fix: ui-audit tears down its guest accounts even when the browser crashes

The audit signs in as a guest per device, which creates a real account. A single
long-lived browser was crashing partway through the third device, and the crash
took the teardown with it — leaving throwaway accounts in production.

Now: one browser per device, and teardown in a finally block so it runs whichever
way the run ends.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tools/ui-audit.mjs

@@ -207,7 +207,8 @@ async function goToScene(page, scene) {
 
 // ---------------------------------------------------------------------------
 fs.mkdirSync(OUT, { recursive: true });
-const browser = await puppeteer.launch({
+
+const launch = () => puppeteer.launch({
   executablePath: CHROME, headless: 'new',
   args: ['--no-sandbox', '--disable-dev-shm-usage', '--font-render-hinting=none'],
 });
@@ -215,7 +216,12 @@ const browser = await puppeteer.launch({
 const report = { base: BASE, when: new Date().toISOString(), devices: {} };
 const consoleErrors = [];
 
+// A browser per device. One long-lived instance was crashing partway through the
+// run, which took the guest teardown with it and left throwaway accounts behind.
+let browser;
+try {
 for (const device of DEVICES) {
+  browser = await launch();
   const page = await browser.newPage();
   page.on('pageerror', e => consoleErrors.push({ device: device.name, error: String(e).slice(0, 200) }));
   page.on('console', m => {
@@ -243,10 +249,15 @@ for (const device of DEVICES) {
     }
   }
   await page.close();
+  await browser.close();
+  browser = null;
+}
+} finally {
+  // Teardown must run even if the browser dies mid-run.
+  try { if (browser) await browser.close(); } catch (e) {}
+  await removeGuests();
 }
 report.consoleErrors = consoleErrors;
-await browser.close();
-await removeGuests();
 
 fs.writeFileSync(path.join(OUT, 'report.json'), JSON.stringify(report, null, 2));