The parallel streaming walker accumulated match_count toward the
first-page stop budget, but match_count can exceed the matches actually
returned (collected) by one whenever a file overflows its per-file cap.
With the production config (max_count=2000, max_count_per_file=21) that
over-count could quit the walk a few percent short of the requested
page. Budget on collected instead, matching run_sequential_grep and
aggregate_parallel_results.