Every architecture team has a rule that looks excellent in a slide deck. The trouble starts when a delivery team needs to make a decision on Tuesday afternoon and can't tell whether the rule applies.
Take a requirement that customer data must not leave an approved boundary. A diagram may explain the intention, but a deploy-time policy, permission check or contract test is what catches a violation. Without that feedback, the rule relies on somebody remembering it at exactly the right moment.
Good guardrails belong in the tools engineers already use. Templates can set sensible defaults. CI checks can catch forbidden dependencies. Runtime policies can restrict access. The point is to make the safe choice straightforward and the unusual choice visible.
Exceptions will happen. Give each one an owner, a reason and a review date. Then pick one high-impact rule and automate its verification. A modest rule that works beats a magnificent handbook nobody opens.