feat(paint-slots): unified slot defaults + paint for slab, ceiling, wall (phase 5)

Brings slab, ceiling, and wall onto the unified slot contract the shelf
established, so each declares its paintable slots with a declarative default and
(slab/ceiling) is painted through the registry capabilities.paint dispatch.

- Shared helper packages/nodes/src/shared/slot-paint.ts: a node.slots-based
  PaintCapability factory (commit/resolve/effective generic; preview injected).
  Distinct from surface-paint.ts, which writes the legacy inline node.material.
- slab: schema slots; def.geometry resolves node.slots.surface -> legacy
  material -> declared default, tags the mesh userData.slotId; slabPaint +
  capabilities.slots. Retires DEFAULT_SLAB_MATERIAL in the slab path.
- ceiling: schema slots; material builders extracted to ceiling/materials.ts
  (shared by renderer + paint preview, built BackSide so the hover preview is
  visible from below); renderer resolves the slot; ceilingPaint + slots.
- wall: WALL_SLOT_DEFAULT in core; the viewer's getMaterialsForWall renders an
  unpainted face with its declared default instead of the themed wall role;
  capabilities.slots (interior/exterior). wallPaint's inline interior/exterior
  fields are unchanged (node.slots migration is a later step).
- selection-manager + material-paint: drop slab/ceiling from the legacy
  single-surface arms (now registry-driven).

Behavior change (intended, matches the shelf precedent + the phase-5 plan):
colored-mode UNPAINTED slab/ceiling/wall surfaces now render their fixed slot
default (#e5e5e5 / #f5f5dc / #ffffff) instead of the theme role colour. The
textures-off (monochrome) role collapse is unchanged — the escape hatch.

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

packages/nodes/src/ceiling/definition.ts

@@ -10,8 +10,10 @@ import {
   ceilingMoveVertexAffordance,
 } from './floorplan-affordances'
 import { ceilingFloorplanMoveTarget } from './floorplan-move'
+import { ceilingPaint } from './paint'
 import { ceilingParametrics } from './parametrics'
 import { CeilingNode } from './schema'
+import { ceilingSlots } from './slots'
 
 const HEIGHT_HANDLE_OFFSET = 0.22
 const MIN_CEILING_HEIGHT = 0.5
@@ -102,6 +104,10 @@ export const ceilingDefinition: NodeDefinition<typeof CeilingNode> = {
     },
     duplicable: true,
     deletable: true,
+    // Unified slot model: one paintable underside surface with a declared
+    // default, painted through the registry `capabilities.paint` dispatch.
+    slots: () => ceilingSlots(),
+    paint: ceilingPaint,
   },
 
