画像最適化CIパイプライン構築：Quality Ladder/差分メトリクス/PRコメント自動化

# 代表画像セット構築
find public/images -maxdepth 1 -type f | grep -E '\.(jpg|png|webp)$' | shuf -n 40 > samples.txt
node scripts/bucket-diversity.js samples.txt --min-categories 5 --out ladder-set.txt

# 差分アーティファクトS3ライフサイクル
aws s3 cp diff/ s3://image-ci-artifacts/pr-$PR_NUMBER/ --recursive
# 30日後自動削除のLifecycle設定

name: image-ci
on: [pull_request]
jobs:
  metrics:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: 20
      - name: Install deps
        run: npm ci
      - name: Generate ladder JSON (before/after)
        run: |
          node scripts/ladder.js --image sample.png --out base.json --ref origin/main
          node scripts/ladder.js --image sample.png --out head.json --ref ${{ github.sha }}
      - name: Compare metrics
        run: node scripts/metrics-compare.js base.json head.json --psnr-threshold 0.25 --ssim-threshold 0.004
      - name: Visual regression
        run: npm run test:vr
      - name: Post PR comment
        if: always()
        run: node scripts/post-pr-comment.js base.json head.json reports/vr-summary.md

# 並列ワーカー数 = (物理コア - 1) * 0.75 切り捨て
node scripts/run-metrics.js --workers 6

// scripts/metrics-compare.js (simplified)
import fs from 'node:fs';
const [basePath, headPath] = process.argv.slice(2);
const base = JSON.parse(fs.readFileSync(basePath,'utf8'));
const head = JSON.parse(fs.readFileSync(headPath,'utf8'));
let fail = false;
function check(name, get){
  const b = get(base);
  const h = get(head);
  const delta = h - b;
  if (name==='psnr' && delta < -0.25) fail = true;
  if (name==='ssim' && delta < -0.004) fail = true;
  return { name, base:b, head:h, delta };
}
const rows = [
  check('psnr', x=>x.global.psnr),
  check('ssim', x=>x.global.ssim),
  check('bytes', x=>x.global.bytes)
];
console.table(rows);
if (fail) {
  console.error('Regression detected');
  process.exit(1);
}

// scripts/post-pr-comment.js (excerpt)
import { Octokit } from 'octokit';
import fs from 'node:fs';
const token = process.env.GITHUB_TOKEN;
const octokit = new Octokit({ auth: token });
// build Markdown table
// ... collect ladder deltas & vr summary
await octokit.rest.issues.createComment({
  owner: 'ORG', repo: 'REPO', issue_number: Number(process.env.PR_NUMBER),
  body: mdReport
});

// tests/visual.spec.ts (excerpt)
import { test, expect } from '@playwright/test';
import { compare } from './pixel-compare';
test('hero image stable', async ({ page }) => {
  await page.goto('http://localhost:3000');
  const shot = await page.locator('img.hero').screenshot();
  const base = Buffer.from(process.env.BASE_SHOT!, 'base64');
  const result = compare(base, shot, { threshold: 0.04 });
  expect(result.mismatchPercentage).toBeLessThan(0.8);
});

# 失敗パターン検知
node scripts/overfitting-check.js --history metrics/*.json --psnr-variance-th 0.05