fix(ssr): extract page-specific Astro CSS

[tenphi]

Summary

• extract artifacts emitted by every styled Astro page into one content-hashed shared stylesheet
• extract each page strict remainder into a content-hashed page stylesheet, linked afterward as the page override cascade
• respect Astro base, build.assets, and string/CSS-specific/fallback build.assetsPrefix values
• fail clearly on page-relative or fragment-only CSS url() values whose targets would change after external extraction
• cover every collector rule kind, CSP nonces, deterministic hashes, empty/shared-only cases, and production output

Fully shared pages omit an empty page asset; pages with no common artifacts receive only their page asset. The shared-base/page-override order is the extraction-mode cascade contract.

Verification

• pnpm typecheck
• pnpm lint
• pnpm format / pnpm format:check
• pnpm build
• pnpm size
• pnpm test (82 files, 2,180 tests)
• pnpm check:test-only
• pnpm knip
• production fixture verifies a conflicting page rule overrides shared CSS in Chromium

Tested in a disposable build of tenphi.me with the branch linked locally:

• all 8 routes emitted shared CSS first and page CSS second
• shared asset: 89,655 bytes; page assets: 3,853–23,907 bytes
• no inline Tasty CSS or extraction metadata remained
• all computed styles matched the released 3.5.0 output across 4,051 rendered elements, with no browser console errors
• the final URL validation passes all real-site styles

[github-actions]

📦 Snapshot release

Published 0.0.0-snapshot.05bff63.

pnpm add @tenphi/tasty@0.0.0-snapshot.05bff63