feat: enhance styling_preflight to run all 7 CSS validators

[himerus]

Summary

• styling_preflight was only running 2 of 7 CSS validators — agents calling it thought they were fully validated but were missing token fallbacks, scope, shorthand, color contrast, and specificity checks
• Now runs all 7 CSS validators in a single call, catching the full range of styling anti-patterns
• Refactors checkTokenFallbacks and checkCssScope to expose *FromMeta variants that accept ComponentMetadata directly, avoiding redundant CEM re-parsing

New validators added to preflight:

Validator	What it catches
Token fallbacks	var() without fallback values
Scope	Component tokens on :root instead of host
Shorthand	Risky shorthand + var() combinations
Color contrast	Low-contrast color pairs
Specificity	!important, ID selectors, deep nesting

Test plan

• 22 preflight tests pass (6 new for added validators)
• 23 scope-checker tests pass (existing, no regression)
• 15 token-fallback-checker tests pass (existing, no regression)
• 1790/1791 full suite passes (1 pre-existing cem-source-fidelity failure)

🤖 Generated with Claude Code

[coderabbitai]

Warning

Rate limit exceeded

@himerus has exceeded the limit for the number of commits that can be reviewed per hour. Please wait 8 minutes and 56 seconds before requesting another review.

⌛ How to resolve this issue?

After the wait time has elapsed, a review can be triggered using the @coderabbitai review command as a PR comment. Alternatively, push new commits to this PR.

We recommend that you space out your commits to avoid hitting the rate limit.

🚦 How do rate limits work?

CodeRabbit enforces hourly rate limits for each developer per organization.

Our paid plans have higher rate limits than the trial, open-source and free plans. In all cases, we re-allow further reviews after a brief timeout.

Please see our FAQ for further information.

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 9a5eb6bd-52da-41b8-9d4c-fdc3e54311e5

📥 Commits

Reviewing files that changed from the base of the PR and between 65084c8 and a68fdf2.

📒 Files selected for processing (6)

• .changeset/preflight-full-validation.md
• custom-elements.json
• packages/core/src/handlers/scope-checker.ts
• packages/core/src/handlers/styling-preflight.ts
• packages/core/src/handlers/token-fallback-checker.ts
• tests/handlers/styling-preflight.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/preflight-full-validation

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}