A single tall reading lifted a 15-minute average past the usual height on its own, so one slow request opened a row that stayed open until the reading rolled out of the window. Four of the seven rows that occurred after the 10-30 detection change were this: HA web (one 6.7 s check), error-pages, codex and mailcow-svc latency. detect() now opens by height only when the window is still past the usual height, and still departs, with its highest reading left out. A window that fails that falls through to the held test, which now needs at least HELD_FEWEST (3) readings behind its median, so a lone reading on a quiet router opens nothing either way. The median and the topless average share one per-key read (_per_key). The architecture doc and get_metric_normal's description state the rule. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>