requires_stop now probes is_swarm_task per container, which runs a real
docker inspect; the unit CI container has no docker socket, so the three
whitelist tests died with BackupException. Mock the probe to False so
they assert the unchanged whitelist logic, and add a swarm case proving
a task container never triggers a stop and skips the image check
entirely.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
