Function combine 

pub fn combine(
    outcomes: impl IntoIterator<Item = (PolicyId, Outcome)>,
) -> Verdict

Fold a set of (policy, outcome) pairs into one Verdict, taking the most severe outcome regardless of the order the pairs arrive in — the structural half of “order is presentational, not semantic”.

Ties (more than one outcome at the worst severity) are broken by input order: the first one seen is reported. That is the only thing the order of outcomes can change.