What state machines have going for them is the absolute knowledge, nay proof, that “if you are in this state, then all the previous states must have been comple

What state machines have going for them is the absolute knowledge, nay proof, that “if you are in this state, then all the previous states must have been completed”. When it’s about money, that’s kinda important. I would use a state machine, and log the transitions (“events”, if you insist).