Cookie does not store if a Partioned attribute is set.

It can be implemented just like the secure flag with a simple boolean.

It's needed for the "Cookies Having Independent Partitioned State" (CHIPS) feature, which all browsers support already.
More details here: https://developers.google.com/privacy-sandbox/cookies/chips

Thanks!

PS: Regarding browser support if you interested:

• Supported already by Chrome/Edge according to https://caniuse.com/mdn-http_headers_set-cookie_partitioned
  • Data seems to be incomplete however, see next points
• In Firefox since v131: https://www.mozilla.org/en-US/firefox/131.0/releasenotes/#note-790397
• Coming to Safari 18.4 (https://developer.apple.com/documentation/safari-release-notes/safari-18_4-release-notes#Networking)