Extension Points skill: what it does and how to install it

What it does. Explains MSBuild hook properties, wildcard import directories and control properties, NuGet build and buildTransitive layouts, and Directory.Build discovery. It traces import paths across source and packed layouts, including per-TFM forwarders, and covers creating extension points.

When to use it. For diagnosing or designing MSBuild import and hook flows, including missing or replaced assets. Not for focused import-safety verdicts, incremental build behaviour, target Inputs/Outputs, or props-versus-targets placement.