feat(paint-slots): migrate wall + procedural kinds onto node.slots

Retire the inline material fields on every slot-model kind, moving them
onto the unified node.slots model on load so painting, edit-propagation,
and the picker behave uniformly.

Walls: slots {interior,exterior}; slot-first viewer resolution threading
sceneMaterials (content folded into the wall material hash); WallRenderer
subscribes to the scene-material palette so a scene-material edit
re-renders live; wallPaint rebuilt on createSlotPaintCapability.

Load migration generalizes legacy -> slots across slab/ceiling (surface),
fence (posts/infill/base/rail), column (shaft/base/capital/frame), shelf
(shelves/frame/back), and stair (per-role tread/side/railing). Library/
scene refs pass through; inline customs mint a deduped scene material;
legacy fields cleared. No visual change (renderers already fell back to
the legacy fields). Roof/chimney/dormer/vents intentionally stay on their
role system.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/core/src/schema/nodes/wall.ts

@@ -20,6 +20,13 @@ export const WallNode = BaseNode.extend({
   interiorMaterialPreset: z.string().optional(),
   exteriorMaterial: MaterialSchema.optional(),
   exteriorMaterialPreset: z.string().optional(),
+  // Per-slot material overrides on the unified slot model, mirroring
+  // `SlabNode.slots`. Key = slot id (`interior` / `exterior`), value = a
+  // `MaterialRef` (`library:<id>` / `scene:<id>`). Absent = the declared slot
+  // default (`WALL_SLOT_DEFAULT`). The legacy `*Material*` fields above are
+  // read only by the load migration that moves them into `slots`; delete them
+  // in a follow-up once migrated scenes are the norm.
+  slots: z.record(z.string(), z.string()).optional(),
   thickness: z.number().optional(),
   height: z.number().optional(),
   curveOffset: z.number().optional(),

