Source: extracted verbatim from the Engineering PRD, docs/prd/11-performance-ledger.md (REQ-DOC-004). From M0 onward this file is the canonical, living ADR record; status changes happen here and in the index, with the PRD text remaining the historical record.
Status: Accepted.
Context: Charter §6.4 fixes the policy surface (≥10 process repetitions, median+min, nonparametric 95% CIs, CV); the PRD owes the estimator mechanics. Survey §7.4 documents the two legitimate schools (min-is-best; distribution-aware) — the charter already committed to reporting both median and min.
Alternatives for the CI: (1) parametric t-intervals — rejected: timing distributions are skewed, non-normal (Survey §7.4); (2) rank-based exact intervals — viable but awkward at R = 10 for the median; (3) seeded percentile bootstrap (selected): distribution-free, works for both median and min, trivially reproducible with a recorded seed, B = 10,000 is cheap offline.
Decision: percentile bootstrap, B = 10,000, seed recorded per entry; CV = stddev/mean of repetitions (reported for stability screening only, never as the headline statistic).
Consequences: first-party ~80-line implementation in the runner with golden tests against committed fixtures (REQ 05 §9); documented caveat: CI width at R = 10 is coarse — R may be raised per entry, recorded in repetitions.
Reconsideration: if a methodology reviewer (paper referee, M9) requires Kalibera-Jones multi-level design, bump QLM.