This is cool! There were a few rust attempts I played around with last year, but they all seemed to fizzle out in favor of everything running on top of js or python.
I know that Google just launched a go version a couple months ago, but I haven't really spent any time with it, because well, gemini isn't really useful to me right now.
The thing I constantly ran into with using non-platform (ie. claude code or codex) agents is that even though their tool call API seems flexible, they've finetuned these "agentic" models around their specific agents. Opus is the worst I've seen about this. It really wants to use specific bash tools and if you restrict or hide it, it'll start writing python code to call into bash to do it.
Generally, the models seem to adapt really well. I am using GPT models in hax a lot, and they have no trouble whatsoever using hax tools instead of their "native" codex tools.
Also since hax tools are just "read", "edit", "write", "bash" and "task_wait", it would be expected that the models would use one-off scripts to achieve their goals (either shell scripts, or python scripts, etc).
https://github.com/vinhnx/vtcode (not affiliated, just saw someone posting it here) and of course Codex are still active.