fix(issue-18): bind the heartbeat timer to the agent process; scope started to the attempt; ignore re-sent finished dispatches

Review round 1 (claude NOT PASS) corrections:
- B2: the timer now watches a process - `--watch-pid`, or by default the
  nearest agent-CLI ancestor of the publishing command - and stops within
  one period once it is gone, so a crashed agent stops heartbeating and is
  closed after K x N; a remote runner watches itself. Documented as process
  liveness (an alive-but-stuck agent keeps heartbeating).
- R1: `_wait_started` accepts an events.log `started` only when it carries
  the current dispatch token (loop jobs share one events.log).
- R2: the remote runner ignores a re-sent dispatch of an attempt that
  already reached its terminal.
- R3: registry.md EOF blank line (git diff --check clean).
- R4: the ack error states the effective budget when the wall clock cut it.
- P3: stop_timer verifies the pidfile pid is this job's timer before
  signalling; a retained state message keeps its own seq watermark so it
  can never make the monotonic guard drop its own event.
- MULTI_AGENT_RULES.md timeout section updated for the contract.
- tests: agent-process death stops the timer, recycled-pid safety,
  attempt-scoped started, re-sent dispatch; acceptance 3 now kills the
  agent process instead of the timer. Help captures refreshed
  (--watch-pid). The wrapper can be sourced with
  MAM_DELEGATE_JOB_NO_MAIN=1 for helper-level tests.

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

.agents/MULTI_AGENT_RULES.md

@@ -168,7 +168,8 @@ To ensure that agents running in TMUX environments do not lose debug logs or pre
 - **Identity Verification**: The guard validates process liveness via `pid` + `lstart` to prevent livelocks on PID rollover.
 
 ### ⏱️ Timeout Configuration & Alignment Rules
-- **Job Execution Limits (`timeout_sec` & `idle_timeout_sec`)**: Each job independently manages its overall execution timeout (`timeout_sec`, default 3600s) and idle timeout without receiving messages (`idle_timeout_sec`, default 120s).
+- **Job Execution Limits (`timeout_sec` & `idle_timeout_sec`)**: Each job independently manages its overall execution timeout (`timeout_sec`, default 3600s) and idle timeout without receiving messages (`idle_timeout_sec`). Since v4.5.0 (Issue #18) the idle timeout is the liveness contract's K x N: the agent heartbeats every `heartbeat_sec` (N, default 30 — automatic once it publishes `started --heartbeat N`), and `heartbeat_misses` (K, default 4) missed heartbeats close the job as `deadline_timeout` (default 120 s, `--idle-timeout` overrides). `started` must arrive within `ack_timeout_sec` (T, default 60) of the injection or the job fails as `agent_blocked` without re-injection. herdr status and pane text are never used for these decisions.
+- **Heartbeat timer and agent life**: the automatic timer is bound to the agent process that ran the start command (the nearest agent-CLI ancestor, or `--watch-pid`) and stops within one period once that process is gone; a crashed agent is therefore closed after K x N like any silent one, while an agent that is alive but stuck keeps heartbeating (process liveness, not work liveness).
 - **Monitor Idle Waiting (`SUB_IDLE_TIMEOUT`)**: The idle timeout for the monitor script (`reconcile.sh`), `SUB_IDLE_TIMEOUT`, must always be set generously to `3600s` (1 hour) or more to align with the maximum job budget. This prevents the monitor from terminating early due to idle detection, which would lose control over background tasks before they finish.
 
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