It's been a couple years but I think janet has the primitives for this in the netrepl module which I think is part of the standard library. I remember being really surprised at how much introspection and control over the env when you responded to a repl connection, just at that time no one had put it together into what you want. I also seem to remember the actual janet repl being a different implementation which always seemed weird to me.
Yeah that standard lib extension has always been extremely underdocumented.
I thought I remembered being able to manipulate the env as a dynamic which I think could get you what you need. But reading the source now I guess not? I'm pretty out of practice reading janet.