   relations: {

packages/nodes/src/ceiling/materials.ts

@@ -0,0 +1,80 @@
+import {
+  getMaterialPresetByRef,
+  parseMaterialRef,
+  resolveMaterial,
+  type SceneMaterial,
+  type SceneMaterialId,
+} from '@pascal-app/core'
+import { float, mix, positionWorld, smoothstep } from 'three/tsl'
+import { BackSide, FrontSide, MeshBasicNodeMaterial } from 'three/webgpu'
+
+/**
+ * Ceiling material builders, shared by the renderer (mesh appearance) and the
+ * paint capability (hover preview). A ceiling is a flat tinted surface: the
+ * underside (`bottom`, seen from inside the room, `BackSide`) is opaque, while
+ * the `top` carries a transparent TSL grid overlay used while placing /
+ * selecting ceiling-hosted items. Both derive from a single colour, so slot
+ * painting resolves a colour and rebuilds these — it never applies a PBR map.
+ */
+
+const gridScale = 5
+const gridX = positionWorld.x.mul(gridScale).fract()
+const gridY = positionWorld.z.mul(gridScale).fract()
+const lineWidth = 0.05
+const lineX = smoothstep(lineWidth, 0, gridX).add(smoothstep(1.0 - lineWidth, 1.0, gridX))
+const lineY = smoothstep(lineWidth, 0, gridY).add(smoothstep(1.0 - lineWidth, 1.0, gridY))
+const gridPattern = lineX.max(lineY)
+const gridOpacity = mix(float(0.2), float(0.6), gridPattern)
+
+export type CeilingMaterials = {
+  topMaterial: MeshBasicNodeMaterial
+  bottomMaterial: MeshBasicNodeMaterial
+}
+
+function createCeilingMaterials(color = '#999999'): CeilingMaterials {
+  const topMaterial = new MeshBasicNodeMaterial({
+    color,
+    transparent: true,
+    depthWrite: false,
+    side: FrontSide,
+  })
+  topMaterial.opacityNode = gridOpacity
+
+  const bottomMaterial = new MeshBasicNodeMaterial({
+    color,
+    transparent: true,
+    side: BackSide,
+  })
+
+  return { topMaterial, bottomMaterial }
+}
+
+const ceilingMaterialCache = new Map<string, CeilingMaterials>()
+
+export function getCeilingMaterials(color = '#999999'): CeilingMaterials {
+  const cached = ceilingMaterialCache.get(color)
+  if (cached) return cached
+  const materials = createCeilingMaterials(color)
+  ceilingMaterialCache.set(color, materials)
+  return materials
+}
+
+/**
+ * Resolve a slot `MaterialRef` to a flat colour for the ceiling surface.
+ * `library:` refs use the catalog preset's base colour; `scene:` refs use the
+ * stored material's colour. Returns null for a dangling / unparseable ref so
+ * the caller falls back to its default.
+ */
+export function ceilingColorFromRef(
+  ref: string | undefined,
+  sceneMaterials: Record<SceneMaterialId, SceneMaterial> | undefined,
+): string | null {
+  const parsed = parseMaterialRef(ref)
+  if (!parsed) return null
+  if (parsed.kind === 'library') {
+    return getMaterialPresetByRef(ref)?.mapProperties.color ?? null
+  }
+  const sceneMaterial = sceneMaterials?.[parsed.id as SceneMaterialId]
+  if (!sceneMaterial) return null
+  return resolveMaterial(sceneMaterial.material).color ?? null
+}

packages/nodes/src/ceiling/paint.ts

@@ -0,0 +1,42 @@
+import {
+  type AnyNode,
+  type CeilingNode,
+  getMaterialPresetByRef,
+  resolveMaterial,
+} from '@pascal-app/core'
+import type { Mesh } from 'three'
+import { createSlotPaintCapability } from '../shared/slot-paint'
+import { getCeilingMaterials } from './materials'
+
+/**
+ * Ceiling paint on the unified slot model. A ceiling has one paintable surface,
+ * so every hit resolves to `surface`; commit writes `node.slots.surface`. The
+ * preview swaps the registered underside mesh to the ceiling's own flat-tinted
+ * material (built `BackSide`, the way it renders), so the hover preview matches
+ * the committed result — a generic PBR preview would be invisible from below.
+ */
+export const ceilingPaint = createSlotPaintCapability({
+  resolveRole: () => 'surface',
+  applyPreview: ({ material, materialPreset, root }) => {
+    const color = materialPreset
+      ? (getMaterialPresetByRef(materialPreset)?.mapProperties.color ?? null)
+      : material
+        ? (resolveMaterial(material).color ?? null)
+        : null
+    if (!color) return () => {}
+    const mesh = root as Mesh
+    if (!mesh.isMesh) return null
+    const previous = mesh.material
+    mesh.material = getCeilingMaterials(color).bottomMaterial
+    return () => {
+      mesh.material = previous
+    }
+  },
+  legacyEffective: (node: AnyNode) => {
+    const ceiling = node as CeilingNode
+    if (ceiling.materialPreset || ceiling.material) {
+      return { material: ceiling.material, materialPreset: ceiling.materialPreset }
+    }
+    return null
+  },
+})

