Independent test oracle

Acceptance tests written before implementation by a different agent, which the implementers must satisfy and may never edit.

The tests are written from each task's accepted scope, so they measure the specification rather than the implementation's opinion of it. The implementers are told to make them pass, and to stop and report rather than edit a test that looks wrong.

This is about who writes the oracle, not about designing through tests. The behaviour was fixed when the scope was accepted, and red tests at the start are the expected state.