Nice. I built something basically just like this for work for the same reason last year. It only look a few hours though, cause I just used Acorn [0] to parse my JS, then directly evaluated the AST. It also had an iteration limit and other configurable limits so I can eval stuff in the browser without crashing the tab. I did not use an LLM.
Haha nice! It's a good library, and it's flexible enough that you can extend the syntax of JS however you like (with some difficulty, as it's not exactly documented). I experimented with adding my own type system to JS by using Acorn. Can recommend.
[0]: https://github.com/acornjs/acorn