I was recently working on an AI harness too, but I wasn't using AI to code it. It's really easy and requires little code. I wasn't even using langchain - that would require even less code.

UI is harder for sure, but it's not that bad. You need to think though where to catch which exceptions.

LLMs might opt for langchain which has had multiple breaking changes after the knowledge cutoff, making it hard for the LLM to work with it. This is probably going to lead to the LLM having to make many changes to it's code, making it messy and leading to further code being less maintainable.