The deployment comment that the Vercel GitHub app posts on pull requests ends with a "Request Review" button. It is rendered as a <picture> element with a light and a dark source:

https://agents-vade-review.vercel.sh/request-review-light.svg 200, image/svg+xml https://agents-vade-review.vercel.sh/request-review-dark.svg 404

The dark variant was never published, and GitHub's image proxy passes the 404 through. Anyone viewing GitHub in dark mode sees either a broken image with the alt text "Request Review" (when GitHub follows the system theme) or an invisible link with no button at all (when GitHub is set to a single dark theme). The light theme works because that file exists.

The link behind the button works fine; only the image is affected.