Function ensure 

pub(crate) async fn ensure(
    base: &str,
    agent_id: &str,
    token: &str,
    http: &Client,
    still_subscribed: impl Fn() -> bool,
) -> Outcome

Claim or renew agent_id’s WAN lease, at most every RENEW_EVERY. base is the relay’s REST base URL (super::relay::rest_base_url).