sounds like it would pair well with a suitably smart compiler

I wrote one! It works well with cutting-edge LLMs. You feed it one or more source files that contain natural language, or stdin, and it produces a design spec, a README, and a test suite. Then it writes C code, compiles with cosmocc (for portability) and tests, in a loop, until everything is passing. All in one binary. It's been a great personal tool and I plan to open source it soon.