That's already what an agent is though.

It's LLM invocation inside a loop where the exit condition is supposed to be some goal for the agent to have met, which you generally provide some heuristic or deterministic criteria so it can assert that the goal is reached or not.

I'm not sure about Claude Code, but with Amazon Q, if you prompt it in a vibe coded way, and give it a goal like that and say to keep going until the goal criteria is met (which could be running tests and passing them, or running a sub-agent that evaluates if the goal is met). Then I've seen it go for like 2 hours before it ended.