4 tests verifying server-client rendering parity:
1. SSR renders visible content without JavaScript (headings, islands, logo)
2. JS-rendered content matches SSR structure (same article text)
3. CSSX styling works without JS (violet class, rules in <head>)
4. SPA navigation preserves island state (colour + copyright path)
Run: cd tests/playwright && npx playwright test
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
