Function answer 

pub fn answer(
    peer_supports: bool,
    requested: Option<SessionExpires>,
    peer_min_se: Option<Duration>,
    floor: Duration,
) -> Answer

Decide the UAS side of the negotiation (RFC 4028 §9, Table 2).

floor is local policy — the shortest interval this side is willing to be driven at. It is raised to ABSOLUTE_MIN_INTERVAL rather than trusted, because a floor below ninety seconds is exactly the amplification the RFC forbids, and a configuration mistake should not become a protocol violation.