packages/core/src/store/use-scene-wall-slot-migration.test.ts

@@ -0,0 +1,264 @@
+import { beforeEach, describe, expect, test } from 'bun:test'
+import type { AnyNode } from '../schema'
+import useScene from './use-scene'
+
+type WallNode = Extract<AnyNode, { type: 'wall' }>
+
+function sceneWithWall(wall: Record<string, unknown>): Record<string, AnyNode> {
+  return {
+    site_test: {
+      object: 'node',
+      id: 'site_test',
+      type: 'site',
+      parentId: null,
+      visible: true,
+      metadata: {},
+      children: ['level_test'],
+    },
+    level_test: {
+      object: 'node',
+      id: 'level_test',
+      type: 'level',
+      parentId: 'site_test',
+      visible: true,
+      metadata: {},
+      children: ['wall_test'],
+      level: 0,
+    },
+    wall_test: {
+      object: 'node',
+      id: 'wall_test',
+      type: 'wall',
+      parentId: 'level_test',
+      visible: true,
+      metadata: {},
+      children: [],
+      start: [0, 0],
+      end: [4, 0],
+      ...wall,
+    },
+  } as unknown as Record<string, AnyNode>
+}
+
+function sceneWithNode(node: Record<string, unknown>): Record<string, AnyNode> {
+  return {
+    site_test: {
+      object: 'node',
+      id: 'site_test',
+      type: 'site',
+      parentId: null,
+      visible: true,
+      metadata: {},
+      children: ['level_test'],
+    },
+    level_test: {
+      object: 'node',
+      id: 'level_test',
+      type: 'level',
+      parentId: 'site_test',
+      visible: true,
+      metadata: {},
+      children: ['node_test'],
+      level: 0,
+    },
+    node_test: {
+      object: 'node',
+      id: 'node_test',
+      visible: true,
+      metadata: {},
+      parentId: 'level_test',
+      ...node,
+    },
+  } as unknown as Record<string, AnyNode>
+}
+
+function resetScene() {
+  useScene.setState({
+    nodes: {},
+    rootNodeIds: [],
+    dirtyNodes: new Set(),
+    collections: {},
+    materials: {},
+  } as never)
+  useScene.temporal.getState().clear()
+}
+
+describe('wall surface-material → slots migration', () => {
+  beforeEach(() => {
+    resetScene()
+  })
+
+  test('moves legacy library presets into slots and clears the inline fields', () => {
+    useScene.getState().setScene(
+      sceneWithWall({
+        interiorMaterialPreset: 'library:concrete-plate',
+        exteriorMaterialPreset: 'library:wood-woodplank48',
+      }),
+      ['site_test'] as never,
+    )
+
+    const wall = useScene.getState().nodes.wall_test as WallNode
+    expect(wall.slots).toEqual({
+      interior: 'library:concrete-plate',
+      exterior: 'library:wood-woodplank48',
+    })
+    expect(wall.interiorMaterialPreset).toBeUndefined()
+    expect(wall.exteriorMaterialPreset).toBeUndefined()
+  })
+
+  test('mints a scene material for an inline legacy material and references it', () => {
+    useScene.getState().setScene(
+      sceneWithWall({
+        interiorMaterial: { properties: { color: '#abcdef' } },
+      }),
+      ['site_test'] as never,
+    )
+
+    const wall = useScene.getState().nodes.wall_test as WallNode
+    const interiorRef = wall.slots?.interior
+    expect(interiorRef?.startsWith('scene:')).toBe(true)
+    expect(wall.interiorMaterial).toBeUndefined()
+
+    const materials = useScene.getState().materials
+    const id = interiorRef!.slice('scene:'.length)
+    expect(materials[id as keyof typeof materials]?.material).toEqual({
+      properties: { color: '#abcdef' },
+    } as never)
+  })
+
+  test('legacy catch-all material applies to both faces; identical inline customs share one scene material', () => {
+    useScene.getState().setScene(
+      sceneWithWall({
+        material: { properties: { color: '#112233' } },
+      }),
+      ['site_test'] as never,
+    )
+
+    const wall = useScene.getState().nodes.wall_test as WallNode
+    expect(wall.slots?.interior).toBeDefined()
+    expect(wall.slots?.interior).toBe(wall.slots?.exterior as string)
+    expect(wall.material).toBeUndefined()
+    // One minted datablock shared across both faces.
+    expect(Object.keys(useScene.getState().materials)).toHaveLength(1)
+  })
+
+  test('leaves an already slot-modelled wall untouched and mints nothing for unpainted walls', () => {
+    useScene
+      .getState()
+      .setScene(sceneWithWall({ slots: { interior: 'library:concrete-drywall' } }), [
+        'site_test',
+      ] as never)
+
+    const migratedWall = useScene.getState().nodes.wall_test as WallNode
+    expect(migratedWall.slots).toEqual({ interior: 'library:concrete-drywall' })
+    expect(Object.keys(useScene.getState().materials)).toHaveLength(0)
+
+    useScene.getState().setScene(sceneWithWall({}), ['site_test'] as never)
+    const plainWall = useScene.getState().nodes.wall_test as WallNode
+    expect(plainWall.slots).toBeUndefined()
+    expect(Object.keys(useScene.getState().materials)).toHaveLength(0)
+  })
+})
+
+type SlottedNode = AnyNode & { slots?: Record<string, string>; material?: unknown }
+
+describe('procedural kind surface-material → slots migration', () => {
+  beforeEach(resetScene)
+
+  test('slab: legacy preset → slots.surface, legacy cleared', () => {
+    useScene.getState().setScene(
+      sceneWithNode({
+        type: 'slab',
+        polygon: [
+          [0, 0],
+          [2, 0],
+          [2, 2],
+          [0, 2],
+        ],
+        materialPreset: 'library:flooring-tiles3',
+      }),
+      ['site_test'] as never,
+    )
+
+    const slab = (useScene.getState().nodes as Record<string, SlottedNode>).node_test!
+    expect(slab.slots).toEqual({ surface: 'library:flooring-tiles3' })
+    expect((slab as { materialPreset?: unknown }).materialPreset).toBeUndefined()
+  })
+
+  test('ceiling: inline custom material mints a scene material on slots.surface', () => {
+    useScene.getState().setScene(
+      sceneWithNode({
+        type: 'ceiling',
+        polygon: [
+          [0, 0],
+          [2, 0],
+          [2, 2],
+        ],
+        material: { properties: { color: '#ddeeff' } },
+      }),
+      ['site_test'] as never,
+    )
+
+    const ceiling = (useScene.getState().nodes as Record<string, SlottedNode>).node_test!
+    const ref = ceiling.slots?.surface
+    expect(ref?.startsWith('scene:')).toBe(true)
+    expect(ceiling.material).toBeUndefined()
+    expect(Object.keys(useScene.getState().materials)).toHaveLength(1)
+  })
+
+  test('fence: legacy preset fans out to every slot id (one shared ref)', () => {
+    useScene.getState().setScene(
+      sceneWithNode({
+        type: 'fence',
+        start: [0, 0],
+        end: [4, 0],
+        materialPreset: 'library:wood-woodplank48',
+      }),
+      ['site_test'] as never,
+    )
+
+    const fence = (useScene.getState().nodes as Record<string, SlottedNode>).node_test!
+    expect(fence.slots).toEqual({
+      posts: 'library:wood-woodplank48',
+      infill: 'library:wood-woodplank48',
+      base: 'library:wood-woodplank48',
+      rail: 'library:wood-woodplank48',
+    })
+  })
+
+  test('stair: per-role legacy fields map tread→treads, side→body, railing→railing', () => {
+    useScene.getState().setScene(
+      sceneWithNode({
+        type: 'stair',
+        treadMaterialPreset: 'library:wood-woodplank48',
+        sideMaterialPreset: 'library:concrete-plate',
+        railingMaterialPreset: 'library:metal-chrome',
+      }),
+      ['site_test'] as never,
+    )
+
+    const stair = (useScene.getState().nodes as Record<string, SlottedNode>).node_test!
+    expect(stair.slots?.treads).toBe('library:wood-woodplank48')
+    expect(stair.slots?.body).toBe('library:concrete-plate')
+    expect(stair.slots?.railing).toBe('library:metal-chrome')
+    expect((stair as { treadMaterialPreset?: unknown }).treadMaterialPreset).toBeUndefined()
+  })
+
+  test('unpainted procedural node mints nothing and stays slot-less', () => {
+    useScene.getState().setScene(
+      sceneWithNode({
+        type: 'slab',
+        polygon: [
+          [0, 0],
+          [2, 0],
+          [2, 2],
+        ],
+      }),
+      ['site_test'] as never,
+    )
+
+    const slab = (useScene.getState().nodes as Record<string, SlottedNode>).node_test!
+    expect(slab.slots).toBeUndefined()
+    expect(Object.keys(useScene.getState().materials)).toHaveLength(0)
+  })
+})

packages/core/src/store/use-scene.ts

@@ -3,6 +3,7 @@
 import type { TemporalState } from 'zundo'
 import { temporal } from 'zundo'
 import { create, type StoreApi, type UseBoundStore } from 'zustand'
+import { parseMaterialRef, toSceneMaterialRef } from '../material-library'
 import { nodeRegistry } from '../registry/registry'
 import { BuildingNode } from '../schema'
 import type { Collection, CollectionId } from '../schema/collections'
@@ -18,9 +19,17 @@ import {
 import { segmentPointToRoofWallFace } from '../schema/nodes/roof-segment-walls'
 import { ShelfNode as ShelfNodeSchema } from '../schema/nodes/shelf'
 import { SiteNode } from '../schema/nodes/site'
-import { StairNode as StairNodeSchema } from '../schema/nodes/stair'
+import {
+  getEffectiveStairSurfaceMaterial,
+  StairNode as StairNodeSchema,
+} from '../schema/nodes/stair'
 import { StairSegmentNode as StairSegmentNodeSchema } from '../schema/nodes/stair-segment'
-import type { SceneMaterial, SceneMaterialId } from '../schema/scene-material'
+import { getEffectiveWallSurfaceMaterial, type WallSurfaceSide } from '../schema/nodes/wall'
+import {
+  generateSceneMaterialId,
+  type SceneMaterial,
+  type SceneMaterialId,
+} from '../schema/scene-material'
 import type { AnyNode, AnyNodeId } from '../schema/types'
 import * as nodeActions from './actions/node-actions'
 import { resetSceneHistoryPauseDepth } from './history-control'
@@ -231,49 +240,164 @@ function migrateElevatorParent(
   }
 }
 
