diff --git a/backend/src/app.ts b/backend/src/app.ts
index 86563f1..9172962 100755
--- a/backend/src/app.ts
+++ b/backend/src/app.ts
@@ -14,6 +14,7 @@ import publicRouter from './routes/public';
 import cartRouter from './routes/cart';
 import shippingAddressesRouter from './routes/shippingAddresses';
 import { attachCustomer } from './middleware/customerAuth';
+import { asyncRoute } from './asyncRoute';
 
 const app = express();
 // Express advertises itself in X-Powered-By by default, which hands an
@@ -24,7 +25,10 @@ app.set('trust proxy', 1);
 app.use('/webhooks/paypal', express.json(), cartCheckoutWebhookRouter);
 app.use(express.json());
 app.use(cookieParser());
-app.use(attachCustomer);
+// Wrapped like any route: attachCustomer awaits a session lookup, and mounted
+// globally an unforwarded rejection here would hang every request in the app —
+// including the routes that wrap their own handlers correctly.
+app.use(asyncRoute(attachCustomer));
 app.use('/uploads', express.static(process.env.UPLOADS_DIR || '/app/uploads'));
 
 app.get('/api/config', (_req, res) => {
diff --git a/backend/src/routes/admin.ts b/backend/src/routes/admin.ts
index d83fe32..fda676a 100755
--- a/backend/src/routes/admin.ts
+++ b/backend/src/routes/admin.ts
@@ -140,7 +140,7 @@ router.get('/items', asyncRoute(async (req: Request, res: Response) => {
   res.json(rows);
 }));
 
-router.post('/items', uploadImages, async (req: Request, res: Response) => {
+router.post('/items', uploadImages, asyncRoute(async (req: Request, res: Response) => {
   const { name, description, price } = req.body;
 
   const categoryId = readCategoryId(req.body.category_id);
@@ -180,9 +180,9 @@ router.post('/items', uploadImages, async (req: Request, res: Response) => {
   } finally {
     client.release();
   }
-});
+}));
 
-router.put('/items/:id', uploadImages, async (req: Request, res: Response) => {
+router.put('/items/:id', uploadImages, asyncRoute(async (req: Request, res: Response) => {
   const { name, description, price } = req.body;
 
   const categoryId = readCategoryId(req.body.category_id);
@@ -233,7 +233,7 @@ router.put('/items/:id', uploadImages, async (req: Request, res: Response) => {
   } finally {
     client.release();
   }
-});
+}));
 
 router.delete('/items/:id', asyncRoute(async (req: Request, res: Response) => {
   const itemId = Number(req.params.id);
@@ -251,12 +251,12 @@ router.delete('/items/:id', asyncRoute(async (req: Request, res: Response) => {
   res.status(204).end();
 }));
 
-router.delete('/items/:id/images/:imageId', async (req: Request, res: Response) => {
+router.delete('/items/:id/images/:imageId', asyncRoute(async (req: Request, res: Response) => {
   await pool.query(`DELETE FROM item_images WHERE id = $1 AND item_id = $2`, [req.params.imageId, req.params.id]);
   res.status(204).end();
-});
+}));
 
-router.post('/items/:id/mark-sold', async (req: Request, res: Response) => {
+router.post('/items/:id/mark-sold', asyncRoute(async (req: Request, res: Response) => {
   const { rows } = await pool.query(
     `UPDATE items SET status='sold', sold_at=now() WHERE id=$1 RETURNING *`,
     [req.params.id]
@@ -265,15 +265,15 @@ router.post('/items/:id/mark-sold', async (req: Request, res: Response) => {
   // customer, so everyone watching it hears about it.
   await notifyFavoritersOfSale([Number(req.params.id)], null);
   res.json(rows[0]);
-});
+}));
 
-router.post('/items/:id/mark-available', async (req: Request, res: Response) => {
+router.post('/items/:id/mark-available', asyncRoute(async (req: Request, res: Response) => {
   const { rows } = await pool.query(
     `UPDATE items SET status='available', sold_at=NULL, reserved_until=NULL, paypal_order_id=NULL
      WHERE id=$1 RETURNING *`,
     [req.params.id]
   );
   res.json(rows[0]);
-});
+}));
 
 export default router;
diff --git a/backend/src/routes/adminSettings.ts b/backend/src/routes/adminSettings.ts
index def7528..02a8e9c 100644
--- a/backend/src/routes/adminSettings.ts
+++ b/backend/src/routes/adminSettings.ts
@@ -1,18 +1,19 @@
 import { Router, Request, Response } from 'express';
 import { pool } from '../db';
+import { asyncRoute } from '../asyncRoute';
 
 const router = Router();
 
