まだWIPですけどObservationの実装出てきましたね。swift-async-algorithmにあったCritical Regionを作る仕組みとかを持ってきているようですね

https://github.com/apple/swift/pull/63725 (edited)

[WIP] Initial draft of observation by phausler · Pull Request #6372...

This is an initial draft of the observation feature. It includes an implementation of the Observation module and associated protocols and utility types. This does not yet include the macro synthesi...