I just keep them in separate directories and use .bat files to copy files back and forth. Crude but effective enough.

1) Fable generates updated .c sources and .md design documents in myproj_fab

2) A batch file in myproj_sol copies the updated files from myproj_fab to myproj_sol

3) I tell Codex to "Review updated files, write findings to review.md"

4) Sol rips Fable a new one, usually

5) Another batch file copies review.md back to myproj_fab, where I tell Claude Code "See review.md"

I don't want to automate it any more than that, because I'll get lazy, stop watching the tennis match, and miss something important. Which will probably happen anyway...