• I have read the contributing guideline and understand that I have made the correct modifications

Description:

Run the BookStack async queue worker as the abc user using s6-setuidgid.

A corresponding changelog entry has also been added to readme-vars.yml.

Benefits of this PR and context:

The queue worker currently inherits root privileges from s6, while PHP-FPM runs as the abc user.

If the queue worker is the first process to write to /config/log/bookstack/laravel.log, such as during a transient Redis failure, the file is created as root:root with mode 0644. PHP-FPM cannot subsequently append to it, causing Laravel logging to throw an UnexpectedValueException and web requests to return HTTP 500 errors.

Running the queue worker as abc:

• Prevents root-owned Laravel log files.
• Ensures PHP-FPM and the queue worker can safely share application files.
• Consistently applies the configured PUID and PGID.
• Avoids requiring startup-time ownership repairs as a workaround.

How Has This Been Tested?

• Successfully built the complete image using docker build --no-cache --pull.
• Started an isolated container from the resulting image with PUID=1000, PGID=1000, and QUEUE_CONNECTION=redis.
• Confirmed the async queue worker ran as UID/GID 1000:1000.
• Triggered the failure path using an unavailable Redis endpoint.
• Confirmed the queue worker created /config/log/bookstack/laravel.log as 1000:1000 with mode 0644.
• Confirmed the PHP-FPM UID could write to the resulting log file.
• Confirmed PHP-FPM workers also ran as UID/GID 1000:1000.
• Ran bash -n and git diff --check successfully.

Source / References:

• Current queue-worker service: https://github.com/linuxserver/docker-bookstack/blob/master/root/etc/s6-overlay/s6-rc.d/svc-queue-worker/run
• LinuxServer contribution guidelines: https://github.com/linuxserver/docker-bookstack/blob/master/.github/CONTRIBUTING.md

AI assistance disclosure:

The issue investigation and preparation of this change were assisted by OpenAI Codex. The resulting diagnosis, code change, and validation results were reviewed by the contributor.