Function merge_frontiers 

pub(super) fn merge_frontiers(
    limit: usize,
    frontiers: impl IntoIterator<Item = FuzzBranchFrontier>,
) -> Vec<FuzzBranchFrontier>

Merges per-worker frontier records into a single bounded, globally deduplicated set.

Each worker deduplicates its own records by comparison site key while keeping the smallest operand_delta, but workers run independently, so the same site can appear in several workers’ records with different observed deltas. This applies the same key dedup and smallest-delta policy across all workers so the artifact keeps one globally closest record per site and does not spend limit on duplicates. Iteration continues after limit is reached because a later record may be a smaller-delta duplicate of an already retained key.