-router.get('/', async (_req: Request, res: Response) => {
+router.get('/', asyncRoute(async (_req: Request, res: Response) => {
   const { rows } = await pool.query(`SELECT key, value FROM admin_settings`);
   const map: Record<string, string> = {};
   for (const r of rows) map[r.key] = r.value;
   res.json({
     cartExpiryHours: parseFloat(map.cart_expiry_hours || '24')
   });
-});
+}));
 
-router.put('/', async (req: Request, res: Response) => {
+router.put('/', asyncRoute(async (req: Request, res: Response) => {
   const { cartExpiryHours } = req.body;
   const hours = parseFloat(cartExpiryHours);
   if (Number.isNaN(hours) || hours <= 0) {
@@ -24,6 +25,6 @@ router.put('/', async (req: Request, res: Response) => {
     [String(hours)]
   );
   res.json({ cartExpiryHours: hours });
-});
+}));
 
 export default router;
diff --git a/backend/src/routes/cart.ts b/backend/src/routes/cart.ts
index 6e36362..b40578a 100644
--- a/backend/src/routes/cart.ts
+++ b/backend/src/routes/cart.ts
@@ -1,5 +1,6 @@
 import { Router, Request, Response } from 'express';
 import { pool } from '../db';
+import { asyncRoute } from '../asyncRoute';
 import { requireCustomer } from '../middleware/customerAuth';
 
 const router = Router();
@@ -26,14 +27,14 @@ const CART_ITEM_SELECT = `
   ORDER BY ci.added_at DESC
 `;
 
-router.get('/', requireCustomer, async (req: Request, res: Response) => {
+router.get('/', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { rows: cartRows } = await pool.query(`SELECT id FROM carts WHERE customer_id = $1`, [req.customerId]);
   if (!cartRows.length) return res.json({ items: [] });
   const { rows: items } = await pool.query(CART_ITEM_SELECT, [cartRows[0].id]);
   res.json({ items });
-});
+}));
 
-router.post('/items/:itemId', requireCustomer, async (req: Request, res: Response) => {
+router.post('/items/:itemId', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const itemId = req.params.itemId;
   const client = await pool.connect();
   try {
@@ -75,9 +76,9 @@ router.post('/items/:itemId', requireCustomer, async (req: Request, res: Respons
   } finally {
     client.release();
   }
-});
+}));
 
-router.delete('/items/:itemId', requireCustomer, async (req: Request, res: Response) => {
+router.delete('/items/:itemId', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const itemId = req.params.itemId;
   const client = await pool.connect();
   try {
@@ -103,6 +104,6 @@ router.delete('/items/:itemId', requireCustomer, async (req: Request, res: Respo
   } finally {
     client.release();
   }
-});
+}));
 
 export default router;
diff --git a/backend/src/routes/cartCheckout.ts b/backend/src/routes/cartCheckout.ts
index fdd1c51..5e2e3be 100644
--- a/backend/src/routes/cartCheckout.ts
+++ b/backend/src/routes/cartCheckout.ts
@@ -1,5 +1,6 @@
 import { Router, Request, Response } from 'express';
 import { pool } from '../db';
+import { asyncRoute } from '../asyncRoute';
 import { requireCustomer } from '../middleware/customerAuth';
 import { notifyFavoritersOfSale } from '../favoriteAlerts';
 
@@ -93,7 +94,7 @@ async function openCheckout(
   return { ok: true, checkoutId, cart };
 }
 
-router.post('/paypal/create', requireCustomer, async (req: Request, res: Response) => {
+router.post('/paypal/create', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { shippingAddressId } = req.body;
   if (!shippingAddressId) return res.status(400).json({ error: 'shippingAddressId is required' });
 
@@ -139,7 +140,7 @@ router.post('/paypal/create', requireCustomer, async (req: Request, res: Respons
   } finally {
     client.release();
   }
-});
+}));
 
 // Returns the sold item ids and the buyer, so the caller can notify favoriters
 // *after* COMMIT. Sending inside the transaction would email people about a
@@ -169,7 +170,7 @@ async function completeCheckout(client: any, checkoutId: number, processor: stri
   };
 }
 