-function migrateWallSurfaceMaterials(node: Record<string, any>) {
-  const hasInterior =
-    node.interiorMaterial !== undefined || typeof node.interiorMaterialPreset === 'string'
-  const hasExterior =
-    node.exteriorMaterial !== undefined || typeof node.exteriorMaterialPreset === 'string'
-  const legacyFinish = {
-    material: node.material,
-    materialPreset: typeof node.materialPreset === 'string' ? node.materialPreset : undefined,
+// Reuse an already-minted scene material for an identical inline legacy
+// material so a whole building painted one custom colour collapses to one
+// shared datablock (mirrors `commitSlotPaint`'s dedupe-on-match).
+function findMintedSceneMaterialRef(
+  material: unknown,
+  mintedMaterials: Record<SceneMaterialId, SceneMaterial>,
+): string | undefined {
+  const target = JSON.stringify(material)
+  for (const sceneMaterial of Object.values(mintedMaterials)) {
+    if (JSON.stringify(sceneMaterial.material) === target) {
+      return toSceneMaterialRef(sceneMaterial.id)
+    }
+  }
+  return undefined
 }
 
-  if (!(hasInterior || hasExterior)) {
-    if (legacyFinish.material === undefined && legacyFinish.materialPreset === undefined) {
+// Turn a legacy surface spec (`{ material, materialPreset }`) into a
+// `MaterialRef`: a preset that's already a `library:`/`scene:` ref is used
+// as-is; an inline material mints (or reuses) a scene material. Returns
+// undefined when the spec carries no material. Shared by every legacy→slots
+// migration below.
+function legacySpecToMaterialRef(
+  spec: { material?: unknown; materialPreset?: unknown },
+  mintedMaterials: Record<SceneMaterialId, SceneMaterial>,
+): string | undefined {
+  if (typeof spec.materialPreset === 'string' && parseMaterialRef(spec.materialPreset)) {
+    return spec.materialPreset
+  }
+  if (spec.material !== undefined) {
+    const existing = findMintedSceneMaterialRef(spec.material, mintedMaterials)
+    if (existing) return existing
+    const id = generateSceneMaterialId()
+    mintedMaterials[id] = {
+      id,
+      name: `Material ${Object.keys(mintedMaterials).length + 1}`,
+      material: spec.material as SceneMaterial['material'],
+    }
+    return toSceneMaterialRef(id)
+  }
+  return undefined
+}
+
+// Move the retired inline `material*` / `interiorMaterial*` / `exteriorMaterial*`
+// fields onto the unified `node.slots` model (interior / exterior → a
+// `library:`/`scene:` ref), minting scene materials for inline customs into
+// `mintedMaterials` (merged into the scene material map by the caller). Already
+// slot-modelled walls and walls with no legacy material are left untouched.
+function migrateWallSurfaceMaterials(
+  node: Record<string, any>,
+  mintedMaterials: Record<SceneMaterialId, SceneMaterial>,
+) {
+  if (node.slots && (node.slots.interior !== undefined || node.slots.exterior !== undefined)) {
+    return node
+  }
+
+  const slots: Record<string, string> = { ...(node.slots ?? {}) }
+  for (const side of ['interior', 'exterior'] as WallSurfaceSide[]) {
+    const spec = getEffectiveWallSurfaceMaterial(
+      node as Parameters<typeof getEffectiveWallSurfaceMaterial>[0],
+      side,
+    )
+    const ref = legacySpecToMaterialRef(spec, mintedMaterials)
+    if (ref) slots[side] = ref
+  }
+
+  if (Object.keys(slots).length === 0) {
     return node
   }
 
   return {
     ...node,
-      interiorMaterial: legacyFinish.material,
-      interiorMaterialPreset: legacyFinish.materialPreset,
-      exteriorMaterial: legacyFinish.material,
-      exteriorMaterialPreset: legacyFinish.materialPreset,
-    }
-  }
-
-  if (!hasInterior) {
-    return {
-      ...node,
-      interiorMaterial: node.exteriorMaterial,
-      interiorMaterialPreset: node.exteriorMaterialPreset,
-    }
-  }
-
-  if (!hasExterior) {
-    return {
-      ...node,
-      exteriorMaterial: node.interiorMaterial,
-      exteriorMaterialPreset: node.interiorMaterialPreset,
+    slots,
+    material: undefined,
+    materialPreset: undefined,
+    interiorMaterial: undefined,
+    interiorMaterialPreset: undefined,
+    exteriorMaterial: undefined,
+    exteriorMaterialPreset: undefined,
   }
 }
 
+// Move a kind's single legacy `material` / `materialPreset` onto its declared
+// slots. A pre-slot-model node painted one material rendered that material on
+// every part (each slot resolves `node.slots[slot]` → legacy → default), so the
+// migration writes the same ref to every slot id the kind can expose — unused
+// conditional slots are harmless. Already slot-modelled or unpainted nodes are
+// left untouched. Mirrors `migrateWallSurfaceMaterials` for single-surface and
+// whole-object kinds (slab, ceiling, fence, column, shelf).
+function migrateSingleMaterialSlots(
+  node: Record<string, any>,
+  slotIds: readonly string[],
+  mintedMaterials: Record<SceneMaterialId, SceneMaterial>,
+) {
+  if (node.slots && Object.keys(node.slots).length > 0) {
     return node
   }
 
