reactor-build-and-check

Build & verify

Run after every non-trivial edit. Read the output — dotnet run exits with code 1 on build failure; silent ≠ success.

Single-file .cs (default for new apps)

dotnet run App.cs

The file header needs #:package Microsoft.Windows.SDK.BuildTools.WinApp@0.7.0, which launches the app packaged (needs Developer Mode), or #:property WindowsPackageType=None, which runs it unpackaged. With neither, the app builds, then dies at startup with REGDB_E_CLASSNOTREG. No -p:Platform is needed — only a self-contained app (#:property WindowsAppSDKSelfContained=true) needs an architecture. The Getting Started guide documents the packaged header.