-router.post('/paypal/capture', requireCustomer, async (req: Request, res: Response) => {
+router.post('/paypal/capture', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { orderID } = req.body;
   const client = await pool.connect();
   try {
@@ -201,9 +202,9 @@ router.post('/paypal/capture', requireCustomer, async (req: Request, res: Respon
   } finally {
     client.release();
   }
-});
+}));
 
-router.post('/demo/purchase', requireCustomer, async (req: Request, res: Response) => {
+router.post('/demo/purchase', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   if (process.env.DEMO_MODE === 'false') return res.status(403).json({ error: 'demo mode disabled' });
   const { shippingAddressId } = req.body;
   if (!shippingAddressId) return res.status(400).json({ error: 'shippingAddressId is required' });
@@ -225,9 +226,9 @@ router.post('/demo/purchase', requireCustomer, async (req: Request, res: Respons
   } finally {
     client.release();
   }
-});
+}));
 
-webhookRouter.post('/', async (req: Request, res: Response) => {
+webhookRouter.post('/', asyncRoute(async (req: Request, res: Response) => {
   try {
     const token = await getAccessToken();
     const verifyResp = await fetch(`${PAYPAL_BASE}/v1/notifications/verify-webhook-signature`, {
@@ -272,6 +273,6 @@ webhookRouter.post('/', async (req: Request, res: Response) => {
     console.error('webhook error', err);
     res.status(500).end();
   }
-});
+}));
 
 export { router, webhookRouter };
diff --git a/backend/src/routes/customers.ts b/backend/src/routes/customers.ts
index 4b78366..20a06fc 100755
--- a/backend/src/routes/customers.ts
+++ b/backend/src/routes/customers.ts
@@ -44,7 +44,7 @@ function publicCustomer(c: any) {
   };
 }
 
-router.post('/register', async (req: Request, res: Response) => {
+router.post('/register', asyncRoute(async (req: Request, res: Response) => {
   const { email, password, name, marketingConsent } = req.body;
   if (!email || !isValidEmail(String(email)) || !password || String(password).length < 8) {
     return res.status(400).json({ error: 'valid email and password (min 8 chars) required' });
@@ -83,9 +83,9 @@ router.post('/register', async (req: Request, res: Response) => {
   const sessionToken = await createSession(customer.id);
   setSessionCookie(res, sessionToken);
   res.json(publicCustomer(customer));
-});
+}));
 
-router.post('/verify-email', async (req: Request, res: Response) => {
+router.post('/verify-email', asyncRoute(async (req: Request, res: Response) => {
   const { token } = req.body;
   const { rows } = await pool.query(
     `SELECT * FROM customer_tokens WHERE token = $1 AND kind = 'verify_email' AND expires_at > now()`,
@@ -95,7 +95,7 @@ router.post('/verify-email', async (req: Request, res: Response) => {
   await pool.query(`UPDATE customers SET email_verified = true WHERE id = $1`, [rows[0].customer_id]);
   await pool.query(`DELETE FROM customer_tokens WHERE token = $1`, [token]);
   res.json({ status: 'verified' });
-});
+}));
 
 const RESET_TOKEN_TTL_MS = 60 * 60 * 1000;
 
@@ -196,7 +196,7 @@ router.post('/reset-password', asyncRoute(async (req: Request, res: Response) =>
   res.json(publicCustomer(fresh[0]));
 }));
 
-router.post('/login', async (req: Request, res: Response) => {
+router.post('/login', asyncRoute(async (req: Request, res: Response) => {
   const { email, password } = req.body;
   const { rows } = await pool.query(`SELECT * FROM customers WHERE email = $1`, [String(email || '').toLowerCase().trim()]);
   const customer = rows[0];
@@ -211,14 +211,14 @@ router.post('/login', async (req: Request, res: Response) => {
   const sessionToken = await createSession(customer.id);
   setSessionCookie(res, sessionToken);
   res.json(publicCustomer(customer));
-});
+}));
 
-router.post('/logout', async (req: Request, res: Response) => {
+router.post('/logout', asyncRoute(async (req: Request, res: Response) => {
   const token = req.cookies?.rd_session;
   if (token) await pool.query(`DELETE FROM customer_sessions WHERE token = $1`, [token]);
   res.clearCookie('rd_session');
   res.status(204).end();
-});
+}));
 
 router.get('/me/favorites', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { rows } = await pool.query(
@@ -265,22 +265,22 @@ router.put('/me/favorite-alerts', requireCustomer, asyncRoute(async (req: Reques
   res.json(publicCustomer(rows[0]));
 }));
 