+  const ref = legacySpecToMaterialRef(
+    { material: node.material, materialPreset: node.materialPreset },
+    mintedMaterials,
+  )
+  if (!ref) {
+    return node
+  }
+
+  const slots: Record<string, string> = {}
+  for (const slotId of slotIds) slots[slotId] = ref
+
+  return { ...node, slots, material: undefined, materialPreset: undefined }
+}
+
+// Stair carries per-role legacy fields (`treadMaterial*` / `sideMaterial*` /
+// `railingMaterial*`) plus a catch-all. Map each to its slot via the same
+// fallback chain the renderer uses (`getEffectiveStairSurfaceMaterial`):
+// tread→treads, side→body, railing→railing. Runs after
+// `migrateStairSurfaceMaterials` has normalised the legacy fields.
+function migrateStairSurfaceSlots(
+  node: Record<string, any>,
+  mintedMaterials: Record<SceneMaterialId, SceneMaterial>,
+) {
+  if (node.slots && Object.keys(node.slots).length > 0) {
+    return node
+  }
+
+  const roleToSlot = [
+    ['tread', 'treads'],
+    ['side', 'body'],
+    ['railing', 'railing'],
+  ] as const
+
+  const slots: Record<string, string> = {}
+  for (const [role, slotId] of roleToSlot) {
+    const spec = getEffectiveStairSurfaceMaterial(
+      node as Parameters<typeof getEffectiveStairSurfaceMaterial>[0],
+      role,
+    )
+    const ref = legacySpecToMaterialRef(spec, mintedMaterials)
+    if (ref) slots[slotId] = ref
+  }
+
+  if (Object.keys(slots).length === 0) {
+    return node
+  }
+
+  return {
+    ...node,
+    slots,
+    material: undefined,
+    materialPreset: undefined,
+    treadMaterial: undefined,
+    treadMaterialPreset: undefined,
+    sideMaterial: undefined,
+    sideMaterialPreset: undefined,
+    railingMaterial: undefined,
+    railingMaterialPreset: undefined,
+  }
+}
+
 function migrateStairSurfaceMaterials(node: Record<string, any>) {
   const hasRailing =
     node.railingMaterial !== undefined || typeof node.railingMaterialPreset === 'string'
@@ -414,8 +538,14 @@ function migrateRoofSurfaceMaterials(node: Record<string, any>) {
   return next
 }
 
-function migrateNodes(nodes: Record<string, any>): Record<string, AnyNode> {
+function migrateNodes(nodes: Record<string, any>): {
+  nodes: Record<string, AnyNode>
+  mintedMaterials: Record<SceneMaterialId, SceneMaterial>
+} {
   const patchedNodes = { ...nodes }
+  // Scene materials minted while moving legacy wall fields onto `node.slots`;
+  // merged into the scene material map by the caller (`setScene`).
+  const mintedMaterials: Record<SceneMaterialId, SceneMaterial> = {}
   for (const [id, node] of Object.entries(patchedNodes)) {
     // 1. Item scale migration
     if (node.type === 'item' && !('scale' in node)) {
@@ -502,6 +632,7 @@ function migrateNodes(nodes: Record<string, any>): Record<string, AnyNode> {
       if (normalized) {
         patchedNodes[id] = normalized
       }
+      patchedNodes[id] = migrateStairSurfaceSlots(patchedNodes[id], mintedMaterials)
     }
 
     if (node.type === 'stair-segment') {
@@ -512,7 +643,27 @@ function migrateNodes(nodes: Record<string, any>): Record<string, AnyNode> {
     }
 
     if (node.type === 'wall') {
-      patchedNodes[id] = migrateWallSurfaceMaterials(patchedNodes[id])
+      patchedNodes[id] = migrateWallSurfaceMaterials(patchedNodes[id], mintedMaterials)
+    }
+
+    if (node.type === 'slab' || node.type === 'ceiling') {
+      patchedNodes[id] = migrateSingleMaterialSlots(patchedNodes[id], ['surface'], mintedMaterials)
+    }
+
+    if (node.type === 'fence') {
+      patchedNodes[id] = migrateSingleMaterialSlots(
+        patchedNodes[id],
+        ['posts', 'infill', 'base', 'rail'],
+        mintedMaterials,
+      )
+    }
+
+    if (node.type === 'column') {
+      patchedNodes[id] = migrateSingleMaterialSlots(
+        patchedNodes[id],
+        ['shaft', 'base', 'capital', 'frame'],
+        mintedMaterials,
+      )
     }
 
     if (node.type === 'shelf') {
@@ -520,6 +671,11 @@ function migrateNodes(nodes: Record<string, any>): Record<string, AnyNode> {
       if (normalized) {
         patchedNodes[id] = normalized
       }
+      patchedNodes[id] = migrateSingleMaterialSlots(
+        patchedNodes[id],
+        ['shelves', 'frame', 'back'],
+        mintedMaterials,
+      )
     }
 
     if (node.type === 'elevator') {
@@ -619,7 +775,7 @@ function migrateNodes(nodes: Record<string, any>): Record<string, AnyNode> {
       }
     }
   }
-  return patchedNodes as Record<string, AnyNode>
+  return { nodes: patchedNodes as Record<string, AnyNode>, mintedMaterials }
 }
 
 function getNodeChildIds(node: AnyNode): AnyNodeId[] {
@@ -789,7 +945,11 @@ const useScene: UseSceneStore = create<SceneState>()(
 
       setScene: (nodes, rootNodeIds, extra) => {
         // Apply backward compatibility migrations
-        const patchedNodes = migrateNodes(nodes)
+        const { nodes: patchedNodes, mintedMaterials } = migrateNodes(nodes)
+        // Scene materials minted by the wall legacy→slots migration join the
+        // loaded palette (existing refs win on id collision — there are none,
+        // ids are freshly generated).
+        const materials = { ...mintedMaterials, ...(extra?.materials ?? {}) }
 
