Function tick 

pub fn tick(
    set: &mut RecordSet,
    state: &mut State,
    room: Option<&mut AutoCommit>,
    widget: &dyn Widget,
) -> Option<RecordCheckout>

Run one record tick: if the widget tree names a record other than the live one, park it and check the named one out. tilo_ui::App calls this once per frame, before sync, so a widget that opened a file last frame is editing that file’s document by the time it next reads state. The checkout it returns is the caller’s cue to re-announce its collaboration channel — a checkout is a change of address.