fix(issue-18): admit remote attempts atomically, end timed-out commands with their group, fence heartbeats off the terminal, renew liveness only on news

Review round 2 (planner-reviewer-codex-01, NOT PASS at d09c162):

- R1 remote.mirror_job: admission under the registry lock. The same
  dispatch_token is idempotent (a finished attempt never runs again), a
  lower attempt or the same attempt under another token is refused before
  any write, and only a strictly newer attempt replaces the record
  (register_job(supersede_older_attempt=True); events.log kept, seqs stay
  monotonic).
- R2 remote.handle_dispatch: the --exec command runs in its own session;
  at timeout_sec, or when the runner is interrupted (SIGTERM now unwinds
  it), the whole process group is terminated (TERM, then KILL) before the
  error is published.
- R3 terminal barrier: a terminal publish raises an attempt-scoped barrier
  under the lock that allocates seqs, stops the heartbeat timer, gives it
  MAM_HEARTBEAT_DRAIN_S (default 1 s) to exit and then kills it, and only
  then takes its own seq. Beats are admitted under that lock
  (next_seq(admit=...)); a beat still on the wire is cancelled with the
  timer rather than holding the terminal back; and a late non-terminal
  event never publishes a running state over a terminal record.
- R4 job_subscriber: a retained state renews the idle clock only when its
  seq is newer than everything already accepted; re-delivered or older
  snapshots still recover a terminal status.
- tests: five regressions, all failing on 77f2829; T1-14's wall clock
  15 -> 30 s against public-broker latency.
- docs: MESSAGING 2.5 (barrier, state renewal, detection vs final close),
  heartbeat docstring, loop SKILL.md (remote rows need the Python runner),
  VERSIONS v4.5.0 items 1/4/5 and the test count (25).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HCGpJXhSZasJLU38ksDghe

.agents/skills/lib_py/delegation/job_subscriber.py

@@ -168,6 +168,12 @@ class _Watcher:
         last = max(self.last_seq.get(jid, 0), self.state_seq.get(jid, 0))
         if jid in self.accepted_any and seq > last + 1:
             self._note_seq_gap(jid, last + 1, seq, "state", msg.topic)
+        # Review round 2 (codex R4): a state renews liveness only when it carries
+        # news - a seq beyond every event and state already accepted. The same
+        # retained snapshot re-delivered on every reconnect, or an older one
+        # replayed, still recovers a terminal status in the main loop, but it is
+        # no evidence that the agent is alive now.
+        renews = seq > last
         if seq > self.state_seq.get(jid, 0):
             self.state_seq[jid] = seq
         mqtt_common.append_event(jid, {
@@ -178,7 +184,7 @@ class _Watcher:
             "timestamp": payload.get("timestamp"),
             "detail": "status={} last_event={}".format(payload.get("status"), payload.get("last_event")),
         })
-        self.events.put((msg.topic, payload))
+        self.events.put((msg.topic, dict(payload, _renews_liveness=renews)))
 
     def on_message(self, _client, _userdata, msg) -> None:
         # --- defensive parsing -------------------------------------------
@@ -474,16 +480,18 @@ def _run_subscriber(args) -> int:
                     _check_disk_fallback(pending, args.registry_dir, terminal, dispatch_tokens, attempts)
                 continue
 
-            last_event = time.monotonic()
             retention_checked = True
-            first_event_seen = True
+            if payload.pop("_renews_liveness", True):
+                last_event = time.monotonic()
+                first_event_seen = True
 
             jid = payload["job_id"]
             event = payload.get("event")
             if event == STATE_EVENT:
-                # Issue #18: retained job state. Any state resets the idle
-                # window (the agent is alive enough to have published); a
-                # terminal status ends the wait exactly like the terminal event.
+                # Issue #18: retained job state. It renewed the idle window
+                # above only if it advanced the seq (review round 2, codex R4:
+                # a re-delivered or older snapshot is not liveness); a terminal
+                # status ends the wait exactly like the terminal event.
                 status = payload.get("status")
                 if status in TERMINAL_STATUSES and jid not in terminal:
                     synth = "completed" if status == "completed" else "error"