The host-side updater only backed up code + data/, leaving trigger.json and
result.json unarchived. After a failed update, operators had to reconstruct
'what was being attempted' by joining timestamps across files. Now the
backup captures both files into a 'update-state/' subdir alongside code +
data backups, keyed by from-version.
- New `backup_update_state()` function in dashcaddy-update.sh: idempotent,
tolerates absent files (cleans up empty subdir), tolerates chattr +i
(unlock/copy/relock).
- Wired into main() right after `backup_data_dir`, before `cleanup_old_backups`.
- Deliberately does NOT auto-restore trigger.json on rollback — the rollback
handler reads a fresh trigger.json written by the operator/container;
restoring the previous attempt's trigger would clobber the active rollback
request. Backups are read-only forensic evidence.
- New `dashcaddy-api/scripts/test-dashcaddy-update-backup.sh` (14 assertions,
5 test groups): both-files-present, partial-present, no-files-present,
idempotency, main() flow ordering. All 14 pass.
- Synced the duplicate at `dashcaddy-api/scripts/dashcaddy-update.sh`
(md5-identical to scripts/dashcaddy-update.sh).
Tests: 1214/1214 pass (zero change). Lint: 150 warnings, all pre-existing
in untouched files (zero new warnings introduced).
