Function cluster_matches_expected 

pub(crate) fn cluster_matches_expected(
    state: &CatalogState,
    cluster_id: ClusterId,
    expected: &ExpectedClusterState,
) -> bool

Whether cluster_id’s current managed state still equals expected. A missing or unmanaged cluster never matches. This is the compare half of the compare-and-append, evaluated inside the catalog transaction so the check and the commit cannot be separated.