feat(core): expose generic host integration primitives

packages/core/src/events/bus.ts

@@ -198,6 +198,15 @@ export interface CameraControlFitSceneEvent {
   }
 }
 
+export interface CameraPose {
+  position: [number, number, number]
+  target: [number, number, number]
+  projection: 'perspective' | 'orthographic'
+  /** Width, in scene units, of the visible plane through `target`. */
+  viewWidth?: number
+  fov?: number
+}
+
 type CameraControlEvents = {
   'camera-controls:view': CameraControlEvent
   'camera-controls:focus': CameraControlEvent
@@ -207,6 +216,10 @@ type CameraControlEvents = {
   'camera-controls:orbit-ccw': undefined
   'camera-controls:fit-scene': CameraControlFitSceneEvent
   'camera-controls:generate-thumbnail': ThumbnailGenerateEvent
+  'camera-controls:pose': CameraPose
+  'camera-controls:apply-pose': CameraPose
+  'camera-controls:cancel-pose': undefined
+  'camera-controls:interaction-start': undefined
 }
 
 type ToolEvents = {

packages/core/src/index.ts

@@ -5,6 +5,7 @@ export type {
   CabinetModuleEvent,
   CameraControlEvent,
   CameraControlFitSceneEvent,
+  CameraPose,
   CeilingEvent,
   ChimneyEvent,
   ColumnEvent,
@@ -179,6 +180,11 @@ export {
   resetSceneHistoryPauseDepth,
   resumeSceneHistory,
   runAsSingleSceneHistoryStep,
+  type SceneCommit,
+  type SceneCommitListener,
+  type SceneCommitOrigin,
+  type SceneSnapshot,
+  subscribeSceneCommits,
 } from './store/history-control'
 export {
   type ControlValue,
@@ -199,7 +205,17 @@ export {
   type LiveNodeOverrides,
 } from './store/use-live-node-overrides'
 export { default as useLiveTransforms, type LiveTransform } from './store/use-live-transforms'
-export { clearSceneHistory, default as useScene } from './store/use-scene'
+export {
+  type ApplySceneSnapshotOptions,
+  acquireSceneReadOnlyLease,
+  applyScenePatch,
+  applySceneSnapshot,
+  clearSceneHistory,
+  default as useScene,
+  type SceneMaterialPatch,
+  type SceneNodePatch,
+  type ScenePatch,
+} from './store/use-scene'
 export { resolveElevatorDispatchTarget } from './systems/elevator/elevator-dispatch'
 export {
   type ElevatorDoorSide,

packages/core/src/schema/nodes/level.test.ts

@@ -0,0 +1,51 @@
+import { describe, expect, test } from 'bun:test'
+import { DuctFittingNode } from './duct-fitting'
+import { DuctSegmentNode } from './duct-segment'
+import { DuctTerminalNode } from './duct-terminal'
+import { HvacEquipmentNode } from './hvac-equipment'
+import { LevelNode } from './level'
+import { LinesetNode } from './lineset'
+import { LiquidLineNode } from './liquid-line'
+import { PipeFittingNode } from './pipe-fitting'
+import { PipeSegmentNode } from './pipe-segment'
+import { PipeTrapNode } from './pipe-trap'
+
+describe('LevelNode', () => {
+  test('accepts every level-hosted MEP node ID', () => {
+    const nodes = [
+      DuctSegmentNode.parse({
+        path: [
+          [0, 0, 0],
+          [1, 0, 0],
+        ],
+      }),
+      DuctFittingNode.parse({}),
+      DuctTerminalNode.parse({}),
+      HvacEquipmentNode.parse({}),
+      LinesetNode.parse({
+        path: [
+          [0, 0, 0],
+          [1, 0, 0],
+        ],
+      }),
+      LiquidLineNode.parse({
+        path: [
+          [0, 0, 0],
+          [1, 0, 0],
+        ],
+      }),
+      PipeSegmentNode.parse({
+        path: [
+          [0, 0, 0],
+          [1, 0, 0],
+        ],
+      }),
+      PipeFittingNode.parse({}),
+      PipeTrapNode.parse({}),
+    ]
+
+    expect(LevelNode.parse({ children: nodes.map((node) => node.id) }).children).toEqual(
+      nodes.map((node) => node.id),
+    )
+  })
+})

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

@@ -3,10 +3,19 @@ import { z } from 'zod'
 import { BaseNode, nodeType, objectId } from '../base'
 import { CeilingNode } from './ceiling'
 import { ColumnNode } from './column'
+import { DuctFittingNode } from './duct-fitting'
+import { DuctSegmentNode } from './duct-segment'
+import { DuctTerminalNode } from './duct-terminal'
 import { FenceNode } from './fence'
 import { GuideNode } from './guide'
+import { HvacEquipmentNode } from './hvac-equipment'
 import { ItemNode } from './item'
+import { LinesetNode } from './lineset'
+import { LiquidLineNode } from './liquid-line'
 import { MeasurementNode } from './measurement'
+import { PipeFittingNode } from './pipe-fitting'
+import { PipeSegmentNode } from './pipe-segment'
+import { PipeTrapNode } from './pipe-trap'
 import { RoofNode } from './roof'
 import { ScanNode } from './scan'
 import { ShelfNode } from './shelf'
@@ -36,6 +45,15 @@ export const LevelNode = BaseNode.extend({
         MeasurementNode.shape.id,
         SpawnNode.shape.id,
         ShelfNode.shape.id,
+        DuctSegmentNode.shape.id,
+        DuctFittingNode.shape.id,
+        DuctTerminalNode.shape.id,
+        HvacEquipmentNode.shape.id,
+        LinesetNode.shape.id,
+        LiquidLineNode.shape.id,
+        PipeSegmentNode.shape.id,
+        PipeFittingNode.shape.id,
+        PipeTrapNode.shape.id,
       ]),
     )
     .default([]),
@@ -44,7 +62,7 @@ export const LevelNode = BaseNode.extend({
 }).describe(
   dedent`
   Level node - used to represent a level in the building
-  - children: array of floor, wall, ceiling, roof, item nodes
+  - children: array of architectural, equipment, and MEP distribution nodes
   - level: level number
   `,
 )

packages/core/src/services/single-undo-dance.test.ts

@@ -125,12 +125,7 @@ describe('Single-undo dance', () => {
     expect((useScene.getState().nodes[FENCE_ID] as { curveOffset: number }).curveOffset).toBe(0)
   })
 
-  test('commit-returns-false (no change) does NOT consume the prior pastState', () => {
+  test('commit-returns-false adds no step; a later standalone undo reaches the prior action', () => {
-    // This is the suspected bend regression: when action.commit returns
-    // false (draft.curveOffset === ctx.originalCurveOffset), session.commit
-    // calls scene.restoreAll() but doesn't push to pastStates. Subsequent
-    // undo pops the PRIOR action (e.g. fence creation), not the no-op
-    // bend.
     useScene.getState().createNode(makeFence(0))
     const pastBeforeBend = useScene.temporal.getState().pastStates.length
 
@@ -143,20 +138,13 @@ describe('Single-undo dance', () => {
     scene.resumeHistory()
 
     const pastAfterNoOp = useScene.temporal.getState().pastStates.length
-    expect(pastAfterNoOp).toBe(pastBeforeBend) // no entries added
+    expect(pastAfterNoOp).toBe(pastBeforeBend)
 
-    // Now undo — this should be a no-op (state unchanged), but pops the create.
+    // This is an independent undo after the gesture has finished, so it
+    // correctly reaches the preceding real action rather than inventing a
+    // no-op history boundary for the cancelled bend.
     useScene.temporal.getState().undo()
-    // ⚠️ Reproduces the bug — undo removes the fence:
+    expect(useScene.getState().nodes[FENCE_ID]).toBeUndefined()
-    const fence = useScene.getState().nodes[FENCE_ID]
-    if (fence === undefined) {
-      // Bug reproduced. The "no-op bend" allowed Ctrl-Z to fall through
-      // to the fence creation. Fix is in action.commit: don't return false
-      // — push a no-op entry instead, or guard against the cancel path.
-      expect(fence).toBeUndefined()
-    } else {
-      expect((fence as { curveOffset: number }).curveOffset).toBe(0)
-    }
   })
 
   test('full session flow via createDragSession with real action.commit dance', async () => {

packages/core/src/store/history-control.ts

@@ -1,5 +1,27 @@
+import type { Collection, CollectionId } from '../schema/collections'
+import type { SceneMaterial, SceneMaterialId } from '../schema/scene-material'
+import type { AnyNode, AnyNodeId } from '../schema/types'
+
 let sceneHistoryPauseDepth = 0
 
+export type SceneSnapshot = {
+  nodes: Record<AnyNodeId, AnyNode>
+  rootNodeIds: AnyNodeId[]
+  collections: Record<CollectionId, Collection>
+  materials: Record<SceneMaterialId, SceneMaterial>
+  installedPlugins: string[]
+}
+
+export type SceneCommitOrigin = 'local' | 'load' | 'host'
+
+export type SceneCommit = {
+  origin: SceneCommitOrigin
+  before: SceneSnapshot
+  current: SceneSnapshot
+}
+
+export type SceneCommitListener = (commit: SceneCommit) => void
+
 type TemporalStoreLike = {
   temporal: {
     getState(): {
@@ -18,6 +40,104 @@ type TemporalHistoryStoreLike<TPastState> = {
   }
 }
 
+const sceneCommitListeners = new Set<SceneCommitListener>()
+let sceneCommitTransactionDepth = 0
+let pendingSceneCommit: SceneCommit | null = null
+
+function areSemanticValuesEqual(left: unknown, right: unknown): boolean {
+  if (Object.is(left, right)) return true
+  if (typeof left !== typeof right || left === null || right === null) return false
+
+  if (Array.isArray(left) || Array.isArray(right)) {
+    if (!(Array.isArray(left) && Array.isArray(right)) || left.length !== right.length) return false
+    return left.every((value, index) => areSemanticValuesEqual(value, right[index]))
+  }
+
+  if (typeof left !== 'object' || typeof right !== 'object') return false
+
+  const leftRecord = left as Record<string, unknown>
+  const rightRecord = right as Record<string, unknown>
+  const leftKeys = Object.keys(leftRecord)
+  const rightKeys = Object.keys(rightRecord)
+  if (leftKeys.length !== rightKeys.length) return false
+
+  for (const key of leftKeys) {
+    if (!(key in rightRecord) || !areSemanticValuesEqual(leftRecord[key], rightRecord[key])) {
+      return false
+    }
+  }
+  return true
+}
+
+export function areSceneSnapshotsEqual(left: SceneSnapshot, right: SceneSnapshot): boolean {
+  return (
+    areSemanticValuesEqual(left.nodes, right.nodes) &&
+    areSemanticValuesEqual(left.rootNodeIds, right.rootNodeIds) &&
+    areSemanticValuesEqual(left.collections, right.collections) &&
+    areSemanticValuesEqual(left.materials, right.materials) &&
+    areSemanticValuesEqual(left.installedPlugins, right.installedPlugins)
+  )
+}
+
+export function subscribeSceneCommits(listener: SceneCommitListener): () => void {
+  sceneCommitListeners.add(listener)
+  return () => {
+    sceneCommitListeners.delete(listener)
+  }
+}
+
+function emitSceneCommit(commit: SceneCommit): void {
+  for (const listener of [...sceneCommitListeners]) {
+    try {
+      listener(commit)
+    } catch (error) {
+      console.error('[Scene] Scene commit listener failed', error)
+    }
+  }
+}
+
+export function notifySceneCommit(commit: SceneCommit): void {
+  if (areSceneSnapshotsEqual(commit.before, commit.current)) return
+
+  if (sceneCommitTransactionDepth > 0) {
+    if (pendingSceneCommit) {
+      pendingSceneCommit = {
+        origin: pendingSceneCommit.origin,
+        before: pendingSceneCommit.before,
+        current: commit.current,
+      }
+    } else {
+      pendingSceneCommit = commit
+    }
+    return
+  }
+
+  emitSceneCommit(commit)
+}
+
+function beginSceneCommitTransaction(): void {
+  sceneCommitTransactionDepth += 1
+}
+
+function pendingSceneCommitIsNoOp(): boolean {
+  return Boolean(
+    pendingSceneCommit &&
+      areSceneSnapshotsEqual(pendingSceneCommit.before, pendingSceneCommit.current),
+  )
+}
+
+function endSceneCommitTransaction(): void {
+  if (sceneCommitTransactionDepth === 0) return
+  sceneCommitTransactionDepth -= 1
+  if (sceneCommitTransactionDepth > 0) return
+
+  const commit = pendingSceneCommit
+  pendingSceneCommit = null
+  if (commit && !areSceneSnapshotsEqual(commit.before, commit.current)) {
+    emitSceneCommit(commit)
+  }
+}
+
 export function pauseSceneHistory(sceneStore: TemporalStoreLike): void {
   if (sceneHistoryPauseDepth === 0) {
     sceneStore.temporal.getState().pause()
@@ -65,11 +185,16 @@ export function runAsSingleSceneHistoryStep<TPastState, TResult>(
   run: () => TResult,
 ): TResult {
   const beforePastStates = sceneStore.temporal.getState().pastStates
+  beginSceneCommitTransaction()
+  try {
     const result = run()
     const afterPastStates = sceneStore.temporal.getState().pastStates
     const retainedCount = retainedPastStateCount(beforePastStates, afterPastStates)
     const addedCount = afterPastStates.length - retainedCount
-  if (addedCount > 1) {
+
+    if (addedCount > 0 && pendingSceneCommitIsNoOp()) {
+      sceneStore.temporal.setState({ pastStates: afterPastStates.slice(0, retainedCount) })
+    } else if (addedCount > 1) {
       const firstAddedState = afterPastStates[retainedCount]
       if (firstAddedState !== undefined) {
         sceneStore.temporal.setState({
@@ -78,4 +203,7 @@ export function runAsSingleSceneHistoryStep<TPastState, TResult>(
       }
     }
     return result
+  } finally {
+    endSceneCommitTransaction()
+  }
 }

