Function eligible 

pub fn eligible<'a>(
    open: &'a [Entry],
    skips: &[Mark],
    delivered: &[Mark],
    visits: &[Visit],
    session: &str,
    repos: &[String],
    now: i64,
) -> Option<(usize, &'a Entry)>

The question to deliver in session, pure. None once delivered has one for this session (one per session). Else an open question of one of repos (never another repo’s), not skipped within SKIP_MS, and, if delivered before, only once more than REOFFER_SESSIONS sessions of visits (first-seen order) began since. The engineer’s decisions about the work come first: a 0.3.0 hive task’s question (legacy_hive) only when none of them is eligible. Then never-delivered questions first, then asking order. The index is into open.