Rationale
When done means the worker said so, every task is done. A contract written first is what makes a refusal possible, and a refusal is the whole point of supervision.
Required behaviour
Know the contract a task must meet before starting it, and let the contract, not the worker's word, decide whether it is finished.
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.