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

@@ -0,0 +1,422 @@
+import { afterEach, beforeEach, describe, expect, mock, test } from 'bun:test'
+import { BuildingNode } from '../schema/nodes/building'
+import { LevelNode } from '../schema/nodes/level'
+import { SceneMaterial, type SceneMaterialId } from '../schema/scene-material'
+import type { AnyNode, AnyNodeId } from '../schema/types'
+import {
+  areSceneSnapshotsEqual,
+  pauseSceneHistory,
+  resumeSceneHistory,
+  runAsSingleSceneHistoryStep,
+  type SceneCommit,
+  type SceneSnapshot,
+  subscribeSceneCommits,
+} from './history-control'
+import useLiveNodeOverrides from './use-live-node-overrides'
+import useLiveTransforms from './use-live-transforms'
+import useScene, {
+  acquireSceneReadOnlyLease,
+  applyScenePatch,
+  applySceneSnapshot,
+  clearSceneHistory,
+} from './use-scene'
+
+type RafFn = (cb: (time: number) => void) => number
+;(globalThis as unknown as { requestAnimationFrame?: RafFn }).requestAnimationFrame ??= (cb) => {
+  cb(0)
+  return 0
+}
+;(globalThis as unknown as { cancelAnimationFrame?: (id: number) => void }).cancelAnimationFrame ??=
+  () => {}
+
+const BUILDING_ID = 'building_commit' as AnyNodeId
+const LEVEL_ID = 'level_commit' as AnyNodeId
+
+let unsubscribe = () => {}
+
+function resetScene(): void {
+  const level = LevelNode.parse({
+    id: LEVEL_ID,
+    parentId: BUILDING_ID,
+    children: [],
+    level: 0,
+  })
+  const building = BuildingNode.parse({
+    id: BUILDING_ID,
+    parentId: null,
+    children: [LEVEL_ID],
+  })
+  useScene.setState({
+    nodes: { [BUILDING_ID]: building, [LEVEL_ID]: level },
+    rootNodeIds: [BUILDING_ID],
+    dirtyNodes: new Set<AnyNodeId>(),
+    collections: {},
+    materials: {},
+    readOnly: false,
+  } as never)
+  clearSceneHistory()
+  useLiveNodeOverrides.getState().clearAll()
+  useLiveTransforms.getState().clearAll()
+}
+
+function levelNumber(): number {
+  return (useScene.getState().nodes[LEVEL_ID] as { level: number }).level
+}
+
+function currentSnapshot(): SceneSnapshot {
+  const { nodes, rootNodeIds, collections, materials, installedPlugins } = useScene.getState()
+  return { nodes, rootNodeIds, collections, materials, installedPlugins }
+}
+
+function applyHostNodePatches(
+  nodeUpdates: Array<
+    Omit<Parameters<typeof applyScenePatch>[0]['nodeUpdates'][number], 'removeFields'>
+  >,
+) {
+  return applyScenePatch({
+    materialChanges: [],
+    nodeUpdates: nodeUpdates.map((update) => ({ ...update, removeFields: [] })),
+  })
+}
+
+describe('scene commit boundary', () => {
+  beforeEach(() => {
+    unsubscribe()
+    unsubscribe = () => {}
+    resetScene()
+  })
+
+  afterEach(() => {
+    unsubscribe()
+    unsubscribe = () => {}
+  })
+
+  test('emits one local commit with before/current snapshots and skips semantic no-ops', () => {
+    const commits: SceneCommit[] = []
+    unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
+
+    useScene.getState().updateNode(LEVEL_ID, { level: 1 } as Partial<AnyNode>)
+    expect(commits).toHaveLength(1)
+    expect(commits[0]?.origin).toBe('local')
+    expect((commits[0]?.before.nodes[LEVEL_ID] as { level: number }).level).toBe(0)
+    expect((commits[0]?.current.nodes[LEVEL_ID] as { level: number }).level).toBe(1)
+    expect(useScene.temporal.getState().pastStates).toHaveLength(1)
+
+    useScene.getState().updateNode(LEVEL_ID, { level: 1 } as Partial<AnyNode>)
+    expect(commits).toHaveLength(1)
+    expect(useScene.temporal.getState().pastStates).toHaveLength(1)
+  })
+
+  test('coalesces a compound transaction into one commit and one undo step', () => {
+    const commits: SceneCommit[] = []
+    unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
+
+    runAsSingleSceneHistoryStep(useScene, () => {
+      useScene.getState().updateNode(LEVEL_ID, { level: 1 } as Partial<AnyNode>)
+      useScene.getState().updateNode(LEVEL_ID, { level: 2 } as Partial<AnyNode>)
+    })
+
+    expect(commits).toHaveLength(1)
+    expect((commits[0]?.before.nodes[LEVEL_ID] as { level: number }).level).toBe(0)
+    expect((commits[0]?.current.nodes[LEVEL_ID] as { level: number }).level).toBe(2)
+    expect(useScene.temporal.getState().pastStates).toHaveLength(1)
+
+    useScene.temporal.getState().undo()
+    expect(levelNumber()).toBe(0)
+  })
+
+  test('drops a compound transaction that returns to its semantic baseline', () => {
+    const commits: SceneCommit[] = []
+    unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
+
+    runAsSingleSceneHistoryStep(useScene, () => {
+      useScene.getState().updateNode(LEVEL_ID, { level: 1 } as Partial<AnyNode>)
+      useScene.getState().updateNode(LEVEL_ID, { level: 0 } as Partial<AnyNode>)
+    })
+
+    expect(commits).toHaveLength(0)
+    expect(useScene.temporal.getState().pastStates).toHaveLength(0)
+  })
+
+  test('applies host patches without local history and marks node and parent dirty', () => {
+    const commits: SceneCommit[] = []
+    unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
+    useLiveNodeOverrides.getState().set(LEVEL_ID, { level: 99 })
+    useLiveTransforms.getState().set(LEVEL_ID, { position: [1, 0, 1], rotation: 0 })
+
+    expect(applyHostNodePatches([{ id: LEVEL_ID, data: { level: 3 } as Partial<AnyNode> }])).toBe(
+      true,
+    )
+
+    expect(levelNumber()).toBe(3)
+    expect(commits.map((commit) => commit.origin)).toEqual(['host'])
+    expect(commits.filter((commit) => commit.origin === 'local')).toHaveLength(0)
+    expect(useScene.temporal.getState().pastStates).toHaveLength(0)
+    expect(useScene.getState().dirtyNodes.has(LEVEL_ID)).toBe(true)
+    expect(useScene.getState().dirtyNodes.has(BUILDING_ID)).toBe(true)
+    expect(useLiveNodeOverrides.getState().get(LEVEL_ID)).toBeUndefined()
+    expect(useLiveTransforms.getState().get(LEVEL_ID)).toBeUndefined()
+  })
+
+  test('applies material patches atomically and dirties nodes that reference them', () => {
+    const materialId = 'mat_host' as SceneMaterialId
+    const material = SceneMaterial.parse({
+      id: materialId,
+      name: 'Host red',
+      material: { properties: { color: '#ff0000' } },
+    })
+    useScene.setState((state) => ({
+      nodes: {
+        ...state.nodes,
+        [LEVEL_ID]: {
+          ...state.nodes[LEVEL_ID],
+          slots: { surface: `scene:${materialId}` },
+        } as AnyNode,
+      },
+    }))
+    clearSceneHistory()
+    useScene.getState().dirtyNodes.clear()
+    const commits: SceneCommit[] = []
+    unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
+
+    expect(
+      applyScenePatch({
+        materialChanges: [{ id: materialId, material }],
+        nodeUpdates: [],
+      }),
+    ).toBe(true)
+
+    expect(useScene.getState().materials[materialId]).toEqual(material)
+    expect(useScene.getState().dirtyNodes.has(LEVEL_ID)).toBe(true)
+    expect(useScene.getState().dirtyNodes.has(BUILDING_ID)).toBe(true)
+    expect(commits.map((commit) => commit.origin)).toEqual(['host'])
+    expect(useScene.temporal.getState().pastStates).toHaveLength(0)
+
+    expect(
+      applyScenePatch({
+        materialChanges: [{ id: materialId, material: null }],
+        nodeUpdates: [{ id: LEVEL_ID, data: {}, removeFields: ['slots'] }],
+      }),
+    ).toBe(true)
+    expect(useScene.getState().materials[materialId]).toBeUndefined()
+    expect(useScene.getState().nodes[LEVEL_ID]).not.toHaveProperty('slots')
+    expect(useScene.temporal.getState().pastStates).toHaveLength(0)
+  })
+
+  test('keeps host patches untracked across nested history pauses', () => {
+    const commits: SceneCommit[] = []
+    unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
+    const unsubscribeNestedPause = useScene.subscribe((state, previousState) => {
+      if (state.nodes === previousState.nodes) return
+      pauseSceneHistory(useScene)
+      resumeSceneHistory(useScene)
+    })
+
+    try {
+      expect(applyHostNodePatches([{ id: LEVEL_ID, data: { level: 3 } as Partial<AnyNode> }])).toBe(
+        true,
+      )
+    } finally {
+      unsubscribeNestedPause()
+    }
+
+    expect(levelNumber()).toBe(3)
+    expect(commits.map((commit) => commit.origin)).toEqual(['host'])
+    expect(useScene.temporal.getState().pastStates).toHaveLength(0)
+  })
+
+  test('applies host patches through read-only and restores the UI lock', () => {
+    const commits: SceneCommit[] = []
+    unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
+    useScene.getState().setReadOnly(true)
+    const beforeState = useScene.getState()
+    const levelBefore = beforeState.nodes[LEVEL_ID]
+    const buildingBefore = beforeState.nodes[BUILDING_ID]
+
+    expect(applyHostNodePatches([{ id: LEVEL_ID, data: { level: 3 } as Partial<AnyNode> }])).toBe(
+      true,
+    )
+
+    expect(levelNumber()).toBe(3)
+    expect(useScene.getState().readOnly).toBe(true)
+    expect(commits.map((commit) => commit.origin)).toEqual(['host'])
+    expect(useScene.temporal.getState().pastStates).toHaveLength(0)
+    expect(useScene.getState().nodes[LEVEL_ID]).toEqual({
+      ...levelBefore,
+      level: 3,
+    } as AnyNode)
+    expect(useScene.getState().nodes[BUILDING_ID]).toBe(buildingBefore)
+    expect(useScene.getState().rootNodeIds).toBe(beforeState.rootNodeIds)
+    expect(useScene.getState().collections).toBe(beforeState.collections)
+    expect(useScene.getState().materials).toBe(beforeState.materials)
+
+    useScene.getState().updateNode(LEVEL_ID, { level: 4 } as Partial<AnyNode>)
+    expect(levelNumber()).toBe(3)
+  })
+
+  test('keeps read-only active until every owner releases its lease', () => {
+    const releaseHost = acquireSceneReadOnlyLease()
+    const releasePreview = acquireSceneReadOnlyLease()
+
+    expect(useScene.getState().readOnly).toBe(true)
+    releaseHost()
+    expect(useScene.getState().readOnly).toBe(true)
+    releaseHost()
+    expect(useScene.getState().readOnly).toBe(true)
+    releasePreview()
+    expect(useScene.getState().readOnly).toBe(false)
+  })
+
+  test('restores read-only and history tracking when a host patch throws', () => {
+    const throwingData = {} as Partial<AnyNode>
+    Object.defineProperty(throwingData, 'level', {
+      enumerable: true,
+      get: () => {
+        throw new Error('update failed')
+      },
+    })
+    useScene.getState().setReadOnly(true)
+
+    expect(() => applyHostNodePatches([{ id: LEVEL_ID, data: throwingData }])).toThrow(
+      'update failed',
+    )
+
+    expect(levelNumber()).toBe(0)
+    expect(useScene.getState().readOnly).toBe(true)
+    expect(useScene.temporal.getState().isTracking).toBe(true)
+  })
+
+  test('rejects a host patch atomically when any target is missing', () => {
+    const commits: SceneCommit[] = []
+    unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
+
+    expect(
+      applyHostNodePatches([
+        { id: LEVEL_ID, data: { level: 4 } as Partial<AnyNode> },
+        { id: 'level_missing' as AnyNodeId, data: { level: 5 } as Partial<AnyNode> },
+      ]),
+    ).toBe(false)
+
+    expect(levelNumber()).toBe(0)
+    expect(commits).toHaveLength(0)
+    expect(useScene.temporal.getState().pastStates).toHaveLength(0)
+  })
+
+  test('rejects patches that would change a node identity', () => {
+    const commits: SceneCommit[] = []
+    unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
+
+    expect(
+      applyHostNodePatches([
+        {
+          id: LEVEL_ID,
+          data: { id: 'level_rekeyed', level: 6 } as Partial<AnyNode>,
+        },
+      ]),
+    ).toBe(false)
+
+    expect(levelNumber()).toBe(0)
+    expect(useScene.getState().nodes[LEVEL_ID]?.id).toBe(LEVEL_ID)
+    expect(commits).toHaveLength(0)
+  })
+
+  test('defers host patches while a local interaction has history paused', () => {
+    pauseSceneHistory(useScene)
+    try {
+      expect(applyHostNodePatches([{ id: LEVEL_ID, data: { level: 7 } as Partial<AnyNode> }])).toBe(
+        false,
+      )
+      expect(levelNumber()).toBe(0)
+      expect(useScene.temporal.getState().isTracking).toBe(false)
+    } finally {
+      resumeSceneHistory(useScene)
+    }
+  })
+
+  test('applies a host snapshot as a history floor and clears live state', () => {
+    useScene.getState().updateNode(LEVEL_ID, { level: 1 } as Partial<AnyNode>)
+    expect(useScene.temporal.getState().pastStates).toHaveLength(1)
+    useLiveNodeOverrides.getState().set(LEVEL_ID, { level: 99 })
+    useLiveTransforms.getState().set(LEVEL_ID, { position: [1, 0, 1], rotation: 0 })
+
+    const snapshot = currentSnapshot()
+    snapshot.nodes = {
+      ...snapshot.nodes,
+      [LEVEL_ID]: { ...snapshot.nodes[LEVEL_ID], level: 8 } as AnyNode,
+    }
+    snapshot.installedPlugins = ['pascal:trees']
+    const commits: SceneCommit[] = []
+    unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
+    useScene.getState().dirtyNodes.clear()
+
+    expect(applySceneSnapshot(snapshot, { origin: 'host' })).toBe(true)
+    expect(levelNumber()).toBe(8)
+    expect(useScene.getState().installedPlugins).toEqual(['pascal:trees'])
+    expect(commits.map((commit) => commit.origin)).toEqual(['host'])
+    expect(useScene.temporal.getState().pastStates).toHaveLength(0)
+    expect(useScene.temporal.getState().futureStates).toHaveLength(0)
+    expect(useScene.getState().dirtyNodes.has(LEVEL_ID)).toBe(true)
+    expect(useScene.getState().dirtyNodes.has(BUILDING_ID)).toBe(true)
+    expect(useLiveNodeOverrides.getState().get(LEVEL_ID)).toBeUndefined()
+    expect(useLiveTransforms.getState().get(LEVEL_ID)).toBeUndefined()
+  })
+
+  test('rejects snapshot replacement during a paused interaction', () => {
+    const snapshot = currentSnapshot()
+    snapshot.nodes = {
+      ...snapshot.nodes,
+      [LEVEL_ID]: { ...snapshot.nodes[LEVEL_ID], level: 9 } as AnyNode,
+    }
+
+    pauseSceneHistory(useScene)
+    try {
+      expect(() => applySceneSnapshot(snapshot, { origin: 'host' })).toThrow('active interaction')
+      expect(levelNumber()).toBe(0)
+      expect(useScene.temporal.getState().isTracking).toBe(false)
+    } finally {
+      resumeSceneHistory(useScene)
+    }
+  })
+
+  test('isolates a throwing listener so later listeners and Zundo still run', () => {
+    const originalConsoleError = console.error
+    const errorLog = mock(() => {})
+    console.error = errorLog
+    const stopThrowing = subscribeSceneCommits(() => {
+      throw new Error('listener failed')
+    })
+    const healthyListener = mock(() => {})
+    unsubscribe = subscribeSceneCommits(healthyListener)
+
+    try {
+      useScene.getState().updateNode(LEVEL_ID, { level: 2 } as Partial<AnyNode>)
+      expect(healthyListener).toHaveBeenCalledTimes(1)
+      expect(errorLog).toHaveBeenCalledTimes(1)
+      expect(useScene.temporal.getState().pastStates).toHaveLength(1)
+    } finally {
+      stopThrowing()
+      console.error = originalConsoleError
+    }
+  })
+
+  test('semantic equality short-circuits shared nodes in a large scene', () => {
+    const nodes: Record<AnyNodeId, AnyNode> = {}
+    for (let index = 0; index < 1_000; index += 1) {
+      const id = `level_${index}` as AnyNodeId
+      nodes[id] = { id, type: 'level', level: index, children: [] } as unknown as AnyNode
+    }
+    const left: SceneSnapshot = {
+      nodes,
+      rootNodeIds: [],
+      collections: {},
+      installedPlugins: [],
+      materials: {},
+    }
+    const right: SceneSnapshot = {
+      ...left,
+      nodes: { ...nodes, level_999: { ...nodes.level_999 } as AnyNode },
+    }
+
+    expect(areSceneSnapshotsEqual(left, right)).toBe(true)
+  })
+})

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

@@ -34,7 +34,18 @@ import {
 import type { AnyNode, AnyNodeId } from '../schema/types'
 import { healSceneNodes } from '../utils/heal-scene-graph'
 import * as nodeActions from './actions/node-actions'
-import { resetSceneHistoryPauseDepth } from './history-control'
+import {
+  areSceneSnapshotsEqual,
+  getSceneHistoryPauseDepth,
+  notifySceneCommit,
+  pauseSceneHistory,
+  resetSceneHistoryPauseDepth,
+  resumeSceneHistory,
+  type SceneCommitOrigin,
+  type SceneSnapshot,
+} from './history-control'
+import useLiveNodeOverrides from './use-live-node-overrides'
+import useLiveTransforms from './use-live-transforms'
 
 function getFiniteNumber(value: unknown, fallback: number) {
   return typeof value === 'number' && Number.isFinite(value) ? value : fallback
@@ -1015,6 +1026,16 @@ type UseSceneStore = UseBoundStore<StoreApi<SceneState>> & {
   >
 }
 
+function sceneHistorySnapshotFromState(
+  state: Pick<
+    SceneState,
+    'nodes' | 'rootNodeIds' | 'collections' | 'materials' | 'installedPlugins'
+  >,
+): SceneSnapshot {
+  const { nodes, rootNodeIds, collections, materials, installedPlugins } = state
+  return { nodes, rootNodeIds, collections, materials, installedPlugins }
+}
+
 const useScene: UseSceneStore = create<SceneState>()(
   temporal(
     (set, get) => ({
@@ -1311,9 +1332,14 @@ const useScene: UseSceneStore = create<SceneState>()(
       },
     }),
     {
-      partialize: (state) => {
+      partialize: (state: SceneState) => sceneHistorySnapshotFromState(state),
-        const { nodes, rootNodeIds, collections, materials, installedPlugins } = state
+      equality: (pastState, currentState) => areSceneSnapshotsEqual(pastState, currentState),
-        return { nodes, rootNodeIds, collections, materials, installedPlugins }
+      onSave: (pastState, currentState) => {
+        notifySceneCommit({
+          origin: 'local',
+          before: sceneHistorySnapshotFromState(pastState),
+          current: sceneHistorySnapshotFromState(currentState),
+        })
       },
       limit: 50, // Limit to last 50 actions
     },
@@ -1322,6 +1348,165 @@ const useScene: UseSceneStore = create<SceneState>()(
 
