"About a decade ago, I built a small web app using Common Lisp (SNACK) and a lot of the development I did was done through adding new features and debugging in the REPL. While I saved the VM, reading the code months later to add a feature was terrible because the app was hacked together. I wonder of there's a way to fix this." -- I think you might like clojure.spec, I feel that it is a step in the right direction towards keeping the flexibility and interactivity of lisp while making the code more maintainable. You can find more about it here -- [https://clojure.org/about/spec].

I also wrote a small article on it, not very detailed but maybe it can help you get a rough idea of the power of clojure.spec when combined with generative testing -- [http://abhirag.in/articles/spec_oracle.html]