-router.get('/me', requireCustomer, async (req: Request, res: Response) => {
+router.get('/me', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { rows } = await pool.query(`SELECT * FROM customers WHERE id = $1`, [req.customerId]);
   if (!rows.length) return res.status(404).json({ error: 'not found' });
   res.json(publicCustomer(rows[0]));
-});
+}));
 
-router.put('/me', requireCustomer, async (req: Request, res: Response) => {
+router.put('/me', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { name } = req.body;
   const { rows } = await pool.query(
     `UPDATE customers SET name = $1 WHERE id = $2 RETURNING *`,
     [name || null, req.customerId]
   );
   res.json(publicCustomer(rows[0]));
-});
+}));
 
-router.post('/change-password', requireCustomer, async (req: Request, res: Response) => {
+router.post('/change-password', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { currentPassword, newPassword } = req.body;
   if (!newPassword || String(newPassword).length < 8) {
     return res.status(400).json({ error: 'new password must be at least 8 characters' });
@@ -293,18 +293,18 @@ router.post('/change-password', requireCustomer, async (req: Request, res: Respo
   const newHash = await bcrypt.hash(newPassword, 12);
   await pool.query(`UPDATE customers SET password_hash = $1 WHERE id = $2`, [newHash, req.customerId]);
   res.status(204).end();
-});
+}));
 
-router.post('/me/consent', requireCustomer, async (req: Request, res: Response) => {
+router.post('/me/consent', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const consent = !!req.body.marketingConsent;
   await pool.query(
     `UPDATE customers SET marketing_consent = $1, marketing_consent_at = now(), marketing_consent_text = $2 WHERE id = $3`,
     [consent, consent ? MARKETING_CONSENT_TEXT : 'Withdrew consent via account settings', req.customerId]
   );
   res.status(204).end();
-});
+}));
 
-router.get('/me/orders', requireCustomer, async (req: Request, res: Response) => {
+router.get('/me/orders', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { rows } = await pool.query(
     `SELECT o.id, o.processor, o.amount_cents, o.status, o.created_at, i.name AS item_name
      FROM orders o JOIN items i ON i.id = o.item_id
@@ -312,9 +312,9 @@ router.get('/me/orders', requireCustomer, async (req: Request, res: Response) =>
     [req.customerId]
   );
   res.json(rows);
-});
+}));
 
-router.get('/me/export', requireCustomer, async (req: Request, res: Response) => {
+router.get('/me/export', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { rows: customerRows } = await pool.query(`SELECT * FROM customers WHERE id = $1`, [req.customerId]);
   const { rows: orderRows } = await pool.query(`SELECT * FROM orders WHERE customer_id = $1`, [req.customerId]);
   res.setHeader('Content-Disposition', 'attachment; filename="my-data.json"');
@@ -323,13 +323,13 @@ router.get('/me/export', requireCustomer, async (req: Request, res: Response) =>
     orders: orderRows,
     exported_at: new Date().toISOString()
   });
-});
+}));
 
-router.delete('/me', requireCustomer, async (req: Request, res: Response) => {
+router.delete('/me', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   await pool.query(`UPDATE orders SET customer_id = NULL WHERE customer_id = $1`, [req.customerId]);
   await pool.query(`DELETE FROM customers WHERE id = $1`, [req.customerId]);
   res.clearCookie('rd_session');
   res.status(204).end();
-});
+}));
 
 export default router;
diff --git a/backend/src/routes/public.ts b/backend/src/routes/public.ts
index 51d9d4b..6cc1c79 100755
--- a/backend/src/routes/public.ts
+++ b/backend/src/routes/public.ts
@@ -1,9 +1,10 @@
 import { Router, Request, Response } from 'express';
 import { pool } from '../db';
+import { asyncRoute } from '../asyncRoute';
 
 const router = Router();
 
