A one-page decision boundary saves more arguments than any policy document we have seen.
Before the first line of code, we write a single page listing every decision in the workflow and who owns it: the system alone, the system with a named reviewer, or a person outright. It gets signed by the operations lead and the risk team.
It sounds bureaucratic. In practice it is the fastest document in the project, and it removes the two questions that otherwise stall a launch for a month — what happens when the model is wrong, and who is accountable when it is.