arcbox-snapshot

Snapshot lineage for ArcBox computers: the checkpoint catalog, the copy-on-write rootfs manager the checkpoints are cloned through, and the template catalog that promotes a snapshot into a reusable, versioned base image.

This is an engine-layer crate — daemon-free and platform-neutral. It owns durable on-disk state and knows nothing about who boots the VM: the guest-side sandbox manager (arcbox-vm) drives it today, and the future registry client belongs here rather than above it.

The device-mapper paths (snapshot_cow) only do anything on Linux, where dmsetup and thin pools exist; they compile everywhere so the layer above can too.