Function settle_item 

pub fn settle_item<'a, Item, Interpreter, RootEvent, Path>(
    progress: &'a mut Option<InterpretationProgress<Item, Item::Custody, ItemSettlement<Item, Item::Accepted, Item::Rejection, Item::Prerequisite>>>,
    interpreter: &'a mut Interpreter,
) -> impl Future<Output = ()> + Send + 'a
where
    Item: ActionItem + 'a,
    Interpreter: InterpretItem<Item, RootEvent, Path> + 'a,

Loan only the current lower input and its outside reply destination. The producer returns unit; the caller finalizes after producer disposal. Empty input or an occupied destination remains an incomplete owned fact.