The hive-ci-prefetch oneshot has RemainAfterExit=true and is wired to the
container only via wantedBy + before. Once it runs successfully it stays
'active (exited)' indefinitely, so systemd skips it on subsequent container
restarts. The runner-token file it wrote is never refreshed.
This breaks the runner after its first registration: the token written on
the first successful boot is either a placeholder (forge-core-token wasn't
ready yet) or a registration token that has since been consumed/rotated.
On the next container restart prefetch does not re-run, the stale token
persists, and the in-container register service fails with
'invalid_argument: runner registration token not found' — exactly the
symptom in the field (worked briefly, two orphan runners registered, then
permanently offline).
Add partOf = [ nixos-container@hive-ci.service ] so a container stop/restart
propagates to the prefetch unit, forcing it to re-run and fetch a fresh
registration token before the container comes back up. before= still orders
it ahead of the container start within the same transaction.