Run fork PRs through visual regression; drop the manual CSS-hash baseline - #215
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Fork PRs can now run Chromatic. The job no longer requires a same-repo branch; approved fork runs get the token and run VR, gated by the repo Setting that requires maintainer approval for outside-collaborator fork workflows. Replace the committed css-output-hash.txt baseline with a detect-css-change job that diffs freshly built base vs PR CSS. This removes the manual baseline refresh (which fork contributors could not perform and which generated a stream of "refresh CSS output hash" commits) and stays correct against a PR's merge-base even as main moves.
…udience Correct the setup step from npm install to npm ci so a local build matches the lockfile and CI. Document the detect-css-change trigger and fold the contributor-facing visual-regression note into a "PR checks and visual regression" section. Reorganize CONTRIBUTING.md so maintainer-only material stops interrupting the contributor flow: move the "Upgrading USWDS" runbook to ARCHITECTURE.md (beside the USWDS integrity gates it describes), leaving a one-line pointer.
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What this PR does
External fork PRs could not run visual regression and had no way to resolve the resulting failed check. This enables approval-gated Chromatic on fork PRs and replaces the manually-refreshed CSS-hash baseline with a live base-vs-PR comparison, so no one hand-maintains a baseline anymore.
Type of change
How to review
Focus on
.github/workflows/ci.yml:detect-css-changejob: builds base + PR CSS, compares hashes, sets the Chromatic trigger.chromaticjob: same-repo condition removed; the "DO NOT remove that Setting" comment documents the fork-approval safety gate.Companion GitHub Setting (already enabled): Actions > General > Fork pull request workflows > "Require approval for all outside collaborators". This is the safety mechanism that gates fork code's access to the Chromatic token; the token can only upload snapshots (verified against Chromatic docs), so worst-case exposure is burned budget, resettable from the dashboard.
Deleted with no replacement needed:
scripts/check-css-hash.sh,scripts/css-output-hash.txt, and thecheck:css-hash/update:css-hashnpm scripts.Before requesting review
npm run lint,npm run format, andnpm testpass locallyNotes for reviewers
No changeset: this is CI tooling and docs only, nothing in the published package changes (AGENTS.md public-artifact rule).