Function format_holders 

fn format_holders(
    folder: &Path,
    key: &[u8; 32],
    computer: &str,
    memory: &Memory,
    now_ms: i64,
) -> Vec<(String, Holds)>

The devices that hold back format 2 (FORMAT), and why: of the devices that count (present), each must say in its sealed entry that it reads format 2 (devices::Entry::format), and all it wrote up to that entry (wrote) must be read here (read_n). A device whose entry does not read here, or known by its records alone, holds it back: an older Sioul cannot read format 2 and would double what it changes (an entry that no longer reads is said as such, even when an older one was seen here). A hostile folder can only hold it back longer, never open it.