love it :) next step, some tiny scripting language bindings? s7 would fit in well e.g. https://ccrma.stanford.edu/software/snd/snd/s7.html
Not sure how these facilities compare to Slime + Common Lisp.
[0]: https://ccrma.stanford.edu/software/snd/snd/s7.html#repl
I might be misunderstanding your requirements; "embedded" can mean so many things these days. But what do you think of ECL (https://ecl.common-lisp.dev/main.html)?
I don't know if ECL is disciplined enough to actually constraint itself in all these ways to be a good embedded citizen.