[hirasso]

Description

swup validate's transition-styles check was flaky under load. It added is-animating, waited a fixed duration + 100ms and then read the computed styles. With --parallel on a slow CI runner (e.g. 61 pages on a 2-core GitHub runner), Chromium falls behind rendering. The transition often hadn't moved yet after the fixed wait, so valid sites failed with Styles not changed.

This PR removes the waiting entirely:

• Temporarily inject transition: none !important; animation: none !important
• Compare computed styles of is-changing vs. is-changing is-animating. These now resolve instantly to their end values
• Clean up classes and the injected style tag afterwards

The duration is still verified separately by the transition-duration check.

Also adds bypassCSP so that validateAnimationStyles works against websites using a CSP (style tag injected).

Testing

Against the swup docs site (61 pages):

• swup validate --parallel: 61/61 passed (previously 17 failures on CI)
• --styles=color (a property that doesn't change): correctly fails with Styles not changed

Note

addStyleTag injects an inline <style>, so a strict CSP style-src could block it. Can add bypassCSP to the page context if needed.

Checks

• The PR is submitted to the main branch
• The code was linted before pushing (npm run lint)
• All tests are passing (npm run test)