fix(issue-19): arm the subscriber's stop handlers before it connects; read $! with nounset off

Review round 3 (reviewer-grok-01, NOT PASS N1; non-blocking B1):

- reconcile.sh (N1): the python subscriber installs its SIGTERM/SIGINT
  handlers before connect/loop_start. A signal during the broker handshake,
  the CONNACK wait, or right after the paho thread logs "subscribed to" now
  takes the clean path (the signal line, loop_stop/disconnect, rc 0) instead
  of Python's default action; the CONNACK wait ends on it, and a signalled
  subscriber never falls back to polling (rc 3).
- reconcile.sh (B1): `_sub_stop` reads `$!` with nounset off. On bash 3.2
  `${!:-}` and `${!+x}` are both unbound before the first `&`, so the trap
  died with rc 1 instead of 143.
- tests: SIGTERM during a CONNACK wait against a silent local listener (no
  broker needed), and the verbatim `_sub_stop` run without and with a
  child; both fail on 8f9745b.
- docs: monitor SKILL.md and VERSIONS.md state the handler order; test
  count 16.

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

tests/test_issue19_subscriber_daemon_lifecycle.py

@@ -358,6 +358,58 @@ def test_poll_fallback_sigterm_exits_promptly(mam_sandbox, mock_herdr, monkeypat
             proc.kill()
 
 
+def test_sigterm_during_broker_handshake_takes_the_clean_path(mam_sandbox, mock_herdr, monkeypatch):
+    """Review N1: the python handlers are installed before connect/loop_start,
+    so a SIGTERM while the subscriber still waits for CONNACK (a local listener
+    that never answers) exits through the same clean path as a later one - the
+    "signal 15 received" line, rc 143 from the wrapper - and never drops into
+    the polling fallback."""
+    import socket
+
+    monkeypatch.delenv("MAM_NO_SUBSCRIBER_DAEMON", raising=False)
+    silent = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    silent.bind(("127.0.0.1", 0))
+    silent.listen(1)  # the kernel completes the TCP handshake; no CONNACK ever comes
+    log = mam_sandbox / "sub.log"
+    proc = _start_subscriber(mam_sandbox, log, {
+        "MQTT_BROKER": "127.0.0.1", "MQTT_PORT": str(silent.getsockname()[1]), "MQTT_TLS": "0",
+    })
+    try:
+        assert _wait_for(log, r"MQTT Monitor: connecting to 127\.0\.0\.1", 30), log.read_text()
+        time.sleep(1.0)  # well inside the 5 s CONNACK wait
+        t0 = time.time()
+        proc.send_signal(signal.SIGTERM)
+        rc = _wait_exit(proc, 10)
+        assert rc is not None, "SIGTERM was deferred: daemon still running after 10s"
+        assert time.time() - t0 < 5
+        assert rc == 143, (rc, log.read_text())
+        text = log.read_text()
+        assert "signal 15 received, exiting" in text, text
+        assert "falling back to polling" not in text, text
+    finally:
+        if proc.poll() is None:
+            proc.kill()
+        silent.close()
+
+
+def test_sub_stop_trap_exits_143_before_the_first_background_child():
+    """Review B1: the wrapper's `_sub_stop` trap must end with rc 143 even when
+    the signal lands before the first `&` - bash 3.2 treats `$!` as unbound
+    under `set -u` there, and the trap died with rc 1. The function is taken
+    verbatim from reconcile.sh and run without and with a child to stop."""
+    src = (Path(__file__).resolve().parent.parent / ".agents" / "skills" / "multi-agent-mux-monitor"
+           / "scripts" / "reconcile.sh").read_text(encoding="utf-8")
+    m = re.search(r"^  _sub_stop\(\) \{\n.*?^  \}\n", src, re.S | re.M)
+    assert m, "_sub_stop not found in reconcile.sh"
+    # With a child, let it exec first: a TERM forwarded in the instant between
+    # its fork and its exec is swallowed by the child's copy of the trap - a
+    # separate window from B1, which is about reading `$!` at all.
+    for child in ("", "sleep 30 &\nsleep 0.5\n"):
+        script = "set -euo pipefail\n_sub_pid=''\n{}trap _sub_stop TERM INT\n{}kill -TERM $$\nsleep 5\n".format(m.group(0), child)
+        res = subprocess.run(["bash", "-c", script], capture_output=True, text=True, timeout=30)
+        assert res.returncode == 143, (child, res.returncode, res.stderr)
+
+
 # ---------------------------------------------------------------------------
 # 4. self-termination and signals - MQTT loop (needs a reachable broker)
 # ---------------------------------------------------------------------------