 export default useScene
 
+let sceneReadOnlyLeaseCount = 0
+let sceneReadOnlyLeaseBaseline = false
+
+export function acquireSceneReadOnlyLease(): () => void {
+  if (sceneReadOnlyLeaseCount === 0) {
+    sceneReadOnlyLeaseBaseline = useScene.getState().readOnly
+  }
+  sceneReadOnlyLeaseCount += 1
+  useScene.setState({ readOnly: true })
+
+  let released = false
+  return () => {
+    if (released) return
+    released = true
+    sceneReadOnlyLeaseCount = Math.max(0, sceneReadOnlyLeaseCount - 1)
+    if (sceneReadOnlyLeaseCount > 0) return
+    useScene.setState({ readOnly: sceneReadOnlyLeaseBaseline })
+    sceneReadOnlyLeaseBaseline = false
+  }
+}
+
+export type SceneNodePatch = {
+  id: AnyNodeId
+  data: Partial<AnyNode>
+  removeFields: string[]
+}
+
+export type SceneMaterialPatch = {
+  id: SceneMaterialId
+  material: SceneMaterial | null
+}
+
+export type ScenePatch = {
+  materialChanges: SceneMaterialPatch[]
+  nodeUpdates: SceneNodePatch[]
+}
+
+export function applyScenePatch(changes: ScenePatch): boolean {
+  const beforeState = useScene.getState()
+  const hasInvalidNodeTarget = changes.nodeUpdates.some(({ id, data, removeFields }) => {
+    const node = beforeState.nodes[id]
+    if (!node) return true
+    if ('id' in data && data.id !== node.id) return true
+    if ('type' in data && data.type !== node.type) return true
+    if ('object' in data && data.object !== node.object) return true
+    if (removeFields.some((field) => field === 'id' || field === 'object' || field === 'type')) {
+      return true
+    }
+    return removeFields.some((field) => Object.hasOwn(data, field))
+  })
+  const hasInvalidMaterialTarget = changes.materialChanges.some(
+    ({ id, material }) => material !== null && material.id !== id,
+  )
+  if (
+    (changes.nodeUpdates.length === 0 && changes.materialChanges.length === 0) ||
+    hasInvalidNodeTarget ||
+    hasInvalidMaterialTarget
+  ) {
+    return false
+  }
+
+  const temporalState = useScene.temporal.getState()
+  if (!temporalState.isTracking || getSceneHistoryPauseDepth() > 0) return false
+
+  const before = sceneHistorySnapshotFromState(beforeState)
+  pauseSceneHistory(useScene)
+  try {
+    // Host-owned fields bypass the UI lock without running local mutation cascades.
+    useScene.setState((state) => {
+      const nodes = changes.nodeUpdates.length > 0 ? { ...state.nodes } : state.nodes
+      for (const { id, data, removeFields } of changes.nodeUpdates) {
+        const node = nodes[id]
+        if (!node) return {}
+        const nextNode = { ...node, ...data }
+        for (const field of removeFields) delete nextNode[field as keyof typeof nextNode]
+        nodes[id] = nextNode as AnyNode
+      }
+      const materials =
+        changes.materialChanges.length > 0 ? { ...state.materials } : state.materials
+      for (const { id, material } of changes.materialChanges) {
+        if (material === null) {
+          delete materials[id]
+        } else {
+          materials[id] = material
+        }
+      }
+      return { materials, nodes }
+    })
+  } finally {
+    resumeSceneHistory(useScene)
+  }
+
+  const currentState = useScene.getState()
+  const current = sceneHistorySnapshotFromState(currentState)
+  for (const { id } of changes.nodeUpdates) {
+    useLiveNodeOverrides.getState().clear(id)
+    useLiveTransforms.getState().clear(id)
+  }
+  if (areSceneSnapshotsEqual(before, current)) return false
+
+  for (const { id } of changes.nodeUpdates) {
+    currentState.markDirty(id)
+    const beforeParentId = before.nodes[id]?.parentId as AnyNodeId | null | undefined
+    const currentParentId = current.nodes[id]?.parentId as AnyNodeId | null | undefined
+    if (beforeParentId) currentState.markDirty(beforeParentId)
+    if (currentParentId) currentState.markDirty(currentParentId)
+  }
+  if (changes.materialChanges.length > 0) {
+    const materialRefs = new Set(changes.materialChanges.map(({ id }) => toSceneMaterialRef(id)))
+    for (const node of Object.values(current.nodes)) {
+      const slots = 'slots' in node ? node.slots : undefined
+      if (!(slots && Object.values(slots).some((ref) => materialRefs.has(ref)))) continue
+      currentState.markDirty(node.id)
+      if (node.parentId) currentState.markDirty(node.parentId as AnyNodeId)
+    }
+  }
+
+  notifySceneCommit({
+    origin: 'host',
+    before,
+    current,
+  })
+  return true
+}
+
+export type ApplySceneSnapshotOptions = {
+  origin: Extract<SceneCommitOrigin, 'load' | 'host'>
+}
+
+export function applySceneSnapshot(
+  snapshot: SceneSnapshot,
+  options: ApplySceneSnapshotOptions,
+): boolean {
+  const before = sceneHistorySnapshotFromState(useScene.getState())
+  const temporalState = useScene.temporal.getState()
+  if (!temporalState.isTracking || getSceneHistoryPauseDepth() > 0) {
+    throw new Error('Cannot replace the scene snapshot during an active interaction')
+  }
+  pauseSceneHistory(useScene)
+  try {
+    useScene.getState().setScene(snapshot.nodes, snapshot.rootNodeIds, {
+      collections: snapshot.collections,
+      installedPlugins: snapshot.installedPlugins,
+      materials: snapshot.materials,
+    })
+    useScene.temporal.getState().clear()
+  } finally {
+    resumeSceneHistory(useScene)
+  }
+
+  useLiveNodeOverrides.getState().clearAll()
+  useLiveTransforms.getState().clearAll()
+
+  const current = sceneHistorySnapshotFromState(useScene.getState())
+  if (areSceneSnapshotsEqual(before, current)) return false
+  notifySceneCommit({ origin: options.origin, before, current })
+  return true
+}
+
 // Track previous temporal state lengths and node snapshot for diffing
 let prevPastLength = 0
 let prevFutureLength = 0

packages/core/src/systems/elevator/elevator-opening-system.test.ts

@@ -0,0 +1,166 @@
+import { afterEach, beforeEach, describe, expect, test } from 'bun:test'
+import {
+  type AnyNode,
+  type AnyNodeId,
+  BuildingNode,
+  ElevatorNode,
+  LevelNode,
+  SlabNode,
+} from '../../schema'
+import { type SceneCommit, subscribeSceneCommits } from '../../store/history-control'
+import useScene, { clearSceneHistory } from '../../store/use-scene'
+import { initializeElevatorOpeningSync } from './elevator-opening-system'
+
+type RafFn = (callback: (time: number) => void) => number
+;(globalThis as unknown as { requestAnimationFrame?: RafFn }).requestAnimationFrame ??= (
+  callback,
+) => {
+  callback(0)
+  return 0
+}
+;(globalThis as unknown as { cancelAnimationFrame?: (id: number) => void }).cancelAnimationFrame ??=
+  () => {}
+
+const BUILDING_ID = 'building_elevator_opening_commit' as AnyNodeId
+const ELEVATOR_ID = 'elevator_opening_commit' as AnyNodeId
+const GROUND_LEVEL_ID = 'level_elevator_opening_ground' as AnyNodeId
+const UPPER_LEVEL_ID = 'level_elevator_opening_upper' as AnyNodeId
+const UPPER_SLAB_ID = 'slab_elevator_opening_upper' as AnyNodeId
+
+let stopOpeningSync = () => {}
+let stopCommitSubscription = () => {}
+
+function resetScene() {
+  const ground = LevelNode.parse({
+    id: GROUND_LEVEL_ID,
+    children: [],
+    level: 0,
+    parentId: BUILDING_ID,
+  })
+  const upper = LevelNode.parse({
+    id: UPPER_LEVEL_ID,
+    children: [UPPER_SLAB_ID],
+    level: 1,
+    parentId: BUILDING_ID,
+  })
+  const elevator = ElevatorNode.parse({
+    id: ELEVATOR_ID,
+    depth: 1.6,
+    fromLevelId: GROUND_LEVEL_ID,
+    parentId: BUILDING_ID,
+    position: [2, 0, 1.5],
+    toLevelId: UPPER_LEVEL_ID,
+    visible: false,
+    width: 1.6,
+  })
+  const upperSlab = SlabNode.parse({
+    id: UPPER_SLAB_ID,
+    holes: [],
+    parentId: UPPER_LEVEL_ID,
+    polygon: [
+      [0, 0],
+      [4, 0],
+      [4, 3],
+      [0, 3],
+    ],
+  })
+  const building = BuildingNode.parse({
+    id: BUILDING_ID,
+    children: [GROUND_LEVEL_ID, UPPER_LEVEL_ID, ELEVATOR_ID],
+  })
+
+  useScene.setState({
+    collections: {},
+    dirtyNodes: new Set<AnyNodeId>(),
+    materials: {},
+    nodes: Object.fromEntries(
+      [building, ground, upper, elevator, upperSlab].map((node) => [node.id, node]),
+    ) as Record<AnyNodeId, AnyNode>,
+    readOnly: false,
+    rootNodeIds: [BUILDING_ID],
+  } as never)
+  clearSceneHistory()
+}
+
+function getOpeningCenter(nodes: Record<AnyNodeId, AnyNode>): [number, number] | null {
+  const slab = nodes[UPPER_SLAB_ID] as { holes?: [number, number][][] }
+  const opening = slab.holes?.[0]
+  if (!opening || opening.length === 0) return null
+
+  const [x, z] = opening.reduce(([sumX, sumZ], point) => [sumX + point[0], sumZ + point[1]], [0, 0])
+  return [x / opening.length, z / opening.length]
+}
+
+function getElevatorPosition(nodes: Record<AnyNodeId, AnyNode>) {
+  return (nodes[ELEVATOR_ID] as { position?: [number, number, number] }).position
+}
+
+describe('ElevatorOpeningSystem scene commit boundary', () => {
+  beforeEach(() => {
+    stopOpeningSync()
+    stopCommitSubscription()
+    stopOpeningSync = () => {}
+    stopCommitSubscription = () => {}
+    resetScene()
+  })
+
+  afterEach(() => {
+    stopOpeningSync()
+    stopCommitSubscription()
+    stopOpeningSync = () => {}
+    stopCommitSubscription = () => {}
+  })
+
+  test('includes the elevator edit and derived slab opening in one commit and undo step', () => {
+    const commits: SceneCommit[] = []
+    stopOpeningSync = initializeElevatorOpeningSync()
+    stopCommitSubscription = subscribeSceneCommits((commit) => commits.push(commit))
+
+    useScene.getState().updateNode(ELEVATOR_ID, { visible: true } as Partial<AnyNode>)
+
+    expect(commits).toHaveLength(1)
+    expect(commits[0]?.origin).toBe('local')
+    expect(commits[0]?.before.nodes[ELEVATOR_ID]?.visible).toBe(false)
+    expect(commits[0]?.current.nodes[ELEVATOR_ID]?.visible).toBe(true)
+    expect((commits[0]?.before.nodes[UPPER_SLAB_ID] as { holes?: unknown[] }).holes).toEqual([])
+    expect((commits[0]?.current.nodes[UPPER_SLAB_ID] as { holes?: unknown[] }).holes).toHaveLength(
+      1,
+    )
+    expect(
+      (commits[0]?.current.nodes[UPPER_SLAB_ID] as { holeMetadata?: unknown[] }).holeMetadata,
+    ).toEqual([{ elevatorId: ELEVATOR_ID, source: 'elevator' }])
+    expect(useScene.temporal.getState().pastStates).toHaveLength(1)
+
+    useScene.temporal.getState().undo()
+
+    expect(useScene.getState().nodes[ELEVATOR_ID]?.visible).toBe(false)
+    expect((useScene.getState().nodes[UPPER_SLAB_ID] as { holes?: unknown[] }).holes).toEqual([])
+  })
+
+  test('processes a second relevant elevator mutation in the same turn', () => {
+    const commits: SceneCommit[] = []
+    stopOpeningSync = initializeElevatorOpeningSync()
+    stopCommitSubscription = subscribeSceneCommits((commit) => commits.push(commit))
+
+    useScene.getState().updateNode(ELEVATOR_ID, { visible: true } as Partial<AnyNode>)
+    useScene.getState().updateNode(ELEVATOR_ID, { position: [3, 0, 1.5] } as Partial<AnyNode>)
+
+    expect(commits).toHaveLength(2)
+    expect(getOpeningCenter(commits[0]!.current.nodes)).toEqual([2, 1.5])
+    expect(getElevatorPosition(commits[1]!.before.nodes)).toEqual([2, 0, 1.5])
+    expect(getOpeningCenter(commits[1]!.before.nodes)).toEqual([2, 1.5])
+    expect(getElevatorPosition(commits[1]!.current.nodes)).toEqual([3, 0, 1.5])
+    expect(getOpeningCenter(commits[1]!.current.nodes)).toEqual([3, 1.5])
+    expect(useScene.temporal.getState().pastStates).toHaveLength(2)
+
+    useScene.temporal.getState().undo()
+
+    expect(getElevatorPosition(useScene.getState().nodes)).toEqual([2, 0, 1.5])
+    expect(getOpeningCenter(useScene.getState().nodes)).toEqual([2, 1.5])
+
+    useScene.temporal.getState().undo()
+
+    expect(useScene.getState().nodes[ELEVATOR_ID]?.visible).toBe(false)
+    expect((useScene.getState().nodes[UPPER_SLAB_ID] as { holes?: unknown[] }).holes).toEqual([])
+  })
+})

packages/core/src/systems/elevator/elevator-opening-system.tsx

@@ -1,7 +1,8 @@
 'use client'
 
-import { useEffect, useRef } from 'react'
+import { useEffect } from 'react'
 import type { AnyNode } from '../../schema'
+import { pauseSceneHistory, resumeSceneHistory } from '../../store/history-control'
 import useScene from '../../store/use-scene'
 import { syncAutoElevatorOpenings } from './elevator-opening-sync'
 
@@ -32,27 +33,32 @@ function hasOpeningRelevantNodeChange(
   return false
 }
 
-export const ElevatorOpeningSystem = () => {
+export function initializeElevatorOpeningSync() {
-  const syncingAutoOpeningsRef = useRef(false)
+  let syncingAutoOpenings = false
 
-  useEffect(() => {
   const applyUpdates = (updates: ReturnType<typeof syncAutoElevatorOpenings>) => {
     if (updates.length === 0) return
-      syncingAutoOpeningsRef.current = true
+    syncingAutoOpenings = true
+    pauseSceneHistory(useScene)
+    try {
       useScene.getState().updateNodes(updates)
-      queueMicrotask(() => {
+    } finally {
-        syncingAutoOpeningsRef.current = false
+      resumeSceneHistory(useScene)
-      })
+      syncingAutoOpenings = false
+    }
   }
 
   applyUpdates(syncAutoElevatorOpenings(useScene.getState().nodes))
 
   return useScene.subscribe((state, prevState) => {
-      if (syncingAutoOpeningsRef.current) return
+    if (syncingAutoOpenings) return
     if (!hasOpeningRelevantNodeChange(state.nodes, prevState.nodes)) return
     applyUpdates(syncAutoElevatorOpenings(state.nodes))
   })
-  }, [])
+}
+
+export const ElevatorOpeningSystem = () => {
+  useEffect(() => initializeElevatorOpeningSync(), [])
 
   return null
 }

packages/editor/src/components/editor-2d/floorplan-registry-move-overlay.tsx

@@ -197,6 +197,10 @@ export function FloorplanRegistryMoveOverlay() {
 
       const commitFinalStateOrRevert = () => {
         const commitValid = session.canCommit()
+        const freshPlacement = isFreshPlacementMetadata(
+          (useScene.getState().nodes[movingNode.id] as { metadata?: unknown } | undefined)
+            ?.metadata,
+        )
 
         // Claim ownership of the drag teardown so the 3D move tool's
         // unmount-time cleanup skips its restore-from-snapshot — see
@@ -210,6 +214,29 @@ export function FloorplanRegistryMoveOverlay() {
         // planner). For those we still do Phase 1 (revert to baseline)
         // and Phase 2's resume — but Phase 2's write is delegated, and
         // we skip the snapshot-diff finalUpdates path.
+        if (commitValid && freshPlacement) {
+          session.commit?.()
+          const stagedNode = useScene.getState().nodes[movingNode.id]
+          const committedId = stagedNode
+            ? commitFreshPlacementSubtree(
+                movingNode.id as AnyNodeId,
+                {
+                  metadata: stripPlacementMetadataFlags(stagedNode.metadata),
+                  visible: true,
+                } as Partial<AnyNode>,
+              )
+            : null
+          if (historyPaused) {
+            resumeSceneHistory(useScene)
+            historyPaused = false
+          }
+          if (committedId) {
+            sfxEmitter.emit('sfx:item-place')
+            useViewer.getState().setSelection({ selectedIds: [committedId] })
+          }
+          return
+        }
+
         if (commitValid && session.commit) {
           useScene.getState().updateNodes(snapshotsToUpdates(snapshots))
           if (historyPaused) {

packages/editor/src/components/editor-2d/renderers/floorplan-placement-preview-layer.tsx

@@ -12,6 +12,48 @@ import { memo } from 'react'
 import usePlacementPreview from '../../../store/use-placement-preview'
 import { FloorplanGeometryRenderer } from './floorplan-geometry-renderer'
 
+export interface FloorplanNodePreviewProps {
+  node: AnyNode
+  parentNode?: AnyNode | null
+  opacity?: number
+  className?: string
+}
+
+/**
+ * Stateless floor-plan ghost for an already-positioned node. Hosts can use
+ * this to render host-owned placement previews without publishing transient
+ * state into the editor's local placement-preview store.
+ */
+export const FloorplanNodePreview = memo(function FloorplanNodePreview({
+  node,
+  parentNode = null,
+  opacity = 0.5,
+  className,
+}: FloorplanNodePreviewProps) {
+  const builder = nodeRegistry.get(node.type)?.floorplan
+  if (!builder) return null
+
+  const ctx = {
+    resolve: (id: AnyNodeId) => useScene.getState().nodes[id],
+    children: [],
+    siblings: [],
+    parent: parentNode,
+    viewState: undefined,
+  } as unknown as GeometryContext
+
+  const geometry = (builder as (n: AnyNode, c: GeometryContext) => FloorplanGeometry | null)(
+    node,
+    ctx,
+  )
+  if (!geometry) return null
+
+  return (
+    <g className={className} opacity={opacity} pointerEvents="none">
+      <FloorplanGeometryRenderer geometry={geometry} />
+    </g>
+  )
+})
+
 /**
  * Renders a faint, non-interactive ghost of the node being placed by a
  * registry placement tool (e.g. column), following the cursor in the floor
@@ -30,33 +72,9 @@ export const FloorplanPlacementPreviewLayer = memo(function FloorplanPlacementPr
   const parentNode = usePlacementPreview((s) => s.parentNode)
   if (!node) return null
 