         // Remove orphans: nodes whose parentId points to a non-existent node
         const cleanedNodes = { ...patchedNodes }
@@ -811,7 +971,7 @@ const useScene: UseSceneStore = create<SceneState>()(
           rootNodeIds,
           dirtyNodes: new Set<AnyNodeId>(),
           collections: extra?.collections ?? {},
-          materials: extra?.materials ?? {},
+          materials,
         })
 
         const normalizedRootNodeIds = normalizeRootNodeIds(cleanedNodes, rootNodeIds)
@@ -829,7 +989,7 @@ const useScene: UseSceneStore = create<SceneState>()(
           rootNodeIds: normalizedRootNodeIds,
           dirtyNodes: new Set<AnyNodeId>(),
           collections: extra?.collections ?? {},
-          materials: extra?.materials ?? {},
+          materials,
         })
         // Mark all nodes as dirty to trigger re-validation
         Object.values(cleanedNodes).forEach((node) => {

packages/editor/src/index.tsx

@@ -221,7 +221,6 @@ export {
   buildRoofSurfaceMaterialPatch,
   buildSingleSurfaceMaterialPatch,
   buildStairSurfaceMaterialPatch,
-  buildWallSurfaceMaterialPatch,
   getActivePaintMaterialLabel,
   hasActivePaintMaterial,
 } from './lib/material-paint'

packages/editor/src/lib/material-paint.ts

@@ -13,7 +13,6 @@ import {
   getEffectiveRoofSurfaceMaterial,
   getEffectiveSegmentSurfaceMaterial,
   getEffectiveStairSurfaceMaterial,
-  getEffectiveWallSurfaceMaterial,
   getLibraryMaterialIdFromRef,
   type MaterialSchema,
   type MaterialTarget,
@@ -26,7 +25,6 @@ import {
   type SlabNode,
   type StairNode,
   type StairSurfaceMaterialRole,
-  type WallNode,
   type WallSurfaceSide,
 } from '@pascal-app/core'
 
@@ -78,32 +76,6 @@ export function getActivePaintMaterialLabel(material: ActivePaintMaterial | null
   return getCatalogEntryForActivePaintMaterial(material)?.label ?? 'Custom'
 }
 
-export function buildWallSurfaceMaterialPatch(
-  node: WallNode,
-  targetSide: WallSurfaceSide,
-  material: MaterialSchema | undefined,
-  materialPreset: string | undefined,
-): Partial<WallNode> {
-  const nextSurfaceMaterial = { material, materialPreset }
-  const nextInterior =
-    targetSide === 'interior'
-      ? nextSurfaceMaterial
-      : getEffectiveWallSurfaceMaterial(node, 'interior')
-  const nextExterior =
-    targetSide === 'exterior'
-      ? nextSurfaceMaterial
-      : getEffectiveWallSurfaceMaterial(node, 'exterior')
-
-  return {
-    interiorMaterial: nextInterior.material,
-    interiorMaterialPreset: nextInterior.materialPreset,
-    exteriorMaterial: nextExterior.material,
-    exteriorMaterialPreset: nextExterior.materialPreset,
-    material: undefined,
-    materialPreset: undefined,
-  }
-}
-
 export function buildRoofSurfaceMaterialPatch(
   node: RoofNode,
   targetRole: RoofSurfaceMaterialRole,

packages/nodes/src/wall/move-shared.ts

@@ -2,7 +2,9 @@ import {
   type AnyNodeId,
   DEFAULT_WALL_HEIGHT,
   getMaterialPresetByRef,
+  parseMaterialRef,
   resolveMaterial,
+  type SceneMaterialId,
   useScene,
   type WallMoveBridgePlan,
   type WallNode,
@@ -109,7 +111,25 @@ function wallSegmentExists(
   )
 }
 
+// Resolve a wall slot ref (`library:`/`scene:`) to a swatch colour, or
+// undefined when the ref is absent / dangling / colourless.
+function resolveWallSlotRefColor(ref: string | undefined): string | undefined {
+  const parsed = parseMaterialRef(ref)
+  if (!parsed) return undefined
+  if (parsed.kind === 'library') {
+    return getMaterialPresetByRef(ref)?.mapProperties.color ?? undefined
+  }
+  const sceneMaterial = useScene.getState().materials[parsed.id as SceneMaterialId]
+  return sceneMaterial ? resolveMaterial(sceneMaterial.material).color : undefined
+}
+
 export function getWallGhostColor(wall: WallNode) {
+  const slotColor =
+    resolveWallSlotRefColor(wall.slots?.interior) ?? resolveWallSlotRefColor(wall.slots?.exterior)
+  if (slotColor) {
+    return slotColor
+  }
+
   const presetColor =
     getMaterialPresetByRef(wall.materialPreset)?.mapProperties.color ??
     getMaterialPresetByRef(wall.interiorMaterialPreset)?.mapProperties.color ??

packages/nodes/src/wall/paint.ts

@@ -1,14 +1,15 @@
 import {
+  type AnyNode,
   type AnyNodeId,
   getEffectiveWallSurfaceMaterial,
-  type MaterialSchema,
   type PaintCapability,
+  type PaintPreviewArgs,
   sceneRegistry,
   type WallNode,
   type WallSurfaceSide,
 } from '@pascal-app/core'
-import { getVisibleWallMaterials } from '@pascal-app/viewer'
 import type { Material, Mesh } from 'three'
+import { buildSlotPreviewMaterial, createSlotPaintCapability } from '../shared/slot-paint'
 
