Rationale
Activity is easy to report and impossible to check. An outcome that a command produced, with its exit code and duration recorded, is checkable by anyone later.
Required behaviour
Accept a verification command's recorded exit code as evidence of completion, and accept nothing that merely describes verification.
Failure behaviour
Nothing decides this rule directly, so a violation is reported by nobody; it is the rules that depend on it that decide what a machine can decide and stop or warn accordingly.
Verification
The enforced rules whose depends_on names this one carry the validators, the tests and the CI wiring. majordomus doctrine list shows them.