Default error page UI does not match Next.js design

This issue was created by an agent analysing CI failures from the Next.js Deploy Suite (vinext main vs Next.js v16.2.6, 2026-05-20).

Problem

vinext's built-in error page does not match Next.js's default error page UI. Tests look for specific elements like #error-page-heading, a "Reload page" button, an error reference code, and specific styling. These elements do not exist in vinext's error page.

Tests time out waiting for selectors like #error-page-heading that never appear.

Estimated Impact

~5 test failures.

Affected Test Suites

• test/e2e/app-dir/default-error-page-ui/default-error-page-ui.test.ts (5 failures)

Recommendation

1. Reproduce first in vinext's own test suite. Trigger an unhandled error in a page component and verify the error page contains the expected elements (heading, reload button, error digest). Confirm they are missing.

2. Study the Next.js default error page. Search .nextjs-ref/packages/next/src/client/ for the default error boundary component to understand what elements it renders, their IDs, and styling.

3. Update vinext's built-in error page. Match the structure and element IDs of the Next.js default error page. Key elements: heading with id="error-page-heading", a "Reload page" button, and an error reference display.