ECC/docker/context-profiles/complex-eval/cases2/event-stats-api/query.md

The /stats endpoint in this repo is wrong on edge cases and too slow — customers on big dashboards are timing out. It currently rescans and resorts the whole 300k-event log on every request, and the analytics team says the numbers don't match the documented semantics (nearest-rank percentiles, half-up two-decimal averages, null fields when nothing matches, proper 400s). Make it correct per the README and fast enough to meet the documented performance budget, without changing the API shape. npm test must stay green.