-router.get('/unsubscribe', async (req: Request, res: Response) => {
+router.get('/unsubscribe', asyncRoute(async (req: Request, res: Response) => {
   const token = req.query.token as string;
   const { rows } = await pool.query(`SELECT id FROM customers WHERE unsubscribe_token = $1`, [token]);
   if (!rows.length) {
@@ -16,6 +17,6 @@ router.get('/unsubscribe', async (req: Request, res: Response) => {
     [rows[0].id]
   );
   res.send('<html><body><h2>You\'ve been unsubscribed.</h2><p>You will no longer receive marketing emails from Redefined Designs.</p></body></html>');
-});
+}));
 
 export default router;
diff --git a/backend/src/routes/shippingAddresses.ts b/backend/src/routes/shippingAddresses.ts
index 3cc09c5..571bfcc 100644
--- a/backend/src/routes/shippingAddresses.ts
+++ b/backend/src/routes/shippingAddresses.ts
@@ -1,19 +1,20 @@
 import { Router, Request, Response } from 'express';
 import { pool } from '../db';
+import { asyncRoute } from '../asyncRoute';
 import { requireCustomer } from '../middleware/customerAuth';
 import { validateAddress, uspsConfigured, UspsValidationResult } from '../usps';
 
 const router = Router();
 
-router.get('/', requireCustomer, async (req: Request, res: Response) => {
+router.get('/', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { rows } = await pool.query(
     `SELECT * FROM shipping_addresses WHERE customer_id = $1 ORDER BY is_default DESC, created_at DESC`,
     [req.customerId]
   );
   res.json(rows);
-});
+}));
 
-router.post('/', requireCustomer, async (req: Request, res: Response) => {
+router.post('/', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { fullName, addressLine1, addressLine2, city, state, postalCode, country, isDefault } = req.body;
   if (!fullName || !addressLine1 || !city || !state || !postalCode) {
     return res.status(400).json({ error: 'fullName, addressLine1, city, state, and postalCode are required' });
@@ -48,9 +49,9 @@ if ((country || 'US') === 'US') {
   } finally {
     client.release();
   }
-});
+}));
 
-router.put('/:id', requireCustomer, async (req: Request, res: Response) => {
+router.put('/:id', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const { fullName, addressLine1, addressLine2, city, state, postalCode, country, isDefault } = req.body;
   const client = await pool.connect();
   try {
@@ -75,14 +76,14 @@ router.put('/:id', requireCustomer, async (req: Request, res: Response) => {
   } finally {
     client.release();
   }
-});
+}));
 
-router.delete('/:id', requireCustomer, async (req: Request, res: Response) => {
+router.delete('/:id', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   await pool.query(`DELETE FROM shipping_addresses WHERE id = $1 AND customer_id = $2`, [req.params.id, req.customerId]);
   res.status(204).end();
-});
+}));
 
-router.post('/:id/set-default', requireCustomer, async (req: Request, res: Response) => {
+router.post('/:id/set-default', requireCustomer, asyncRoute(async (req: Request, res: Response) => {
   const client = await pool.connect();
   try {
     await client.query('BEGIN');
@@ -99,6 +100,6 @@ router.post('/:id/set-default', requireCustomer, async (req: Request, res: Respo
   } finally {
     client.release();
   }
-});
+}));
 
