It can only be spent by signing a message with their private key. If I request a token from the mint with locked to your npub, the mint will only accept it as a subsequent payment if it is signed with your nsec. I literally cannot spend it because in the eyes of the mint, I've already given it to you.

They can. Nobody other than the receiver could have spent it, therefore they can verify it's not spent.

Yes I’m w you now, I must’ve not read the original comment through