 /**
  * Resolve which side of a wall the user clicked. Walls expose two
@@ -56,81 +57,59 @@ export function resolveWallRole(args: {
   return hitFace === 'front' ? 'interior' : 'exterior'
 }
 
-export function buildWallSurfaceMaterialPatch(
-  node: WallNode,
-  targetSide: WallSurfaceSide,
-  material: MaterialSchema | undefined,
-  materialPreset: string | undefined,
-): Partial<WallNode> {
-  const nextSurfaceMaterial = { material, materialPreset }
-  const nextInterior =
-    targetSide === 'interior'
-      ? nextSurfaceMaterial
-      : getEffectiveWallSurfaceMaterial(node, 'interior')
-  const nextExterior =
-    targetSide === 'exterior'
-      ? nextSurfaceMaterial
-      : getEffectiveWallSurfaceMaterial(node, 'exterior')
-
-  return {
-    interiorMaterial: nextInterior.material,
-    interiorMaterialPreset: nextInterior.materialPreset,
-    exteriorMaterial: nextExterior.material,
-    exteriorMaterialPreset: nextExterior.materialPreset,
-    material: undefined,
-    materialPreset: undefined,
-  }
+// The wall's 3-material array maps side → group index (see
+// `getVisibleWallMaterials`): 0 = edge/cap, 1 = interior, 2 = exterior.
+const WALL_SIDE_MATERIAL_INDEX: Record<WallSurfaceSide, 1 | 2> = {
+  interior: 1,
+  exterior: 2,
 }
 
 /**
- * Apply a preview to the wall's registered mesh by synthesising the
- * post-paint node, asking the viewer's `getVisibleWallMaterials` for
- * the corresponding material array, and swapping the mesh's
- * material assignment until the editor calls the returned cleanup.
+ * Preview a wall paint by swapping just the painted face's entry in the wall
+ * mesh's material array. The array is the shared cached `WallMaterials.visible`,
+ * so we clone it before swapping and restore the original reference on cleanup
+ * (never mutate the cache).
  */
-function applyWallPreview(
-  node: WallNode,
-  role: WallSurfaceSide,
-  material: MaterialSchema | undefined,
-  materialPreset: string | undefined,
-): (() => void) | null {
-  const mesh = sceneRegistry.nodes.get(node.id as AnyNodeId)
+function applyWallPreview(args: PaintPreviewArgs): (() => void) | null {
+  const { role, material, materialPreset } = args
+  const side = role as WallSurfaceSide
+  const index = WALL_SIDE_MATERIAL_INDEX[side]
+  if (!index) return null
+
+  const mesh = sceneRegistry.nodes.get(args.node.id as AnyNodeId)
   if (!(mesh && (mesh as Mesh).isMesh)) return null
   const wallMesh = mesh as Mesh
 
-  const previewNode: WallNode = {
-    ...node,
-    ...buildWallSurfaceMaterialPatch(node, role, material, materialPreset),
-  }
-  const nextMaterial = getVisibleWallMaterials(previewNode)
-  if (!nextMaterial) return null
+  const current = wallMesh.material
+  if (!Array.isArray(current)) return null
+
+  const preview = buildSlotPreviewMaterial(material, materialPreset)
+  if (!preview) return () => {}
+
+  const previous = current as Material[]
+  const next = previous.slice()
+  next[index] = preview
+  wallMesh.material = next
 
-  const previousMaterial = wallMesh.material as Material | Material[]
-  wallMesh.material = nextMaterial
   return () => {
-    wallMesh.material = previousMaterial
+    wallMesh.material = previous
   }
 }
 
 /**
- * Capability binding for the wall kind. The editor's
- * selection-manager invokes these in place of the legacy
- * `if (node.type === 'wall') { ... }` arms.
+ * Capability binding for the wall kind on the unified slot model. Painting
+ * writes `node.slots[interior|exterior]` (a `library:` ref or a minted
+ * `scene:` material) exactly like every other kind; `legacyEffective` reads
+ * the retired inline `interiorMaterial*` / `exteriorMaterial*` fields so the
+ * picker still shows the current value on a pre-migration scene.
  */
-export const wallPaint: PaintCapability = {
+export const wallPaint: PaintCapability = createSlotPaintCapability({
   resolveRole: ({ node, materialIndex, normal, localPosition }) =>
     resolveWallRole({ node: node as WallNode, materialIndex, normal, localPosition }),
-  buildPatch: ({ node, role, material, materialPreset }) =>
-    buildWallSurfaceMaterialPatch(
-      node as WallNode,
-      role as WallSurfaceSide,
-      material,
-      materialPreset,
-    ),
-  applyPreview: ({ node, role, material, materialPreset }) =>
-    applyWallPreview(node as WallNode, role as WallSurfaceSide, material, materialPreset),
-  getEffectiveMaterial: ({ node, role }) => {
+  applyPreview: applyWallPreview,
+  legacyEffective: (node: AnyNode, role: string) => {
     const spec = getEffectiveWallSurfaceMaterial(node as WallNode, role as WallSurfaceSide)
+    if (spec.material === undefined && spec.materialPreset === undefined) return null
     return { material: spec.material, materialPreset: spec.materialPreset }
   },
-}
+})

packages/nodes/src/wall/renderer.tsx

@@ -49,7 +49,19 @@ const WallRenderer = ({ node }: { node: WallNode }) => {
   const textures = useViewer((s) => s.textures)
   const colorPreset = useViewer((s) => s.colorPreset)
   const sceneTheme = useViewer((s) => s.sceneTheme)
-  const material = getVisibleWallMaterials(node, shading, textures, colorPreset, sceneTheme)
+  // Subscribe to the scene-material palette so editing a `scene:` material a
+  // wall slot references re-renders the wall live (the wall-system geometry
+  // dirty loop never fires for a material-only edit). `getMaterialsForWall`'s
+  // content hash keeps unaffected walls on their cached materials.
+  const sceneMaterials = useScene((s) => s.materials)
+  const material = getVisibleWallMaterials(
+    node,
+    shading,
+    textures,
+    colorPreset,
+    sceneTheme,
+    sceneMaterials,
+  )
 
   return (
     <mesh

packages/nodes/src/wall/slots.ts

@@ -1,13 +1,11 @@
 import { type SlotDeclaration, WALL_SLOT_DEFAULT } from '@pascal-app/core'
 
