Easy, you put the transaction in the previous block. So the miner can only mine a block if they have already made the expenditure.

What if I create a whole new chain? Will the transactions at the very beginning of that chain have to be added to the big, old chain? How far back do the common ancestors of two chains have to be for your auto-merging to happen? What happens if two histories conflict? Then in Version Control parlance, we have a "merge conflict".

What stops me from doing a hard fork to roll back both blocks?

If you spend more tokens than the tokens that were spent mining the last two blocks you can erase the transactions in those blocks, but isn't that also the case with PoW?

You aren’t following. The hard fork lets me double spend the tokens from those blocks.

Indeed, I'm not following your argument.

Stop asking people to do your homework.