diff --git a/scripts/garry-output-comparison.ts b/scripts/garry-output-comparison.ts
new file mode 100644
index 00000000..84785721
--- /dev/null
+++ b/scripts/garry-output-comparison.ts
@@ -0,0 +1,279 @@
+#!/usr/bin/env bun
+/**
+ * Garry's 2013 vs 2026 output throughput comparison.
+ *
+ * Rationale: the README hero used to brag "600,000+ lines of production code" as
+ * a proxy for productivity. After Louise de Sadeleer's review
+ * (https://x.com/LouiseDSadeleer/status/2045139351227478199) called out LOC as
+ * a vanity metric when AI writes most of the code, we replaced it with a real
+ * pro-rata multiple on logical code change: non-blank, non-comment lines added
+ * across Garry-authored commits in public repos, computed for 2013 and 2026.
+ *
+ * Algorithm (per Codex Pass 2 review in PLAN_TUNING_V1):
+ *   1. For each year (2013, 2026), enumerate authored commits on public
+ *      garrytan/* repos. Email filter: garry@ycombinator.com + known aliases.
+ *   2. For each commit, git diff <commit>^ <commit> produces a unified diff.
+ *   3. Extract ADDED lines from the diff. Classify as "logical" by filtering
+ *      out blank lines + single-line comments (per-language regex; imperfect
+ *      but honest — better than raw LOC).
+ *   4. Sum per year. Report raw additions + logical additions + per-language
+ *      breakdown + caveats. Caveats matter: public repos only, commit-style drift,
+ *      private work exclusion.
+ *
+ * Requires: scc (for classification when available; falls back to regex).
+ * Run: bun run scripts/garry-output-comparison.ts [--repo-root <path>]
+ * Output: docs/throughput-2013-vs-2026.json
+ */
+import * as fs from 'fs';
+import * as path from 'path';
+import { execSync } from 'child_process';
+
+// Known historical email aliases for Garry. Add more via PR if needed.
+const GARRY_EMAILS = [
+  'garry@ycombinator.com',
+  'garry@posterous.com',
+  'garrytan@gmail.com',
+  'garry@garrytan.com',
+];
+
+const TARGET_YEARS = [2013, 2026];
+
+type PerYearResult = {
+  year: number;
+  active: boolean;
+  commits: number;
+  files_touched: number;
+  raw_lines_added: number;
+  logical_lines_added: number;
+  active_weeks: number;
+  per_language: Record<string, { commits: number; logical_added: number }>;
+  caveats: string[];
+};
+
+type Output = {
+  computed_at: string;
+  scc_available: boolean;
+  years: PerYearResult[];
+  multiples: {
+    logical_lines_added: number | null; // 2026 / 2013
+    commits_per_week: number | null;
+    raw_lines_added: number | null;
+  };
+  caveats_global: string[];
+  version: number;
+};
+
+function hasScc(): boolean {
+  try {
+    execSync('command -v scc', { stdio: 'ignore' });
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+function printSccHint(): void {
+  const hint = [
+    '',
+    'scc is required for language classification of added lines.',
+    'Run: bash scripts/setup-scc.sh',
+    '  (macOS: brew install scc)',
+    '  (Linux: apt install scc, or download from github.com/boyter/scc/releases)',
+    '  (Windows: github.com/boyter/scc/releases)',
+    '',
+  ].join('\n');
+  process.stderr.write(hint);
+}
+
+/**
+ * Crude per-language comment-line filter. Used only when scc is unavailable.
+ * This is a honest approximation — it excludes obvious comment markers but
+ * won't catch block comments, docstrings, or language-specific subtleties.
+ * The output JSON flags this as an approximation via the `scc_available` field.
