I tinkered with Anarki a whole bunch and finally got this working smoothly. There was a missing step, because it turns out we need to load certain Racket-side bindings into a namespace in order to be able to evaluate Arc code there. It seems more obvious in hindsight. :)
I approached this with the secondary goal of letting a Racket program (or a determined Arc program) instantiate multiple independent intances of Anarki. The ac.rkt module was the only place we were performing side effects when a Racket module was visited, and Racket's caching of modules makes it hard to repeat those side effects on demand, so I moved most of them into a procedure called `anarki-init`.
By adding one line to the example I gave...
(let my-ns (nsobj)
; Load the Arc builtins into the namespace so we can evaluate
(w/current-ns my-ns ($.anarki-init))
...it becomes possible to evaluate Arc code in that namespace, and the example works.
Before I started on that, I did a bunch of cleanup to get the Anarki unit tests and entrypoints running smoothly on all our CI platforms. To get started on this cleanup, I had a few questions hjek and akkartik were able to discuss with me on issue #94: https://github.com/arclanguage/anarki/issues/94
A lot of the problems I'm fixing here are ones I created, so it's a little embarrassing. :) It's nice to finally put in some of this missing work, though. I want to say thanks to shader and hjek for talking about modules and packages, provoking me to work on this stuff!