auditor: kb_index aggregator + nine-consecutive empirical test

Phase 1 — definition-layer over append-only JSONL scratchpads.

auditor/kb_index.ts is the single shared aggregator:

  aggregate<T>(jsonlPath, { keyFn, scopeFn, checkFn, tailLimit })
      → Map<signature, {count, distinct_scopes, confidence,
                        first_seen, last_seen, representative_summary, ...}>

  ratingSeverity(agg) — confidence × count severity policy shared
    across all KB readers. Kills the "same unfixed PR inflates its
    own recurrence score" failure mode by design: confidence =
    distinct_scopes/count, so same-scope noise stays below the 0.3
    escalation threshold no matter how many times it repeats.

checkAuditLessons now routes through aggregate + ratingSeverity.
Net effect: the recurrence detector's bespoke Map/Set bookkeeping is
gone; same behavior, shared discipline, reusable by scrum/observer.

Also: symbolsExistInRepo now skips files >500KB so the audit can't
get stuck slurping a fixture.

Phase 2 — nine-consecutive audit runner.

tests/real-world/nine_consecutive_audits.ts pushes 9 empty commits,
waits for each verdict, captures the audit_lessons aggregate state
after each run, reports:

  - sig_count trajectory (should stabilize, not grow linearly)
  - max_count trajectory (same-signature repeat rate)
  - max_confidence trajectory (must stay LOW on same-PR noise)
  - verdict_stable across runs (must NOT oscillate)

This is the empirical proof that the KB compounds favorably:
noise doesn't escalate itself, and signal stays distinguishable.

Unit-tested both failure modes: same-PR × 9 repeats = conf=0.11
(info); cross-PR × 5 distinct = conf=1.00 (block). The rating
function correctly discriminates.