-  const builder = nodeRegistry.get(node.type)?.floorplan
-  if (!builder) return null
-
-  // Minimal, unselected context — preview never shows selection chrome
-  // (move handles / resize arrows / hatch live behind `viewState.selected`).
-  // `resolve` reads the scene lazily (a builder rarely calls it for a ghost,
-  // and `parent: null` short-circuits the elevator's level walk) so the layer
-  // never subscribes to / bulk-reads the nodes map during render.
-  // `parentNode` is the synthetic wall for an off-wall door/window ghost so
-  // its builder draws the real swing-arc / pane symbol (see use-placement-preview).
-  const ctx = {
-    resolve: (id: AnyNodeId) => useScene.getState().nodes[id],
-    children: [],
-    siblings: [],
-    parent: parentNode ?? null,
-    viewState: undefined,
-  } as unknown as GeometryContext
-
-  const geometry = (builder as (n: AnyNode, c: GeometryContext) => FloorplanGeometry | null)(
-    node,
-    ctx,
-  )
-  if (!geometry) return null
-
   return (
-    <g data-floorplan-placement-preview opacity={0.5} pointerEvents="none">
+    <g data-floorplan-placement-preview>
-      <FloorplanGeometryRenderer geometry={geometry} />
+      <FloorplanNodePreview node={node} parentNode={parentNode} />
     </g>
   )
 })

packages/editor/src/components/editor/custom-camera-controls.tsx

@@ -4,6 +4,7 @@ import {
   type AnyNodeId,
   type CameraControlEvent,
   type CameraControlFitSceneEvent,
+  type CameraPose,
   emitter,
   sceneRegistry,
   useScene,
@@ -20,6 +21,13 @@ import {
   Spherical,
   Vector3,
 } from 'three'
+import {
+  type CameraPoseApplicationPlan,
+  normalizeCameraPose,
+  planCameraPoseApplication,
+  stepCameraPoseInterpolation,
+  withCameraPoseDistance,
+} from '../../lib/camera-pose'
 import { EDITOR_LAYER } from '../../lib/constants'
 import useEditor from '../../store/use-editor'
 import {
@@ -35,6 +43,8 @@ const tempDelta = new Vector3()
 const tempPosition = new Vector3()
 const tempSize = new Vector3()
 const tempTarget = new Vector3()
+const transitionFreezePosition = new Vector3()
+const transitionFreezeTarget = new Vector3()
 const syncTarget = new Vector3()
 const syncSpherical = new Spherical()
 const keyboardPanSpherical = new Spherical()
@@ -97,6 +107,21 @@ function restoreCameraPose(control: CameraControlsImpl, pose: CameraPoseSnapshot
   )
 }
 
+function freezeCameraControlTransition(control: CameraControlsImpl) {
+  // `stop()` snaps to the transition endpoint, so replace it with the current pose instead.
+  control.getPosition(transitionFreezePosition, false)
+  control.getTarget(transitionFreezeTarget, false)
+  void control.setLookAt(
+    transitionFreezePosition.x,
+    transitionFreezePosition.y,
+    transitionFreezePosition.z,
+    transitionFreezeTarget.x,
+    transitionFreezeTarget.y,
+    transitionFreezeTarget.z,
+    false,
+  )
+}
+
 function isEditableKeyboardTarget(target: EventTarget | null) {
   return (
     target instanceof HTMLInputElement ||
@@ -272,14 +297,18 @@ function resolveCameraViewWidthUpdate(
   return { type: 'none', viewWidth }
 }
 
-function applyCameraViewWidth(control: CameraControlsImpl, update: CameraViewWidthUpdate) {
+function applyCameraViewWidth(
+  control: CameraControlsImpl,
+  update: CameraViewWidthUpdate,
+  enableTransition = true,
+) {
   if (update.type === 'distance') {
-    control.dollyTo(update.distance, true)
+    control.dollyTo(update.distance, enableTransition)
     return
   }
 
   if (update.type === 'zoom') {
-    control.zoomTo(update.zoom, true)
+    control.zoomTo(update.zoom, enableTransition)
   }
 }
 
@@ -347,6 +376,13 @@ function useFirstPersonCameraPoseRestore(
 
 export const CustomCameraControls = () => {
   const controls = useRef<CameraControlsImpl | null>(null)
+  const pendingAppliedPose = useRef<CameraPoseApplicationPlan | null>(null)
+  const activePoseInterpolation = useRef<{
+    camera: Camera
+    control: CameraControlsImpl
+    plan: CameraPoseApplicationPlan
+  } | null>(null)
+  const suppressPoseEvents = useRef(false)
   const keyboardPanKeys = useRef<KeyboardPanState>({
     forward: false,
     backward: false,
@@ -391,6 +427,120 @@ export const CustomCameraControls = () => {
     raycaster.layers.enable(ZONE_LAYER)
   }, [camera, raycaster])
 
+  const freezeActivePoseInterpolation = useCallback(() => {
+    const active = activePoseInterpolation.current
+    if (!active) return
+
+    activePoseInterpolation.current = null
+    freezeCameraControlTransition(active.control)
+  }, [])
+
+  const cancelPoseApplication = useCallback(() => {
+    pendingAppliedPose.current = null
+    try {
+      freezeActivePoseInterpolation()
+    } finally {
+      suppressPoseEvents.current = false
+    }
+  }, [freezeActivePoseInterpolation])
+
+  const beginLocalCameraInteraction = useCallback(() => {
+    cancelPoseApplication()
+    emitter.emit('camera-controls:interaction-start', undefined)
+  }, [cancelPoseApplication])
+
+  const applyPendingPose = useCallback(() => {
+    if (isFirstPersonMode) {
+      cancelPoseApplication()
+      return
+    }
+
+    const plan = pendingAppliedPose.current
+    const control = controls.current
+
+    const active = activePoseInterpolation.current
+    if (active && (active.camera !== camera || active.control !== control)) {
+      try {
+        freezeActivePoseInterpolation()
+      } finally {
+        if (!plan) suppressPoseEvents.current = false
+      }
+    }
+
+    if (!(plan && control)) return
+
+    const cameraMatchesProjection =
+      (plan.pose.projection === 'perspective' && isPerspectiveCamera(camera)) ||
+      (plan.pose.projection === 'orthographic' && isOrthographicCamera(camera))
+    if (!cameraMatchesProjection) return
+
+    pendingAppliedPose.current = null
+    if (plan.perspectiveFov !== null && isPerspectiveCamera(camera)) {
+      camera.fov = plan.perspectiveFov
+      camera.updateProjectionMatrix()
+    }
+    let appliedPlan = plan
+    if (plan.pose.viewWidth !== undefined) {
+      const viewWidthUpdate = resolveCameraViewWidthUpdate(
+        control,
+        camera,
+        plan.pose.viewWidth,
+        viewportSize,
+      )
+      if (viewWidthUpdate.type === 'distance') {
+        appliedPlan = {
+          ...plan,
+          pose: withCameraPoseDistance(plan.pose, viewWidthUpdate.distance),
+        }
+      } else if (viewWidthUpdate.type === 'zoom') {
+        applyCameraViewWidth(control, viewWidthUpdate, false)
+      }
+    }
+
+    clearPendingFloorplanNavigationPose()
+    activePoseInterpolation.current = { camera, control, plan: appliedPlan }
+  }, [
+    camera,
+    cancelPoseApplication,
+    clearPendingFloorplanNavigationPose,
+    freezeActivePoseInterpolation,
+    isFirstPersonMode,
+    viewportSize,
+  ])
+
+  useEffect(() => {
+    applyPendingPose()
+  }, [applyPendingPose])
+
+  useEffect(() => {
+    const handleAppliedPose = (pose: CameraPose) => {
+      if (isFirstPersonMode) return
+
+      const plan = planCameraPoseApplication(pose)
+      if (!plan) return
+
+      pendingAppliedPose.current = plan
+      suppressPoseEvents.current = true
+
+      if (useViewer.getState().cameraMode !== plan.pose.projection) {
+        freezeActivePoseInterpolation()
+        useViewer.getState().setCameraMode(plan.pose.projection)
+        return
+      }
+
+      applyPendingPose()
+    }
+
+    emitter.on('camera-controls:apply-pose', handleAppliedPose)
+    emitter.on('camera-controls:cancel-pose', cancelPoseApplication)
+    return () => {
+      emitter.off('camera-controls:apply-pose', handleAppliedPose)
+      emitter.off('camera-controls:cancel-pose', cancelPoseApplication)
+    }
+  }, [applyPendingPose, cancelPoseApplication, freezeActivePoseInterpolation, isFirstPersonMode])
+
+  useEffect(() => cancelPoseApplication, [cancelPoseApplication])
+
   useEffect(() => {
     // Dev-only: deterministic camera poses for screenshot/automation tooling.
     // A getter, not a snapshot — drei recreates the impl when the default
@@ -568,6 +718,36 @@ export const CustomCameraControls = () => {
     })
   }, [camera, clearPendingFloorplanNavigationPose, isFirstPersonMode, viewportSize])
 
+  const publishCurrentPose = useCallback(() => {
+    if (isFirstPersonMode || suppressPoseEvents.current || !controls.current) return
+
+    controls.current.getPosition(tempPosition, false)
+    controls.current.getTarget(tempTarget, false)
+    const targetDistance = tempPosition.distanceTo(tempTarget)
+    const projection = isPerspectiveCamera(camera)
+      ? 'perspective'
+      : isOrthographicCamera(camera)
+        ? 'orthographic'
+        : null
+    if (!projection) return
+
+    const pose = normalizeCameraPose({
+      position: [tempPosition.x, tempPosition.y, tempPosition.z],
+      target: [tempTarget.x, tempTarget.y, tempTarget.z],
+      projection,
+      viewWidth: getCameraViewWidth(camera, targetDistance, viewportSize),
+      ...(isPerspectiveCamera(camera) ? { fov: camera.fov } : {}),
+    })
+    if (pose) {
+      emitter.emit('camera-controls:pose', pose)
+    }
+  }, [camera, isFirstPersonMode, viewportSize])
+
+  const handleCameraUpdate = useCallback(() => {
+    publishCurrentNavigationPose()
+    publishCurrentPose()
+  }, [publishCurrentNavigationPose, publishCurrentPose])
+
   useEffect(() => {
     if (isFirstPersonMode || (!isFloorplanOpen && currentLevelId === null)) return
 
@@ -584,6 +764,49 @@ export const CustomCameraControls = () => {
   useFrame((_, delta) => {
     if (isFirstPersonMode || !controls.current) return
 
+    const activePose = activePoseInterpolation.current
+    if (activePose) {
+      const control = controls.current
+      if (activePose.camera !== camera || activePose.control !== control) {
+        try {
+          freezeActivePoseInterpolation()
+        } finally {
+          if (!pendingAppliedPose.current) suppressPoseEvents.current = false
+        }
+      } else {
+        control.getPosition(tempPosition, false)
+        control.getTarget(tempTarget, false)
+        const step = stepCameraPoseInterpolation(
+          [tempPosition.x, tempPosition.y, tempPosition.z],
+          [tempTarget.x, tempTarget.y, tempTarget.z],
+          activePose.plan.pose,
+          delta,
+        )
+        try {
+          // Transition-enabled calls retain one rest listener each, so this frame loop owns smoothing.
+          void control.setLookAt(
+            step.position[0],
+            step.position[1],
+            step.position[2],
+            step.target[0],
+            step.target[1],
+            step.target[2],
+            false,
+          )
+          control.update(0)
+        } catch {
+          if (activePoseInterpolation.current === activePose) {
+            activePoseInterpolation.current = null
+            suppressPoseEvents.current = false
+          }
+        }
+        if (step.settled && activePoseInterpolation.current === activePose) {
+          activePoseInterpolation.current = null
+          suppressPoseEvents.current = false
+        }
+      }
+    }
+
     const panKeys = keyboardPanKeys.current
     const horizontal = (panKeys.right ? 1 : 0) - (panKeys.left ? 1 : 0)
     const vertical = (panKeys.forward ? 1 : 0) - (panKeys.backward ? 1 : 0)
@@ -602,7 +825,7 @@ export const CustomCameraControls = () => {
     clearPendingFloorplanNavigationPose()
     if (horizontal !== 0) control.truck(horizontal * step, 0, true)
     if (vertical !== 0) control.forward(vertical * step, true)
-  })
+  }, 0)
 
   // Configure mouse buttons based on control mode and camera mode
   const mouseButtons = useMemo(() => {
@@ -750,7 +973,8 @@ export const CustomCameraControls = () => {
           !(event.metaKey || event.ctrlKey || event.altKey) &&
           !isEditableKeyboardTarget(event.target)
         ) {
-          setKeyboardPanKey(keyboardPanKeys.current, event.code, true)
+          const changed = setKeyboardPanKey(keyboardPanKeys.current, event.code, true)
+          if (changed) beginLocalCameraInteraction()
           clearPendingFloorplanNavigationPose()
           event.preventDefault()
           event.stopPropagation()
@@ -823,6 +1047,7 @@ export const CustomCameraControls = () => {
     }
 
     const onWheel = () => {
+      beginLocalCameraInteraction()
       clearPendingFloorplanNavigationPose()
     }
 
@@ -851,7 +1076,7 @@ export const CustomCameraControls = () => {
     window.addEventListener('pointerup', onPointerUp, true)
     window.addEventListener('pointercancel', onPointerUp, true)
     window.addEventListener('blur', onBlur)
-    gl.domElement.addEventListener('wheel', onWheel, { passive: true })
+    gl.domElement.addEventListener('wheel', onWheel, { capture: true, passive: true })
     updateConfig()
 
     return () => {
@@ -861,29 +1086,27 @@ export const CustomCameraControls = () => {
       window.removeEventListener('pointerup', onPointerUp, true)
       window.removeEventListener('pointercancel', onPointerUp, true)
       window.removeEventListener('blur', onBlur)
-      gl.domElement.removeEventListener('wheel', onWheel)
+      gl.domElement.removeEventListener('wheel', onWheel, true)
       clearKeyboardPanKeys()
       clearNavigationCursor()
     }
-  }, [cameraMode, gl, isPreviewMode, isFirstPersonMode, clearPendingFloorplanNavigationPose])
+  }, [
+    beginLocalCameraInteraction,
+    cameraMode,
+    gl,
+    isPreviewMode,
+    isFirstPersonMode,
+    clearPendingFloorplanNavigationPose,
+  ])
 
   // Cancel any in-progress 2D-origin navigation pose when the user starts
   // dragging (right-click orbit, middle-click pan, touch). `controlstart`
   // fires only for user pointer interactions — not for programmatic
   // moveTo/rotateTo which emit `transitionstart` instead.
-  useEffect(() => {
+  const handleControlStart = useCallback(() => {
-    if (isFirstPersonMode) return
-    const control = controls.current
-    if (!control) return
-
-    const onControlStart = () => {
     clearPendingFloorplanNavigationPose()
-    }
+    beginLocalCameraInteraction()
-    control.addEventListener('controlstart', onControlStart)
+  }, [beginLocalCameraInteraction, clearPendingFloorplanNavigationPose])
-    return () => {
-      control.removeEventListener('controlstart', onControlStart)
-    }
-  }, [isFirstPersonMode, clearPendingFloorplanNavigationPose])
 
   // Preview mode: auto-navigate camera to selected node (viewer behavior)
   const previewTargetNodeId = isPreviewMode
@@ -1211,7 +1434,8 @@ export const CustomCameraControls = () => {
       minDistance={minDistance}
       minPolarAngle={0}
       mouseButtons={mouseButtons}
-      onUpdate={publishCurrentNavigationPose}
+      onControlStart={handleControlStart}
+      onUpdate={handleCameraUpdate}
       onRest={onRest}
       onSleep={onRest}
       onTransitionStart={onTransitionStart}

packages/editor/src/components/editor/floorplan-panel.tsx

@@ -62,6 +62,7 @@ import {
   type ComponentProps,
   memo,
   type MouseEvent as ReactMouseEvent,
+  type ReactNode,
   type PointerEvent as ReactPointerEvent,
   useCallback,
   useEffect,
@@ -5195,8 +5196,10 @@ export function FloorplanPanel({
    * in 2d, 3d, and split modes, while this panel itself may be display:none.
    */
   compassHost,
+  floorplanSceneSlot,
 }: {
   compassHost?: HTMLElement | null
+  floorplanSceneSlot?: ReactNode
 }) {
   const viewportHostRef = useRef<HTMLDivElement>(null)
   const svgRef = useRef<SVGSVGElement>(null)
@@ -5371,6 +5374,18 @@ export function FloorplanPanel({
   )
   const [ceilingDraftPoints, setCeilingDraftPoints] = useState<WallPlanPoint[]>([])
   const [slabDraftPoints, setSlabDraftPoints] = useState<WallPlanPoint[]>([])
+  // Mirror the per-click draft START anchors into the shared draft store so
+  // out-of-tree consumers (such as host-owned preview publishers) see the whole open
+  // segment without subscribing to this panel's state.
+  useEffect(() => {
+    useFloorplanDraftPreview.getState().setWallDraftStart(draftStart)
+  }, [draftStart])
+  useEffect(() => {
+    useFloorplanDraftPreview.getState().setFenceDraftStart(fenceDraftStart)
+  }, [fenceDraftStart])
+  useEffect(() => {
+    useFloorplanDraftPreview.getState().setRoofDraftStart(roofDraftStart)
+  }, [roofDraftStart])
   const [zoneDraftPoints, setZoneDraftPoints] = useState<WallPlanPoint[]>([])
   const [siteBoundaryDraft, setSiteBoundaryDraft] = useState<SiteBoundaryDraft | null>(null)
   const [siteVertexDragState, setSiteVertexDragState] = useState<SiteVertexDragState | null>(null)
@@ -6402,6 +6417,18 @@ export function FloorplanPanel({
     slabDraftPoints,
     zoneDraftPoints,
   ])
+  const activePolygonDraftType = isCeilingBuildActive
+    ? 'ceiling'
+    : isZoneBuildActive
+      ? 'zone'
+      : isSlabBuildActive
+        ? 'slab'
+        : null
+  useEffect(() => {
+    useFloorplanDraftPreview
+      .getState()
+      .setPolygonDraft(activePolygonDraftType, activePolygonDraftPoints)
+  }, [activePolygonDraftPoints, activePolygonDraftType])
   // The cursor-following polygon-draft preview (slab / zone / ceiling) moved into
   // `FloorplanDraftCursorLayer`, which reads the live cursor from the draft store
   // so it re-renders per move without re-rendering this panel.
@@ -8240,9 +8267,17 @@ export function FloorplanPanel({
         setShiftPressed(true)
       }
 
