A comment in two parts:
First and most relevant to this task: It certainly would be nice to get some of this into documentation! It took me quite awhile to figure this out when doing my own extension development.

How an extension can have their unit tests then? 🤔

Did that Phactory: Hosting Projects Here

@avivey to do now:

I've used phorge-devcontainer as well and it works great!

I managed to compile xhpast on windows using llvm installed via Scoop. I also have Visual Studio C++ 19 installed which may be required (I saw some suspicious output that indicated that some include files were being pulled from that install somehow).

Nice. Maybe a start-extension Arcanist workflow is a bit overkill, but a boilerplate extension would be lovely