A green test result is evidence of a specific check under specific conditions. It is not automatically evidence that a larger system claim is true. The gap between those two statements is where confident errors enter engineering workflows.
Name the evidence boundary
Fixtures, simulation, replay, integration checks, and observed runtime behavior each answer different questions. A validation packet should say which layer ran, what it covered, and what remains outside the observation boundary.
Fail closed
Failing closed does not mean stopping at the first imperfect signal. It means refusing to promote a conclusion beyond its evidence. The next action can be to collect more evidence, narrow the claim, or ask for human review.