The node container has no udev, so LOOP_CTL_GET_FREE hands out a minor whose
/dev node never appears; it also cannot load kernel modules, so those nodes
stay dead unless the host carries the loop driver. Materialize the nodes,
verify one can actually be attached, and expose the host prerequisite as a
bootstrap step instead of failing three hours in with a cryptsetup message.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>