token are no longer delivery signals.
- wrapper: --heartbeat/--heartbeat-misses/--ack-timeout (MAM_* env),
  injected start command arms the timer, brief states the contract,
  _wait_started (registry / events.log / subscriber log, bounded by T and
  the wall clock) replaces the 10 s inject grace, R1 grace uses only the
  on-disk event age (herdr/pane logged once as a diagnostic),
  remote:<name> sessions skip preflight/idle/pane and dispatch over the
  broker (remote_dispatch).
- remote.py (+ scripts shim): signed retained dispatch (MAM_DISPATCH_SECRET)
  and a runner that mirrors the job into its own registry with the
  orchestrator's identity, publishes started --heartbeat, runs --exec and
  publishes the terminal event.
- loop runner: passes MAM_HEARTBEAT_SEC / MAM_HEARTBEAT_MISSES /
  MAM_ACK_TIMEOUT_S through; YAML rows with transport: remote delegate as
  remote:<name>.
- docs: MESSAGING.md 2.5 contract + remote transport, delegate-job SKILL.md,
  registry.md, loop SKILL.md.
- tests: tests/test_issue18_liveness_contract.py (16); issue 14 pane-signal
  tests flipped to started-based; issue 6 working-agent tests acknowledge
  with started; CLI snapshot/help captures refreshed.

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

.agents/skills/multi-agent-mux-delegate-job/SKILL.md

@@ -40,7 +40,16 @@ multi-agent-mux-delegate-job submit \
   --agent-session herdr:<session_name> \
   --prompt "Task description or instructions here" \
   --role <Worker|Planner|Reviewer> \
-  --timeout 3600 --idle-timeout 120
+  --timeout 3600 [--heartbeat 30 --heartbeat-misses 4 --ack-timeout 60] [--idle-timeout <sec>]
+  #   Liveness contract (Issue #18): the agent heartbeats every N s (automatic),
+  #   the job is unresponsive after K x N s (--idle-timeout overrides), `started`
+  #   must arrive within T s of the injection or the inject fails closed.
+
+# 1b) Same, for an agent on another host (no herdr pane, no shared disk):
+#     the brief travels over the broker as a signed retained dispatch and a
+#     `remote.py run --session <name>` runner on that host executes it.
+multi-agent-mux-delegate-job submit --agent remote --agent-session remote:<runner_session> \
+  --prompt "Task description" --role Worker      # needs MAM_DISPATCH_SECRET on both hosts
 
 # 2) Submit a job with a feedback loop (Worker-Reviewer Loop)
 multi-agent-mux-delegate-job submit \
@@ -77,8 +86,8 @@ Under fail-closed operation (`MAM_DELEGATE_FAIL_CLOSED=1`, default), the CLI ret
 | Exit Code | Meaning | Final Registry Status | Failure Behavior & Resilience |
 |:---:|:---:|:---:|---|
 | `0` | Success | `completed` | Job succeeded and completed event received or verified on disk with approval (`PASS`/`AGREE`). |
-| `1` | Failure | `error` | Execution failure / Agent injection error (`inject_agent`). |
-| `2` | Timeout | `error` (`deadline_timeout`) | Subscriber timeout (total budget or idle timeout reached without terminal event). **R1 Working-Agent Resilience**: If the agent in Herdr is still actively `working`, the wrapper does not immediately fail-close; it re-observes disk status at intervals up to the wall-clock `--timeout` deadline before fail-closing. |
+| `1` | Failure | `error` | Execution failure / delivery failure: no `started` within `--ack-timeout` T s after the injection (`agent_blocked`; the prompt is never re-injected), or the input never reached the pane. |
+| `2` | Timeout | `error` (`deadline_timeout`) | Subscriber timeout (total budget or idle timeout reached without terminal event). **R1 liveness grace (Issue #18)**: after the subscriber idles out the wrapper keeps re-observing the disk while the job's events.log shows an event at most K x N (`--idle-timeout`) old - the automatic heartbeat counts - up to the wall-clock `--timeout`. herdr status and the pane are logged as a diagnostic only. |
 | `3` | Broker Error | `error` (`deadline_timeout`) | Broker unavailable (`MQTT_BROKER_UNAVAILABLE`) and terminal status not found on disk during deadline. |
 | `5` | Session Busy | `cancelled` (`session_busy`) | Precondition failed / `session_busy`: Preflight check (`preflight_agent`) or TUI idle handshake wait failed (prompt never delivered, retryable). |
 
@@ -131,11 +140,12 @@ a fresh interpreter — but a test harness could.
 
 Every agent participating in the delegation contract must follow the same lifecycle publishing protocol using `publish_event.py`:
 
-1. **On Start**: Publish `started` event.
-   `python3 .agents/skills/multi-agent-mux-delegate-job/scripts/publish_event.py --job "$JOB_ID" --event started`
+1. **On Start** (first thing, within the ack timeout T): Publish `started` and arm the heartbeat timer.
+   `python3 .agents/skills/multi-agent-mux-delegate-job/scripts/publish_event.py --job "$JOB_ID" --event started --heartbeat <N>`
+   The timer publishes `progress` every N s until your terminal event (Issue #18); the brief and the injected instructions carry the exact command.
 2. **On Tool/Permission Prompt**: Publish `permission_required` event.
    `python3 ... --job "$JOB_ID" --event permission_required --detail "<tool>:<reason>"`
-3. **On Progress Update (Optional)**: Publish `progress` event.
+3. **On Progress Update**: Publish `progress` at check-points (the heartbeat timer already satisfies the every-N-seconds obligation).
    `python3 ... --job "$JOB_ID" --event progress --detail "<status_update>"`
 4. **On Success**: Publish `completed` event.
    `python3 ... --job "$JOB_ID" --event completed --detail "<summary>"` (Reviewer should include `"PASS"` in the detail to approve).