The volume manager, per-sender range confinement + gate, medium_changed
event, per-volume spawning + supervision, ownership-gated fs_unmount, and
the removal half of the lifecycle are built. Left honestly pending: the
volumes.csv/filesystems.csv maps, the fuller identity ladder, multi-volume,
the VM consuming medium_changed (removal uses device-presence polling), and
remount-on-replug end-to-end (bench-pending — QEMU can't re-present the
boot-controller device). Full suite 127/127.