(just to clarify: I'm more laying out a bit of my confusion here rather than anything else, plus noting that we seem to have been, in our quest to find reductions for aspects of consciousness, implicitly treating agents as irreducible in certain ways)

Indeed. It's not obvious what we can reduce agents down further into without losing agents entirely; bit-for-bit identity is at least clear in a few situations.

(To continue the example - if we see the unaccessed memory as being part of the agent, then obviously we can't mess with it without changing the agent; but if we intuitively see it as like the agent having Internet access and the memory being a webpage, then we wouldn't regard it as part of its identity.)