Back up and rehearse an isolated recovery
Preserve the database, encryption key and both application trees, then verify a separate restore.
What a complete backup includes
Keep the consistent database snapshot, original .env and application key, private application code and dependencies, public web root, attachments, integration configuration, trust material and durable update or recovery state together.
Host-managed DNS, certificates, cron, database users, filesystem ownership and external provider state need their own inventory. Restoring local files does not reverse a remote payment, hosting or registrar action.
Use the supplied snapshot tool
The release provides tools/platform-upgrade-backup.php. Use a new private destination outside both installed roots and every public web root, as described by the exact release guide. Retain its manifest digest independently from the backup.
Verify before promoting
Use tools/installation-restore.php with that independently retained digest to verify the snapshot. Restore into a new private directory and a separate empty target database where required. The restored installation remains quarantined; no web server, queue, scheduler or provider operation should start automatically.
Verify database integrity, invoice and customer counts, attachments and decryption with the original key. Review pending jobs and reconcile external-provider actions before an intentional promotion. Never delete an isolation marker or an interrupted-update journal merely to make the application respond.

