AFAIK TBB doesn't create per-domain circuits for every subresource on a site (that would kill performance on many sites with 10s of third-party trackers, CDN ho

AFAIK TBB doesn't create per-domain circuits for every subresource on a site (that would kill performance on many sites with 10s of third-party trackers, CDN hosts, etc.), but rather one circuit per "URL-bar domain". That domain doesn't change when a CloudFlare site renders reCAPTCHA.