-      if (isStairBuildActive && (event.key === 'r' || event.key === 'R')) {
+      if (
+        isStairBuildActive &&
+        useEditor.getState().viewMode === '2d' &&
+        (event.key === 'r' || event.key === 'R')
+      ) {
         useStairBuildPreview.getState().rotateBy(Math.PI / 4)
-      } else if (isStairBuildActive && (event.key === 't' || event.key === 'T')) {
+      } else if (
+        isStairBuildActive &&
+        useEditor.getState().viewMode === '2d' &&
+        (event.key === 't' || event.key === 'T')
+      ) {
         useStairBuildPreview.getState().rotateBy(-Math.PI / 4)
       }
 
@@ -11220,6 +11255,7 @@ export function FloorplanPanel({
           // panel, so pan/zoom is preserved across the toggle.
           <svg
             className="h-full w-full touch-none"
+            data-pascal-floorplan-2d
             onClick={isMarqueeSelectionToolActive ? undefined : handleSvgClick}
             onContextMenu={(event) => event.preventDefault()}
             onDoubleClick={isMarqueeSelectionToolActive ? undefined : handleBackgroundDoubleClick}
@@ -11396,6 +11432,7 @@ export function FloorplanPanel({
                   <FloorplanWallMoveGhostLayer />
                 </g>
                 <FloorplanMeasurementToolLayer />
+                {floorplanSceneSlot}
               </FloorplanRenderProvider>
               {/* Cursor-driven placement ghost for movingNode when the
                   active kind is registry-driven. Renders via a portal

packages/editor/src/components/editor/index.tsx

@@ -2,6 +2,7 @@
 
 import { Icon } from '@iconify/react'
 import {
+  acquireSceneReadOnlyLease,
   getCatalogMaterialById,
   getLibraryMaterialIdFromRef,
   getSceneMaterialIdFromRef,
@@ -153,6 +154,11 @@ export interface EditorProps {
    */
   inspectorFooter?: ReactNode
 
+  /** Host-owned content mounted inside the editor's React Three Fiber scene. */
+  viewerSceneSlot?: ReactNode
+  /** Host-owned SVG content mounted in the transformed floor-plan scene. */
+  floorplanSceneSlot?: ReactNode
+
   projectId?: string | null
 
   // Persistence — defaults to localStorage when omitted
@@ -715,12 +721,14 @@ const ViewerSceneContent = memo(function ViewerSceneContent({
   isFirstPersonMode,
   isStudioMode,
   onThumbnailCapture,
+  viewerSceneSlot,
 }: {
   isVersionPreviewMode: boolean
   isLoading: boolean
   isFirstPersonMode: boolean
   isStudioMode: boolean
   onThumbnailCapture?: (blob: Blob, cameraData: SnapshotCameraData) => void
+  viewerSceneSlot?: ReactNode
 }) {
   // Studio mode is a clean render/snapshot surface — no selection or editing
   // affordances. It mirrors version-preview's chrome gating on the canvas.
@@ -759,6 +767,7 @@ const ViewerSceneContent = memo(function ViewerSceneContent({
       <ThumbnailGenerator onThumbnailCapture={onThumbnailCapture} />
       {!isFirstPersonMode && <SiteEdgeLabels />}
       <InteractiveSystem />
+      {!noEditing && viewerSceneSlot}
     </>
   )
 })
@@ -941,6 +950,8 @@ const ViewerCanvas = memo(function ViewerCanvas({
   sceneReadyKey,
   onSceneReadyChange,
   onThumbnailCapture,
+  viewerSceneSlot,
+  floorplanSceneSlot,
 }: {
   isVersionPreviewMode: boolean
   isLoading: boolean
@@ -951,6 +962,8 @@ const ViewerCanvas = memo(function ViewerCanvas({
   sceneReadyKey: number
   onSceneReadyChange: (ready: boolean) => void
   onThumbnailCapture?: (blob: Blob, cameraData: SnapshotCameraData) => void
+  viewerSceneSlot?: ReactNode
+  floorplanSceneSlot?: ReactNode
 }) {
   const viewMode = useEditor((s) => s.viewMode)
   const floorplanPaneRatio = useEditor((s) => s.floorplanPaneRatio)
@@ -1027,7 +1040,7 @@ const ViewerCanvas = memo(function ViewerCanvas({
           }}
         >
           <div className="h-full w-full overflow-hidden">
-            <FloorplanPanel compassHost={viewerAreaEl} />
+            <FloorplanPanel compassHost={viewerAreaEl} floorplanSceneSlot={floorplanSceneSlot} />
           </div>
           {viewMode === 'split' && (
             <div
@@ -1075,6 +1088,7 @@ const ViewerCanvas = memo(function ViewerCanvas({
               isStudioMode={isStudioMode}
               isVersionPreviewMode={isVersionPreviewMode}
               onThumbnailCapture={onThumbnailCapture}
+              viewerSceneSlot={viewerSceneSlot}
             />
           </Viewer>
         </div>
@@ -1094,6 +1108,8 @@ export default function Editor({
   viewerToolbarRight,
   stageOverlay,
   inspectorFooter,
+  viewerSceneSlot,
+  floorplanSceneSlot,
   projectId,
   onLoad,
   onSave,
@@ -1209,13 +1225,10 @@ export default function Editor({
 
   // Lock scene graph and reset to select mode when entering version preview
   useEffect(() => {
-    useScene.getState().setReadOnly(isVersionPreviewMode)
+    if (!isVersionPreviewMode) return
-    if (isVersionPreviewMode) {
+    const releaseReadOnly = acquireSceneReadOnlyLease()
     useEditor.getState().setMode('select')
-    }
+    return releaseReadOnly
-    return () => {
-      useScene.getState().setReadOnly(false)
-    }
   }, [isVersionPreviewMode])
 
   useEffect(() => {
@@ -1314,6 +1327,8 @@ export default function Editor({
       onThumbnailCapture={onThumbnailCapture}
       sceneReadyKey={sceneReadyKey}
       showLoader={showLoader}
+      viewerSceneSlot={viewerSceneSlot}
+      floorplanSceneSlot={floorplanSceneSlot}
     />
   )
 

packages/editor/src/components/tools/roof/roof-tool.tsx

@@ -31,6 +31,7 @@ import { EDITOR_LAYER } from '../../../lib/constants'
 import { sfxEmitter } from '../../../lib/sfx-bus'
 import { snapWorldXZForActiveBuilding } from '../../../lib/world-grid-snap'
 import useEditor, { isGridSnapActive, isMagneticSnapActive } from '../../../store/use-editor'
+import { useFloorplanDraftPreview } from '../../../store/use-floorplan-draft-preview'
 import { CursorSphere } from '../shared/cursor-sphere'
 
 const DEFAULT_WALL_HEIGHT = 0.5
@@ -476,6 +477,9 @@ export const RoofTool: React.FC = () => {
       })
 
       if (corner1Ref.current) {
+        const draftPreview = useFloorplanDraftPreview.getState()
+        draftPreview.setRoofDraftStart([corner1Ref.current[0], corner1Ref.current[2]])
+        draftPreview.setRoofDraftEnd([gridX, gridZ])
         updateOutline(corner1Ref.current, cursorPosition)
       }
     }
@@ -497,11 +501,17 @@ export const RoofTool: React.FC = () => {
         setSelection({ selectedIds: [roofId as AnyNode['id']] })
 
         corner1Ref.current = null
+        const draftPreview = useFloorplanDraftPreview.getState()
+        draftPreview.setRoofDraftStart(null)
+        draftPreview.setRoofDraftEnd(null)
         outlineRef.current.visible = false
         alignmentCandidates = collectRoofAlignmentAnchors(useScene.getState().nodes, currentLevelId)
         clearSurfacePlanSnapFeedback()
       } else {
         corner1Ref.current = [gridX, y, gridZ]
+        const draftPreview = useFloorplanDraftPreview.getState()
+        draftPreview.setRoofDraftStart([gridX, gridZ])
+        draftPreview.setRoofDraftEnd([gridX, gridZ])
         sfxEmitter.emit('sfx:structure-build-start')
         setPreview((prev) => ({
           ...prev,
@@ -514,6 +524,9 @@ export const RoofTool: React.FC = () => {
       if (corner1Ref.current) {
         markToolCancelConsumed()
         corner1Ref.current = null
+        const draftPreview = useFloorplanDraftPreview.getState()
+        draftPreview.setRoofDraftStart(null)
+        draftPreview.setRoofDraftEnd(null)
         outlineRef.current.visible = false
         setPreview((prev) => ({ ...prev, corner1: null }))
       }
@@ -531,6 +544,9 @@ export const RoofTool: React.FC = () => {
       clearSurfacePlanSnapFeedback()
 
       corner1Ref.current = null
+      const draftPreview = useFloorplanDraftPreview.getState()
+      draftPreview.setRoofDraftStart(null)
+      draftPreview.setRoofDraftEnd(null)
     }
   }, [currentLevelId, setSelection])
 

packages/editor/src/components/tools/stair/stair-tool.tsx

@@ -31,6 +31,7 @@ import useEditor, {
 } from '../../../store/use-editor'
 
 import useFacingPose from '../../../store/use-facing-pose'
+import { useStairBuildPreview } from '../../../store/use-stair-build-preview'
 import { CursorSphere } from '../shared/cursor-sphere'
 import { getFloorStackPreviewPosition } from '../shared/floor-stack-preview'
 import {
@@ -233,6 +234,7 @@ export const StairTool: React.FC = () => {
 
     // Reset rotation when tool activates
     rotationRef.current = 0
+    useStairBuildPreview.getState().reset()
     if (previewRef.current) previewRef.current.rotation.y = 0
     lastCanonicalPositionRef.current = null
 
@@ -285,6 +287,7 @@ export const StairTool: React.FC = () => {
       const key = `${position[0].toFixed(3)},${position[2].toFixed(3)},${rotation.toFixed(4)}`
       if (key === lastPreviewKey) return
       lastPreviewKey = key
+      useStairBuildPreview.getState().setPreview([position[0], position[2]], rotation)
       const preview = buildPreviewScene(position, rotation)
       const visualPosition = preview
         ? getFloorStackPreviewPosition({
@@ -510,6 +513,7 @@ export const StairTool: React.FC = () => {
       useAlignmentGuides.getState().clear()
       openingPreview.clear()
       useFacingPose.getState().clear()
+      useStairBuildPreview.getState().reset()
     }
   }, [currentLevelId])
 

packages/editor/src/components/tools/zone/zone-tool.tsx

@@ -18,6 +18,7 @@ import {
 } from './../../../lib/surface-plan-snap'
 import { snapWorldXZForActiveBuilding } from './../../../lib/world-grid-snap'
 import useEditor, { isAngleSnapActive, isGridSnapActive } from './../../../store/use-editor'
+import { useFloorplanDraftPreview } from './../../../store/use-floorplan-draft-preview'
 import { CursorSphere } from '../shared/cursor-sphere'
 
 const Y_OFFSET = 0.02
@@ -79,6 +80,20 @@ export const ZoneTool: React.FC = () => {
     levelY: 0,
   })
 
+  useEffect(() => {
+    useFloorplanDraftPreview.getState().setPolygonDraft('zone', preview.points)
+  }, [preview.points])
+  useEffect(
+    () => () => {
+      const draftPreview = useFloorplanDraftPreview.getState()
+      if (draftPreview.polygonDraftType === 'zone') {
+        draftPreview.setPolygonDraft(null, [])
+      }
+      draftPreview.setCursorPoint(null)
+    },
+    [],
+  )
+
   useEffect(() => {
     if (!currentLevelId) return
 
@@ -192,6 +207,7 @@ export const ZoneTool: React.FC = () => {
         event.localPosition[2],
       ])
       snappedCursorPosition = displayPoint
+      useFloorplanDraftPreview.getState().setCursorPoint(displayPoint)
 
       // Play snap sound when the snapped position changes during drawing — only
       // when a quantizing mode is active (off / lines move continuously).

packages/editor/src/index.tsx

@@ -2,7 +2,21 @@
 // own shells on top of `@pascal-app/editor` (community-app, embedders)
 // don't have to learn three separate package imports. The canonical
 // definitions still live in `@pascal-app/core` / `@pascal-app/viewer`.
-export { useScene } from '@pascal-app/core'
+export {
+  type ApplySceneSnapshotOptions,
+  acquireSceneReadOnlyLease,
+  applyScenePatch,
+  applySceneSnapshot,
+  type SceneCommit,
+  type SceneCommitListener,
+  type SceneCommitOrigin,
+  type SceneMaterialPatch,
+  type SceneNodePatch,
+  type ScenePatch,
+  type SceneSnapshot,
+  subscribeSceneCommits,
+  useScene,
+} from '@pascal-app/core'
 export { useViewer } from '@pascal-app/viewer'
 export type { EditorProps } from './components/editor'
 export { default as Editor } from './components/editor'
@@ -66,6 +80,10 @@ export {
   type SnapshotCameraData,
   ThumbnailGenerator,
 } from './components/editor/thumbnail-generator'
+export {
+  FloorplanNodePreview,
+  type FloorplanNodePreviewProps,
+} from './components/editor-2d/renderers/floorplan-placement-preview-layer'
 // SVG path builders for arc / annular-sector / arrow-head shapes —
 // inlined into `kind: 'path'` / `kind: 'polygon'` primitives by curved
 // stair rendering in `nodes/src/stair/floorplan.ts`.
@@ -287,12 +305,19 @@ export {
 } from './lib/floorplan'
 export { commitFreshPlacementSubtree } from './lib/fresh-planar-placement'
 export { exportSceneToGlb } from './lib/glb-export'
+export {
+  type HistoryCommandDelegate,
+  installHistoryCommandDelegate,
+  runRedo,
+  runUndo,
+} from './lib/history'
 export {
   boundaryReshapeScope,
   curveReshapeScope,
   endpointReshapeScope,
   holeEditScope,
   movingNodeOf,
+  scopeNodeId,
 } from './lib/interaction/scope'
 export {
   buildResetSurfaceMaterialUpdates,
@@ -429,6 +454,7 @@ export {
 } from './store/use-editor'
 export { default as useFacingPose, type FacingPose } from './store/use-facing-pose'
 export { default as useFenceCurveDraft } from './store/use-fence-curve-draft'
+export { useFloorplanDraftPreview } from './store/use-floorplan-draft-preview'
 export {
   default as useInteractionScope,
   getEditingHole,
@@ -466,6 +492,13 @@ export {
   type PaletteViewProps,
   usePaletteViewRegistry,
 } from './store/use-palette-view-registry'
+export {
+  type PathDraftKind,
+  type PathDraftParameter,
+  type PathDraftParameters,
+  type PathDraftPoint,
+  usePathDraftPreview,
+} from './store/use-path-draft-preview'
 export { default as usePlacementPreview } from './store/use-placement-preview'
 export {
   activateQuickMeasurementHudSource,
@@ -477,6 +510,10 @@ export {
   useQuickMeasurementHud,
 } from './store/use-quick-measurement-hud'
 export { default as useSegmentDraftChain } from './store/use-segment-draft-chain'
+export {
+  type StairPreviewPoint,
+  useStairBuildPreview,
+} from './store/use-stair-build-preview'
 export { useUploadStore } from './store/use-upload'
 export { useWallMoveGhosts, type WallMoveGhostBridge } from './store/use-wall-move-ghosts'
 export {