packages/nodes/src/ceiling/renderer.tsx

@@ -15,53 +15,15 @@ import {
   useViewer,
 } from '@pascal-app/viewer'
 import { useEffect, useLayoutEffect, useMemo, useRef } from 'react'
-import { float, mix, positionWorld, smoothstep } from 'three/tsl'
-import { BackSide, FrontSide, type Mesh, MeshBasicNodeMaterial } from 'three/webgpu'
+import { BackSide, type Mesh } from 'three/webgpu'
 import { createPlaceholderGeometry } from '../shared/placeholder-geometry'
+import { ceilingColorFromRef, getCeilingMaterials } from './materials'
+import { CEILING_SLOT_DEFAULT_COLOR } from './slots'
 
 function createEmptyGeometry() {
   return createPlaceholderGeometry()
 }
 
-const gridScale = 5
-const gridX = positionWorld.x.mul(gridScale).fract()
-const gridY = positionWorld.z.mul(gridScale).fract()
-const lineWidth = 0.05
-const lineX = smoothstep(lineWidth, 0, gridX).add(smoothstep(1.0 - lineWidth, 1.0, gridX))
-const lineY = smoothstep(lineWidth, 0, gridY).add(smoothstep(1.0 - lineWidth, 1.0, gridY))
-const gridPattern = lineX.max(lineY)
-const gridOpacity = mix(float(0.2), float(0.6), gridPattern)
-
-function createCeilingMaterials(color = '#999999') {
-  const topMaterial = new MeshBasicNodeMaterial({
-    color,
-    transparent: true,
-    depthWrite: false,
-    side: FrontSide,
-  })
-  topMaterial.opacityNode = gridOpacity
-
-  const bottomMaterial = new MeshBasicNodeMaterial({
-    color,
-    transparent: true,
-    side: BackSide,
-  })
-
-  return { topMaterial, bottomMaterial }
-}
-
-const ceilingMaterialCache = new Map<string, ReturnType<typeof createCeilingMaterials>>()
-
-function getCeilingMaterials(color = '#999999') {
-  const cacheKey = color
-  const cached = ceilingMaterialCache.get(cacheKey)
-  if (cached) return cached
-
-  const materials = createCeilingMaterials(color)
-  ceilingMaterialCache.set(cacheKey, materials)
-  return materials
-}
-
 export const CeilingRenderer = ({ node }: { node: CeilingNode }) => {
   const ref = useRef<Mesh>(null!)
   const placeholderGeometry = useMemo(createEmptyGeometry, [])
@@ -80,6 +42,9 @@ export const CeilingRenderer = ({ node }: { node: CeilingNode }) => {
   const textures = useViewer((s) => s.textures)
   const colorPreset = useViewer((s) => s.colorPreset)
   const sceneTheme = useViewer((s) => s.sceneTheme)
+  // Subscribe to the scene-material library so editing a `scene:` material the
+  // ceiling slot references re-tints it live.
+  const sceneMaterials = useScene((s) => s.materials)
   const liveTransform = useLiveTransforms((s) => s.get(node.id))
   const ceilingY = (node.height ?? 2.5) - 0.01 + (liveTransform?.position[1] ?? 0)
   const position: [number, number, number] = [
@@ -97,18 +62,15 @@ export const CeilingRenderer = ({ node }: { node: CeilingNode }) => {
   )
 
   const materials = useMemo(() => {
-    // Untextured ceilings (and everything in textures-off mode) take the themed
-    // 'ceiling' role colour; only an explicit preset/material keeps a texture.
-    const hasExplicit = Boolean(node.materialPreset || node.material)
-    if (!textures || !hasExplicit) {
-      // Bottom (seen from inside the room, looking up) stays opaque so the
-      // ceiling reads as a solid surface. Top uses the transparent
-      // grid-pattern material so the ceiling stays see-through whenever
-      // the editor reveals the `ceiling-grid` overlay (placing a
-      // ceiling-hosted item, or selecting one of its children — e.g.
-      // after committing a placement). Without this the top mesh shipped
-      // an opaque surface-role material, so a top-down camera lost view
-      // of everything under the ceiling once the overlay turned on.
+    // Textures-off mode takes the themed 'ceiling' role colour — the guaranteed
+    // escape hatch, independent of any slot override. The bottom (seen from
+    // inside the room, looking up) stays opaque so the ceiling reads as a solid
+    // surface; the top keeps the transparent grid material so a top-down camera
+    // can see through the ceiling whenever the `ceiling-grid` overlay is
+    // revealed (placing a ceiling-hosted item, or selecting one of its
+    // children). Without that the top mesh would ship an opaque surface-role
+    // material and a top-down camera would lose everything under the ceiling.
+    if (!textures) {
       const ceilingColor = resolveSurfaceColor('ceiling', colorPreset, sceneTheme)
       return {
         topMaterial: getCeilingMaterials(ceilingColor).topMaterial,
@@ -116,14 +78,26 @@ export const CeilingRenderer = ({ node }: { node: CeilingNode }) => {
       }
     }
 
