rsync -a copies a read-only source dir (0555) as read-only, so the hourly
prune's rm -rf could not unlink inside it. From 2026-07-18 every pruned
snapshot was left as a 22-entry husk while the run still logged OK. The
1,740 husks on nh3-nas were removed (0 errors; 48 full snapshots kept).
The prune now runs chmod -R u+w before rm -rf, logs its error count and
the number of snapshots kept, and exits 3 on a failed prune (exit 1 on a
failed rsync) so the systemd unit shows failed instead of passing.
Adds the rsync --link-dest hourly snapshot job (nh3-dev:~/development ->
nh3-nas, 48-snapshot retention, secrets/build-dirs excluded) that closes the
no-off-box-backup gap exposed by the 2026-07-12 working-dir clobber. Script
mirrors the live ~/.config/dev-backup/dev-backup.sh; runbook covers restore.
vh