Function early 

pub fn early<'a>(
    challenges: &'a [Challenge],
    context: &str,
    topics: &[String],
    done: &HashSet<&str>,
) -> Vec<&'a Challenge>

Early delivery: the scoped lessons a context brings into scope through one of topics (scope names it just named for the first time), ranked over the whole context, scoring at least RELATIVE × the best of them (done or not), minus those already delivered or asked (done), at most EARLY_CAP. Unscoped lessons never come early: generic hygiene has no topic, and only a named system says the drone is on one. Standing lessons (ratified constraints, Challenge::standing) come first on their topic, matched or not (standing_pool).