First , that’s absolutely not how you run a CL server in production. If you had a debugger installed in production, which you shouldn’t, it wouldn just pause there and time out the sockets. What you could do is attach your client to the Lisp system with swank and then make your image changes, later to be synchronized with the actual code in the repo.

Second, other languages can also do that, Java for example has facilities to recompile functions and then rewind the stack to run the function again from the beginning of it. Dart also does that even better and people use that extensively in Flutter with hot reloading. I do that in a debugger during tests though, never seen it done in prod.