When I said “subjective existence” I’ve meant some model where we don’t need a list of minds or exhaustive search for minds to make them real. After all the brain has its own computing power and requiring additional compute or data to make subjective experiences associated with its computations real looks extraneous. Interactions of a mind with our world, on the other hand, seem crucial for our ability to determine its existence.
BTW, thank you for laying out all this in such detail. It makes reasoning much more focused.
If we are talking about the real world (to the best of our current knowledge, yada, yada) and not its classical approximation, we have the universal wavefunction as the world model, which is independent of agent’s actions as it encompasses them all.
Interacting with the world (by generating a specific pattern) allows to narrow down indexical uncertainty to all the agents that generate the pattern with non-zero probability.