-    const preset = getMaterialPresetByRef(node.materialPreset)
-    const props = preset?.mapProperties ?? resolveMaterial(node.material)
-    const color = props.color || '#999999'
-    return getCeilingMaterials(color)
+    // Unified slot override — shared scene material or catalog `library:` finish
+    // (resolved to its base colour; a ceiling renders flat-tinted, not mapped).
+    const slotColor = ceilingColorFromRef(node.slots?.surface, sceneMaterials)
+    if (slotColor) return getCeilingMaterials(slotColor)
+
+    // Legacy inline material / preset (scenes painted before the slot model).
+    if (node.materialPreset || node.material) {
+      const preset = getMaterialPresetByRef(node.materialPreset)
+      const props = preset?.mapProperties ?? resolveMaterial(node.material)
+      return getCeilingMaterials(props.color || '#999999')
+    }
+
+    // Declared slot default.
+    return getCeilingMaterials(CEILING_SLOT_DEFAULT_COLOR)
   }, [
     textures,
     colorPreset,
     sceneTheme,
+    sceneMaterials,
+    node.slots,
     node.materialPreset,
     node.material,
     node.material?.preset,

packages/nodes/src/ceiling/slots.ts

@@ -0,0 +1,11 @@
+import type { SlotDeclaration } from '@pascal-app/core'
+
+export type CeilingSlotId = 'surface'
+
+// Visual parity with the retired DEFAULT_CEILING_MATERIAL (warm beige).
+export const CEILING_SLOT_DEFAULT_COLOR = '#f5f5dc'
+
+/** A ceiling exposes a single paintable underside surface. */
+export function ceilingSlots(): SlotDeclaration[] {
+  return [{ slotId: 'surface', label: 'Surface', default: CEILING_SLOT_DEFAULT_COLOR }]
+}

