Static LAST_CANDIDATES 

static LAST_CANDIDATES: AtomicUsize

Diagnostic-only counters updated at the end of every sweep() — for the periodic mem_attribution log (sysinfo.rs) to correlate commit/handle growth against reaper activity. A reaper_candidates/reaper_first_seen that climbs sweep over sweep without a matching rise in reaper_reaped_cumulative would mean the reaper keeps finding (but not managing to close) the same growing set of blocks — worth seeing directly rather than inferred from commit numbers alone.