R-232 (a) — DooPlex's backup mails the operator when it fails (2026-10-08)

Operator word: "Yes" in chat (2026-10-08, asked: "May I change DooPlex's backup notification so a failed run sends a mail? One setting, plus one test mail. I will not start a backup run.").

What changed (DooPlex, unversioned scripts — R-231):

/opt/backup/scripts/backup-config.sh: notify_failure now also sends a mail through Resend (the API the CI failure mail uses) from monitoring@felhom.eu to admin@felhom.eu. The webhook branch is unchanged. The mail never changes a backup's exit code (return 0) and logs its outcome to backup.log. Before/after: backup-config.sh.before, backup-config.sh.after (no secret in either). The old file is also kept beside it as backup-config.sh.bak-20261008-080524.
/etc/backup/resend-api-key: new, 600 root, 36 bytes, copied from the k3s Secret felhom-system/resend-api with umask 077 and never printed.
Nothing else in DooPlex's backup changed. No backup run was started.

Proof (two channels):

The function's own output (test-mail.txt): sudo bash -c 'source …/backup-config.sh; notify_failure "TEST - R-232 wiring check, no backup ran"' → notify_failure: mail accepted id=01a11a1d-…, rc=0, and the line [INFO] notify_failure: failure mail sent to admin@felhom.eu in backup.log.
The inbox (Gmail connector, which reads the admin@ catch-all): one message, 2026-10-08T06:05:25Z, from monitoring@felhom.eu, subject [DooPlex backup] FAILED: TEST - R-232 wiring check, no backup ran, label INBOX.

Not proven: a real failure path end to end (no backup was forced to fail, by the brief). The callers are the existing ERR traps and backup-all.sh's component check, unchanged.

Rollback: sudo cp -p /opt/backup/scripts/backup-config.sh.bak-20261008-080524 /opt/backup/scripts/backup-config.sh and sudo rm /etc/backup/resend-api-key.

If the Resend key is rotated: this file must be refreshed too (a second consumer of Secret/resend-api, beside the hub and contact-mailer).