Phase 2 spike: spawn migration (flagged) + new shelf node

The first time registry-driven nodes actually run in the editor.

Spawn migration (under NEXT_PUBLIC_USE_REGISTRY_FOR_SPAWN flag):
- New packages/nodes/src/spawn/ folder with renderer, tool, schema
  (re-exported from core), parametrics, definition, index.
- Spawn definition appended to builtinPlugin.nodes only when the flag
  is set. With the flag off, the Phase 0 shims fall through and the
  legacy SpawnRenderer / SpawnTool keep ownership.
- New no-props SpawnTool reads activeLevelId from useViewer directly,
  matches legacy placement behavior (half-meter snap, singleton-per-
  level, replace-on-reclick).
- Structural parity test (9 cases) validates definition shape +
  schema identity. Pixel-diff defers to Phase 4 alongside more nodes.

New shelf node (no legacy — registered unconditionally):
- ShelfNode schema in core/schema/nodes/shelf.ts (hand-maintained
  AnyNode union for now; Phase 6 derives the union from the registry
  and moves the schema fully into nodes/shelf/).
- packages/nodes/src/shelf/ folder: pure geometry builder
  (buildShelfGeometry returns a Three.js Group of top board +
  brackets), R3F renderer that mounts the built group, no-props
  placement tool, parametrics descriptor (width/depth/thickness/
  height/bracketStyle/color), definition with surfaces.top stackable
  surface for future stacking, and presentation metadata for the
  palette.
- 13 unit tests across schema bounds and geometry behavior.
- Palette wiring: 'shelf' added to StructureTool union + an entry in
  the structure-tools array (placeholder icon, replaced in Phase 4
  when palette is registry-driven).

Framework changes:
- @pascal-app/viewer now exports useNodeEvents from its public barrel
  so node bundles in @pascal-app/nodes can subscribe to node-specific
  pointer events. (Used by spawn renderer; shelf renderer skips it
  for now since useNodeEvents has a hardcoded kind list — Phase 4
  generalizes it via the registry.)
- @pascal-app/nodes gains @pascal-app/viewer as a peer + dev dep so
  node bundles can import from it.

630 tests pass across 76 files (22 new this phase). Editor app
continues to ship green with both legacy spawn and the new shelf
node co-existing through the Phase 0 dispatch shims.

To validate end-to-end in dev:
- bun dev:community → open editor → click 'Shelf' in structure
  toolbar → click to place. Confirms full registry path
  (NodeRenderer dispatch + ToolManager dispatch + sceneRegistry
  byType Proxy).
- Set NEXT_PUBLIC_USE_REGISTRY_FOR_SPAWN=1, restart dev, place spawn
  → visually identical to legacy. Confirms parity.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/nodes/src/spawn/tool.tsx

