Accuracy

How references.yaml and make verify check a part against a reference model of the same standard.

A wrong part still renders, is watertight, and has a stable bounding box. Golden dimensions catch a part moving; only a comparison against someone else's model of the same standard catches it being wrong. references.yaml declares those comparisons; make refs fetches the sources (submodules, or pinned commits into gitignored refs/) and make verify runs them:

• shape — our part and the reference through the same OpenSCAD binary: volume, symmetric surface distance, and cross-section IoU at declared heights. IoU is what catches a mating profile that is the right size and the wrong shape.
• fit — our part and its real counterpart in the assembled pose, intersected: interference volume and smallest clearance.

confidence: exact is a claim, and a test fails if a part makes it without a check behind it. The harness earned its keep: before it existed, the Gridfinity foot was 5.9 mm undersized, the GoPro buckles could not interleave at all, the openGrid cells were invented geometry (IoU 0.23), and three 2020 fittings drove tens to hundreds of mm³ into the rail.

A kind: file reference takes a STEP or STL you supply (manufacturer CAD behind a login) — drop it in refs/manual/ and uncomment the example in references.yaml.