Remember that runc contains quite a few lines of C:
https://github.com/opencontainers/runc/blob/4d4d19ce528ac40c...
https://github.com/opencontainers/runc/blob/4d4d19ce528ac40c...
https://github.com/opencontainers/runc/blob/4d4d19ce528ac40c...
https://github.com/opencontainers/runc/blob/4d4d19ce528ac40c...
This seems like a manageable amount to very carefully maintain and not at all like writing something entirely in C.