For me this is Gleam. Fairly small lang, type safe, compiled, NO NULLS (very important IMO), good FFI, code is readable, and... you get the BEAM!

Agents can pretty much iterate on their own.

The most important thing for me, at least for now (and IMO the foreseeable future) is being able to review and read the output code clearly. I am the bottleneck in the agent -> human loop, so optimizing for that by producing clear and readable code is a massive priority. Gleam eliminates a ton of errors automatically so my reviews are focused on mostly business logic (also need to explicitly call out redundant code often enough).

I could see an argument for full on Erlang too, but I like the static typing.