The author's before-state: "an STL left the CAD tool with no record of what built it. Nothing checked that it was one closed solid, that it matched the CAD volume, or that its holes fitted the parts meant to go in them." The new gates stamp provenance with STL and STEP hashes and CAD volume, refuse stale exports, gauge holes against an ISO 273 fit table, and fail a revision diff on any change the expectation file doesn't list.