It's at the build level. I have a mixed Clojure/Java project. Java calls the Clojure code through some gen-class, thus I have to build Clojure first so that when Java compiles it finds the gen-classes to link against. But, there's a place where I want to have a Clojure gen-class that implements a Java interface. At this point, when Clojure compiles the gen-class, it fails, because it can't find the interface class file, because Java hasn't been built yet.
So I tried moving the interface to Clojure land, but it defines methods that throw exceptions, so it seems that's not possible.