Function is_locked 

pub fn is_locked(block_id: &str) -> bool

Is a human’s input for block_id currently locked out by an agent lease?

The hot path — see the module doc. Prunes the entry when it finds an expired one, so the map stays bounded by the number of currently leased blocks (in practice: the number of agents driving a shell right now, normally zero) rather than by every block ever leased.