"Systems grow brittle when exceptions are treated as errors rather than signals.
A standard is a commitment you make to your future self. In a system boundary decision that affects two teams, it exists so you do not have to reinvent judgment every time the room is loud.
In a system boundary decision that affects two teams, people comply with what is enforced, not what is written. If exceptions are informal, you end up with a standard no one can defend and a process no one trusts. Define the decision rights before the crisis, or the crisis will define them for you.
Erik Hollnagel is useful here because it forces precision. Put the assumption into words, then choose the signal that forces you to revisit it. Do not hide the cost in prose.