packages/nodes/src/shared/slot-paint.ts

@@ -0,0 +1,211 @@
+import {
+  type AnyNode,
+  type AnyNodeId,
+  generateSceneMaterialId,
+  type MaterialSchema,
+  type PaintCapability,
+  type PaintPreviewArgs,
+  type PaintResolveArgs,
+  parseMaterialRef,
+  type SceneMaterial,
+  type SceneMaterialId,
+  toSceneMaterialRef,
+  useScene,
+} from '@pascal-app/core'
+import { createMaterial, createMaterialFromPresetRef, useViewer } from '@pascal-app/viewer'
+import type { Material, Mesh, Object3D } from 'three'
+
+/**
+ * Shared paint capability for procedural kinds on the unified slot model
+ * (`node.slots: Record<slotId, MaterialRef>` + the shared scene-material
+ * palette) — the same data shape items derive from their GLB and the shelf
+ * declares via `capabilities.slots`. Distinct from `surface-paint.ts`, which
+ * writes the legacy inline `node.material` copy the plan is retiring.
+ *
+ * The commit / resolve / effective-material logic is identical across kinds;
+ * only the slot-resolution from a pointer hit and the mesh preview differ, so
+ * those are injected per kind.
+ */
+
+type SlotsNode = AnyNode & { slots?: Record<string, string> }
+
+function deepEqual(a: unknown, b: unknown): boolean {
+  if (Object.is(a, b)) return true
+  if (typeof a !== typeof b) return false
+  if (a === null || b === null) return false
+  if (Array.isArray(a) || Array.isArray(b)) {
+    if (!Array.isArray(a) || !Array.isArray(b) || a.length !== b.length) return false
+    for (let index = 0; index < a.length; index += 1) {
+      if (!deepEqual(a[index], b[index])) return false
+    }
+    return true
+  }
+  if (typeof a === 'object') {
+    const aRecord = a as Record<string, unknown>
+    const bRecord = b as Record<string, unknown>
+    const aKeys = Object.keys(aRecord)
+    const bKeys = Object.keys(bRecord)
+    if (aKeys.length !== bKeys.length) return false
+    for (const key of aKeys) {
+      if (!Object.hasOwn(bRecord, key)) return false
+      if (!deepEqual(aRecord[key], bRecord[key])) return false
+    }
+    return true
+  }
+  return false
+}
+
+function findMatchingSceneMaterial(
+  materials: Record<SceneMaterialId, SceneMaterial>,
+  material: MaterialSchema,
+): SceneMaterial | null {
+  for (const sceneMaterial of Object.values(materials)) {
+    if (deepEqual(sceneMaterial.material, material)) return sceneMaterial
+  }
+  return null
+}
+
+function commitSlotPaint(
+  node: SlotsNode,
+  role: string,
+  material: MaterialSchema | undefined,
+  materialPreset: string | undefined,
+): void {
+  const nodeId = node.id as AnyNodeId
+  const state = useScene.getState()
+  const currentNode = (state.nodes[nodeId] as SlotsNode | undefined) ?? node
+
+  let ref: string | undefined
+  let newSceneMaterial: SceneMaterial | null = null
+
+  if (material === undefined && materialPreset === undefined) {
+    ref = undefined
+  } else if (materialPreset) {
+    ref = materialPreset
+  } else if (material) {
+    const existing = findMatchingSceneMaterial(state.materials, material)
+    if (existing) {
+      ref = toSceneMaterialRef(existing.id)
+    } else {
+      const id = generateSceneMaterialId()
+      newSceneMaterial = {
+        id,
+        name: `Material ${Object.keys(state.materials).length + 1}`,
+        material,
+      }
+      ref = toSceneMaterialRef(id)
+    }
+  } else {
+    return
+  }
+
+  const nextSlots = { ...(currentNode.slots ?? {}) }
+  if (ref) nextSlots[role] = ref
+  else delete nextSlots[role]
+
+  if (newSceneMaterial) {
+    // Creating the scene material and setting the slot ref are one logical
+    // edit, so apply both in a single `set` — zundo records one history entry,
+    // and one undo removes both the ref and its (now orphaned) material.
+    const sceneMaterial = newSceneMaterial
+    useScene.setState((s) => {
+      if (s.readOnly) return s
+      const node2 = s.nodes[nodeId] as SlotsNode | undefined
+      if (!node2) return s
+      return {
+        materials: { ...s.materials, [sceneMaterial.id as SceneMaterialId]: sceneMaterial },
+        nodes: {
+          ...s.nodes,
+          [nodeId]: { ...node2, slots: nextSlots } as AnyNode,
+        },
+      }
+    })
+    useScene.getState().markDirty(nodeId)
+    return
+  }
+
+  state.updateNode(nodeId, { slots: nextSlots } as Partial<AnyNode>)
+}
+
+/** Preview material for a slot paint — mirrors the commit's resolution. */
+export function buildSlotPreviewMaterial(
+  material: MaterialSchema | undefined,
+  materialPreset: string | undefined,
+): Material | null {
+  const shading = useViewer.getState().shading
+  if (materialPreset) return createMaterialFromPresetRef(materialPreset, shading)
+  if (material) return createMaterial(material, shading)
+  return null
+}
+
+/**
+ * Preview for kinds whose meshes are produced by `def.geometry` and tagged
+ * with `userData.slotId` (+ `__fromGeometry`). Swaps every builder mesh whose
+ * slot matches `role`, leaving hosted-child meshes (which can carry a colliding
+ * `userData.slotId` from their own GLB) untouched.
+ */
+export function previewGeometrySlot(args: PaintPreviewArgs): (() => void) | null {
+  const { role, root, material, materialPreset } = args
+  const preview = buildSlotPreviewMaterial(material, materialPreset)
+  if (!preview) return () => {}
+
+  const restores: Array<() => void> = []
+  ;(root as Object3D).traverse((object) => {
+    const mesh = object as Mesh
+    if (!mesh.isMesh) return
+    const userData = mesh.userData as { slotId?: string | null; __fromGeometry?: boolean }
+    if (userData.__fromGeometry !== true) return
+    if (userData.slotId !== role) return
+    const previous = mesh.material
+    mesh.material = preview
+    restores.push(() => {
+      mesh.material = previous
+    })
+  })
+
+  if (restores.length === 0) return null
+  return () => {
+    for (let index = restores.length - 1; index >= 0; index -= 1) restores[index]?.()
+  }
+}
+
+export type SlotPaintConfig = {
+  /** Resolve the slot id for a pointer hit (`null` = not paintable here). */
+  resolveRole: (args: PaintResolveArgs) => string | null
+  /** Apply a preview to the registered mesh subtree for `role`. */
+  applyPreview: (args: PaintPreviewArgs) => (() => void) | null
+  /**
+   * Optional legacy fallback for the picker's current-value indicator — read
+   * when no `node.slots[role]` ref exists yet (e.g. a scene painted before the
+   * kind moved onto the slot model still carries inline `material`/`preset`).
+   */
+  legacyEffective?: (
+    node: AnyNode,
+    role: string,
+  ) => { material: MaterialSchema | undefined; materialPreset: string | undefined } | null
+}
+
+export function createSlotPaintCapability(config: SlotPaintConfig): PaintCapability {
+  return {
+    resolveRole: config.resolveRole,
+    buildPatch: ({ node, role, materialPreset }) => {
+      const slots = { ...((node as SlotsNode).slots ?? {}) }
+      if (materialPreset) slots[role] = materialPreset
+      else delete slots[role]
+      return { slots } as Partial<AnyNode>
+    },
+    commit: ({ node, role, material, materialPreset }) =>
+      commitSlotPaint(node as SlotsNode, role, material, materialPreset),
+    applyPreview: config.applyPreview,
+    getEffectiveMaterial: ({ node, role }) => {
+      const ref = (node as SlotsNode).slots?.[role]
+      const parsed = parseMaterialRef(ref)
+      if (parsed) {
+        if (parsed.kind === 'library') return { material: undefined, materialPreset: ref }
+        const sceneMaterial = useScene.getState().materials[parsed.id as SceneMaterialId]
+        if (sceneMaterial) return { material: sceneMaterial.material, materialPreset: undefined }
+      }
+      return config.legacyEffective?.(node, role) ?? null
+    },
+  }
+}

