OK, my final understanding is that the question is whether to build the two world models with a shared Q node or with separate Q nodes. We have separate calculator nodes so by analogy I see no strong reason for there to be a shared Q node, but also no strong reason for separate Q nodes since the counterfactual calculator is severed from the Q node. My inclination is that sharing nodes (as opposed to structure+parameters) between counterfactual worlds is the wrong thing to do, but sharing nodes is a limiting case of sharing structure+parameters... so the "logical" nodes should be shared and I've been the most wrong (by entertaining all other solutions). (But then the "logical" here is defined exactly as what is shared between all legitimate counterfactuals, so it is weaker than the "classically logical"; not all formulas are logical in this sense, but the ones that a mere calculator can compute probably are.)