Ah, Dune is trying to be too clever here: when it sees (copy a b), it will assume that a is a dependency and b is a target. However, it can’t know that (run make liblzma_7z.a) produces liblzma_7z.a, so it thinks that 7zip/liblzma_7z.a is a dependency of the whole rule. I suppose we could add an option to disable dependency/target inference.