The basic law of contract has been set for many 1000s of years and is pretty much universal across human societies. Legal agreements or contracts require 2 things:
a. An offer;
b. Acceptance of the offer.
There is no requirement for the agreement to be written down and no requirement that the contract be approved by a third party.
Can you imagine ridiculous it would need to be to get the approval of a third party such as "ROBONOTARY" in cases such as this - "Timmy, if you rake my lawn, I will give you $5," "Sure Mrs. Jones."
Why do you dream of a fascist state where robots control most aspects of human interaction?