From what I can tell, the "established wisdom" is to get Fable to plan and Opus to implement (for cost purposes). The problem there is that Opus could ignore whatever it likes from Fable's plan.
The Claude harness effectively summarizes the discovery into a plan document, clears, and starts with just that summary - so you'd be clearing context regardless.
i've yet to see a case where opus "ignores whatever it likes".
opus will definitely ignore instructions if you give it contradictory instructions, or a plan that has steps that obviously don't work with each other. but if you give it a coherent plan, it will follow it.
Honestly this is where I would have fable generate a checklist and you just monitor opus to ensure it is going through the checklist. I think ignore is often the result of a context that is not focused enough.
