The above chain is something I consider a problem, by the way, but I think that's the only correct way to do it with our header files separate from our source files.

AFTER the PnP merge, I want to merge those and reserve the top-level include folder for installed headers, which is the common convention in open source projects.  So that folder will be where we put the interface between plugins and core DGI, and all the other includes will move in with the source, and we'll rejoice.