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-create/SKILL.md

@@ -68,6 +68,8 @@ If any check fails → abort with a non-zero exit and report the reason (automat
 When running multiple agent sessions alongside other workflows (e.g., cmux, background workers, manual herdr sessions), sharing the default herdr server can lead to session name conflicts, monitoring clutter, and accidental destruction of user sessions via global commands.
 
 To prevent this, you can run this skill inside an **isolated herdr session** using the `HERDR_SESSION_NAME` environment variable or the `--herdr-session <name>` flag (opt-in; alias: `--herdr-server`; legacy env alias: `HERDR_SERVER_NAME`).
+On success the script also starts the per-workspace monitor daemon through `start_watchdog` (`reconcile.sh --subscribe --idle-timeout 0`, one per workspace, see the lifecycle contract in [multi-agent-mux-monitor/SKILL.md](../multi-agent-mux-monitor/SKILL.md)). Set `MAM_NO_SUBSCRIBER_DAEMON=1` to skip that spawn when the monitor is supervised elsewhere or the workspace is ephemeral (Issue #19); the `watchdog PID:` line is then empty.
+
 Additionally, you can specify `--herdr-workspace <name>` (default: workspace slug without `mam-` prefix) to name and group the agent panes inside a dedicated Herdr workspace tab in the Herdr runtime (`herdr workspace create --label` / `rename`) as well as recording it in `.mam/agent-sessions.yaml`. Note that `--herdr-workspace` configures the workspace tab label within the session, whereas `--herdr-session` selects the daemon socket itself.
 
 Under the hood this maps to a real, separate herdr **session** (`herdr --session <name>` — its own socket, its own `agent list`/`workspace list`, completely invisible to the default session and vice versa), not just a workspace label inside the same server. `lib.sh`'s shim bootstraps the named session's server headlessly (`herdr --session <name> server`, backgrounded) the first time it's needed, and scopes every subsequent herdr call to it automatically — this headless bootstrap is what lets it work even when the skill itself is running from inside another herdr-managed pane (a plain interactive `herdr --session <name>` launch is blocked there by herdr's "nested herdr is disabled" guard; headless `server` mode isn't).