 export default router;
diff --git a/backend/tests/unit/routesAreWrapped.test.ts b/backend/tests/unit/routesAreWrapped.test.ts
new file mode 100644
index 0000000..734b216
--- /dev/null
+++ b/backend/tests/unit/routesAreWrapped.test.ts
@@ -0,0 +1,154 @@
+import { readdirSync, readFileSync } from 'fs';
+import { join } from 'path';
+
+// Express 4 does not forward a rejected promise from an async handler, so an
+// unwrapped async route never responds at all — the request hangs until the
+// client gives up, nothing reaches the error middleware, and nothing is logged
+// as a failure. That is the shape of the 2026-08-17 incident that put an empty
+// storefront in front of customers.
+//
+// `asyncRoute` fixes it, but a convention only holds while everyone remembers
+// it, and this one was already half-forgotten once: 30 handlers were added
+// unwrapped after the wrapper existed. This test is the part that remembers.
+//
+// Express 5 forwards rejections natively. When the project upgrades, delete
+// `asyncRoute` and delete this test with it.
+
+const SRC = join(__dirname, '..', '..', 'src');
+
+// `router.get(`, `app.use(`, and friends — where a handler gets registered.
+// Any `*Router` name counts, not just `router`: cartCheckout.ts registers the
+// PayPal webhook on a second router, and matching only the common name is how
+// that one stayed unwrapped while everything around it was audited.
+const REGISTRATION = /\b(?:app|\w*[Rr]outer)\.(?:get|post|put|patch|delete|all|use)\s*\(/g;
+
+/**
+ * Returns the full text of the registration call starting at `open` (the index
+ * of its `(`), by counting parens to the matching close. Quotes and comments
+ * are skipped so a path like `'/items/:id'` or a `)` inside a string cannot
+ * throw the count off.
+ */
+function registrationAt(source: string, open: number): string {
+  let depth = 0;
+  for (let i = open; i < source.length; i++) {
+    const c = source[i];
+
+    if (c === "'" || c === '"' || c === '`') {
+      i = skipString(source, i);
+      continue;
+    }
+    if (c === '/' && source[i + 1] === '/') {
+      i = source.indexOf('\n', i);
+      if (i === -1) break;
+      continue;
+    }
+    if (c === '/' && source[i + 1] === '*') {
+      i = source.indexOf('*/', i) + 1;
+      continue;
+    }
+
+    if (c === '(') depth++;
+    if (c === ')') {
+      depth--;
+      if (depth === 0) return source.slice(open, i + 1);
+    }
+  }
+  return source.slice(open);
+}
+
+/** Returns the index of the closing quote of the string opening at `start`. */
+function skipString(source: string, start: number): number {
+  const quote = source[start];
+  for (let i = start + 1; i < source.length; i++) {
+    if (source[i] === '\\') {
+      i++;
+      continue;
+    }
+    if (source[i] === quote) return i;
+  }
+  return source.length;
+}
+
+/**
+ * Every `async` inside a registration must sit directly behind `asyncRoute(`.
+ * Checking the token rather than the line catches a handler whose `async`
+ * lands on its own line, which a line-oriented grep would wave through.
+ */
+function unwrappedHandlers(source: string): string[] {
+  const offenders: string[] = [];
+
+  for (const match of source.matchAll(REGISTRATION)) {
+    const open = match.index! + match[0].length - 1;
+    const call = registrationAt(source, open);
+
+    for (const found of call.matchAll(/\basync\b/g)) {
+      const before = call.slice(0, found.index!).trimEnd();
+      if (!before.endsWith('asyncRoute(')) {
+        offenders.push(`line ${lineOf(source, match.index!)}: ${match[0].trim()}`);
+      }
+    }
+  }
+
+  return offenders;
+}
+
+function lineOf(source: string, index: number): number {
+  return source.slice(0, index).split('\n').length;
+}
+
+const routeFiles = readdirSync(join(SRC, 'routes'))
+  .filter((f) => f.endsWith('.ts'))
+  .map((f) => join('routes', f));
+
+describe.each([...routeFiles, 'app.ts'])('%s', (relative) => {
+  it('wraps every async handler in asyncRoute', () => {
+    const source = readFileSync(join(SRC, relative), 'utf8');
+
+    expect(unwrappedHandlers(source)).toEqual([]);
+  });
+});
+
+describe('async middleware', () => {
+  // `attachCustomer` is mounted globally, so a rejection there hangs every
+  // request in the application — including the routes that are wrapped
+  // correctly. It is the one handler whose failure is not contained.
+  it('wraps attachCustomer where app.ts mounts it', () => {
+    const source = readFileSync(join(SRC, 'app.ts'), 'utf8');
+
+    expect(source).toContain('app.use(asyncRoute(attachCustomer))');
+  });
+});
+
+// Keeps the helper honest: if the paren-walking ever silently stops finding
+// registrations, the tests above would pass by finding nothing at all.
+describe('the guard itself', () => {
+  it('finds a bare async handler', () => {
+    const bad = `router.get('/', requireCustomer, async (req, res) => { res.json({}); });`;
+
+    expect(unwrappedHandlers(bad)).toHaveLength(1);
+  });
+
+  it('accepts a wrapped one', () => {
+    const good = `router.get('/', requireCustomer, asyncRoute(async (req, res) => { res.json({}); }));`;
+
+    expect(unwrappedHandlers(good)).toEqual([]);
+  });
+
+  it('sees an async handler that starts on a later line', () => {
+    const bad = `router.post(\n  '/items/:id',\n  uploadImages,\n  async (req, res) => { res.json({}); }\n);`;
+
+    expect(unwrappedHandlers(bad)).toHaveLength(1);
+  });
+
+  it('is not fooled by a paren inside a route path', () => {
+    const bad = `router.get('/odd(path', async (req, res) => { res.json({}); });`;
+
+    expect(unwrappedHandlers(bad)).toHaveLength(1);
+  });
+
+  it('leaves a synchronous handler alone', () => {
+    const sync = `router.get('/', (req, res) => { res.json({}); });`;
+
+    expect(unwrappedHandlers(sync)).toEqual([]);
+  });
+});