written: /home/jwoltje/darkwing-scratch/tmp/tmp.u27G38M1Cw/mosaic-bus@.service
next, for one business (one per data root):
  mkdir -m 0700 -p <dataRoot>/notify/<business>               the notifier refuses a looser directory
  write <dataRoot>/notify/<business>/notify.json, mode 0600:
    {"notifyVersion": 1, "binding": "<discord binding>"}   or "binding": null for no DMs
  systemctl --user enable --now mosaic-bus@<business>      start now and at login
  systemctl --user status mosaic-bus@<business>
  journalctl --user -u mosaic-bus@<business> -f             the host's log
  systemctl --user stop mosaic-bus@<business>               SIGTERM; restartable
survive logout and reboot only with lingering on: loginctl enable-linger jwoltje
