Microsoft.UI.Reactor: a C#-first way to build WinUI apps

If you caught our session at Microsoft Build 2026 or you’ve been watching the repo, you’ve seen this one taking shape in public for a while now, and a lot has changed since Build. Here’s the longer tour: Microsoft.UI.Reactor, an experimental C# framework that brings the MVU (Model-View-Update) pattern to WinUI desktop…