auditor/kb_index.ts

@@ -0,0 +1,161 @@
+// kb_index — generic on-the-fly aggregation over append-only JSONL
+// scratchpads (audit_lessons, scrum_reviews, outcomes, observer ops).
+//
+// The mem0 insight: raw rows are CHEAP and tell the full story, but
+// downstream prompts need a DEFINITION, not a log. A definition is
+// the aggregate: "this signature has fired N times across M distinct
+// scopes, first_seen=X, last_seen=Y, confidence=M/N."
+//
+// This library is the single shared aggregator. Every KB writer keeps
+// appending raw rows; every KB reader uses aggregate() instead of
+// tailing the raw stream. No second file to sync, no ADD/UPDATE/NOOP
+// routing — the stats roll up from the raw rows every time.
+//
+// Why this works past hundreds of runs:
+//   - aggregate() is bounded by distinct_signatures, not total_rows.
+//   - confidence = distinct_scopes / count — low for same-scope noise,
+//     high for cross-scope patterns. Downstream severity ramps on
+//     confidence × count, not raw count, so one unfixed PR can't
+//     inflate its own recurrence score (the classic mem0 failure).
+//   - rotation (later) moves old raw to archive files; aggregate()
+//     can still read both to compute lifetime counts when needed.
+
+import { readFile } from "node:fs/promises";
+
+export interface AggregateRow {
+  signature: string;
+  count: number;
+  distinct_scopes: number;
+  first_seen: string;
+  last_seen: string;
+  confidence: number;        // distinct_scopes / count — capped at 1.0
+  representative_summary: string;  // most-recent summary for this signature
+  scopes: string[];          // up to 20 most-recent scopes for debugging
+  checks: string[];          // distinct `check` values (audit_lessons-specific)
+}
+
+export interface AggregateOptions<T> {
+  /** How to extract the dedup key from a row. */
+  keyFn: (row: T) => string | undefined;
+  /** How to extract the "scope" — distinct scopes count gives confidence. */
+  scopeFn: (row: T) => string | undefined;
+  /** How to extract the timestamp (defaults to row.audited_at / row.reviewed_at / row.timestamp). */
+  timeFn?: (row: T) => string | undefined;
+  /** How to extract a representative summary (defaults to row.summary). */
+  summaryFn?: (row: T) => string | undefined;
+  /** Max rows to read from the JSONL tail; 0 = read all. */
+  tailLimit?: number;
+  /** Include per-row check field (for multi-check aggregates). */
+  checkFn?: (row: T) => string | undefined;
+}
+
+/**
+ * Read a JSONL file and produce the aggregate map keyed by signature.
+ * Safe on missing or malformed files — returns empty map.
+ */
+export async function aggregate<T = any>(
+  jsonlPath: string,
+  opts: AggregateOptions<T>,
+): Promise<Map<string, AggregateRow>> {
+  const out = new Map<string, AggregateRow>();
+  let raw: string;
+  try { raw = await readFile(jsonlPath, "utf8"); } catch { return out; }
+  const lines = raw.split("\n").filter(l => l.length > 0);
+  const sliceFrom = opts.tailLimit && opts.tailLimit > 0 ? Math.max(0, lines.length - opts.tailLimit) : 0;
+
+  const timeFn = opts.timeFn ?? ((r: any) => r?.audited_at ?? r?.reviewed_at ?? r?.timestamp ?? r?.ran_at);
+  const summaryFn = opts.summaryFn ?? ((r: any) => r?.summary ?? r?.representative_summary);
+
+  // Per-signature scope tracking — need counts by scope to compute
+  // distinct_scopes without double-counting a scope that appears 50
+  // times. Using a Set<scope> per signature.
+  const scopeSets = new Map<string, Set<string>>();
+  const checkSets = new Map<string, Set<string>>();
+
+  for (let i = sliceFrom; i < lines.length; i++) {
+    let row: T;
+    try { row = JSON.parse(lines[i]) as T; } catch { continue; }
+    const sig = opts.keyFn(row);
+    if (!sig) continue;
+
+    let agg = out.get(sig);
+    if (!agg) {
+      agg = {
+        signature: sig,
+        count: 0,
+        distinct_scopes: 0,
+        first_seen: "",
+        last_seen: "",
+        confidence: 0,
+        representative_summary: "",
+        scopes: [],
+        checks: [],
+      };
+      out.set(sig, agg);
+      scopeSets.set(sig, new Set<string>());
+      checkSets.set(sig, new Set<string>());
+    }
+
+    agg.count += 1;
+
+    const scope = opts.scopeFn(row);
+    if (scope !== undefined && scope !== null && scope !== "") {
+      scopeSets.get(sig)!.add(String(scope));
+      // Keep scopes array ordered by recency (newest wins — shift
+      // oldest when at cap).
+      const arr = agg.scopes;
+      const s = String(scope);
+      const existing = arr.indexOf(s);
+      if (existing >= 0) arr.splice(existing, 1);
+      arr.push(s);
+      if (arr.length > 20) arr.shift();
+    }
+
+    if (opts.checkFn) {
+      const c = opts.checkFn(row);
+      if (c) checkSets.get(sig)!.add(String(c));
+    }
+
+    const t = timeFn(row);
+    if (t) {
+      if (!agg.first_seen || t < agg.first_seen) agg.first_seen = t;
+      if (!agg.last_seen  || t > agg.last_seen)  agg.last_seen = t;
+    }
+
+    const s = summaryFn(row);
+    if (s) agg.representative_summary = String(s);
+  }
+
+  // Finalize derived fields.
+  for (const [sig, agg] of out) {
+    const scopes = scopeSets.get(sig) ?? new Set<string>();
+    agg.distinct_scopes = scopes.size;
+    agg.confidence = agg.count > 0 ? Math.min(1, agg.distinct_scopes / agg.count) : 0;
+    const checks = checkSets.get(sig);
+    if (checks) agg.checks = Array.from(checks).sort();
+  }
+  return out;
+}
+
+/**
+ * Severity policy derived from aggregate stats. The rating lives here
+ * (not in each check) so all KB readers ramp severity consistently.
+ *
+ *   - confidence × count product is the real signal.
+ *   - Low confidence (< 0.3) = same-scope noise → info regardless of count.
+ *   - Mid confidence (0.3-0.6) = mixed signal → warn at count ≥ 3.
+ *   - High confidence (> 0.6) with count ≥ 5 = block-worthy cross-cutting pattern.
+ *
+ * Callers can override by reading agg directly; this is the default
+ * policy that matches the "don't escalate one unfixed PR" discipline.
+ */
+export function ratingSeverity(agg: AggregateRow): "info" | "warn" | "block" {
+  if (agg.confidence >= 0.6 && agg.count >= 5) return "block";
+  if (agg.confidence >= 0.3 && agg.count >= 3) return "warn";
+  return "info";
+}
+
+/** Human-friendly one-line summary of an aggregate row for finding evidence. */
+export function formatAgg(agg: AggregateRow): string {
+  return `count=${agg.count} distinct_scopes=${agg.distinct_scopes} confidence=${agg.confidence.toFixed(2)} seen=[${agg.first_seen.slice(0, 10)}..${agg.last_seen.slice(0, 10)}]`;
+}