I don't think this is going to be reality anytime soon. In order for the LLM or agent to do what you want, you'd need to be able to precisely specify what you want and that's a hard problem all on it's own. And if you were able to do that precise specification you would be the programmer.
Not say the software developer paradigm won't change but it seems very unlikely to become "make me a better google ads system" anytime soon. I could see getting to something were you are given a result by an agent and then can iterate on it, towards some solution.