packages/nodes/src/slab/definition.ts

@@ -12,8 +12,10 @@ import {
 } from './floorplan-affordances'
 import { slabFloorplanMoveTarget } from './floorplan-move'
 import { buildSlabGeometry } from './geometry'
+import { slabPaint } from './paint'
 import { slabParametrics } from './parametrics'
 import { SlabNode } from './schema'
+import { slabSlots } from './slots'
 
 const HEIGHT_HANDLE_OFFSET = 0.22
 const MIN_SLAB_ELEVATION = 0.02
@@ -155,6 +157,10 @@ export const slabDefinition: NodeDefinition<typeof SlabNode> = {
     },
     duplicable: true,
     deletable: true,
+    // Unified slot model: one paintable floor surface with a declared default,
+    // painted through the registry `capabilities.paint` dispatch like the shelf.
+    slots: () => slabSlots(),
+    paint: slabPaint,
   },
 
   relations: {

packages/nodes/src/slab/geometry.ts

@@ -1,25 +1,27 @@
-import { getMaterialPresetByRef, type SlabNode } from '@pascal-app/core'
+import { type GeometryContext, getMaterialPresetByRef, type SlabNode } from '@pascal-app/core'
 import {
   applyMaterialPresetToMaterials,
   type ColorPreset,
   createDefaultMaterial,
   createMaterial,
   createSurfaceRoleMaterial,
-  DEFAULT_SLAB_MATERIAL,
   generateSlabGeometry,
   type RenderShading,
+  resolveMaterialRef,
 } from '@pascal-app/viewer'
 import { FrontSide, Group, type Material, Mesh, type Texture } from 'three'
+import { SLAB_SLOT_DEFAULT_COLOR } from './slots'
 
