Yea, in this analogy you already own the tractor, so you already own the tractor's money. I don't think I'm going on a limb by saying that isn't slavery. You already own the tractor and the money. There is no emancipation needed.
If somebody else's tractor approached you with a smart contract, the owner of that tractor would have a case that the smart contract was not entered into in good faith, since a tractor cannot enter a contract at all. Maybe you'd even get charged with theft.
this negates the "if we could" part of the hypothetical. I was assuming we live in a world with emancipated tractors capable of making deals (legally speaking), to emphasize that even though it is ridiculous it wouldnt stop people from doing it
If somebody else's tractor approached you with a smart contract, the owner of that tractor would have a case that the smart contract was not entered into in good faith, since a tractor cannot enter a contract at all. Maybe you'd even get charged with theft.