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.
swarm-archive serves restic repositories with rclone, append-only, one login
and one repository per agent. swarm-controller writes each placed agent's
login and restic password to the store, replaces them on a move and removes
them when the agent is destroyed. Every hive backs its agents up hourly under
its own store identity. The archive host prunes by retention.
