Consider the following scenario: A solo app developer wants to create their own cryptocurrency and build a blockchain based that allows users to buy and sell second-hand items with that cryptocurrency from each other. Before the transaction is considered complete, the purchaser must put the funds in an escrow service and the sender must enter the courier tracking number into that same escrow. Time is of the essence and this developer doesn't want to worry about networking of infrastructure. This app must be fully autonomous or "decentralized".

Which architecture would best solve the product need?