How do you prevent it from just taking the reins and writing an entire function or class for you when all you wanted to do was just talk about the code you already had.
"Talk with me first:" (Implying anything other than talking, like coding, would be a separate distinct step that is not to be done)
Proposal is the best keyword imo if it fits what you'd like.
"Propose changes you would make to (this repo|staged changes|latest commit)."
"Propose alternatives."
"Propose flaws." / "Propose flaws in my reasoning."