feat(marketplace): add sync-design-system.mjs script

Vendors shared/playground-design-system/ into a plugin's
playground/vendor/playground-design-system/ tree so each plugin stays
standalone (no marketplace-rot dependency at runtime).

Features:
- Generates MANIFEST.json with SHA-256 per file, source commit hash, sync date
- Drift detection: refuses overwrite if vendored file changed since last sync
- --force flag to override drift
- Injects "DO NOT EDIT" header into copied CSS files
- Pure Node.js, zero npm deps (uses fs.cp from Node 16.7+)

Usage: node scripts/sync-design-system.mjs <plugin-name> [--force]

scripts/sync-design-system.mjs

@@ -0,0 +1,182 @@
+#!/usr/bin/env node
+/**
+ * sync-design-system.mjs
+ *
+ * Vendors shared/playground-design-system/ into a plugin's
+ * playground/vendor/playground-design-system/ tree.
+ *
+ * Usage:
+ *   node scripts/sync-design-system.mjs <plugin-name> [--force]
+ *
+ * Each plugin keeps its own pinned copy so it stays standalone.
+ * MANIFEST.json records SHA-256 per file + source commit + sync date.
+ * Drift detection refuses overwrite if a vendored file was modified
+ * locally after sync; pass --force to overwrite anyway.
+ *
+ * No npm dependencies. Node 16.7+ for fs.cp().
+ */
+
+import { createHash } from 'node:crypto';
+import { promises as fs } from 'node:fs';
+import path from 'node:path';
+import { execSync } from 'node:child_process';
+import { fileURLToPath } from 'node:url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const MARKETPLACE_ROOT = path.resolve(__dirname, '..');
+const SOURCE_DIR = path.join(MARKETPLACE_ROOT, 'shared', 'playground-design-system');
+const GENERATED_HEADER = '/* Code generated by sync-design-system.mjs; DO NOT EDIT. */\n';
+
+function parseArgs(argv) {
+  const args = { plugin: null, force: false };
+  for (const a of argv.slice(2)) {
+    if (a === '--force') args.force = true;
+    else if (a.startsWith('--')) {
+      throw new Error(`Unknown flag: ${a}`);
+    } else if (!args.plugin) {
+      args.plugin = a;
+    } else {
+      throw new Error(`Unexpected positional arg: ${a}`);
+    }
+  }
+  if (!args.plugin) {
+    throw new Error('Missing plugin name. Usage: node scripts/sync-design-system.mjs <plugin-name> [--force]');
+  }
+  return args;
+}
+
+async function sha256(filePath) {
+  const buf = await fs.readFile(filePath);
+  return createHash('sha256').update(buf).digest('hex');
+}
+
+async function walk(dir, base = dir) {
+  const entries = await fs.readdir(dir, { withFileTypes: true });
+  const out = [];
+  for (const e of entries) {
+    const full = path.join(dir, e.name);
+    if (e.isDirectory()) {
+      out.push(...(await walk(full, base)));
+    } else if (e.isFile()) {
+      out.push(path.relative(base, full));
+    }
+  }
+  return out;
+}
+
+async function readJsonIfExists(p) {
+  try {
+    return JSON.parse(await fs.readFile(p, 'utf8'));
+  } catch (e) {
+    if (e.code === 'ENOENT') return null;
+    throw e;
+  }
+}
+
+async function detectDrift(targetDir, prevManifest) {
+  if (!prevManifest || !prevManifest.files) return [];
+  const drifted = [];
+  for (const [rel, prevHash] of Object.entries(prevManifest.files)) {
+    const tgt = path.join(targetDir, rel);
+    try {
+      const cur = await sha256(tgt);
+      if (cur !== prevHash) drifted.push(rel);
+    } catch (e) {
+      if (e.code === 'ENOENT') drifted.push(`${rel} (missing)`);
+      else throw e;
+    }
+  }
+  return drifted;
+}
+
+async function injectGeneratedHeader(targetDir, files) {
+  for (const rel of files) {
+    if (!rel.endsWith('.css')) continue;
+    const p = path.join(targetDir, rel);
+    const content = await fs.readFile(p, 'utf8');
+    if (content.startsWith(GENERATED_HEADER)) continue;
+    await fs.writeFile(p, GENERATED_HEADER + content, 'utf8');
+  }
+}
+
+async function buildManifest(targetDir, files, sourceCommit) {
+  const fileHashes = {};
+  for (const rel of files.sort()) {
+    fileHashes[rel] = await sha256(path.join(targetDir, rel));
+  }
+  return {
+    generated_by: 'scripts/sync-design-system.mjs',
+    do_not_edit: true,
+    source: 'shared/playground-design-system/',
+    source_commit: sourceCommit,
+    sync_date: new Date().toISOString(),
+    file_count: files.length,
+    files: fileHashes,
+  };
+}
+
+function getCurrentCommit() {
+  try {
+    return execSync('git rev-parse HEAD', {
+      cwd: MARKETPLACE_ROOT,
+      encoding: 'utf8',
+    }).trim();
+  } catch {
+    return 'unknown';
+  }
+}
+
+async function main() {
+  const args = parseArgs(process.argv);
+  const pluginDir = path.join(MARKETPLACE_ROOT, 'plugins', args.plugin);
+
+  try {
+    const stat = await fs.stat(pluginDir);
+    if (!stat.isDirectory()) throw new Error('not a directory');
+  } catch {
+    throw new Error(`Plugin directory not found: ${pluginDir}`);
+  }
+
+  try {
+    await fs.access(SOURCE_DIR);
+  } catch {
+    throw new Error(`Source directory missing: ${SOURCE_DIR}`);
+  }
+
+  const targetDir = path.join(pluginDir, 'playground', 'vendor', 'playground-design-system');
+  const manifestPath = path.join(targetDir, 'MANIFEST.json');
+
+  const prevManifest = await readJsonIfExists(manifestPath);
+  const drifted = await detectDrift(targetDir, prevManifest);
+  if (drifted.length && !args.force) {
+    console.error(`Refusing sync: ${drifted.length} vendored file(s) drifted from previous MANIFEST:`);
+    for (const f of drifted) console.error(`  - ${f}`);
+    console.error('Pass --force to overwrite local changes.');
+    process.exit(2);
+  }
+  if (drifted.length && args.force) {
+    console.warn(`--force: overwriting ${drifted.length} drifted file(s).`);
+  }
+
+  await fs.mkdir(path.dirname(targetDir), { recursive: true });
+  await fs.rm(targetDir, { recursive: true, force: true });
+  await fs.cp(SOURCE_DIR, targetDir, { recursive: true, force: true });
+
+  const files = await walk(targetDir);
+  await injectGeneratedHeader(targetDir, files);
+
+  const sourceCommit = getCurrentCommit();
+  const finalFiles = await walk(targetDir);
+  const manifest = await buildManifest(targetDir, finalFiles, sourceCommit);
+  await fs.writeFile(manifestPath, JSON.stringify(manifest, null, 2) + '\n', 'utf8');
+
+  console.log(`Synced shared/playground-design-system/ → plugins/${args.plugin}/playground/vendor/playground-design-system/`);
+  console.log(`  Files: ${manifest.file_count + 1} (incl. MANIFEST.json)`);
+  console.log(`  Source commit: ${sourceCommit}`);
+  console.log(`  Sync date: ${manifest.sync_date}`);
+}
+
+main().catch(err => {
+  console.error(`Error: ${err.message}`);
+  process.exit(1);
+});