@@ -0,0 +1,128 @@
+'use client'
+
+import { emitter, type GridEvent, SpawnNode, sceneRegistry, useScene } from '@pascal-app/core'
+import { useViewer } from '@pascal-app/viewer'
+import { useEffect, useRef, useState } from 'react'
+import { type Group, Vector3 } from 'three'
+
+/**
+ * Registry-driven spawn placement tool. No props — reads `activeLevelId` from
+ * `useViewer` directly and broadcasts placement events through the store.
+ *
+ * Behavior parity with the legacy tool in
+ * `@pascal-app/editor/components/tools/spawn/spawn-tool.tsx`:
+ * - Grid-snap to half-meter increments on X/Z
+ * - Project click position into the active level's local frame
+ * - Singleton: if a spawn already exists for this level, reuse it and clean
+ *   up any duplicates
+ * - On commit: select the placed spawn and exit build mode
+ *
+ * Mounted by `ToolManager`'s registry-first dispatch (Phase 0 shim) when
+ * `nodeRegistry.has('spawn')` and the active tool is 'spawn'.
+ */
+
+const roundToHalf = (value: number) => Math.round(value * 2) / 2
+const worldVector = new Vector3()
+
+function getExistingSpawnIds() {
+  const nodes = useScene.getState().nodes
+  return Object.values(nodes)
+    .filter((node) => node.type === 'spawn')
+    .map((node) => node.id)
+    .sort()
+}
+
+function getLevelLocalPosition(levelId: string, event: GridEvent): [number, number, number] {
+  const levelObject = sceneRegistry.nodes.get(levelId)
+  if (!levelObject) {
+    return [
+      roundToHalf(event.localPosition[0]),
+      event.localPosition[1],
+      roundToHalf(event.localPosition[2]),
+    ]
+  }
+  worldVector.set(event.position[0], event.position[1], event.position[2])
+  levelObject.updateWorldMatrix(true, false)
+  levelObject.worldToLocal(worldVector)
+  return [roundToHalf(worldVector.x), worldVector.y, roundToHalf(worldVector.z)]
+}
+
+const SpawnTool = () => {
+  const activeLevelId = useViewer((state) => state.selection.levelId)
+  const [, setCursor] = useState<[number, number, number] | null>(null)
+  const cursorRef = useRef<Group>(null)
+
+  useEffect(() => {
+    if (!activeLevelId) return
+
+    const onGridMove = (event: GridEvent) => {
+      const next: [number, number, number] = [
+        roundToHalf(event.localPosition[0]),
+        event.localPosition[1],
+        roundToHalf(event.localPosition[2]),
+      ]
+      setCursor(next)
+      cursorRef.current?.position.set(next[0], next[1], next[2])
+    }
+
+    const onGridClick = (event: GridEvent) => {
+      const next = getLevelLocalPosition(activeLevelId, event)
+      const [existingSpawnId, ...duplicates] = getExistingSpawnIds()
+      let placedId: SpawnNode['id']
+
+      if (existingSpawnId) {
+        useScene.getState().updateNode(existingSpawnId, {
+          parentId: activeLevelId,
+          position: next,
+          rotation: 0,
+        })
+        if (duplicates.length > 0) {
+          useScene.getState().deleteNodes(duplicates)
+        }
+        placedId = existingSpawnId
+      } else {
+        const spawn = SpawnNode.parse({
+          name: 'Spawn Point',
+          position: next,
+          rotation: 0,
+        })
+        useScene.getState().createNode(spawn, activeLevelId)
+        placedId = spawn.id
+      }
+
+      useViewer.getState().setSelection({ selectedIds: [placedId] })
+      // Note: legacy tool also emits sfx:structure-build and resets the editor
+      // tool/mode. We rely on the legacy ToolManager to do the latter via the
+      // build-tool exit path; this commit doesn't replicate the SFX since the
+      // registry doesn't yet bridge to the editor's sfx-emitter. Phase 4's
+      // command surface adds a clean path.
+    }
+
+    emitter.on('grid:move', onGridMove)
+    emitter.on('grid:click', onGridClick)
+
+    return () => {
+      emitter.off('grid:move', onGridMove)
+      emitter.off('grid:click', onGridClick)
+    }
+  }, [activeLevelId])
+
+  if (!activeLevelId) return null
+
+  // Visible marker for the cursor — using a simple group + box. The legacy
+  // tool used a CursorSphere component from @pascal-app/editor; here we keep
+  // the dependency arrow flowing nodes→editor (which is allowed by the layer
+  // rules) but use a minimal inline mesh to avoid the dependency entirely for
+  // the spike. Phase 4 ports CursorSphere to the editor framework so node
+  // tools can reuse it.
+  return (
+    <group ref={cursorRef}>
+      <mesh position={[0, 1.1, 0]}>
+        <sphereGeometry args={[0.18, 16, 12]} />
+        <meshStandardMaterial color="#60a5fa" transparent opacity={0.6} />
+      </mesh>
+    </group>
+  )
+}
+
+export default SpawnTool