[FEATURE] BuildingKit binds materials, not just meshes — the path to a contemporary city facade

[Noisemaker111]

Problem

BuildingKit binds a facade part slot to a mesh. That works when a modular part kit exists for the genre — the-robots uses quaternius-modular-scifi. For a contemporary city (vice-isle) no such CC0 pack exists:

• kaykit-city-builder is whole buildings only. KayKit's full public catalogue is 10 repos and contains no facade-parts pack.
• Poly Haven's modular_urban_apartments_facade / modular_factory_facade are CC0 and contemporary, but each ships as one 118K–175K-tri assembly ~51 m wide, not per-slot files. Wrong shape for a kit, and far off vice-isle's stylized low-poly look.
• Kenney is out by project policy.
• Quaternius Downtown City MegaKit is the one live lead and is unverified — see the source-entry bug filed alongside this.

So the mesh path is blocked on assets we do not have.

The material path is available today

packages/assets/src/sources/ambientcg.ts:44 already declares a Facade family (Facade001–006) plus Bricks ×30, Concrete ×25, Plaster ×7, RoofingTiles ×8 — all CC0, all pullable now, all resolvable through buildMaterialCatalog with no reindex step.

What blocks using them: unbound parts render as solid-colour instanced boxes. BuildingMaterialPalette is Record<kind, string> — a hex colour — and batchMaterialFor builds a MeshStandardMaterial({ color }) with no map slot. BuildingKitPart.tint is likewise colour-only.

For a contemporary city this is arguably the better result anyway: tiled brick/concrete/glass-curtain-wall PBR on the generator's per-bay boxes reads more like a real city than any stylized low-poly panel kit would.

Acceptance criteria

• A palette value may be a material reference, not only a hex colour — something like { color?, material?: ModelMaterialMaps, repeat? } — with the plain string still accepted.
• BuildingKitPart can name a material for the same reason.
• The shell loads and applies it. The seam already exists: packages/shell/src/materialOverride.ts + ModelMaterialMaps (color/normal/roughness/ao), used by SceneModels.tsx:183.
• UV tiling is sane. Within one building panelScale makes every wall slot uniformly bayWidth*0.92 × floorHeight*ratio, so one repeat per kind is correct; it drifts across buildings with different bayWidth. Fixed repeat is acceptable to start, an instance attribute is the exact fix.
• vice-isle is the first adopter, with before/after screenshots.

Note

vice-isle does not currently use the facade generator at all — it places whole-building GLBs via scene.object.place, and world.ts:91 records that structures: [building(...)] was removed because the clusters blocked NPC navigation. Adopting this means putting vice-isle back on the generator, and that navigation problem has to be solved again. Worth scoping before starting.