message: In a prior PR, the modification to tier combinators introduced a bug in the find_root invariant.
  The recovery QC should be the highest QC by round, not the lowest. This fixes it.
  Closes:
  Approved by: dmitri-perelman
diff: @@ -197,7 +197,7 @@ impl<T: Payload> RecoveryData<T> {
  qc.committed_block_id()
  .and_then(|bid| id_to_id_and_round.get(&bid))
  })
  - .min_by_key(|(_id, round)| round);
  + .max_by_key(|(_id, round)| round);
  match root_id_and_round {
  Some((id, _)) => *id,
  