 /**
- * A wall exposes two paintable faces — interior + exterior. Painting still
- * writes the legacy `interiorMaterial*` / `exteriorMaterial*` fields via
- * `wallPaint` (the inline model isn't migrated to `node.slots` yet); this
+ * A wall exposes two paintable faces — interior + exterior. Painting writes
+ * `node.slots[interior|exterior]` via `wallPaint` like every other kind; this
  * declaration surfaces the slot list + declared defaults for the picker and
- * keeps walls on the same `{ slotId, label, default }` contract as every other
- * paintable kind. The defaults come from core so the viewer's material
- * resolver renders the identical value.
+ * keeps walls on the same `{ slotId, label, default }` contract. The defaults
+ * come from core so the viewer's material resolver renders the identical value.
  */
 export function wallSlots(): SlotDeclaration[] {
   return [

packages/viewer/src/systems/wall/wall-cutout.tsx

@@ -104,7 +104,14 @@ export const WallCutout = () => {
         const hideWall = getWallHideState(wallNode, wallMesh as Mesh, wallMode, u)
         const isDeleteHighlighted = deleteHoveredWallId === wallId
         const isSelectionHighlighted = !isDeleteHighlighted && highlightedWallIds.has(wallId)
-        const materials = getMaterialsForWall(wallNode, shading, textures, colorPreset, sceneTheme)
+        const materials = getMaterialsForWall(
+          wallNode,
+          shading,
+          textures,
+          colorPreset,
+          sceneTheme,
+          useScene.getState().materials,
+        )
 
         if (hideWall) {
           ;(wallMesh as Mesh).material = isDeleteHighlighted
@@ -145,6 +152,7 @@ export const WallCutout = () => {
           useViewer.getState().textures,
           useViewer.getState().colorPreset,
           useViewer.getState().sceneTheme,
+          useScene.getState().materials,
         )
         const current = wallMesh.material as Material | Material[]
         snapshot.set(wallMesh, current)

packages/viewer/src/systems/wall/wall-materials.ts

@@ -4,9 +4,12 @@ import {
   getWallSurfaceMaterialSignature,
   parseMaterialRef,
   resolveMaterial,
+  type SceneMaterial,
+  type SceneMaterialId,
   WALL_SLOT_DEFAULT,
   type WallNode,
   type WallSurfaceMaterialSpec,
+  type WallSurfaceSide,
 } from '@pascal-app/core'
 import { Color, type Material } from 'three'
 import { Fn, float, fract, length, mix, positionLocal, smoothstep, step, vec2 } from 'three/tsl'
@@ -19,9 +22,12 @@ import {
   createMaterialFromPresetRef,
   createSurfaceRoleMaterial,
   type RenderShading,
+  resolveMaterialRef,
   resolveSurfaceColor,
 } from '../../lib/materials'
 
+type SceneMaterials = Record<SceneMaterialId, SceneMaterial> | undefined
+
 const DEFAULT_WALL_COLOR = '#f2f0ed'
 
 const WALL_HIGHLIGHT_PROFILES = {
@@ -100,6 +106,77 @@ function resolveWallSlotDefault(slotDefault: string, shading: RenderShading): Ma
   return createDefaultMaterial(slotDefault, 0.9, shading)
 }
 
+// Slot-first resolution for one wall face, matching every other paintable kind:
+//   node.slots[side] ref → legacy inline fields → declared slot default.
+// A dangling `scene:` ref (material deleted / copied across scenes) falls back
+// to the declared default — it never blocks rendering (the dangling-ref rule).
+function resolveWallFaceMaterial(
+  wallNode: WallNode,
+  side: WallSurfaceSide,
+  shading: RenderShading,
+  sceneMaterials: SceneMaterials,
+): Material {
+  const ref = wallNode.slots?.[side]
+  if (ref) {
+    return (
+      resolveMaterialRef(ref, sceneMaterials, shading) ??
+      resolveWallSlotDefault(WALL_SLOT_DEFAULT[side], shading)
+    )
+  }
+
+  const spec = getEffectiveWallSurfaceMaterial(wallNode, side)
+  if (hasExplicitMaterial(spec)) {
+    return getSurfaceVisibleMaterial(spec, shading)
+  }
+
+  return resolveWallSlotDefault(WALL_SLOT_DEFAULT[side], shading)
+}
+
+// Cache-key fragment for one face: the slot ref plus, for a `scene:` ref, the
+// referenced material's *content* — so editing a scene material assigned to a
+// wall invalidates the cache (a `library:` ref is static catalog content, so
+// its id alone is enough). Falls back to the legacy signature when unmigrated.
+function wallFaceMaterialSignature(
+  wallNode: WallNode,
+  side: WallSurfaceSide,
+  sceneMaterials: SceneMaterials,
+): string {
+  const ref = wallNode.slots?.[side]
+  if (ref) {
+    const parsed = parseMaterialRef(ref)
+    if (parsed?.kind === 'scene') {
+      return JSON.stringify({
+        ref,
+        material: sceneMaterials?.[parsed.id as SceneMaterialId]?.material ?? null,
+      })
+    }
+    return JSON.stringify({ ref })
+  }
+  return getWallSurfaceMaterialSignature(getEffectiveWallSurfaceMaterial(wallNode, side))
+}
+
+// Slot-first tint for the cutaway/invisible wall variant.
+function resolveWallFaceColor(
+  wallNode: WallNode,
+  side: WallSurfaceSide,
+  sceneMaterials: SceneMaterials,
+  fallback: string,
+): string {
+  const ref = wallNode.slots?.[side]
+  if (ref) {
+    const parsed = parseMaterialRef(ref)
+    if (parsed?.kind === 'library') {
+      return getMaterialPresetByRef(ref)?.mapProperties?.color ?? fallback
+    }
+    if (parsed?.kind === 'scene') {
+      const sceneMaterial = sceneMaterials?.[parsed.id as SceneMaterialId]
+      return sceneMaterial ? resolveMaterial(sceneMaterial.material).color : fallback
+    }
+    return fallback
+  }
+  return getSurfaceColor(getEffectiveWallSurfaceMaterial(wallNode, side), fallback)
+}
+
 function getSurfaceColor(spec: WallSurfaceMaterialSpec, fallback = DEFAULT_WALL_COLOR): string {
   const preset = getMaterialPresetByRef(spec.materialPreset)
   if (preset?.mapProperties?.color) {
@@ -185,15 +262,15 @@ function disposeOwnedMaterials(materials: WallMaterialArray[]) {
   })
 }
 
