squib-host — macOS host-side primitives that back the snapshot subsystem.
Phase 5.5 lands the Mach-exception-port pager that powers --mem-backend=Uffd
and --mem-backend=File postcopy restore (per
16-snapshots.md § 5).
The crate is host-specific: on macOS it wires raw Mach syscalls; elsewhere it
exposes the same trait surface with stub backends so the snapshot crate's tests
still build cross-platform.
The crate is the unsafe boundary alongside squib-hv and squib-net::sys.