This is cool, I worked on something similar sort of thing over the winter, more focused on a local-first leetcode/coderpad, with a way to execute code in the browser using WebAssembly, and a way to share code over WebRTC
It's a pretty big lift. Python was somewhat easy with pyodide, but I couldn't get Java to work locally. There's a company called CheerpJ that can do it over an API though.
I think if I was going to look into code execution in Tachi Code, it’d probably as part of a transformation into some sort of remote development experience rather than pursue wasm and all its complexities.
https://codenow-mu.vercel.app/problems/0001-fizzbuzz