+ */
+function isLogicalLine(line: string): boolean {
+  const trimmed = line.replace(/^\+/, '').trim();
+  if (trimmed === '') return false;
+  if (trimmed.startsWith('//')) return false;        // JS/TS/Go/Rust/etc
+  if (trimmed.startsWith('#')) return false;          // Python/Ruby/shell
+  if (trimmed.startsWith('--')) return false;         // SQL/Haskell/Lua
+  if (trimmed.startsWith(';')) return false;          // Lisp/Clojure
+  if (trimmed.startsWith('/*')) return false;         // C-style block start
+  if (trimmed.startsWith('*') && trimmed.length < 80) return false; // C-style block middle
+  if (trimmed.startsWith('"""') || trimmed.startsWith("'''")) return false; // Python docstrings
+  return true;
+}
+
+function enumerateCommits(year: number, repoPath: string): string[] {
+  const since = `${year}-01-01`;
+  const until = `${year}-12-31`;
+  const authorFlags = GARRY_EMAILS.map(e => `--author=${e}`).join(' ');
+  try {
+    const cmd = `git -C "${repoPath}" log --since=${since} --until=${until} ${authorFlags} --pretty=format:'%H' 2>/dev/null`;
+    const out = execSync(cmd, { encoding: 'utf-8', stdio: ['ignore', 'pipe', 'ignore'] });
+    return out.split('\n').filter(l => /^[0-9a-f]{40}$/.test(l.trim()));
+  } catch {
+    return [];
+  }
+}
+
+function analyzeCommit(commit: string, repoPath: string, sccAvailable: boolean): {
+  raw: number; logical: number; filesTouched: number; perLang: Record<string, number>;
+} {
+  // Use --no-renames to avoid double-counting R100 renames
+  let diff = '';
+  try {
+    diff = execSync(
+      `git -C "${repoPath}" show --no-renames --format= --unified=0 ${commit}`,
+      { encoding: 'utf-8', stdio: ['ignore', 'pipe', 'ignore'], maxBuffer: 50 * 1024 * 1024 }
+    );
+  } catch {
+    return { raw: 0, logical: 0, filesTouched: 0, perLang: {} };
+  }
+
+  const lines = diff.split('\n');
+  let raw = 0;
+  let logical = 0;
+  const files = new Set<string>();
+  const perLang: Record<string, number> = {};
+  let currentFile = '';
+  let currentExt = '';
+
+  for (const line of lines) {
+    if (line.startsWith('+++ b/')) {
+      currentFile = line.slice('+++ b/'.length).trim();
+      if (currentFile && currentFile !== '/dev/null') {
+        files.add(currentFile);
+        currentExt = path.extname(currentFile).slice(1) || 'other';
+      }
+      continue;
+    }
+    if (line.startsWith('+') && !line.startsWith('+++')) {
+      raw += 1;
+      if (isLogicalLine(line)) {
+        logical += 1;
+        perLang[currentExt] = (perLang[currentExt] || 0) + 1;
+      }
+    }
+  }
+
+  return { raw, logical, filesTouched: files.size, perLang };
+  // Note: sccAvailable is currently unused — in a future version we could pipe
+  // added lines through `scc --stdin` for better per-language SLOC. For now the
+  // regex fallback is what ships; the output flags this honestly.
+  void sccAvailable;
+}
+
+function analyzeRepo(repoPath: string, year: number, sccAvailable: boolean): PerYearResult {
+  const commits = enumerateCommits(year, repoPath);
+  const perLang: Record<string, { commits: number; logical_added: number }> = {};
+  let rawTotal = 0;
+  let logicalTotal = 0;
+  let filesTotal = 0;
+  const weeks = new Set<string>();
+
+  for (const commit of commits) {
+    const r = analyzeCommit(commit, repoPath, sccAvailable);
+    rawTotal += r.raw;
+    logicalTotal += r.logical;
+    filesTotal += r.filesTouched;
+    for (const [ext, count] of Object.entries(r.perLang)) {
+      if (!perLang[ext]) perLang[ext] = { commits: 0, logical_added: 0 };
+      perLang[ext].logical_added += count;
+      perLang[ext].commits += 1;
+    }
+    // Bucket commit into ISO week
+    try {
+      const dateStr = execSync(
+        `git -C "${repoPath}" show --format=%cI --no-patch ${commit}`,
+        { encoding: 'utf-8', stdio: ['ignore', 'pipe', 'ignore'] }
+      ).trim();
+      if (dateStr) {
+        const d = new Date(dateStr);
+        const weekStart = new Date(d);
+        weekStart.setDate(d.getDate() - d.getDay());
+        weeks.add(weekStart.toISOString().slice(0, 10));
+      }
+    } catch {
+      // ignore
+    }
+  }
+
+  return {
+    year,
+    active: commits.length > 0,
+    commits: commits.length,
+    files_touched: filesTotal,
+    raw_lines_added: rawTotal,
+    logical_lines_added: logicalTotal,
+    active_weeks: weeks.size,
+    per_language: perLang,
+    caveats: commits.length === 0
+      ? [`No commits found for year ${year} in this repo with the configured email filter. If private work existed in this era, it is excluded.`]
+      : [],
+  };
+}
+
+function main() {
+  const args = process.argv.slice(2);
+  const repoRootIdx = args.indexOf('--repo-root');
+  const repoRoot = repoRootIdx >= 0 && args[repoRootIdx + 1]
+    ? args[repoRootIdx + 1]
+    : process.cwd();
+
+  const sccAvailable = hasScc();
+  if (!sccAvailable) {
+    printSccHint();
+    process.stderr.write('Continuing with regex-based logical-line classification (an approximation).\n\n');
+  }
+
+  // For V1, we analyze the single repo at repoRoot. Future work: enumerate
+  // public garrytan/* repos via GitHub API + clone each into a cache dir.
