feat(paint-slots): paintable slots for windows + doors (frame/glass, panel/glass)

Windows and doors build all visuals in their viewer systems from module-global
materials, so this threads per-node slot materials + userData.slotId tags
through those builders without restructuring them:

- window: 'frame' + 'glass' slots. door: 'panel' (body = casing + leaf) +
  'glass'; the opening reveal keeps its own material.
- Each system captures per-frame viewer state, then updateWindow/DoorMesh points
  the builder-facing base/glass materials at the node's resolved slot override
  (recomputed per node, so the next node resets without a restore). Meshes are
  auto-tagged in the shared addBox/addShape helpers by which material they got.
- Textures-off still collapses to the role material (escape hatch); a slot
  override only applies in colored mode.
- Editing a referenced scene material re-dirties the window/door (these systems
  aren't covered by GeometrySystem's scene-material re-dirty).
- New paint capabilities (resolve role from userData.slotId, preview by
  userData.slotId) + capabilities.slots; window/door dropped from the paint
  disabled list. Shared previewSlotByUserData helper.

Defaults unchanged: unpainted windows/doors render exactly as before (the slot
fallback is the existing frame/glass material), so no visual regression.

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

packages/nodes/src/window/definition.ts

@@ -11,8 +11,10 @@ import { buildRoofWallOpeningCut } from '../shared/roof-wall-opening-cut'
 import { buildWindowFloorplan } from './floorplan'
 import { windowWidthAffordance } from './floorplan-affordances'
 import { windowFloorplanMoveTarget } from './floorplan-move'
+import { windowPaint } from './paint'
 import { windowParametrics } from './parametrics'
 import { WindowNode } from './schema'
+import { windowSlots } from './slots'
 
 const SIDE_HANDLE_OFFSET = 0.24
 const HEIGHT_HANDLE_OFFSET = 0.24
@@ -162,6 +164,10 @@ export const windowDefinition: NodeDefinition<typeof WindowNode> = {
     // `wallId` / `roofSegmentId` are re-derived from the surface under
     // the cursor at preset placement time — see door for the pattern.
     hostRefFields: ['wallId', 'roofSegmentId', 'roofFace'],
+    // Frame / glass slots painted through the registry. The window system tags
+    // each mesh with its `userData.slotId`; paint writes `node.slots`.
+    slots: () => windowSlots(),
+    paint: windowPaint,
   },
 
   parametrics: windowParametrics,

packages/nodes/src/window/paint.ts

@@ -0,0 +1,17 @@
+import type { PaintResolveArgs } from '@pascal-app/core'
+import { createSlotPaintCapability, previewSlotByUserData } from '../shared/slot-paint'
+
+/**
+ * Window paint on the unified slot model. The window's viewer system tags each
+ * built mesh with `userData.slotId` (`frame` / `glass`), so the role resolves
+ * straight from the pointer hit; commit writes `node.slots[slotId]`.
+ */
+function resolveWindowRole(args: PaintResolveArgs): string | null {
+  const slotId = (args.hitObject?.userData as { slotId?: string | null } | undefined)?.slotId
+  return typeof slotId === 'string' ? slotId : null
+}
+
+export const windowPaint = createSlotPaintCapability({
+  resolveRole: resolveWindowRole,
+  applyPreview: previewSlotByUserData,
+})

packages/nodes/src/window/slots.ts

@@ -0,0 +1,16 @@
+import type { SlotDeclaration } from '@pascal-app/core'
+
+export type WindowSlotId = 'frame' | 'glass'
+
+// Picker swatches. Rendering falls back to the live frame/glass defaults (which
+// already track shading + theme), so these are just the indicator colours.
+const FRAME_DEFAULT = '#f2f0ed'
+const GLASS_DEFAULT = '#87ceeb'
+
+/** A window exposes two paintable slots: the joinery frame and the glass. */
+export function windowSlots(): SlotDeclaration[] {
+  return [
+    { slotId: 'frame', label: 'Frame', default: FRAME_DEFAULT },
+    { slotId: 'glass', label: 'Glass', default: GLASS_DEFAULT },
+  ]
+}