@matigo Something beyond my understanding. There's a plugin for Grav that promises to do two-way sync for Grav so in theory (and in practice if you're not me) you can create new posts live in production or in github and each will sync to the other. I'm pretty sure it would work well if you enabled it at the outset, rather than try to force it to use an existing repo. I tried that, and it did all sorts of weird things that completely messed up the back end.
Lesson learned.