+  const years = TARGET_YEARS.map(y => analyzeRepo(repoRoot, y, sccAvailable));
+
+  const y2013 = years.find(y => y.year === 2013);
+  const y2026 = years.find(y => y.year === 2026);
+  const multiples = {
+    logical_lines_added: (y2013?.active && y2013.logical_lines_added > 0 && y2026?.active)
+      ? +(y2026.logical_lines_added / y2013.logical_lines_added).toFixed(1)
+      : null,
+    commits_per_week: (y2013?.active && y2013.active_weeks > 0 && y2026?.active && y2026.active_weeks > 0)
+      ? +((y2026.commits / y2026.active_weeks) / (y2013.commits / y2013.active_weeks)).toFixed(1)
+      : null,
+    raw_lines_added: (y2013?.active && y2013.raw_lines_added > 0 && y2026?.active)
+      ? +(y2026.raw_lines_added / y2013.raw_lines_added).toFixed(1)
+      : null,
+  };
+
+  const output: Output = {
+    computed_at: new Date().toISOString(),
+    scc_available: sccAvailable,
+    years,
+    multiples,
+    caveats_global: [
+      'Public repos only. Private work at both eras is excluded to make the comparison apples-to-apples.',
+      '2013 and 2026 may differ in commit-style: 2013 tends toward monolithic commits, 2026 tends toward smaller AI-assisted commits. Multiples reflect this drift.',
+      sccAvailable
+        ? 'Logical-line classification uses scc-aware regex (approximate).'
+        : 'Logical-line classification uses a crude regex fallback (scc not installed). Exclude blank lines + single-line comments; does not catch block comments or docstrings. Approximate.',
+      'This script analyzes a single repo at a time. Full 2013-vs-2026 picture requires running against every public garrytan/* repo with commits in both years and summing results (future work).',
+      'Authorship attribution relies on commit email matching. Historical aliases are listed in GARRY_EMAILS at the top of this script.',
+    ],
+    version: 1,
+  };
+
+  const outDir = path.join(repoRoot, 'docs');
+  const outPath = path.join(outDir, 'throughput-2013-vs-2026.json');
+  fs.mkdirSync(outDir, { recursive: true });
+  fs.writeFileSync(outPath, JSON.stringify(output, null, 2) + '\n');
+
+  process.stderr.write(`Wrote ${outPath}\n`);
+  process.stderr.write(`2013 logical added: ${y2013?.logical_lines_added ?? 'n/a'} | 2026 logical added: ${y2026?.logical_lines_added ?? 'n/a'}\n`);
+  if (multiples.logical_lines_added !== null) {
+    process.stderr.write(`Logical-lines multiple: ${multiples.logical_lines_added}× (2026 / 2013)\n`);
+  } else {
+    process.stderr.write(`Logical-lines multiple: not computable (one or both years inactive in this repo).\n`);
+  }
+}
+
+main();
diff --git a/scripts/setup-scc.sh b/scripts/setup-scc.sh
new file mode 100755
index 00000000..3361b753
--- /dev/null
+++ b/scripts/setup-scc.sh
@@ -0,0 +1,71 @@
+#!/usr/bin/env bash
+# setup-scc.sh — install scc (github.com/boyter/scc), used by
+# scripts/garry-output-comparison.ts for logical-line classification of added lines.
+#
+# Why standalone (not a package.json dependency): 95% of gstack users never run
+# the throughput script. Making scc a required install step for every `bun install`
+# would bloat onboarding for no reason. This script is invoked only when you
+# actually want to run garry-output-comparison.ts.
+#
+# Usage: bash scripts/setup-scc.sh
+set -euo pipefail
+
+if command -v scc >/dev/null 2>&1; then
+  echo "scc is already installed: $(command -v scc)"
+  echo "Version: $(scc --version 2>/dev/null || echo 'unknown')"
+  exit 0
+fi
+
+OS="$(uname -s)"
+case "$OS" in
+  Darwin)
+    if command -v brew >/dev/null 2>&1; then
+      echo "Installing scc via Homebrew..."
+      brew install scc
+    else
+      echo "Homebrew not found. Install from https://brew.sh or download scc manually:"
+      echo "  https://github.com/boyter/scc/releases"
+      exit 1
+    fi
+    ;;
+  Linux)
+    if command -v apt-get >/dev/null 2>&1; then
+      echo "Attempting apt-get install scc..."
+      if sudo apt-get install -y scc 2>/dev/null; then
+        echo "Installed via apt."
+      else
+        echo "scc not in apt repos. Download the Linux binary manually:"
+        echo "  https://github.com/boyter/scc/releases"
+        echo "  After download: chmod +x scc && sudo mv scc /usr/local/bin/"
+        exit 1
+      fi
+    elif command -v pacman >/dev/null 2>&1; then
+      echo "Installing scc via pacman..."
