Function ref_is_ancestor 

pub fn ref_is_ancestor(
    project_root: &Path,
    ancestor: &str,
    descendant: &str,
) -> AncestorStatus

Whether the ancestor ref is an ancestor of the descendant ref, against ALREADY-FETCHED local refs — issues NO git fetch. Generalises origin_main_ancestor_status to an arbitrary ref pair (used by release --verify’s post-cut checks: is the release tag on main, and has the main→develop sync run). Distinguishes “not an ancestor” (exit 1) from “a ref is absent” (exit 128) so the caller can degrade to an actionable git fetch message instead of reporting a false divergence.