The auto-restart path in `hermes update` verifies systemd unit health with
`time.sleep(3)` + a single `systemctl is-active` call. The unit's
Stopped -> Started transition after a graceful SIGUSR1 exit (or a hard
restart) is not always complete inside that 3s window, so the verify
races and reports 'drained but didn't relaunch' even though systemd is
about to bring the unit back up a fraction of a second later. Users
then see a spurious warning, a redundant fallback `systemctl restart`
fires, and adapters (Discord, WhatsApp) get restarted twice.
Replace the three sleep+oneshot sites with a small `_wait_for_service_active()`
closure that polls `is-active` every 0.5s for up to 10s. Behaviour
is unchanged when the unit is healthy or truly dead — only the race
window around a clean restart is now handled correctly.
Tests: tests/hermes_cli/test_update_gateway_restart.py (41/41).
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