test(web): cover unhandled-rejection suppression in readiness probe

New test attaches a process-level 'unhandledRejection' listener and
asserts that the readiness probe does not surface the check
promise's rejection to it, even when the race has already returned
the timeout error. Locks in the no-op `.catch` in `withTimeout`.

Author: Harsh23Kashyap

packages/web/src/app/api/(server)/health/ready/route.test.ts

@@ -149,4 +149,37 @@ describe('GET /api/health/ready', () => {
         // Generous upper bound to avoid flakes; serial would be ~3x delay.
         expect(elapsed).toBeLessThan(delay * 2.5);
     });
+
+    test('does not surface check rejections as unhandled promise rejections', async () => {
+        // The check rejects synchronously (well within the 2s timeout). The
+        // no-op `.catch` attached in `withTimeout` must absorb that
+        // rejection so the Node process does not log an
+        // unhandled-promise-rejection warning while the readiness request
+        // has already moved on.
+        const checkRejection = new Error('check rejected');
+        const unhandled: unknown[] = [];
+        const onUnhandled = (err: unknown) => { unhandled.push(err); };
+        process.on('unhandledRejection', onUnhandled);
+
+        try {
+            mocks.unsafePrisma.$queryRaw.mockRejectedValue(checkRejection);
+            mocks.redisPing.mockResolvedValue('PONG');
+            mocks.zoektList.mockImplementation(
+                (_request: unknown, callback: (err: Error | null) => void) => {
+                    callback(null);
+                },
+            );
+
+            const response = await GET();
+            const body = await response.json();
+
+            expect(response.status).toBe(503);
+            expect(body.checks.postgres.status).toBe('error');
+            // Give the rejection microtask a chance to fire and propagate.
+            await new Promise((resolve) => setTimeout(resolve, 50));
+            expect(unhandled).not.toContain(checkRejection);
+        } finally {
+            process.off('unhandledRejection', onUnhandled);
+        }
+    });
 });