-export function getWallMaterialHash(wallNode: WallNode, shading: RenderShading): string {
+export function getWallMaterialHash(
+  wallNode: WallNode,
+  shading: RenderShading,
+  sceneMaterials?: SceneMaterials,
+): string {
   return JSON.stringify({
     shading,
-    interior: getWallSurfaceMaterialSignature(
-      getEffectiveWallSurfaceMaterial(wallNode, 'interior'),
-    ),
-    exterior: getWallSurfaceMaterialSignature(
-      getEffectiveWallSurfaceMaterial(wallNode, 'exterior'),
-    ),
+    interior: wallFaceMaterialSignature(wallNode, 'interior', sceneMaterials),
+    exterior: wallFaceMaterialSignature(wallNode, 'exterior', sceneMaterials),
   })
 }
 
@@ -203,10 +280,11 @@ export function getMaterialsForWall(
   textures = true,
   colorPreset: ColorPreset = 'clay',
   sceneTheme?: string,
+  sceneMaterials?: SceneMaterials,
 ): WallMaterials {
   const cacheKey = `${wallNode.id}-${shading}-${textures}-${colorPreset}-${sceneTheme ?? 'base'}`
   const materialHash = textures
-    ? getWallMaterialHash(wallNode, shading)
+    ? getWallMaterialHash(wallNode, shading, sceneMaterials)
     : JSON.stringify({ textures, colorPreset, sceneTheme })
 
   const existing = wallMaterialCache.get(cacheKey)
@@ -224,23 +302,17 @@ export function getMaterialsForWall(
     ])
   }
 
-  const interiorSpec = getEffectiveWallSurfaceMaterial(wallNode, 'interior')
-  const exteriorSpec = getEffectiveWallSurfaceMaterial(wallNode, 'exterior')
   const wallRoleMaterial = createSurfaceRoleMaterial('wall', colorPreset, undefined, sceneTheme)
 
-  // Colored mode: an unpainted face takes its declared slot default (parity
-  // with the retired DEFAULT_WALL_MATERIAL); only an explicit preset/material
-  // keeps a texture. Textures-off collapses every face to the themed wall role
-  // (the guaranteed escape hatch). The edge/cap slot (index 0) stays role-based.
+  // Colored mode: each face resolves slot-first (node.slots ref → legacy inline
+  // fields → declared slot default, parity with the retired DEFAULT_WALL_MATERIAL).
+  // Textures-off collapses every face to the themed wall role (the guaranteed
+  // escape hatch). The edge/cap slot (index 0) stays role-based.
   const visible: WallMaterialArray = textures
     ? [
         wallRoleMaterial,
-        hasExplicitMaterial(interiorSpec)
-          ? getSurfaceVisibleMaterial(interiorSpec, shading)
-          : resolveWallSlotDefault(WALL_SLOT_DEFAULT.interior, shading),
-        hasExplicitMaterial(exteriorSpec)
-          ? getSurfaceVisibleMaterial(exteriorSpec, shading)
-          : resolveWallSlotDefault(WALL_SLOT_DEFAULT.exterior, shading),
+        resolveWallFaceMaterial(wallNode, 'interior', shading, sceneMaterials),
+        resolveWallFaceMaterial(wallNode, 'exterior', shading, sceneMaterials),
       ]
     : [wallRoleMaterial, wallRoleMaterial, wallRoleMaterial]
 
@@ -248,11 +320,15 @@ export function getMaterialsForWall(
   const invisible: WallMaterialArray = [
     createInvisibleWallMaterial(wallRoleColor, textures ? shading : 'solid'),
     createInvisibleWallMaterial(
-      textures ? getSurfaceColor(interiorSpec, wallRoleColor) : wallRoleColor,
+      textures
+        ? resolveWallFaceColor(wallNode, 'interior', sceneMaterials, wallRoleColor)
+        : wallRoleColor,
       textures ? shading : 'solid',
     ),
     createInvisibleWallMaterial(
-      textures ? getSurfaceColor(exteriorSpec, wallRoleColor) : wallRoleColor,
+      textures
+        ? resolveWallFaceColor(wallNode, 'exterior', sceneMaterials, wallRoleColor)
+        : wallRoleColor,
       textures ? shading : 'solid',
     ),
   ]
@@ -290,6 +366,8 @@ export function getVisibleWallMaterials(
   textures = true,
   colorPreset: ColorPreset = 'clay',
   sceneTheme?: string,
+  sceneMaterials?: SceneMaterials,
 ): WallMaterialArray {
-  return getMaterialsForWall(wallNode, shading, textures, colorPreset, sceneTheme).visible
+  return getMaterialsForWall(wallNode, shading, textures, colorPreset, sceneTheme, sceneMaterials)
+    .visible
 }