packages/editor/src/lib/camera-pose.test.ts

@@ -0,0 +1,213 @@
+import { describe, expect, test } from 'bun:test'
+import {
+  normalizeCameraPose,
+  planCameraPoseApplication,
+  stepCameraPoseInterpolation,
+  withCameraPoseDistance,
+} from './camera-pose'
+
+describe('camera pose', () => {
+  test('normalizes a finite pose without retaining input tuples', () => {
+    const position: [number, number, number] = [1, 2, 3]
+    const target: [number, number, number] = [4, 5, 6]
+    const pose = normalizeCameraPose({
+      position,
+      target,
+      projection: 'perspective',
+      fov: 50,
+      viewWidth: 12,
+    })
+
+    expect(pose).toEqual({
+      fov: 50,
+      position,
+      projection: 'perspective',
+      target,
+      viewWidth: 12,
+    })
+    expect(pose?.position).not.toBe(position)
+    expect(pose?.target).not.toBe(target)
+  })
+
+  test('rejects non-finite, malformed, and unknown camera poses', () => {
+    expect(normalizeCameraPose(null)).toBeNull()
+    expect(
+      normalizeCameraPose({
+        position: [1, 2],
+        target: [4, 5, 6],
+        projection: 'perspective',
+      }),
+    ).toBeNull()
+    expect(
+      normalizeCameraPose({
+        position: [1, Number.NaN, 3],
+        target: [4, 5, 6],
+        projection: 'perspective',
+      }),
+    ).toBeNull()
+    expect(
+      normalizeCameraPose({
+        position: [1, 2, 3],
+        target: [4, 5, Number.POSITIVE_INFINITY],
+        projection: 'perspective',
+      }),
+    ).toBeNull()
+    expect(
+      normalizeCameraPose({
+        position: [1, 2, 3],
+        target: [4, 5, 6],
+        projection: 'panoramic',
+      }),
+    ).toBeNull()
+    expect(
+      normalizeCameraPose({
+        position: [1, 2, 3],
+        target: [4, 5, 6],
+        projection: 'perspective',
+        fov: Number.NaN,
+      }),
+    ).toBeNull()
+    expect(
+      normalizeCameraPose({
+        position: [1, 2, 3],
+        target: [4, 5, 6],
+        projection: 'orthographic',
+        viewWidth: 0,
+      }),
+    ).toBeNull()
+    expect(
+      normalizeCameraPose({
+        position: [1, 2, 3],
+        target: [4, 5, 6],
+        projection: 'orthographic',
+        viewWidth: Number.POSITIVE_INFINITY,
+      }),
+    ).toBeNull()
+  })
+
+  test('plans only perspective fov application and clamps it to a safe range', () => {
+    expect(
+      planCameraPoseApplication({
+        position: [1, 2, 3],
+        target: [4, 5, 6],
+        projection: 'perspective',
+        fov: 0,
+      })?.perspectiveFov,
+    ).toBe(1)
+    expect(
+      planCameraPoseApplication({
+        position: [1, 2, 3],
+        target: [4, 5, 6],
+        projection: 'perspective',
+        fov: 200,
+      })?.perspectiveFov,
+    ).toBe(179)
+    expect(
+      planCameraPoseApplication({
+        position: [1, 2, 3],
+        target: [4, 5, 6],
+        projection: 'orthographic',
+        fov: 70,
+      })?.perspectiveFov,
+    ).toBeNull()
+  })
+
+  test('interpolates toward the latest pose and converges exactly', () => {
+    const destination = {
+      position: [12, 6, -4] as [number, number, number],
+      target: [2, 1, 3] as [number, number, number],
+      projection: 'perspective' as const,
+    }
+    const first = stepCameraPoseInterpolation([0, 0, 0], [0, 0, 0], destination, 0.016)
+    expect(first.settled).toBe(false)
+    expect(first.position[0]).toBeGreaterThan(0)
+    expect(first.position[0]).toBeLessThan(destination.position[0])
+
+    let position = first.position
+    let target = first.target
+    let settled = first.settled
+    for (let frame = 0; frame < 240 && !settled; frame += 1) {
+      const step = stepCameraPoseInterpolation(position, target, destination, 0.016)
+      position = step.position
+      target = step.target
+      settled = step.settled
+    }
+
+    expect(settled).toBe(true)
+    expect(position).toEqual(destination.position)
+    expect(target).toEqual(destination.target)
+  })
+
+  test('settles an already-current pose without advancing on an invalid delta', () => {
+    const destination = {
+      position: [1, 2, 3] as [number, number, number],
+      target: [4, 5, 6] as [number, number, number],
+      projection: 'orthographic' as const,
+    }
+    expect(
+      stepCameraPoseInterpolation(
+        destination.position,
+        destination.target,
+        destination,
+        Number.NaN,
+      ),
+    ).toEqual({
+      position: destination.position,
+      settled: true,
+      target: destination.target,
+    })
+    expect(stepCameraPoseInterpolation([0, 0, 0], [0, 0, 0], destination, Number.NaN)).toEqual({
+      position: [0, 0, 0],
+      settled: false,
+      target: [0, 0, 0],
+    })
+  })
+
+  test('retargets the bounded interpolation owner to the latest pose', () => {
+    const first = stepCameraPoseInterpolation(
+      [0, 0, 0],
+      [0, 0, 0],
+      {
+        position: [10, 0, 0],
+        target: [5, 0, 0],
+        projection: 'perspective',
+      },
+      0.016,
+    )
+    const retargeted = stepCameraPoseInterpolation(
+      first.position,
+      first.target,
+      {
+        position: [-10, 0, 0],
+        target: [-5, 0, 0],
+        projection: 'perspective',
+      },
+      0.1,
+    )
+
+    expect(retargeted.position[0]).toBeLessThan(first.position[0])
+    expect(retargeted.target[0]).toBeLessThan(first.target[0])
+  })
+
+  test('preserves view direction while adapting distance to the local viewport', () => {
+    const pose = {
+      position: [4, 6, 12] as [number, number, number],
+      target: [1, 2, 3] as [number, number, number],
+      projection: 'perspective' as const,
+      viewWidth: 20,
+    }
+    const adapted = withCameraPoseDistance(pose, 5)
+    const sourceDirection = pose.position.map((value, index) => value - pose.target[index]!)
+    const adaptedDirection = adapted.position.map((value, index) => value - adapted.target[index]!)
+    const sourceLength = Math.hypot(...sourceDirection)
+
+    expect(Math.hypot(...adaptedDirection)).toBeCloseTo(5)
+    const expectedDirection = sourceDirection.map((component) => component * (5 / sourceLength))
+    expect(adaptedDirection[0]).toBeCloseTo(expectedDirection[0]!)
+    expect(adaptedDirection[1]).toBeCloseTo(expectedDirection[1]!)
+    expect(adaptedDirection[2]).toBeCloseTo(expectedDirection[2]!)
+    expect(adapted.target).toEqual(pose.target)
+    expect(adapted.target).not.toBe(pose.target)
+    expect(pose.position).toEqual([4, 6, 12])
+  })
+})

packages/editor/src/lib/camera-pose.ts

@@ -0,0 +1,160 @@
+import type { CameraPose } from '@pascal-app/core'
+
+const MIN_PERSPECTIVE_FOV = 1
+const MAX_PERSPECTIVE_FOV = 179
+const INTERPOLATION_TIME_CONSTANT_SECONDS = 0.08
+const MAX_INTERPOLATION_DELTA_SECONDS = 0.1
+const INTERPOLATION_SETTLE_DISTANCE = 0.001
+
+export type CameraPoseApplicationPlan = {
+  pose: CameraPose
+  perspectiveFov: number | null
+}
+
+export type CameraPoseInterpolationStep = {
+  position: [number, number, number]
+  settled: boolean
+  target: [number, number, number]
+}
+
+function finiteVectorTuple(value: unknown): [number, number, number] | null {
+  if (
+    !(
+      Array.isArray(value) &&
+      value.length === 3 &&
+      value.every((component) => typeof component === 'number' && Number.isFinite(component))
+    )
+  ) {
+    return null
+  }
+
+  return [value[0], value[1], value[2]]
+}
+
+export function normalizeCameraPose(value: unknown): CameraPose | null {
+  if (!(typeof value === 'object' && value !== null)) {
+    return null
+  }
+
+  const candidate = value as Partial<CameraPose>
+  const position = finiteVectorTuple(candidate.position)
+  const target = finiteVectorTuple(candidate.target)
+  if (
+    !(
+      position &&
+      target &&
+      (candidate.projection === 'perspective' || candidate.projection === 'orthographic')
+    )
+  ) {
+    return null
+  }
+
+  if (
+    candidate.fov !== undefined &&
+    !(typeof candidate.fov === 'number' && Number.isFinite(candidate.fov))
+  ) {
+    return null
+  }
+
+  if (
+    candidate.viewWidth !== undefined &&
+    !(
+      typeof candidate.viewWidth === 'number' &&
+      Number.isFinite(candidate.viewWidth) &&
+      candidate.viewWidth > 0
+    )
+  ) {
+    return null
+  }
+
+  return {
+    ...(candidate.fov === undefined ? {} : { fov: candidate.fov }),
+    position,
+    projection: candidate.projection,
+    target,
+    ...(candidate.viewWidth === undefined ? {} : { viewWidth: candidate.viewWidth }),
+  }
+}
+
+export function planCameraPoseApplication(value: unknown): CameraPoseApplicationPlan | null {
+  const pose = normalizeCameraPose(value)
+  if (!pose) {
+    return null
+  }
+
+  return {
+    pose,
+    perspectiveFov:
+      pose.projection === 'perspective' && pose.fov !== undefined
+        ? Math.min(Math.max(pose.fov, MIN_PERSPECTIVE_FOV), MAX_PERSPECTIVE_FOV)
+        : null,
+  }
+}
+
+function interpolateVectorTuple(
+  current: [number, number, number],
+  destination: [number, number, number],
+  alpha: number,
+): { settled: boolean; value: [number, number, number] } {
+  const dx = destination[0] - current[0]
+  const dy = destination[1] - current[1]
+  const dz = destination[2] - current[2]
+  const settleDistanceSquared = INTERPOLATION_SETTLE_DISTANCE ** 2
+  if (dx * dx + dy * dy + dz * dz <= settleDistanceSquared) {
+    return { settled: true, value: [...destination] }
+  }
+
+  const value: [number, number, number] = [
+    current[0] + dx * alpha,
+    current[1] + dy * alpha,
+    current[2] + dz * alpha,
+  ]
+  const remainingX = destination[0] - value[0]
+  const remainingY = destination[1] - value[1]
+  const remainingZ = destination[2] - value[2]
+  const settled =
+    remainingX * remainingX + remainingY * remainingY + remainingZ * remainingZ <=
+    settleDistanceSquared
+
+  return { settled, value: settled ? [...destination] : value }
+}
+
+export function withCameraPoseDistance(pose: CameraPose, distance: number): CameraPose {
+  const dx = pose.position[0] - pose.target[0]
+  const dy = pose.position[1] - pose.target[1]
+  const dz = pose.position[2] - pose.target[2]
+  const currentDistance = Math.hypot(dx, dy, dz)
+  if (!(Number.isFinite(distance) && distance > 0 && currentDistance > 0)) {
+    return { ...pose, position: [...pose.position], target: [...pose.target] }
+  }
+
+  const scale = distance / currentDistance
+  return {
+    ...pose,
+    position: [
+      pose.target[0] + dx * scale,
+      pose.target[1] + dy * scale,
+      pose.target[2] + dz * scale,
+    ],
+    target: [...pose.target],
+  }
+}
+
+export function stepCameraPoseInterpolation(
+  currentPosition: [number, number, number],
+  currentTarget: [number, number, number],
+  destination: CameraPose,
+  deltaSeconds: number,
+): CameraPoseInterpolationStep {
+  const finiteDelta = Number.isFinite(deltaSeconds) ? deltaSeconds : 0
+  const elapsed = Math.min(Math.max(finiteDelta, 0), MAX_INTERPOLATION_DELTA_SECONDS)
+  const alpha = 1 - Math.exp(-elapsed / INTERPOLATION_TIME_CONSTANT_SECONDS)
+  const position = interpolateVectorTuple(currentPosition, destination.position, alpha)
+  const target = interpolateVectorTuple(currentTarget, destination.target, alpha)
+
+  return {
+    position: position.value,
+    settled: position.settled && target.settled,
+    target: target.value,
+  }
+}

packages/editor/src/lib/fresh-planar-placement.test.ts

@@ -8,6 +8,8 @@ import {
   findLevelAncestorId,
   nodeRegistry,
   registerNode,
+  type SceneCommit,
+  subscribeSceneCommits,
   useScene,
 } from '@pascal-app/core'
 import { z } from 'zod'
@@ -170,12 +172,15 @@ describe('commitFreshPlacementSubtree', () => {
   })
 
   test('commits a fresh draft as one undoable clean subtree', () => {
+    const commits: SceneCommit[] = []
+    const unsubscribe = subscribeSceneCommits((commit) => commits.push(commit))
     useScene.temporal.getState().pause()
 
     const committedId = commitFreshPlacementSubtree(SHELF_ID, {
       position: [2, 0, 3],
       visible: true,
     } as Partial<AnyNode>)
+    unsubscribe()
 
     expect(committedId).toBeTruthy()
     expect(committedId).not.toBe(SHELF_ID)
@@ -192,6 +197,12 @@ describe('commitFreshPlacementSubtree', () => {
     expect((useScene.getState().nodes[LEVEL_ID] as { children: AnyNodeId[] }).children).toEqual([
       finalId,
     ])
+    expect(commits).toHaveLength(1)
+    expect(commits[0]?.origin).toBe('local')
+    expect(commits[0]?.before.nodes[SHELF_ID]).toBeUndefined()
+    expect(commits[0]?.before.nodes[finalId]).toBeUndefined()
+    expect(commits[0]?.current.nodes[SHELF_ID]).toBeUndefined()
+    expect(commits[0]?.current.nodes[finalId]).toEqual(committed)
 
     useScene.temporal.getState().resume()
     useScene.temporal.getState().undo()

packages/editor/src/lib/history.test.ts

@@ -0,0 +1,96 @@
+import { afterEach, beforeEach, describe, expect, mock, test } from 'bun:test'
+import {
+  type AnyNode,
+  type AnyNodeId,
+  BuildingNode,
+  clearSceneHistory,
+  LevelNode,
+  useScene,
+} from '@pascal-app/core'
+import { installHistoryCommandDelegate, runRedo, runUndo } from './history'
+
+type RafFn = (cb: (time: number) => void) => number
+;(globalThis as unknown as { requestAnimationFrame?: RafFn }).requestAnimationFrame ??= (cb) => {
+  cb(0)
+  return 0
+}
+;(globalThis as unknown as { cancelAnimationFrame?: (id: number) => void }).cancelAnimationFrame ??=
+  () => {}
+
+const BUILDING_ID = 'building_history_controller' as AnyNodeId
+const LEVEL_ID = 'level_history_controller' as AnyNodeId
+let disposeController = () => {}
+
+function levelNumber(): number {
+  return (useScene.getState().nodes[LEVEL_ID] as { level: number }).level
+}
+
+describe('editor history controller', () => {
+  beforeEach(() => {
+    disposeController()
+    disposeController = () => {}
+    const level = LevelNode.parse({
+      id: LEVEL_ID,
+      parentId: BUILDING_ID,
+      children: [],
+      level: 0,
+    })
+    const building = BuildingNode.parse({
+      id: BUILDING_ID,
+      parentId: null,
+      children: [LEVEL_ID],
+    })
+    useScene.setState({
+      nodes: { [BUILDING_ID]: building, [LEVEL_ID]: level },
+      rootNodeIds: [BUILDING_ID],
+      dirtyNodes: new Set<AnyNodeId>(),
+      collections: {},
+      materials: {},
+      readOnly: false,
+    } as never)
+    clearSceneHistory()
+    useScene.getState().updateNode(LEVEL_ID, { level: 1 } as Partial<AnyNode>)
+  })
+
+  afterEach(() => {
+    disposeController()
+    disposeController = () => {}
+  })
+
+  test('delegates undo and redo while a host delegate is installed', () => {
+    const undo = mock(() => {})
+    const redo = mock(() => {})
+    disposeController = installHistoryCommandDelegate({ undo, redo })
+
+    runUndo()
+    runRedo()
+
+    expect(undo).toHaveBeenCalledTimes(1)
+    expect(redo).toHaveBeenCalledTimes(1)
+    expect(levelNumber()).toBe(1)
+    expect(useScene.temporal.getState().pastStates).toHaveLength(1)
+  })
+
+  test('falls back to standalone Zundo undo and redo when no controller is installed', () => {
+    runUndo()
+    expect(levelNumber()).toBe(0)
+    expect(useScene.temporal.getState().futureStates).toHaveLength(1)
+
+    runRedo()
+    expect(levelNumber()).toBe(1)
+    expect(useScene.temporal.getState().pastStates).toHaveLength(1)
+  })
+
+  test('an older cleanup cannot uninstall a newer controller', () => {
+    const firstUndo = mock(() => {})
+    const stopFirst = installHistoryCommandDelegate({ undo: firstUndo, redo: () => {} })
+    const secondUndo = mock(() => {})
+    disposeController = installHistoryCommandDelegate({ undo: secondUndo, redo: () => {} })
+
+    stopFirst()
+    runUndo()
+
+    expect(firstUndo).toHaveBeenCalledTimes(0)
+    expect(secondUndo).toHaveBeenCalledTimes(1)
+  })
+})

packages/editor/src/lib/history.ts

@@ -1,5 +1,19 @@
 import { useLiveNodeOverrides, useLiveTransforms, useScene } from '@pascal-app/core'
 
