so, a weird and unfortunate fact about the supercollider class inclusion system (as presnetly configured) is that all .sc files in ~/dust/code are āvisibleā at the same time. and of course multiple copies cannot be tolerated by supercollider.
so yes, if Foo.sc [*] exists in ~/dust/code/we then it must not exist anywhere else in ~/dust/code and vice versa.
so unfortunately the user/maintainer of the system must manage script->engine dependencies at the moment. script writers that use existing engines should probably not include local copies of them, but instead clearly indicate that their script requires the installation of another project. this isnāt ideal and it will certainly change at some not-to-distant point.
([*] technically, any file defining class Foo, but this is the convention)