Function record_progress 

fn record_progress<P: PartialEq>(
    acc: &mut Vec<SsaRecoveryProgress<P>>,
    snapshot: SsaRecoveryProgress<P>,
)

Merges a snapshot into the batch’s pending set, keeping the furthest-along one per SSA.

Concurrent batches share a cycle’s counters, so snapshots taken microseconds apart can be unordered. Keeping the maximum means one batch never reports its own SSA going backwards.