pub fn write_self_daemon_pid() -> Result<()>Expand description
Daemon-startup: claim the daemon.pid file for THIS process.
A daemon started directly (wire daemon, not via ensure_background)
must write its own versioned-JSON pidfile so wire status / doctor /
the singleton guard can see it. Idempotent: if the pidfile already
records our PID we leave it untouched. (Historically this lived in
pending_pair::cleanup_on_startup alongside the now-removed SAS
pending-pair recovery; the pidfile write was never SAS-specific.)