Piper is their perforce-like server. You check out certain files, as you'd with p4, work on the tree using git, with reviews, tests, etc. You periodically do a sync which is like pull - - rebase. Then you push your changes back into the perforce-like monorepo.
also they do all the development in one branch / in the trunk https://arxiv.org/abs/1702.01715 ( I never understood the explanations as to why they do that )
Now the article says that with windows they do branches.
