Well, it's extremely rudimentary but I put everything on github :
https://github.com/roblabla/i3-tmux-integration/tree/in-prog...
I'm still stumbling in the dark trying to understand how everything works. Also, the code might be an abomination, my goal was mostly to get stuff working, refactoring will come later.
This project is at once a learning project for many things (tmux internals, Rust, IPC in general, i3 IPC) and a tool I've been really needing for a while, so progress is slow but steady (I mostly work on it in sleepless nights and week-ends).