Function snapshot_eligible 

pub fn snapshot_eligible(
    image: &ImageSource,
    add_dirs: &[AddDir],
    snap_present: bool,
    backend_supports_snapshots: bool,
) -> bool

Decide whether snapshot restore is safe for this request.

v2 (issue #7) only enables it for the trivial case: a registered template (so the image has a snapshot at all), no --add-dir extras (so the drive layout matches the snapshot’s recorded layout), and a backend that advertises snapshot support. Adding --add-dir would change the drive count and break the snapshot — that case is tracked separately in #7’s “harder” branch and stays cold-boot for now.