[ThomasDaSilva]

• Architecture: when to dispatch a message rather than an event, the transports, why nothing waits by default, the allow list and the checks on queued mails, retries, how the back office and the workers share a failed job, what a worker sees (the request each job gets), what a failure shows, personal data.
• Reference: settings, commands, the back-office screen, exports and imports, the scheduler, and a complete module (StockSync) with its own queue and a recurring task. The example was run as written.
• Getting started: running workers with supervisor, systemd, cron or DDEV, monitoring with messenger:stats, stopping them for a deployment, the folders the web server and the workers share.
• Security: what the background jobs keep, for how long, and what deletes it, including the file of a failed import deleted from the back office.
• Upgrading: the 3.3 notes in Updating (the Symfony recipes to undo, emptying the queues before going back to none), and a Thelia 3.3 section in Breaking changes for module authors.
• The threat model of a queue (what a writer to a Redis or AMQP queue can do), and the failed jobs purged by maintenance:purge.
• Operations: which cache clear stops the workers by itself and which needs messenger:stop-workers, the locks an import holds and the listeners that run inside its transaction, how a module routes its messages (configureContainer() or #[AsMessage]) and why a queue of its own needs a worker of its own, and the crontab fallback without scheduler_thelia when the tasks stay in a crontab.
• Retention: job rows and import files kept 31 days, a day past the failed jobs; the archive limit counts folders too.
• Known limits, accepted for this version (Reference, Idempotence and replay): a job replayed from the back office and with messenger:failed:retry at the same moment may be sent twice, and a mail sent with the Symfony mailer directly, not through MailerFactory, is not guarded against a second delivery.
• Fixed on the way: the order history page said MailerFactory writes the email_sent line; OrderEmailHistoryListener does, once the mail server accepted the mail.
• Pages are in docs/ only: the feature ships with 3.3.

Documents thelia/thelia#4079 and thelia-templates/default-twig#126. The branch is rebased on main.

Merge order

1. Install Messenger and Scheduler without a default queue nor a default schedule thelia-recipes#14: the CI of the core installs its recipes.
2. Background jobs with Symfony Messenger, a scheduler, and export and import jobs thelia#4079, with Background jobs #71.
3. The 3.3 releases of thelia/config (the new tables) and thelia/setup, then the core requiring them.
4. Background jobs screen, exports and imports as jobs thelia-templates/default-twig#126: it requires thelia/core ^3.3.
5. Declare an empty job queue in .env.dist thelia-project#74.