Rationale
A slow or flaky gate is worked around, and a gate that blocks work in progress trains people to skip it. Only what is settled and decidable may refuse.
Required behaviour
A check that can stop a command is deterministic and cheap; work in progress is reported, never blocked.
Failure behaviour
No command decides this rule; a reviewer does, and a change that violates it is not merged. Where a behavioural case covers part of it, that case is named below.
Verification
Review. Every doctrine's class is declared in the rule package; test/cases/17_doctrine_enforcement.sh proves the class decides whether a command stops.