The nixpkgs gitea-actions-runner module uses tokenFile as a systemd
EnvironmentFile, loaded before any ExecStartPre. Our previous
ExecStartPre override was too late — file didn't exist yet.
Fix: tmpfiles pre-creates /run/hive-ci/runner-token with a placeholder
on every boot. A new hive-ci-register.service oneshot (gated on
ConditionPathExists=!/var/lib/gitea-runner/hive/.runner) fetches the
real token and overwrites before gitea-runner-hive.service starts,
wired via After/Wants. On subsequent boots the placeholder is harmless
— nixpkgs register step exits early when .runner already exists.
Closes#918.
f0bd572b35