So, if a machine demonstrated sapience, agency, and will, then you would grant that it could think?

Yes; but if you showed me a machine that you believed to be doing those things, given my current model, I wouldn't agree with you that it was.

You are saying that even if it did the same thing that animals do that you attribute to thinking, you would refuse to acknowledge it could be thinking?

Is there something particularly unique about biological circuits that allow thought, as opposed to electronic ones?

I believe so, yes. No, I can't explain what it is. (Because I think they're obvious follow-up questions: No, I don't consider myself particularly religious. Yes, I do believe in free will.)

… But you believe there’s something special about intelligence grounded in biology that can’t be true of intelligence grounded in silicon? That just sounds like magical thinking to me.

I agree. Thinking is clearly a compositional process and computers are Turing complete so it seems like and impossibility to me. Unless you reach for some quantum microtubule woo...