A green four-wheeled rover with a turret mount on a grid beside a grey road, two rivals in the distance
Exhibit 1 — A wheeled rally rover with four independent wheels and a turret mount, on the grid beside the road, with two rivals behind it.
Chase camera behind a blue rover on a grey road toward an orange gate, two rivals ahead
Exhibit 2 — Chase view down the road toward an orange checkpoint gate, with rivals ahead.
A green four-wheeled rover on a flat cyan grid next to a grey road
Exhibit 3 — A rover on the flat grid beside the road.

Correction, 29 October 2026. The first version attributed the rail bug below to Backbone Rally and quoted a lap time, speeds and wheel-wear figures that no image or record supports. The bug is real; its story is told correctly here. The first version remains readable in the journal's public history.

Journal history: the site as first published on 27 October

In Pipeline (liminal-pipeline), Backbone Rally is a checkpoint sprint against the clock. Its rovers are assembled from parts, a chassis, four independent wheels and a turret mount, rather than a single collision box sliding along a track (Exhibit 1).

The 75-centimetre step that depended on the runtime

The best terrain bug of the autumn did not come from a race. On 1 October a parity check generated the same open world twice, once on the .NET server and once in Unity's Mono runtime, and compared the terrain cell by cell. In seed 2601002, at (-149, 571), the two disagreed by about 0.75 m on the final height of a rail bed.

The rail generator stamped its bed one segment at a time, and each step read terrain that earlier steps had already changed. At one late cap, a cell's squared distance from the rail came out as 3.9995806 on .NET and 4.00015211 on Mono, either side of the 2 m half-width's threshold of 4: a difference of about a tenth of a millimetre in distance. One runtime included the cell and overwrote a nearer bed height. The other did not.

Left in, that is a step under a vehicle on one side of the network and not the other: the server and the picture you see disagreeing about the ground.

Stamping the Whole Ribbon at Once

The fix was simpler than tuning tolerances. Every terrain cell now measures its distance to the whole rail polyline first and applies one blend, instead of being rewritten segment by segment.

Status: scope. A paired wall probe at another point improved from 0.12 m to 0.003 m, and a new regression fails before the fix and passes after it. This does not establish exact equality between runtimes for every world: generated layouts can still differ, and a seed alone is not a recreation receipt.