+export type HistoryCommandDelegate = {
+  undo: () => void
+  redo: () => void
+}
+
+let historyCommandDelegate: HistoryCommandDelegate | null = null
+
+export function installHistoryCommandDelegate(delegate: HistoryCommandDelegate): () => void {
+  historyCommandDelegate = delegate
+  return () => {
+    if (historyCommandDelegate === delegate) historyCommandDelegate = null
+  }
+}
+
 function refreshSceneAfterHistoryJump() {
   useLiveNodeOverrides.getState().clearAll()
   useLiveTransforms.getState().clearAll()
@@ -11,11 +25,19 @@ function refreshSceneAfterHistoryJump() {
 }
 
 export function runUndo() {
+  if (historyCommandDelegate) {
+    historyCommandDelegate.undo()
+    return
+  }
   useScene.temporal.getState().undo()
   refreshSceneAfterHistoryJump()
 }
 
 export function runRedo() {
+  if (historyCommandDelegate) {
+    historyCommandDelegate.redo()
+    return
+  }
   useScene.temporal.getState().redo()
   refreshSceneAfterHistoryJump()
 }

packages/editor/src/store/live-draft-preview-stores.test.ts

@@ -0,0 +1,136 @@
+import { afterEach, describe, expect, test } from 'bun:test'
+import useFenceCurveDraft from './use-fence-curve-draft'
+import { useFloorplanDraftPreview } from './use-floorplan-draft-preview'
+import { usePathDraftPreview } from './use-path-draft-preview'
+import { useStairBuildPreview } from './use-stair-build-preview'
+
+afterEach(() => {
+  useFenceCurveDraft.getState().reset()
+  useFloorplanDraftPreview.getState().reset()
+  usePathDraftPreview.getState().reset()
+  useStairBuildPreview.getState().reset()
+})
+
+describe('live draft preview stores', () => {
+  test('dedupes polygon snapshots and owns an immutable point copy', () => {
+    let changes = 0
+    const unsubscribe = useFloorplanDraftPreview.subscribe(() => {
+      changes += 1
+    })
+    const points: Array<[number, number]> = [
+      [0, 0],
+      [2, 0],
+    ]
+    useFloorplanDraftPreview.getState().setPolygonDraft('slab', points)
+    useFloorplanDraftPreview.getState().setPolygonDraft('slab', points)
+    points[0]![0] = 9
+
+    expect(changes).toBe(1)
+    expect(useFloorplanDraftPreview.getState().polygonDraftPoints).toEqual([
+      [0, 0],
+      [2, 0],
+    ])
+    unsubscribe()
+  })
+
+  test('publishes stair point and rotation atomically', () => {
+    let changes = 0
+    const unsubscribe = useStairBuildPreview.subscribe(() => {
+      changes += 1
+    })
+    useStairBuildPreview.getState().setPreview([3, 4], Math.PI / 2)
+    useStairBuildPreview.getState().setPreview([3, 4], Math.PI / 2)
+
+    expect(changes).toBe(1)
+    expect(useStairBuildPreview.getState()).toMatchObject({
+      point: [3, 4],
+      rotation: Math.PI / 2,
+    })
+    unsubscribe()
+  })
+
+  test('dedupes curved-fence control points and cursor', () => {
+    let changes = 0
+    const unsubscribe = useFenceCurveDraft.subscribe(() => {
+      changes += 1
+    })
+    const points: Array<[number, number]> = [
+      [0, 0],
+      [1, 1],
+    ]
+    useFenceCurveDraft.getState().setDraft(points, [2, 0])
+    useFenceCurveDraft.getState().setDraft(points, [2, 0])
+    points[0]![0] = 5
+
+    expect(changes).toBe(1)
+    expect(useFenceCurveDraft.getState()).toMatchObject({
+      cursor: [2, 0],
+      pointCount: 2,
+      points: [
+        [0, 0],
+        [1, 1],
+      ],
+    })
+    unsubscribe()
+  })
+
+  test('dedupes path drafts and owns immutable point, parameter, and related-node copies', () => {
+    let changes = 0
+    const unsubscribe = usePathDraftPreview.subscribe(() => {
+      changes += 1
+    })
+    const points: Array<[number, number, number]> = [[0, 1, 2]]
+    const parameters = { diameter: 6, shape: 'round' }
+    const relatedNodes = [
+      {
+        angle: 90,
+        branchAngle: 90,
+        diameter: 6,
+        diameter2: 6,
+        ductMaterial: 'sheet-metal' as const,
+        fittingType: 'elbow' as const,
+        height: 8,
+        height2: 8,
+        id: 'duct-fitting_live-draft-0' as const,
+        metadata: {},
+        object: 'node' as const,
+        parentId: 'level_1' as const,
+        position: [1, 2, 3] as [number, number, number],
+        rotation: [0, 0, 0] as [number, number, number],
+        shape: 'round' as const,
+        shape2: 'round' as const,
+        slots: undefined,
+        system: 'supply' as const,
+        type: 'duct-fitting' as const,
+        visible: true,
+        width: 14,
+        width2: 14,
+      },
+    ]
+    usePathDraftPreview
+      .getState()
+      .setDraft('duct-segment', points, [3, 4, 5], parameters, relatedNodes)
+    usePathDraftPreview
+      .getState()
+      .setDraft('duct-segment', points, [3, 4, 5], parameters, relatedNodes)
+    points[0]![0] = 9
+    parameters.diameter = 12
+    relatedNodes[0]!.position[0] = 9
+
+    expect(changes).toBe(1)
+    expect(usePathDraftPreview.getState()).toMatchObject({
+      cursor: [3, 4, 5],
+      kind: 'duct-segment',
+      parameters: { diameter: 6, shape: 'round' },
+      points: [[0, 1, 2]],
+      relatedNodes: [
+        expect.objectContaining({
+          id: 'duct-fitting_live-draft-0',
+          position: [1, 2, 3],
+          type: 'duct-fitting',
+        }),
+      ],
+    })
+    unsubscribe()
+  })
+})

packages/editor/src/store/use-fence-curve-draft.ts

@@ -1,21 +1,51 @@
-// Ephemeral store: how many points the in-progress curved-fence draft has
+// Ephemeral store for the in-progress curved-fence draft. Written by the 3D
-// placed. Written by the 3D spline draft tool (`@pascal-app/nodes`
+// spline tool and read by the contextual helper plus out-of-tree consumers.
-// fence/tool.tsx) and read by the contextual helper so the "finish curve" hint
+// Reset on commit, cancel, and unmount — never persisted or recorded in undo
-// only surfaces once the user has actually started drawing. Reset on commit,
+// history.
-// cancel, and unmount — never persisted, never in undo history.
 
 import { create } from 'zustand'
 
+export type FenceCurveDraftPoint = [number, number]
+
 type FenceCurveDraftState = {
   pointCount: number
-  setPointCount(count: number): void
+  points: FenceCurveDraftPoint[]
+  cursor: FenceCurveDraftPoint | null
+  setDraft(points: readonly FenceCurveDraftPoint[], cursor: FenceCurveDraftPoint | null): void
   reset(): void
 }
 
+function pointsEqual(a: readonly FenceCurveDraftPoint[], b: readonly FenceCurveDraftPoint[]) {
+  return (
+    a.length === b.length &&
+    a.every((point, index) => point[0] === b[index]?.[0] && point[1] === b[index]?.[1])
+  )
+}
+
 const useFenceCurveDraft = create<FenceCurveDraftState>((set) => ({
   pointCount: 0,
-  setPointCount: (count) => set({ pointCount: count }),
+  points: [],
-  reset: () => set({ pointCount: 0 }),
+  cursor: null,
+  setDraft: (points, cursor) =>
+    set((state) => {
+      const sameCursor =
+        (!cursor && !state.cursor) ||
+        Boolean(
+          cursor && state.cursor && state.cursor[0] === cursor[0] && state.cursor[1] === cursor[1],
+        )
+      if (sameCursor && pointsEqual(state.points, points)) return state
+      return {
+        pointCount: points.length,
+        points: points.map(([x, z]) => [x, z] as FenceCurveDraftPoint),
+        cursor: cursor ? [cursor[0], cursor[1]] : null,
+      }
+    }),
+  reset: () =>
+    set((state) =>
+      state.pointCount === 0 && state.points.length === 0 && state.cursor === null
+        ? state
+        : { pointCount: 0, points: [], cursor: null },
+    ),
 }))
 
 export default useFenceCurveDraft

packages/editor/src/store/use-floorplan-draft-preview.ts

@@ -17,6 +17,8 @@ import { create } from 'zustand'
 /** Screen-space (SVG-local px) cursor point — drives the coordinate badge. */
 type SvgPoint = { x: number; y: number }
 
+export type FloorplanPolygonDraftType = 'ceiling' | 'slab' | 'zone'
+
 type FloorplanDraftPreviewState = {
   /** Snapped plan-XZ point under the cursor; drives the crosshair + the
    *  cursor-following polygon-draft preview. `null` when idle. */
@@ -28,11 +30,18 @@ type FloorplanDraftPreviewState = {
   cursorPosition: SvgPoint | null
   /** Live END point of the open wall / fence / roof draft segment — the per-move
    *  endpoint that drives the 2D draft polygon + measurement. Each is `null`
-   *  unless that tool's draft is open. The START points stay in panel state
+   *  unless that tool's draft is open. The START points are mirrored here (set
-   *  (set per click, low-frequency). */
+   *  per click / per 3D draft move) so out-of-tree consumers — e.g. the hosted
+   *  host-owned preview publishers — can observe the whole open
+   *  segment; panel state remains the 2D interaction source of truth. */
   wallDraftEnd: WallPlanPoint | null
   fenceDraftEnd: WallPlanPoint | null
   roofDraftEnd: WallPlanPoint | null
+  wallDraftStart: WallPlanPoint | null
+  fenceDraftStart: WallPlanPoint | null
+  roofDraftStart: WallPlanPoint | null
+  polygonDraftType: FloorplanPolygonDraftType | null
+  polygonDraftPoints: WallPlanPoint[]
   /** Set the snapped cursor point. No-ops (skips the store update, so
    *  subscribers don't re-render) when unchanged — `grid:move` fires far more
    *  often than the snapped cell actually changes. */
@@ -42,11 +51,28 @@ type FloorplanDraftPreviewState = {
   setWallDraftEnd(point: WallPlanPoint | null): void
   setFenceDraftEnd(point: WallPlanPoint | null): void
   setRoofDraftEnd(point: WallPlanPoint | null): void
+  setWallDraftStart(point: WallPlanPoint | null): void
+  setFenceDraftStart(point: WallPlanPoint | null): void
+  setRoofDraftStart(point: WallPlanPoint | null): void
+  setPolygonDraft(type: FloorplanPolygonDraftType | null, points: readonly WallPlanPoint[]): void
   reset(): void
 }
 
+function planPointsEqual(a: readonly WallPlanPoint[], b: readonly WallPlanPoint[]) {
+  return (
+    a.length === b.length &&
+    a.every((point, index) => point[0] === b[index]?.[0] && point[1] === b[index]?.[1])
+  )
+}
+
 function setPlanPointField(
-  field: 'wallDraftEnd' | 'fenceDraftEnd' | 'roofDraftEnd',
+  field:
+    | 'fenceDraftEnd'
+    | 'fenceDraftStart'
+    | 'roofDraftEnd'
+    | 'roofDraftStart'
+    | 'wallDraftEnd'
+    | 'wallDraftStart',
   point: WallPlanPoint | null,
 ) {
   return (
@@ -65,6 +91,11 @@ export const useFloorplanDraftPreview = create<FloorplanDraftPreviewState>((set)
   wallDraftEnd: null,
   fenceDraftEnd: null,
   roofDraftEnd: null,
+  wallDraftStart: null,
+  fenceDraftStart: null,
+  roofDraftStart: null,
+  polygonDraftType: null,
+  polygonDraftPoints: [],
   setCursorPoint: (point) =>
     set((state) => {
       const prev = state.cursorPoint
@@ -82,13 +113,27 @@ export const useFloorplanDraftPreview = create<FloorplanDraftPreviewState>((set)
   setWallDraftEnd: (point) => set(setPlanPointField('wallDraftEnd', point)),
   setFenceDraftEnd: (point) => set(setPlanPointField('fenceDraftEnd', point)),
   setRoofDraftEnd: (point) => set(setPlanPointField('roofDraftEnd', point)),
+  setWallDraftStart: (point) => set(setPlanPointField('wallDraftStart', point)),
+  setFenceDraftStart: (point) => set(setPlanPointField('fenceDraftStart', point)),
+  setRoofDraftStart: (point) => set(setPlanPointField('roofDraftStart', point)),
+  setPolygonDraft: (type, points) =>
+    set((state) =>
+      state.polygonDraftType === type && planPointsEqual(state.polygonDraftPoints, points)
+        ? state
+        : { polygonDraftType: type, polygonDraftPoints: points.map(([x, z]) => [x, z]) },
+    ),
   reset: () =>
     set((state) =>
       state.cursorPoint === null &&
       state.cursorPosition === null &&
       state.wallDraftEnd === null &&
       state.fenceDraftEnd === null &&
-      state.roofDraftEnd === null
+      state.roofDraftEnd === null &&
+      state.wallDraftStart === null &&
+      state.fenceDraftStart === null &&
+      state.roofDraftStart === null &&
+      state.polygonDraftType === null &&
+      state.polygonDraftPoints.length === 0
         ? state
         : {
             cursorPoint: null,
@@ -96,6 +141,11 @@ export const useFloorplanDraftPreview = create<FloorplanDraftPreviewState>((set)
             wallDraftEnd: null,
             fenceDraftEnd: null,
             roofDraftEnd: null,
+            wallDraftStart: null,
+            fenceDraftStart: null,
+            roofDraftStart: null,
+            polygonDraftType: null,
+            polygonDraftPoints: [],
           },
     ),
 }))

packages/editor/src/store/use-path-draft-preview.ts

@@ -0,0 +1,90 @@
+import type { AnyNode } from '@pascal-app/core'
+import { create } from 'zustand'
+
+export type PathDraftKind = 'duct-segment' | 'lineset' | 'liquid-line' | 'pipe-segment'
+export type PathDraftPoint = [number, number, number]
+export type PathDraftParameter = boolean | number | string
+export type PathDraftParameters = Record<string, PathDraftParameter>
+
+type PathDraftPreviewState = {
+  kind: PathDraftKind | null
+  points: PathDraftPoint[]
+  cursor: PathDraftPoint | null
+  parameters: PathDraftParameters
+  relatedNodes: AnyNode[]
+  setDraft(
+    kind: PathDraftKind,
+    points: readonly PathDraftPoint[],
+    cursor: PathDraftPoint | null,
+    parameters?: Readonly<PathDraftParameters>,
+    relatedNodes?: readonly AnyNode[],
+  ): void
+  clear(kind: PathDraftKind): void
+  reset(): void
+}
+
+function pointEquals(a: PathDraftPoint | null, b: PathDraftPoint | null) {
+  return (!a && !b) || Boolean(a && b && a[0] === b[0] && a[1] === b[1] && a[2] === b[2])
+}
+
+function pointsEqual(a: readonly PathDraftPoint[], b: readonly PathDraftPoint[]) {
+  return a.length === b.length && a.every((point, index) => pointEquals(point, b[index] ?? null))
+}
+
+function parametersEqual(a: PathDraftParameters, b: Readonly<PathDraftParameters>) {
+  const keys = Object.keys(a)
+  const nextKeys = Object.keys(b)
+  return keys.length === nextKeys.length && keys.every((key) => a[key] === b[key])
+}
+
+function relatedNodesEqual(a: readonly AnyNode[], b: readonly AnyNode[]) {
+  return (
+    a.length === b.length &&
+    a.every((node, index) => JSON.stringify(node) === JSON.stringify(b[index]))
+  )
+}
+
+const EMPTY_DRAFT: Pick<
+  PathDraftPreviewState,
+  'cursor' | 'kind' | 'parameters' | 'points' | 'relatedNodes'
+> = {
+  cursor: null,
+  kind: null,
+  parameters: {},
+  points: [],
+  relatedNodes: [],
+}
+
+export const usePathDraftPreview = create<PathDraftPreviewState>((set) => ({
+  ...EMPTY_DRAFT,
+  setDraft: (kind, points, cursor, parameters = {}, relatedNodes = []) =>
+    set((state) => {
+      if (
+        state.kind === kind &&
+        pointEquals(state.cursor, cursor) &&
+        pointsEqual(state.points, points) &&
+        parametersEqual(state.parameters, parameters) &&
+        relatedNodesEqual(state.relatedNodes, relatedNodes)
+      ) {
+        return state
+      }
+      return {
+        cursor: cursor ? [...cursor] : null,
+        kind,
+        parameters: { ...parameters },
+        points: points.map((point) => [...point]),
+        relatedNodes: relatedNodes.map((node) => structuredClone(node)),
+      }
+    }),
+  clear: (kind) => set((state) => (state.kind === kind ? EMPTY_DRAFT : state)),
+  reset: () =>
+    set((state) =>
+      state.kind === null &&
+      state.points.length === 0 &&
+      state.cursor === null &&
+      Object.keys(state.parameters).length === 0 &&
+      state.relatedNodes.length === 0
+        ? state
+        : EMPTY_DRAFT,
+    ),
+}))

packages/editor/src/store/use-stair-build-preview.ts

@@ -10,7 +10,7 @@
 
 import { create } from 'zustand'
 
