Isolation Assumptions

It has always been the plan of record to stage in full strict concurrency checking in two phases: 1. basic actor isolation, and 2. full actor isolation. This plan was outlined in the concurrency roadmap long ago, and it has taken several years of development to reach the milestone of closing all known holes in the static data race checking model. It was well understood that closing these holes would require follow on language design proposals, as further communicated in the progress toward Swift 6 post from November from the Language Steering Group. The nature of these changes is not the same as "critical bug fixes", and it was clearly communicated that Swift 5.10 would contain these changes.