The current setup in the repo is confusing, because some targets are declared in the top level SConscript but reference files in subdirectories, while other targets are declared in per-directory SConscript files. That makes it unclear where new things should go, and also leads to a cluttered top level SConscript. Moving the definitions down into the per directory SConscripts would make clear what the intended usage looks like, as well as make it simpler.