What happened
The Geometry Lab’s smoothness gate is a static screen for road geometry: maximum grade, rate of grade change, no full-block stair steps, crest and sag deviation over a chord, and headroom. It is measured on the real voxel densities, not on the design intent.
On 2026-09-12, the first diamond-interchange quadrant went through it and failed on a cliff that did not exist.
Why it could not pass
For each surface sample, the gate compared against the nearest sample in the neighbouring column, at any height. Where the local road crosses over the mainline, the deck edge and the road nine blocks below it are neighbouring columns. The gate read a normal overpass edge as a nine-block step.
Every crossroad-over-mainline layout would fail. The gate was green on flat roads and red on anything with a bridge in it. It had been passing for weeks because nothing with a bridge had been put through it.
Ask what input would turn a green gate red. Then ask what input would turn it red for the wrong reason. This one had never been asked the second question.
The repair
A neighbour now counts as the same surface only when it sits within half the clearance height. Anything farther apart is a different deck, not a step. Same-level steps inside that band are still measured, and the lane-path checks cover the rest. Both the passing and failing directions have tests.
The repair changed the factory’s source hash, so all six engineering specimens had to be recompiled before their stage routes would verify. After the repair the quadrant measured a maximum grade of 0.063 against a limit of 0.0735, a maximum transition of 0.0157 against 0.031, and zero full-block steps.
The two hidden layers
With the gate green, staging the specimen to the game machine still failed: route disabled or key unknown. The cause was two allowlists that nothing in the configuration mentioned.
- The export-key allowlist. The worker agent on the game machine holds a compiled-in list of permitted export keys. A valid new export definition was rejected because its key was not in that list. Configuration alone could not add it.
- The bridge allowlist. The console bridge keeps a list of permitted text intents. It contained none of the six specimen reload intents. A successfully staged specimen would have been refused at load time.
Both are deliberate fail-closed lists, and both are correct to exist. The defect was that they were invisible to anyone reading the config, so a change looked complete while two layers below it still said no. The rule that came out: three layers, one deploy.
Where it stands
Geometry built, static gates green, tests in both directions. Not yet editor-observed, not driven, not deployed to a live world, not accepted. The owner’s verdict is still owed and will be filed here when it lands.
This is what a gate audit looks like: not “is it green,” but “what would make it red, and would it be red for the right reason.” The contact button opens with this report as the subject.