Unfortunately, all the code is proprietary at the moment. If you are willing to get your hands dirty, the main thing to realize is that container layers are "just" tar files (see, for instance, this article: https://ochagavia.nl/blog/crafting-container-images-without-...). Contact details are in my profile, in case you'd like to chat ;)
Thanks for the link! Though I'm less worried about the tarball / OCI spec part, more about platform compatibility. I tried running runc/crun by hand at some point and let's just say I've done things before that were more fun. :)