 /**
  * Stage B builder for slab. Reuses `generateSlabGeometry` (pure
  * triangulation + hole CSG from viewer) and the same material cache
  * pattern the legacy slab renderer used.
  *
- * Materials are cached by `{material, materialPreset}` signature so
- * slabs sharing settings share the GPU resource. Cached entry mutation
- * (preset apply) is preserved — async texture loads still update the
- * rendered material after re-mount.
+ * Materials follow the unified slot model: the single `surface` slot resolves
+ * `node.slots.surface` (a shared scene material or `library:` finish) → the
+ * legacy inline `node.material` / `materialPreset` (pre-slot-model scenes) →
+ * the declared slot default colour. Textures-off collapses to the themed
+ * `floor` role — the guaranteed monochrome escape hatch.
  */
 type SlabMaterial = Material & {
   alphaMap?: Texture | null
@@ -35,19 +37,39 @@ function getSlabMaterial(
   shading: RenderShading,
   textures: boolean,
   colorPreset: ColorPreset,
-  sceneTheme?: string,
+  sceneTheme: string | undefined,
+  sceneMaterials: GeometryContext['materials'],
 ): Material {
-  // Untextured slabs (and everything in textures-off mode) take the themed
-  // 'floor' role colour. createSurfaceRoleMaterial returns a shared cached
-  // material, so it is returned as-is without the mutation below.
-  // FrontSide — DoubleSide on the role material's NodeMaterial poisons the
-  // MRT scene pass (see `materials.ts` line 77 / glazing fix 9400f1c5).
-  // Slab side faces still render correctly because `generateSlabGeometry`
-  // produces outward-facing normals on the top, bottom, and perimeter.
-  if (!textures || (!node.materialPreset && !node.material)) {
+  // Textures-off mode takes the themed 'floor' role colour — the guaranteed
+  // escape hatch, independent of any slot override. createSurfaceRoleMaterial
+  // returns a shared cached material. FrontSide — DoubleSide on the role
+  // material's NodeMaterial poisons the MRT scene pass (see `materials.ts`
+  // line 77 / glazing fix 9400f1c5). Slab side faces still render correctly
+  // because `generateSlabGeometry` produces outward-facing normals.
+  if (!textures) {
     return createSurfaceRoleMaterial('floor', colorPreset, FrontSide, sceneTheme)
   }
 
+  // Unified slot override — shared scene material or catalog `library:` finish.
+  const slotRef = node.slots?.surface
+  if (slotRef) {
+    const resolved = resolveMaterialRef(slotRef, sceneMaterials, shading)
+    if (resolved) return resolved
+  }
+
+  // Legacy inline material / preset, for scenes painted before the slot model.
+  if (node.materialPreset || node.material) {
+    return getLegacySlabMaterial(node, shading)
+  }
+
+  // Declared slot default (visual parity with the retired DEFAULT_SLAB_MATERIAL).
+  return createDefaultMaterial(SLAB_SLOT_DEFAULT_COLOR, 0.8, shading)
+}
+
+function getLegacySlabMaterial(node: SlabNode, shading: RenderShading): Material {
+  // Cached by `{material, materialPreset}` signature so slabs sharing settings
+  // share the GPU resource; cached entry mutation (preset apply) is preserved
+  // so async texture loads still update the rendered material after re-mount.
   const cacheKey = JSON.stringify({
     shading,
     material: node.material ?? null,
@@ -61,7 +83,7 @@ function getSlabMaterial(
     ? createDefaultMaterial('#ffffff', 0.5, shading)
     : node.material
       ? createMaterial(node.material, shading).clone()
-      : DEFAULT_SLAB_MATERIAL(shading).clone()
+      : createDefaultMaterial(SLAB_SLOT_DEFAULT_COLOR, 0.8, shading)
 
