[CS-5]

Summary

Random SVG mask IDs made six HTML pages change on every build, preventing Lighthouse's identical-build cache from matching. Use page-scoped counters for stable IDs, and include Chrome's version, runner OS/architecture, and the workflow in the cache key. Explicitly pass the identified Chrome binary to Lighthouse.

same source → same SVG IDs → identical build bytes
matching successful build + audit environment → skip Lighthouse
otherwise → standard lhci autorun, one sample per page

The only new TypeScript file is a 10-line SVG ID helper. The workflow uses ubuntu-latest, the standard Lighthouse CLI, and the existing budgets and sampling policy.

Evidence

• Before: six HTML files differed across unchanged builds solely because of random oval IDs. After: two complete production/fixture builds produced 469 identical files; all 30 mask IDs were unique within their pages with valid references.
• pnpm check, build, event fixtures, and page metadata pass. A four-page local Lighthouse run passed the existing budgets with performance scores of 99/99/100/100.
• This fixes a demonstrated cache miss. It does not establish or claim to fix the cause of the earlier CI blocking-time failure.

Merge Danger

Door: two-way

Blast Radius: caching

Changes generated SVG IDs and Lighthouse cache eligibility. The new key requires one successful audit before it can be reused.