I'm tagging this as in the spirit of Librarization even though it's already technically separate.
We should treat LuaSandbox as its own project, and not just a component of Scribunto.
This would include having a separate Phab project to track bugs, a wiki page with documentation to begin with. I'm not sure whether it makes sense to also submit it to PECL / how that all works, but that's another thing to consider.
My motivation is that I keep seeing people mention https://github.com/phpv8/v8js but it seems barely anyone knows about luasandbox, and the rationale of why we decided running lua is better than JS.