launchd, systemd --user, and unsupervised are three different answers, not two.
Refuse (die) rather than fall through to kill+nohup when a supervisor is
detected that this script cannot drive (e.g. both signals fire at once), and
add a post-restart check that fails the run if more than one fleetd process
is alive. detect_supervisor()/require_drivable_supervisor()/
count_daemon_pids()/assert_single_daemon() are pure, overridable functions so
scripts/test-redeploy-fleetd.sh can exercise them without a real launchd or
systemd.
Dai Ha