integration: return HTTP 404 for unmatched URLs and close remaining browser-gate gaps

Co-authored-by: Cursor <cursoragent@cursor.com>

e2e/helpers.ts

@@ -13,9 +13,13 @@ export function pagePath(routeId: RouteId, locale: AppLocale): string {
   return routePath(routeId, locale);
 }
 
-export async function readHtml(request: APIRequestContext, path: string): Promise<string> {
+export async function readHtml(
+  request: APIRequestContext,
+  path: string,
+  expectedStatus: number,
+): Promise<string> {
   const response = await request.get(path);
-  expect(response.status(), `GET ${path} failed`).toBeLessThan(400);
+  expect(response.status(), `GET ${path} status`).toBe(expectedStatus);
   return response.text();
 }
 
@@ -42,7 +46,8 @@ export async function expectHead(
         ? '/en/missing-route'
         : '/missing-route'
       : pagePath(routeId, locale);
-  const html = await readHtml(request, path);
+  const expectedStatus = routeId === 'notFound' ? 404 : 200;
+  const html = await readHtml(request, path, expectedStatus);
   const metadata = buildRouteMetadata(routeId, locale, SITE_CONTENT_DATA);
 
   expect(html, `${path} title`).toContain(`<title>${metadata.title}</title>`);
@@ -78,11 +83,11 @@ export async function expectHead(
   expect(html).toContain('name="twitter:description"');
 }
 
-export async function expectNoOverflow(page: Page): Promise<void> {
+export async function expectNoOverflow(page: Page, route: string, width: number): Promise<void> {
   const overflow = await page.evaluate(
     () => document.documentElement.scrollWidth <= window.innerWidth + 1,
   );
-  expect(overflow, `horizontal overflow at ${page.url()}`).toBe(true);
+  expect(overflow, `horizontal overflow at ${width}px on ${route}`).toBe(true);
 }
 
 export async function jsonLdGraph(page: Page): Promise<unknown> {