Function same_message_check 

pub fn same_message_check(
    fwd_offset: u64,
    fwd_length: u64,
    layout_offset: u64,
    layout_length: u64,
) -> bool

true iff a forward Hit and a backward-validated layout describe the same message — used by the dispatch table to detect the 1-message file and odd-count meet-in-the-middle cases.