Bucketed airtime and receive errors used MAX - MIN per bucket, so one zeroed,
replayed or garbage row counted the whole running total (e.g. 47,737 s RX in a
6 h bucket). Buckets are now summed from per-row increments with dips, stale
replays and physically impossible jumps rejected. Ingest skips uptime-only
stats and a migration deletes the rows already stored.
