fix(issue-19): bound the subscriber daemon to its workspace, forward SIGTERM, keep sandboxes from leaking it

create_session.sh detaches `reconcile.sh --subscribe --idle-timeout 0` per
workspace; test sandboxes never reaped it and the daemon neither noticed its
workspace vanish nor honoured SIGTERM (bash deferred the signal behind the
foreground python child). 202 orphans were found holding public-broker
wildcard subscriptions for deleted pytest tmpdirs.

- daemon.py / lib.sh: MAM_NO_SUBSCRIBER_DAEMON=1 (literal) skips the spawn but
  still reports a running daemon; cli prints a stderr note, stdout stays empty.
- reconcile.sh: python subscriber runs as a waited background child with a
  TERM/INT trap (exit 143); the MQTT loop exits when the workspace dir is gone
  or .mam/monitor.lock is no longer the held inode; SIGTERM/SIGINT handled via
  the stop event so loop_stop/disconnect run; the polling fallback checks the
  same and sleeps in a waited child.
- conftest: sandbox default MAM_NO_SUBSCRIBER_DAEMON=1, per-sandbox reaper
  finalizer, session-scope leak guard over the pytest basetemp.
- tests: 11 lifecycle tests (tests/test_issue19_subscriber_daemon_lifecycle.py);
  phase-1 watchdog/daemon characterization tests opt back in.
- docs: monitor SKILL.md lifecycle contract + pitfalls, create SKILL.md note.

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

.agents/skills/multi-agent-mux-monitor/scripts/reconcile.sh

@@ -72,12 +72,27 @@ if [ "$SUBSCRIBE" = "1" ]; then
   # no single interpreter needs both paho and PyYAML (review items 4/5/6).
   PYBIN="$(_delegate_py_bin)"
 
+  # Issue #19: the subscriber runs as a background child and this shell waits
+  # on it, so SIGTERM/SIGINT reach the daemon promptly. With the child in the
+  # foreground bash deferred the signal until the child exited on its own,
+  # which for --idle-timeout 0 was never - only SIGKILL worked.
+  _sub_pid=""
+  _sub_stop() {
+    trap - TERM INT
+    if [ -n "$_sub_pid" ]; then
+      kill -TERM "$_sub_pid" 2>/dev/null || true
+      wait "$_sub_pid" 2>/dev/null || true
+    fi
+    exit 143
+  }
+  trap _sub_stop TERM INT
+
   # The MQTT subscribe loop exits 3 to signal "broker unavailable → poll instead".
   set +e
   YAML_PATH="$AGENT_SESSIONS_YAML" HOME_DIR="$HOME_DIR" CLAUDE_PROJECT_DIR="$CLAUDE_PROJECT_DIR" LOCAL_BIN="$LOCAL_BIN" \
     WORKSPACE_ROOT="$WORKSPACE_ROOT" SUB_TIMEOUT="$SUB_TIMEOUT" SUB_IDLE_TIMEOUT="$SUB_IDLE_TIMEOUT" \
     SKILLS_DIR="$SKILLS_DIR" LIB_SH="$LIB_SH" \
-    "$PYBIN" - <<'PYEOF'
+    "$PYBIN" - <<'PYEOF' &
 import os, sys, json, time, subprocess
 
 lib_sh = os.environ.get('LIB_SH', '')
@@ -100,6 +115,27 @@ except BlockingIOError:
 except Exception as e:
     print(f"MQTT Monitor: failed to acquire monitor lock ({e}). Exiting.", flush=True)
     sys.exit(1)
+lock_ino = os.fstat(lock_file.fileno()).st_ino
+
+
+def _workspace_gone():
+    """Issue #19: the daemon serves exactly one workspace. Once that workspace
+    is deleted (a purged sandbox, an rm -rf'd project) or its `.mam/monitor.lock`
+    is no longer the inode we hold (a re-created `.mam/`, where a fresh daemon
+    could now take a new lock), there is nothing left to reconcile - exit
+    instead of holding a broker subscription forever."""
+    try:
+        root = os.path.abspath(workspace_root) if workspace_root else os.getcwd()
+    except OSError:
+        return "cwd no longer exists"
+    if not os.path.isdir(root):
+        return f"workspace {root} no longer exists"
+    try:
+        if os.stat(lock_file_path).st_ino != lock_ino:
+            return f"{lock_file_path} was replaced"
+    except OSError:
+        return f"{lock_file_path} no longer exists"
+    return None
 
 # Locate skills/multi-agent-mux-delegate-job/scripts to import mqtt_common — relative first, then
 # an upward walk from cwd. No hardcoded absolute path (review item 6).
@@ -271,11 +307,28 @@ if not state['connected']:
     client.loop_stop()
     sys.exit(3)
 
-import threading
+import threading, signal
 stop_event = threading.Event()
+state['stop_signal'] = None
+
+
+def _on_stop_signal(signum, _frame):
+    state['stop_signal'] = signum
+    stop_event.set()
+
+
+signal.signal(signal.SIGTERM, _on_stop_signal)
+signal.signal(signal.SIGINT, _on_stop_signal)
 start = time.time()
 try:
     while True:
+        if state['stop_signal'] is not None:
+            print(f"MQTT Monitor: signal {state['stop_signal']} received, exiting", flush=True)
+            break
+        gone = _workspace_gone()
+        if gone:
+            print(f"MQTT Monitor: {gone}; exiting", flush=True)
+            break
         now = time.time()
         wall_left = (timeout - (now - start)) if timeout else None
         idle_left = (idle_timeout - (now - state['last_msg'])) if idle_timeout else None
@@ -302,19 +355,30 @@ finally:
         pass
 sys.exit(0)
 PYEOF
+  _sub_pid=$!
+  wait "$_sub_pid"
   sub_rc=$?
+  _sub_pid=""
   set -e
 
   if [ "$sub_rc" = "3" ]; then
     echo "MQTT Monitor: broker unavailable — falling back to polling (interval ${POLL_INTERVAL}s)" >&2
     _self="$SKILLS_DIR/multi-agent-mux-monitor/scripts/reconcile.sh"
     _start=$(date +%s)
+    # Issue #19: same lifecycle as the MQTT loop - stop when the workspace is
+    # gone, and sleep in a waited child so SIGTERM/SIGINT are not deferred.
+    trap 'trap - TERM INT; exit 143' TERM INT
     while :; do
+      if [ ! -d "$WORKSPACE_ROOT" ] || [ ! -f "$WORKSPACE_ROOT/.mam/monitor.lock" ]; then
+        echo "MQTT Monitor: workspace $WORKSPACE_ROOT or its monitor.lock is gone; exiting" >&2
+        break
+      fi
       bash "$_self" --once --emit-diff >/dev/null 2>&1 || true
       if [ "$SUB_TIMEOUT" != "0" ] && [ "$(( $(date +%s) - _start ))" -ge "$SUB_TIMEOUT" ]; then
         break
       fi
-      sleep "$POLL_INTERVAL"
+      sleep "$POLL_INTERVAL" &
+      wait $! || true
     done
   fi
   exit 0