I don't see a clean path from partitioned storage to unpartitioned storage within a single navigation. I'd like to propose that we don't allow it, and instead force the frame to reload to get its unpartitioned storage post grant. This leads to a simpler and safer browser implementation, and a cleaner developer mental model.

While a reload may not be ideal from the third party's UX perspective, it should be a rare event since I believe all of the browsers that support requestStorageAccess preserve the access for some number of days. And there could be some ways to improve the UX (e.g., load the unpartitioned frame behind the first until it's ready).

@johnwilander @hober @annevk Thoughts?