Summer alpine road verge

Source implementation, 15 September 2026. Native image acceptance is pending.

The summer stages Alps01 and Alps02 have a separate, narrow worn-ground strip immediately outside the existing 12 m asphalt road. Its lateral extent is 6.0 m to 6.30–6.65 m from the centreline, with independent smooth variation on each side. It uses the existing unchanged AlpineMeadow photographic ground (Leafy Grass by Charlotte Baglioni, Poly Haven, CC0), white material tint and the original HDRP roughness mask. World X/Z texture coordinates repeat at an authored 2.3 m scale. No new external asset or artistic recolouring was introduced.

TrackRuntime.BuildRoad adds this visual mesh only on summer alpine asphalt and only where the existing apron is present. Existing bridge and approach exclusions therefore apply. Alps03, other chapters, gravel surfaces, road markings, road and apron vertices, triangle indices, colliders, surface types, sampling and driving forces are unchanged. The additional renderer has no collider, casts no shadows and still receives normal environmental shadows.

AlpineSummerBankett.Append clips each narrow band against the actual first apron span, between lateral 6 and 8 m. It uses the existing positive-side diagonal a0→b1 and negative-side diagonal a1→b0 independently, since a banking transition can make a full quad nonplanar. Three small triangles per side retain the original two triangle planes. A constant 3 mm vertical offset prevents a coincident depth surface; this is not a terrain-height resampling or a replacement shoulder. Both sides together add at most 288 triangles / 864 vertices and one renderer per existing 48-station chunk. Mesh ownership uses the existing WorldMesh.Emit cleanup; the material is a single cached instance with a distinct key.

The original pre-change TrackRuntime text is retained at ArtSource/Alps/Bankett/TrackRuntime-before-bankett.cs.txt. ArtSource/Alps/Bankett/audit_geometry.py checks that removing the five additive statements restores that text exactly and independently exercises the diagonal clipping on 8,002 deliberately nonplanar cases. Its JSON records the exact errors, source and texture hashes, and limits. This is CPU geometry evidence, not a native renderer or physics pass. The offline managed compilation passed for 92 runtime and 21 editor files with zero warnings or errors; no Unity or Player was started by this task.

Native review should inspect Alps01 view0/view1 and an Alps02 banking bend at road level: the narrow edge should read as worn ground, show no cracks or depth flicker, leave the white road markings unchanged, and stop before a bridge or unpaved section. Its width, material balance and distance readability still require that image check. This change alone is not an AAA or photorealism acceptance.