The thing about `CLEAN.include` is it actually forces the creation of the cleaned object if it is absent, so it can remote it.  Dumb, but that's how it works (try `rake clean` twice in a row.)

One fix is to add a hidden `askari_java.jar` target that creates the file just long enough to delete it.  Another is to not use `CLEAN.include` but instead make a idempotent `task :clean_askari_jar` and wire it in with `task clean: :clean_askari_jar`.