Function write_seen 

fn write_seen(
    sharing: &Sharing<'_>,
    memory: &Memory,
    all: &BTreeMap<String, Vec<u32>>,
    now_ms: i64,
) -> i64

This computer’s notes in the folder, when what they say changes (its round, how far it read the others); else restated a quarter of an hour after the last while this device is in use (its entry says it: another device’s do-not-disturb hears of a computer in use by them), once a day while it is put away (a phone’s background step: how far it read changes rarely, and the sync is not asked to carry a file every few minutes). Returns when they are due again (milliseconds).