I'm also building a web-based literate programming environment called Starboard[1] that's probably a hundred times the amount of code (but then it has additional features such as top-level await, plugin, and Python support).

Consider supporting lit-html[2] literals instead of strings for HTML output, it works really well in notebook environments.

One more thing you can consider: a esm tagged literal that uses import(<data url of the code>), you can then use ES Module imports to dynamically load code. Here's a blog post about that approach [3]

[1]: https://starboard.gg [2]: https://lit-html.polymer-project.org/ [3]: https://2ality.com/2019/10/eval-via-import.html