Yeah, there are a lot of workarounds when you leave the standard tooling. I like the idea of using something like Bazel to build Docker images (since modeling dependencies and caching build steps is its raison d'etre) and eschewing Dockerfiles altogether; however, I haven't tried it (and Bazel has its own costs). I'm not familiar with buildkit in particular, but it's cool that it has an internal representation. I'll have to dig around.