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/lib_py/delegation/daemon.py

@@ -20,6 +20,17 @@ MONITOR_RELPATH = os.path.join(
 )
 LOG_RELPATH = os.path.join(".mam", "multi-agent-mux-monitor.log")
 
+# Issue #19: opt-out switch for the per-workspace subscriber daemon. Test
+# sandboxes set it so that `create_session.sh` under test never leaves a
+# detached `reconcile.sh --subscribe --idle-timeout 0` behind; an operator can
+# set it too when the monitor is supervised elsewhere. Only the literal "1"
+# disables the spawn - any other value keeps the normal behaviour.
+NO_DAEMON_ENV = "MAM_NO_SUBSCRIBER_DAEMON"
+
+
+def daemon_disabled() -> bool:
+    return os.environ.get(NO_DAEMON_ENV, "") == "1"
+
 
 def monitor_script_path(workdir: str) -> str:
     return os.path.join(workdir, MONITOR_RELPATH)
@@ -80,12 +91,19 @@ def ensure_subscriber_daemon(job_id: str, workdir: Optional[str] = None) -> List
     `job_id` is accepted for signature compatibility and is deliberately unused:
     the daemon is per-workspace (log paths anchor on `workdir`), exactly as in
     the shell original. Raises FileNotFoundError when the monitor is absent so
-    the CLI can reproduce the legacy stderr line and exit 1.
+    the CLI can reproduce the legacy stderr line and exit 1. With
+    MAM_NO_SUBSCRIBER_DAEMON=1 (issue #19) nothing is spawned and only the PIDs
+    of a daemon that already runs are returned.
     """
     workdir = workdir or os.getcwd()
     monitor_script = monitor_script_path(workdir)
     if not os.path.isfile(monitor_script):
         raise FileNotFoundError(monitor_script)
+    if daemon_disabled():
+        # Issue #19: report an already-running daemon if there is one, but
+        # never start a new one. Callers echo the (possibly empty) PID list.
+        logger.info("%s=1: not starting the subscriber daemon", NO_DAEMON_ENV)
+        return find_running(monitor_script)
     running = find_running(monitor_script)
     if running:
         return running