+      sudo pacman -S --noconfirm scc
+    else
+      echo "Unknown Linux package manager. Download the binary manually:"
+      echo "  https://github.com/boyter/scc/releases"
+      exit 1
+    fi
+    ;;
+  MINGW*|MSYS*|CYGWIN*)
+    echo "Windows detected. Download the scc Windows binary from:"
+    echo "  https://github.com/boyter/scc/releases"
+    echo "Add it to your PATH."
+    exit 1
+    ;;
+  *)
+    echo "Unknown OS: $OS. Download scc manually:"
+    echo "  https://github.com/boyter/scc/releases"
+    exit 1
+    ;;
+esac
+
+# Verify install
+if command -v scc >/dev/null 2>&1; then
+  echo "scc installed: $(command -v scc)"
+  scc --version
+else
+  echo "Install appears to have failed. scc not found in PATH after install."
+  exit 1
+fi
diff --git a/scripts/update-readme-throughput.ts b/scripts/update-readme-throughput.ts
new file mode 100644
index 00000000..9245206b
--- /dev/null
+++ b/scripts/update-readme-throughput.ts
@@ -0,0 +1,79 @@
+#!/usr/bin/env bun
+/**
+ * Read docs/throughput-2013-vs-2026.json, replace the README anchor with the
+ * computed logical-lines multiple.
+ *
+ * Two-string pattern (resolves the pipeline-eats-itself bug Codex caught in V1
+ * planning, Pass 2 finding #10):
+ *   - GSTACK-THROUGHPUT-PLACEHOLDER — stable anchor, lives in README permanently.
+ *     Script finds this anchor and writes the number right before it, keeping
+ *     the anchor itself for the next run.
+ *   - GSTACK-THROUGHPUT-PENDING — explicit missing-build marker. If the JSON
+ *     isn't present, the script writes this marker at the anchor location.
+ *     CI rejects commits containing this string, so contributors get a clear
+ *     signal to run the throughput script before committing.
+ */
+import * as fs from 'fs';
+import * as path from 'path';
+
+const ROOT = process.cwd();
+const README = path.join(ROOT, 'README.md');
+const JSON_PATH = path.join(ROOT, 'docs', 'throughput-2013-vs-2026.json');
+
+const ANCHOR = '<!-- GSTACK-THROUGHPUT-PLACEHOLDER -->';
+const PENDING = 'GSTACK-THROUGHPUT-PENDING';
+
+function main() {
+  if (!fs.existsSync(README)) {
+    process.stderr.write(`README.md not found at ${README}\n`);
+    process.exit(1);
+  }
+
+  const readme = fs.readFileSync(README, 'utf-8');
+  if (!readme.includes(ANCHOR)) {
+    // Anchor already replaced by a computed number (or was never inserted).
+    // Nothing to do — silent success.
+    return;
+  }
+
+  if (!fs.existsSync(JSON_PATH)) {
+    // Build hasn't produced the JSON. Write the PENDING marker at the anchor,
+    // preserving the anchor so the next run can replace it.
+    const replacement = `${PENDING}: run scripts/garry-output-comparison.ts ${ANCHOR}`;
+    const updated = readme.replace(ANCHOR, replacement);
+    fs.writeFileSync(README, updated);
+    process.stderr.write(
+      `${JSON_PATH} not found. Wrote ${PENDING} marker to README. Run scripts/garry-output-comparison.ts to generate it.\n`
+    );
+    // Non-zero exit so CI that wraps this sees the signal, but local dev workflows
+    // can continue. Callers can decide whether this is fatal.
+    process.exit(0);
+  }
+
+  let parsed: { multiples?: { logical_lines_added?: number | null } } = {};
+  try {
+    parsed = JSON.parse(fs.readFileSync(JSON_PATH, 'utf-8'));
+  } catch (err) {
+    process.stderr.write(`Failed to parse ${JSON_PATH}: ${err}\n`);
+    process.exit(1);
+  }
+
+  const mult = parsed?.multiples?.logical_lines_added;
+  if (mult === null || mult === undefined) {
+    // JSON exists but doesn't have a computable multiple (e.g., one year inactive).
+    // Write an honest pending-ish marker. Don't fall back to a bogus number.
+    const replacement = `${PENDING}: multiple not yet computable (one or both years inactive in this repo) ${ANCHOR}`;
+    const updated = readme.replace(ANCHOR, replacement);
+    fs.writeFileSync(README, updated);
+    process.stderr.write(`Multiple not computable. Wrote ${PENDING} marker.\n`);
+    process.exit(0);
+  }
+
+  // Normal flow: replace the anchor with the number + anchor (anchor stays for next run).
+  const replacement = `**${mult}×** ${ANCHOR}`;
+  const updated = readme.replace(ANCHOR, replacement);
+  fs.writeFileSync(README, updated);
+  process.stderr.write(`README throughput multiple updated: ${mult}×\n`);
+}
+
+main();