feat(ms-ai-architect): Fase 0 steg 2 — verifiserings-fan-out (373 påstander) + gull-sett m/ deterministisk lastmod-join + TDD [skip-docs]

15 batcher (Opus 4.8 xhigh, read-only) verifiserte 55 sample-frame-filer mot live
MS Learn (strikt v2 bevis-krav: correct/outdated/wrong krever hentet learn-sitat,
ellers unsourced). 373 påstander: 259 correct, 29 outdated, 11 wrong, 74 unsourced.
40 reelle feil. lastmod_changed joinet i kode (registry sitemap_lastmod vs filens
dato): 0 filer ville staleness-loopen flagget -> alle 40 feil er judge-unike (rå
funn, krever tolkning i base-rate-rapporten). lib/base-rate.mjs (Wilson, lastmod,
aggregering) TDD 15 tester. Suite 538/538. Steg 3 (compute-base-rate + gate) gjenstår.

scripts/kb-eval/lib/base-rate.mjs

@@ -0,0 +1,125 @@
+// scripts/kb-eval/lib/base-rate.mjs — Fase 0 base-rate aggregation (deterministic).
+//
+// Turns the per-claim subagent verdicts (gold-correctness-set) into a defensible
+// base-rate report. Pure functions only — no I/O, no Date.now/Math.random.
+//
+// Verdict vocabulary (set by the per-file verification subagents):
+//   correct   — a fetched learn.microsoft.com page states the claimed value
+//   outdated  — fetched source shows a different, superseded value (time drift)
+//   wrong     — fetched source contradicts the claim; it was never correct
+//   unsourced — no fetchable MS Learn page states the value (cannot verify)
+//
+// "Genuine errors" = outdated + wrong. unsourced is NOT an error (it is the
+// unverifiable mass: prices on JS-rendered Azure pages a fetch-based judge also
+// cannot reach). The verifiable error rate therefore EXCLUDES unsourced from its
+// denominator. The gate-critical figure is errorsJudgeUnique: genuine errors
+// whose cited source lastmod did NOT change since the file date — the only class
+// a correctness judge catches that the existing staleness loop would miss.
+
+const ERROR_VERDICTS = new Set(['outdated', 'wrong']);
+const VERDICTS = ['correct', 'outdated', 'wrong', 'unsourced'];
+
+// Parse the "**Last updated:** YYYY-MM[-DD]" header. Month-only normalises to the
+// first of the month (the conservative choice for the gate: it makes more sources
+// count as "changed since the file", which understates — never overstates — the
+// judge's unique value). Returns an ISO date string or null.
+export function parseLastUpdated(text) {
+  if (!text) return null;
+  const m = text.match(/\*\*Last updated:\*\*\s*(\d{4})-(\d{2})(?:-(\d{2}))?/i);
+  if (!m) return null;
+  const [, y, mo, d] = m;
+  return `${y}-${mo}-${d || '01'}`;
+}
+
+// Wilson score interval for a binomial proportion. Returns {p, low, high}.
+// Empty sample -> all zero (never NaN). Default z = 1.96 (95%).
+export function wilson(successes, n, z = 1.96) {
+  if (!n || n <= 0) return { p: 0, low: 0, high: 0 };
+  const phat = successes / n;
+  const z2 = z * z;
+  const denom = 1 + z2 / n;
+  const center = (phat + z2 / (2 * n)) / denom;
+  const margin =
+    (z / denom) * Math.sqrt((phat * (1 - phat)) / n + z2 / (4 * n * n));
+  return {
+    p: phat,
+    low: Math.max(0, center - margin),
+    high: Math.min(1, center + margin),
+  };
+}
+
+// Did any of the file's cited sources change on the MS Learn sitemap after the
+// file's own "last updated" date? This is exactly the signal the existing KB
+// staleness loop sees (it polls sitemap_lastmod per cited URL). Returns:
+//   true  — at least one cited source has sitemap_lastmod > fileDate
+//   false — no cited source is newer (staleness loop would NOT flag the file)
+//   null  — fileDate unknown (cannot determine)
+export function fileLastmodChanged(citedUrls, registry, fileDate) {
+  if (!fileDate) return null;
+  const urls = (registry && registry.urls) || {};
+  for (const u of citedUrls || []) {
+    const entry = urls[u];
+    if (entry && entry.sitemap_lastmod && entry.sitemap_lastmod > fileDate) {
+      return true;
+    }
+  }
+  return false;
+}
+
+function emptyBucket() {
+  return {
+    total: 0,
+    byVerdict: { correct: 0, outdated: 0, wrong: 0, unsourced: 0 },
+    errors: 0,
+    verifiable: 0,
+    unsourced: 0,
+    errorsStalenessCatchable: 0,
+    errorsJudgeUnique: 0,
+  };
+}
+
+function tally(bucket, claim) {
+  bucket.total += 1;
+  const v = claim.verdict;
+  if (v in bucket.byVerdict) bucket.byVerdict[v] += 1;
+  if (v === 'unsourced') {
+    bucket.unsourced += 1;
+  } else {
+    bucket.verifiable += 1;
+  }
+  if (ERROR_VERDICTS.has(v)) {
+    bucket.errors += 1;
+    // lastmod_changed === true  -> staleness loop already flags this file
+    // anything else (false/null) -> only a correctness judge would catch it
+    if (claim.lastmod_changed === true) bucket.errorsStalenessCatchable += 1;
+    else bucket.errorsJudgeUnique += 1;
+  }
+}
+
+function finalize(bucket) {
+  bucket.errorRate = bucket.verifiable ? bucket.errors / bucket.verifiable : 0;
+  bucket.errorRateWilson = wilson(bucket.errors, bucket.verifiable);
+  bucket.unsourcedRate = bucket.total ? bucket.unsourced / bucket.total : 0;
+  return bucket;
+}
+
+// Aggregate a flat list of claims into overall + per-skill + per-stratum +
+// per-claim_type base-rate buckets. Each claim needs: verdict, skill, stratum,
+// claim_type, lastmod_changed.
+export function computeBaseRate(claims) {
+  const overall = emptyBucket();
+  const bySkill = {};
+  const byStratum = {};
+  const byClaimType = {};
+  for (const c of claims) {
+    tally(overall, c);
+    (bySkill[c.skill] ||= emptyBucket()), tally(bySkill[c.skill], c);
+    (byStratum[c.stratum] ||= emptyBucket()), tally(byStratum[c.stratum], c);
+    (byClaimType[c.claim_type] ||= emptyBucket()), tally(byClaimType[c.claim_type], c);
+  }
+  finalize(overall);
+  for (const b of Object.values(bySkill)) finalize(b);
+  for (const b of Object.values(byStratum)) finalize(b);
+  for (const b of Object.values(byClaimType)) finalize(b);
+  return { overall, bySkill, byStratum, byClaimType, _verdicts: VERDICTS };
+}