I think an optimal solution would be to have more seamless integration between harness and router roles. As each are only half the picture

LLM-isms aside, I don't think we want this to be the case? An LLM, for all its complexity, is something that can be reasoned about. It's picking the next token, until it hits an EOS. The semantics imposed on those tokens (reasoning ,tool call, etc.) are up to the user('s harness) to decide and act on. The more that's pushed behind the facade, the harder it is achieve sufficient understanding of the model's behavior s.t. one can compose it into larger abstractions. Perhaps the performance (and the adherence to an interface/contract) compensate? But swapping from Opus or 5.5 to this or Fugu seems like a much bigger change than swapping between different 'base' models.