php-fpm executing php-scripts as root

See https://github.com/magento/magento-cloud-docker/blob/develop/images/php/8.3-fpm/etc/php-fpm.conf#L6

There is no user directive, so by default php-fpm will try to run as root, which is allowed since the -R flag is used: https://github.com/magento/magento-cloud-docker/blob/develop/images/php/8.3-fpm/Dockerfile#L151

This in turn can create files as root, like stuff in /app/generated/...

Then when trying to switch to and from developer mode from the cli container (as user www), you will get permission issues.

Very strange that this is the default for an official magento container, is has to be a bug right?

Inspect images/php/8.3-fpm/etc/php-fpm.conf at line 6 and images/php/8.3-fpm/Dockerfile at line 151 to confirm the effective PHP-FPM worker user and root-related startup behavior. Reproduce the generated-file ownership problem and verify that PHP processes no longer create root-owned files and that developer-mode switching from the CLI container avoids permission errors.

Written by the indexing model from the issue text.