The archive host creates a ready marker in the store and swarm-controller
writes no credentials before it exists, so a swarm without an archive, and a
mixed-version swarm, leave every hive backup a logged no-op. A hive with no
declaration no longer counts as placing nothing: its copies and its agents'
user lines stay. The restic password is pinned by tests across a revoke, a
re-placement and a move.
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