As long as you are chunking out the tasks generated from the plan, you can manually (or write an orchestrator to...) give the component tasks to agents that pass along inputs and outputs per the dependency graph derived from the plan.
You can write this plan yourself or review it with the agent. Chunking tasks out of the plan like this has the added benefit of being able to swap for a different model when the time comes (looking forward to Opus-level models I can run on my consumer card...)
Not really convinced using Fable and trusting the harness to orchestrate for you is worth the intelligence upgrade. An understanding of an high level implementation plan of your task is also necessary when working with colleagues who rightfully quiz you. Especially since, at least for my work, there isn't a lot that Opus struggles with.