Success!
For anyone who comes back here looking for the solution, I followed these steps:
- Get the Pipeline Tool Source from Here (Thanks Optimistic_Peach) as suggested on this thread
- Run protobuild inside the repo’s root
- Open
MonoGame.Framework.Windows.slnin vs2017 (other IDEs are available) - Set Pipeline.Windows as startup project
- Build and Run in Debug configuration
- Open your custom processors project in a separate vs2017 instance
- Add
System.Diagnostics.Debugger.Break()to the file you want to debug, in theProcess()function (Thanks nkast) - Build custom processors project in Debug configuration
- Edit your content project file *.mgcb in text editor, ensure that References all point to Debug *.dll files
- Enable Debug Mode in Pipeline Tool (in the Build menu)
- Open your content project file in the Pipeline Tool you’ve run from vs2017
- Rebuild your content
- When prompted, attach your Pipeline tool to the vs2017 instance with your custom processors in it
- Voilà.