feat: eval:flake-rank — the flake-telemetry dial

Aggregates per-test series across every finalized eval-store run (shard
dirs included) plus the free flake ledger: runs, fails, RETRIED PASSES
(the flake signature), avg duration — ranked retries-first. This is the
readable dial behind two policies: a flaky pass never blocks a merge but
is always ranked here, and the WS16 required-check promotion needs weeks
of clean flake-rank, not vibes. --json for machines, --dir for downloaded
CI artifacts.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/eval-flake-rank.ts

@@ -0,0 +1,127 @@
+#!/usr/bin/env bun
+/**
+ * eval-flake-rank — the flake-telemetry dial (WS1).
+ *
+ * Aggregates per-test series across every FINALIZED eval-store run on this
+ * machine (default: ~/.gstack/projects/<slug>/evals/, shard dirs included)
+ * plus the free suite's flake ledger, and ranks tests by flake signal:
+ * retried passes first (a test that needs attempt 2 to go green is the
+ * definition of a flake), then failure rate.
+ *
+ * This is the readable dial behind two policies:
+ *   - a flaky pass never blocks a merge, but it is recorded and RANKED here;
+ *   - the required-check promotion (WS16) needs weeks of clean flake-rank,
+ *     not vibes.
+ *
+ * Usage:
+ *   bun run eval:flake-rank                 # project eval dir
+ *   bun run eval:flake-rank --dir <path>    # e.g. downloaded CI artifacts
+ *   bun run eval:flake-rank --json          # machine-readable
+ */
+
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import { getProjectEvalDir, isPartialEval, type EvalResult } from '../test/helpers/eval-store';
+import { flakeLedgerPath, type FlakeLedgerEntry } from './test-free-shards';
+
+interface TestSeries {
+  name: string;
+  runs: number;
+  passes: number;
+  fails: number;
+  retriedPasses: number;
+  totalAttempts: number;
+  totalCostUsd: number;
+  totalDurationMs: number;
+  lastSeen: string;
+}
+
+export function aggregate(evalFiles: string[]): Map<string, TestSeries> {
+  const series = new Map<string, TestSeries>();
+  for (const file of evalFiles) {
+    let run: EvalResult;
+    try {
+      run = JSON.parse(fs.readFileSync(file, 'utf-8'));
+    } catch { continue; }
+    if (isPartialEval(run, file)) continue; // in-progress accumulators are not runs
+    if (!Array.isArray(run.tests)) continue;
+    // Group this run's entries by name so N attempts = 1 run of that test.
+    const byName = new Map<string, typeof run.tests>();
+    for (const t of run.tests) {
+      const list = byName.get(t.name) ?? [];
+      list.push(t);
+      byName.set(t.name, list);
+    }
+    for (const [name, entries] of byName) {
+      const s = series.get(name) ?? {
+        name, runs: 0, passes: 0, fails: 0, retriedPasses: 0,
+        totalAttempts: 0, totalCostUsd: 0, totalDurationMs: 0, lastSeen: '',
+      };
+      const final = entries[entries.length - 1];
+      s.runs += 1;
+      s.totalAttempts += entries.length;
+      if (final.passed) s.passes += 1; else s.fails += 1;
+      if (final.passed && entries.length > 1) s.retriedPasses += 1;
+      for (const e of entries) {
+        s.totalCostUsd += e.cost_usd || 0;
+        s.totalDurationMs += e.duration_ms || 0;
+      }
+      if (run.timestamp > s.lastSeen) s.lastSeen = run.timestamp;
+      series.set(name, s);
+    }
+  }
+  return series;
+}
+
+export function collectEvalFiles(dir: string): string[] {
+  if (!fs.existsSync(dir)) return [];
+  const out: string[] = [];
+  for (const name of fs.readdirSync(dir, { recursive: true }) as string[]) {
+    if (!name.endsWith('.json') || path.basename(name).startsWith('_partial')) continue;
+    out.push(path.join(dir, name));
+  }
+  return out;
+}
+
+function readFreeLedger(): FlakeLedgerEntry[] {
+  try {
+    return fs.readFileSync(flakeLedgerPath(), 'utf-8')
+      .split('\n').filter(Boolean).map((l) => JSON.parse(l));
+  } catch { return []; }
+}
+
+if (import.meta.main) {
+  const argv = process.argv.slice(2);
+  const dirFlag = argv.indexOf('--dir');
+  const dir = dirFlag !== -1 ? argv[dirFlag + 1] : getProjectEvalDir();
+  const asJson = argv.includes('--json');
+
+  const files = collectEvalFiles(dir);
+  const series = [...aggregate(files).values()]
+    .sort((a, b) => b.retriedPasses - a.retriedPasses || (b.fails / b.runs) - (a.fails / a.runs));
+  const ledger = readFreeLedger();
+
+  if (asJson) {
+    console.log(JSON.stringify({ dir, runsScanned: files.length, tests: series, freeLedger: ledger }, null, 2));
+  } else {
+    console.log(`flake-rank: ${files.length} finalized run file(s) under ${dir}`);
+    const flaky = series.filter((s) => s.retriedPasses > 0 || s.fails > 0);
+    if (flaky.length === 0) {
+      console.log('  no retried passes and no failures recorded — clean series');
+    } else {
+      console.log('  retries  fails/runs  avg-dur  test');
+      for (const s of flaky.slice(0, 30)) {
+        console.log(`  ${String(s.retriedPasses).padStart(7)}  ${String(s.fails).padStart(5)}/${String(s.runs).padEnd(4)}  `
+          + `${Math.round(s.totalDurationMs / s.totalAttempts / 1000).toString().padStart(5)}s  ${s.name}`);
+      }
+    }
+    if (ledger.length > 0) {
+      const byFile = new Map<string, number>();
+      for (const e of ledger) byFile.set(e.file, (byFile.get(e.file) ?? 0) + 1);
+      console.log(`free-suite flaky-passes (${flakeLedgerPath()}):`);
+      for (const [file, n] of [...byFile.entries()].sort((a, b) => b[1] - a[1])) {
+        console.log(`  ${String(n).padStart(3)}x  ${file}`);
+      }
+    }
+  }
+}