How small can the orchestration model in an agent be? (separating it from code-gen — that obviously wants a big model)

I'm building a local-first agent — a plain ReAct loop (think, pick a tool, observe, repeat) on a llama.cpp backend — and I want to be precise about a question that usually just gets answered with "it depends." It does depend. So let me split it into two jobs: (a) Heavy one-shot generation — write a