> It is impossible to duplicate results with an LLM

But that's the fundamental property of it - it is stochastic by nature. The skill is to learn how to sandwich deterministic logic between layers of randomness. Determinism doesn't live in the model. It lives in the harness you build around it. You can't make the model deterministic (it simply cannot be), so you make the system deterministic instead. Validation before, validation after, the randomness stays contained in the middle.

Talking to an LLM is not a skill, having a meaningful conversation leading to practical outcomes is.