-type StairPreviewPoint = [number, number]
+export type StairPreviewPoint = [number, number]
 
 type StairBuildPreviewState = {
   /** Snapped plan-XZ point the ghost staircase sits at; `null` when idle. */
@@ -21,6 +21,7 @@ type StairBuildPreviewState = {
    *  don't re-render) when the point is unchanged — `grid:move` fires far more
    *  often than the snapped cell actually changes. */
   setPoint(point: StairPreviewPoint | null): void
+  setPreview(point: StairPreviewPoint | null, rotation: number): void
   rotateBy(deltaRadians: number): void
   reset(): void
 }
@@ -33,7 +34,16 @@ export const useStairBuildPreview = create<StairBuildPreviewState>((set) => ({
       const prev = state.point
       if (!point && !prev) return state
       if (point && prev && prev[0] === point[0] && prev[1] === point[1]) return state
-      return { point }
+      return { point: point ? [point[0], point[1]] : null }
+    }),
+  setPreview: (point, rotation) =>
+    set((state) => {
+      const samePoint =
+        (!point && !state.point) ||
+        Boolean(point && state.point && state.point[0] === point[0] && state.point[1] === point[1])
+      return samePoint && state.rotation === rotation
+        ? state
+        : { point: point ? [point[0], point[1]] : null, rotation }
     }),
   rotateBy: (deltaRadians) => set((state) => ({ rotation: state.rotation + deltaRadians })),
   reset: () =>

packages/nodes/src/ceiling/tool.tsx

@@ -19,6 +19,7 @@ import {
   resolveCeilingPlanPointSnap,
   triggerSFX,
   useEditor,
+  useFloorplanDraftPreview,
 } from '@pascal-app/editor'
 import { useViewer } from '@pascal-app/viewer'
 import { useEffect, useMemo, useRef, useState } from 'react'
@@ -79,6 +80,20 @@ export const CeilingTool: React.FC = () => {
   }, [points.length])
   useEffect(() => () => useEditor.getState().setDraftVertexCount(0), [])
 
+  useEffect(() => {
+    useFloorplanDraftPreview.getState().setPolygonDraft('ceiling', points)
+  }, [points])
+  useEffect(
+    () => () => {
+      const draftPreview = useFloorplanDraftPreview.getState()
+      if (draftPreview.polygonDraftType === 'ceiling') {
+        draftPreview.setPolygonDraft(null, [])
+      }
+      draftPreview.setCursorPoint(null)
+    },
+    [],
+  )
+
   const verticalGeo = useMemo(
     () =>
       new BufferGeometry().setFromPoints([
@@ -117,6 +132,7 @@ export const CeilingTool: React.FC = () => {
         fallbackPoint: orthoPoint,
         levelId: currentLevelId,
       }).point
+      useFloorplanDraftPreview.getState().setCursorPoint(displayPoint)
       setSnappedCursorPosition(displayPoint)
       if (
         points.length > 0 &&

packages/nodes/src/column/definition.ts

@@ -364,6 +364,7 @@ export const columnDefinition: NodeDefinition<typeof ColumnNode> = {
     kind: 'parametric',
     module: () => import('./renderer'),
   },
+  preview: () => import('./renderer').then(({ ColumnPreview }) => ({ default: ColumnPreview })),
   // Registry-driven placement tool — renders a translucent `ColumnPreview`
   // ghost at the cursor (mirroring the shelf build tool) instead of the
   // bare sphere the legacy editor-side `ColumnTool` showed. `ToolManager`'s

packages/nodes/src/duct-segment/tool.tsx

@@ -21,6 +21,7 @@ import {
   markToolCancelConsumed,
   triggerSFX,
   useEditor,
+  usePathDraftPreview,
 } from '@pascal-app/editor'
 import { useViewer } from '@pascal-app/viewer'
 import { Html } from '@react-three/drei'
@@ -559,6 +560,35 @@ const DuctSegmentTool = () => {
   // the cursor was at key-press time.
   const lastClientYRef = useRef<number | null>(null)
 
+  const ghostFittings = useMemo(() => {
+    const last = draftPoints.at(-1)
+    if (!(activeLevelId && last && cursorPos) || altActive) return []
+    const fittings =
+      planDuctDraw(
+        last,
+        cursorPos,
+        startPortRef.current,
+        startBodyRef.current,
+        endSnap.port,
+        endSnap.body,
+        profile,
+      )?.fittings ?? []
+    return fittings.map(
+      (fitting, index): DuctFittingNode => ({
+        ...fitting,
+        id: `duct-fitting_live-draft-${index}`,
+        parentId: activeLevelId,
+      }),
+    )
+  }, [activeLevelId, altActive, cursorPos, draftPoints, endSnap, profile])
+
+  useEffect(() => {
+    usePathDraftPreview
+      .getState()
+      .setDraft('duct-segment', draftPoints, cursorPos, profile, ghostFittings)
+  }, [cursorPos, draftPoints, ghostFittings, profile])
+  useEffect(() => () => usePathDraftPreview.getState().clear('duct-segment'), [])
+
   useEffect(() => {
     if (!activeLevelId) return
 
@@ -927,22 +957,6 @@ const DuctSegmentTool = () => {
     previewSegments.push({ a: last, b: cursorPos })
   }
 
-  // Ghost the auto-inserted fittings (elbow / tee / cross) the next click
-  // will mint, by running the SAME planner the commit uses against the
-  // in-flight endpoints. Skipped in Alt-vertical mode (no XZ tap there).
-  const ghostFittings =
-    last && cursorPos && !altActive
-      ? (planDuctDraw(
-          last,
-          cursorPos,
-          startPortRef.current,
-          startBodyRef.current,
-          endSnap.port,
-          endSnap.body,
-          profile,
-        )?.fittings ?? [])
-      : []
-
   // Wall-style dimension pill above the cursor: absolute world coords before
   // the first point, signed per-axis deltas from the last placed point while
   // a segment is in flight. The actively-driven axis is emphasised — Y in

packages/nodes/src/fence/tool.tsx

@@ -40,6 +40,7 @@ import {
   useAlignmentGuides,
   useEditor,
   useFenceCurveDraft,
+  useFloorplanDraftPreview,
   useSegmentDraftChain,
 } from '@pascal-app/editor'
 
@@ -511,6 +512,9 @@ const StraightFenceTool: React.FC = () => {
       buildingState.current = 0
       previewRef.current.visible = false
       setDraftMeasurement(null)
+      const draftPreview = useFloorplanDraftPreview.getState()
+      draftPreview.setFenceDraftStart(null)
+      draftPreview.setFenceDraftEnd(null)
       useSegmentDraftChain.getState().clear('fence')
       useAlignmentGuides.getState().clear()
     }
@@ -538,6 +542,9 @@ const StraightFenceTool: React.FC = () => {
           { applySnap: !angleLocked },
         )
         endingPoint.current.set(snappedLocal[0], event.localPosition[1], snappedLocal[1])
+        const draftPreview = useFloorplanDraftPreview.getState()
+        draftPreview.setFenceDraftStart([startingPoint.current.x, startingPoint.current.z])
+        draftPreview.setFenceDraftEnd(snappedLocal)
         cursorRef.current.position.copy(endingPoint.current)
         const currentFenceEnd: FencePlanPoint = [snappedLocal[0], snappedLocal[1]]
         if (
@@ -601,6 +608,9 @@ const StraightFenceTool: React.FC = () => {
         startingPoint.current.set(snappedStart[0], event.localPosition[1], snappedStart[1])
         endingPoint.current.copy(startingPoint.current)
         buildingState.current = 1
+        const draftPreview = useFloorplanDraftPreview.getState()
+        draftPreview.setFenceDraftStart(snappedStart)
+        draftPreview.setFenceDraftEnd(snappedStart)
         triggerSFX('sfx:structure-build-start')
         previewRef.current.visible = true
         setDraftMeasurement(null)
@@ -645,6 +655,10 @@ const StraightFenceTool: React.FC = () => {
         useSegmentDraftChain.getState().setChainStart('fence', [nextStart[0], nextStart[1]])
         startingPoint.current.set(nextStart[0], event.localPosition[1], nextStart[1])
         endingPoint.current.copy(startingPoint.current)
+        const draftPreview = useFloorplanDraftPreview.getState()
+        draftPreview.setFenceDraftEnd(null)
+        draftPreview.setFenceDraftStart(nextStart)
+        draftPreview.setFenceDraftEnd(nextStart)
         cursorRef.current?.position.copy(startingPoint.current)
         previewRef.current.visible = false
         buildingState.current = 1
@@ -669,6 +683,9 @@ const StraightFenceTool: React.FC = () => {
       emitter.off('tool:cancel', onCancel)
       useSegmentDraftChain.getState().clear('fence')
       useAlignmentGuides.getState().clear()
+      const draftPreview = useFloorplanDraftPreview.getState()
+      draftPreview.setFenceDraftStart(null)
+      draftPreview.setFenceDraftEnd(null)
     }
   }, [unit])
 
@@ -725,11 +742,11 @@ const SplineFenceDraft: React.FC = () => {
 
   draftRef.current = draftPoints
 
-  // Mirror the draft length into the HUD store so the "finish curve" hint only
+  // Mirror the full transient curve so additional preview surfaces observe
-  // shows once drafting has started; always clear it when the tool unmounts.
+  // the same snapped control points as the local preview.
   useEffect(() => {
-    useFenceCurveDraft.getState().setPointCount(draftPoints.length)
+    useFenceCurveDraft.getState().setDraft(draftPoints, cursor)
-  }, [draftPoints])
+  }, [cursor, draftPoints])
   useEffect(() => () => useFenceCurveDraft.getState().reset(), [])
 
   useEffect(() => () => useEditor.getState().setToolDefaults('fence', null), [])

packages/nodes/src/level/definition.ts

@@ -9,7 +9,7 @@ import { LevelNode } from './schema'
  */
 export const levelDefinition: NodeDefinition<typeof LevelNode> = {
   kind: 'level',
-  schemaVersion: 1,
+  schemaVersion: 2,
   schema: LevelNode,
   category: 'site',
 

packages/nodes/src/lineset/tool.tsx

@@ -11,6 +11,7 @@ import {
   markToolCancelConsumed,
   triggerSFX,
   useEditor,
+  usePathDraftPreview,
 } from '@pascal-app/editor'
 import { useViewer } from '@pascal-app/viewer'
 import { Html } from '@react-three/drei'
@@ -98,6 +99,11 @@ const LinesetTool = () => {
   const altAnchorRef = useRef<{ clientY: number; baseY: number } | null>(null)
   const lastClientYRef = useRef<number | null>(null)
 
+  useEffect(() => {
+    usePathDraftPreview.getState().setDraft('lineset', draftPoints, cursorPos)
+  }, [cursorPos, draftPoints])
+  useEffect(() => () => usePathDraftPreview.getState().clear('lineset'), [])
+
   useEffect(() => {
     if (!activeLevelId) return
 

packages/nodes/src/liquid-line/tool.tsx

@@ -18,6 +18,7 @@ import {
   markToolCancelConsumed,
   triggerSFX,
   useEditor,
+  usePathDraftPreview,
 } from '@pascal-app/editor'
 import { useViewer } from '@pascal-app/viewer'
 import { Html } from '@react-three/drei'
@@ -285,6 +286,13 @@ const LiquidLineTool = () => {
   // Leaving the tool clears Follow so re-arming it starts in free-draw.
   useEffect(() => () => useLiquidLineToolOptions.getState().setFollow(false), [])
 
+  useEffect(() => {
+    usePathDraftPreview
+      .getState()
+      .setDraft('liquid-line', traceGhost ?? draftPoints, traceGhost ? null : cursorPos)
+  }, [cursorPos, draftPoints, traceGhost])
+  useEffect(() => () => usePathDraftPreview.getState().clear('liquid-line'), [])
+
   useEffect(() => {
     if (!activeLevelId) return
 

packages/nodes/src/pipe-segment/tool.tsx

@@ -11,6 +11,7 @@ import {
   markToolCancelConsumed,
   triggerSFX,
   useEditor,
+  usePathDraftPreview,
 } from '@pascal-app/editor'
 import { useViewer } from '@pascal-app/viewer'
 import { Html } from '@react-three/drei'
@@ -162,6 +163,30 @@ const PipeSegmentTool = () => {
   const altAnchorRef = useRef<{ clientY: number; baseY: number } | null>(null)
   const lastClientYRef = useRef<number | null>(null)
 
+  const displayStart =
+    draftStart &&
+    cursorPos &&
+    sloped &&
+    system === 'waste' &&
+    !startPortRef.current &&
+    !startBodyRef.current &&
+    !snapTarget &&
+    !altActive
+      ? ([
+          draftStart[0],
+          draftStart[1] +
+            Math.hypot(cursorPos[0] - draftStart[0], cursorPos[2] - draftStart[2]) * DRAIN_SLOPE,
+          draftStart[2],
+        ] as [number, number, number])
+      : draftStart
+
+  useEffect(() => {
+    usePathDraftPreview
+      .getState()
+      .setDraft('pipe-segment', displayStart ? [displayStart] : [], cursorPos, { diameter, system })
+  }, [cursorPos, diameter, displayStart, system])
+  useEffect(() => () => usePathDraftPreview.getState().clear('pipe-segment'), [])
+
   useEffect(() => {
     if (!activeLevelId) return
 
@@ -613,26 +638,6 @@ const PipeSegmentTool = () => {
 
   if (!activeLevelId) return null
 
-  // Free waste start lifts at commit so the run falls ONTO the grid —
-  // mirror that here so the preview line / pill match the placed pipe.
-  // A snapped end (snapTarget set) keeps the start where it is.
-  const displayStart =
-    draftStart &&
-    cursorPos &&
-    sloped &&
-    system === 'waste' &&
-    !startPortRef.current &&
-    !startBodyRef.current &&
-    !snapTarget &&
-    !altActive
-      ? ([
-          draftStart[0],
-          draftStart[1] +
-            Math.hypot(cursorPos[0] - draftStart[0], cursorPos[2] - draftStart[2]) * DRAIN_SLOPE,
-          draftStart[2],
-        ] as [number, number, number])
-      : draftStart
-
   const pillParts = cursorPos
     ? [
         ...(['x', 'y', 'z'] as const).map((axis, i) => ({

packages/nodes/src/slab/tool.tsx

@@ -19,6 +19,7 @@ import {
   resolveSlabPlanPointSnap,
   triggerSFX,
   useEditor,
+  useFloorplanDraftPreview,
 } from '@pascal-app/editor'
 import { useViewer } from '@pascal-app/viewer'
 import { useEffect, useMemo, useRef, useState } from 'react'
@@ -77,6 +78,20 @@ export const SlabTool: React.FC = () => {
   }, [points.length])
   useEffect(() => () => useEditor.getState().setDraftVertexCount(0), [])
 
+  useEffect(() => {
+    useFloorplanDraftPreview.getState().setPolygonDraft('slab', points)
+  }, [points])
+  useEffect(
+    () => () => {
+      const draftPreview = useFloorplanDraftPreview.getState()
+      if (draftPreview.polygonDraftType === 'slab') {
+        draftPreview.setPolygonDraft(null, [])
+      }
+      draftPreview.setCursorPoint(null)
+    },
+    [],
+  )
+
   useEffect(() => {
     if (!currentLevelId) return
 
@@ -101,6 +116,7 @@ export const SlabTool: React.FC = () => {
         fallbackPoint: orthoPoint,
         levelId: currentLevelId,
       }).point
+      useFloorplanDraftPreview.getState().setCursorPoint(displayPoint)
       setSnappedCursorPosition(displayPoint)
       if (
         points.length > 0 &&

packages/nodes/src/wall/tool.tsx

@@ -33,6 +33,7 @@ import {
   triggerSFX,
   useAlignmentGuides,
   useEditor,
+  useFloorplanDraftPreview,
   useSegmentDraftChain,
   useWallSnapIndicator,
   WALL_CONNECT_SNAP_RADIUS,
@@ -594,6 +595,9 @@ export const WallTool: React.FC = () => {
       buildingState.current = 0
       chainFirstVertex.current = null
       chainWallIds.current = []
+      const draftPreview = useFloorplanDraftPreview.getState()
+      draftPreview.setWallDraftStart(null)
+      draftPreview.setWallDraftEnd(null)
       if (wallPreviewRef.current) {
         wallPreviewRef.current.visible = false
       }
@@ -637,6 +641,9 @@ export const WallTool: React.FC = () => {
       if (buildingState.current === 1) {
         const snappedLocal = gridPosition
         endingPoint.current.set(snappedLocal[0], event.localPosition[1], snappedLocal[1])
+        const draftPreview = useFloorplanDraftPreview.getState()
+        draftPreview.setWallDraftStart([startingPoint.current.x, startingPoint.current.z])
+        draftPreview.setWallDraftEnd(snappedLocal)
         cursorRef.current.position.copy(endingPoint.current)
         setAxisGuide({
           origin: [startingPoint.current.x, startingPoint.current.z],
@@ -706,6 +713,9 @@ export const WallTool: React.FC = () => {
         chainFirstVertex.current = startingPoint.current.clone()
         endingPoint.current.copy(startingPoint.current)
         buildingState.current = 1
+        const draftPreview = useFloorplanDraftPreview.getState()
+        draftPreview.setWallDraftStart(snappedStart)
+        draftPreview.setWallDraftEnd(snappedStart)
         setAxisGuide({
           origin: snappedStart,
           y: event.localPosition[1],
@@ -783,6 +793,10 @@ export const WallTool: React.FC = () => {
         useSegmentDraftChain.getState().setChainStart('wall', [nextStart[0], nextStart[1]])
         startingPoint.current.set(nextStart[0], event.localPosition[1], nextStart[1])
         endingPoint.current.copy(startingPoint.current)
+        const draftPreview = useFloorplanDraftPreview.getState()
+        draftPreview.setWallDraftEnd(null)
+        draftPreview.setWallDraftStart(nextStart)
+        draftPreview.setWallDraftEnd(nextStart)
         cursorRef.current?.position.copy(startingPoint.current)
         buildingState.current = 1
         setAxisGuide({
@@ -820,6 +834,9 @@ export const WallTool: React.FC = () => {
       useAlignmentGuides.getState().clear()
       useWallSnapIndicator.getState().clear()
       useSegmentDraftChain.getState().clear('wall')
+      const draftPreview = useFloorplanDraftPreview.getState()
+      draftPreview.setWallDraftStart(null)
+      draftPreview.setWallDraftEnd(null)
     }
   }, [unit])