Every backup now writes vaultik-destination.txt at the destination
root. While the local index holds snapshots, a destination without it
is not present: snapshot create refuses before writing, prune and
snapshot purge fail, and snapshot list and snapshot remove warn.
remote nuke deletes the marker last. The file:// backend no longer
creates its destination directory and checks for it on every write;
that protects a directory on a removable volume, not the mount point
itself.
Tests back up into existing directories; fixtures standing for a
written destination carry the marker.
Judgement call: the marker is rewritten on every backup.
Deviation: for the complexity limit, snapshot name selection left CreateSnapshot and the --force/--json test moved into confirmRemoveSnapshot, both unchanged.
Model: opus-5-5
sneak