top_k_scores.sort_by(...) ran over the full k-sized buffer for every
matching document that beat the running threshold (twice in the full
branch), plus another full sort on first reaching k results —
O(m·k log k) for m matching documents. Replace the Vec<f32> buffer
with a BinaryHeap<Reverse<HeapScore>> min-heap of size k, giving
O(m log k). Existing wand_returns_same_results_as_exhaustive test
confirms results are unchanged.
INT-11
ClawHDF5 Coding Agent