   if (preset) {
     applyMaterialPresetToMaterials(material, preset)
@@ -84,7 +106,7 @@ function getSlabMaterial(
 
 export function buildSlabGeometry(
   node: SlabNode,
-  _ctx?: unknown,
+  ctx?: GeometryContext,
   shading: RenderShading = 'rendered',
   textures = true,
   colorPreset: ColorPreset = 'clay',
@@ -92,10 +114,12 @@ export function buildSlabGeometry(
 ): Group {
   const group = new Group()
   const geometry = generateSlabGeometry(node)
-  const material = getSlabMaterial(node, shading, textures, colorPreset, sceneTheme)
+  const material = getSlabMaterial(node, shading, textures, colorPreset, sceneTheme, ctx?.materials)
   const mesh = new Mesh(geometry, material)
   mesh.castShadow = true
   mesh.receiveShadow = true
+  // Tag the surface so the unified slot paint can resolve the hit and preview.
+  mesh.userData.slotId = 'surface'
   const elevation = node.elevation ?? 0.05
   if (elevation < 0) mesh.position.y = elevation
   group.add(mesh)

packages/nodes/src/slab/paint.ts

@@ -0,0 +1,19 @@
+import type { AnyNode, SlabNode } from '@pascal-app/core'
+import { createSlotPaintCapability, previewGeometrySlot } from '../shared/slot-paint'
+
+/**
+ * Slab paint on the unified slot model. A slab has one paintable surface, so
+ * every face resolves to the `surface` slot; commit writes `node.slots.surface`
+ * (a shared scene-material or `library:` ref) like the shelf.
+ */
+export const slabPaint = createSlotPaintCapability({
+  resolveRole: () => 'surface',
+  applyPreview: previewGeometrySlot,
+  legacyEffective: (node: AnyNode) => {
+    const slab = node as SlabNode
+    if (slab.materialPreset || slab.material) {
+      return { material: slab.material, materialPreset: slab.materialPreset }
+    }
+    return null
+  },
+})

packages/nodes/src/slab/slots.ts

@@ -0,0 +1,11 @@
+import type { SlotDeclaration } from '@pascal-app/core'
+
+export type SlabSlotId = 'surface'
+
+// Visual parity with the retired DEFAULT_SLAB_MATERIAL (light grey).
+export const SLAB_SLOT_DEFAULT_COLOR = '#e5e5e5'
+
+/** A slab exposes a single paintable floor surface. */
+export function slabSlots(): SlotDeclaration[] {
+  return [{ slotId: 'surface', label: 'Surface', default: SLAB_SLOT_DEFAULT_COLOR }]
+}

packages/nodes/src/wall/definition.ts

@@ -6,6 +6,7 @@ import { wallFloorplanSiblingOverrides } from './floorplan-overrides'
 import { wallPaint } from './paint'
 import { wallParametrics } from './parametrics'
 import { WallNode } from './schema'
+import { wallSlots } from './slots'
 
 /**
  * Wall — the Phase 3 stress test of the registry-driven node model.
@@ -56,6 +57,11 @@ export const wallDefinition: NodeDefinition<typeof WallNode> = {
     // preview through this entry rather than carrying a kind-name
     // arm.
     paint: wallPaint,
+    // Declared paintable slots (interior / exterior) with their default
+    // appearance — the same `{ slotId, label, default }` contract every other
+    // paintable kind exposes. Paint still writes the legacy inline fields via
+    // `wallPaint`; migrating those into `node.slots` is a later step.
+    slots: () => wallSlots(),
   },
 
   relations: {

packages/nodes/src/wall/slots.ts

@@ -0,0 +1,17 @@
+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
+ * 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.
+ */
+export function wallSlots(): SlotDeclaration[] {
+  return [
+    { slotId: 'interior', label: 'Interior', default: WALL_SLOT_DEFAULT.interior },
+    { slotId: 'exterior', label: 'Exterior', default: WALL_SLOT_DEFAULT.exterior },
+  ]
+}