Captures the gotchas surfaced while building the shelf so the next
contributor adding a registry-driven kind doesn't rediscover them.
`node-definitions.md` — new Pitfalls section + a rule that builders
must emit local-space children. Covers:
- `<GeometrySystem>` must NOT mutate `group.position` / `group.rotation`
after rebuild (the renderer binds them via JSX prop).
- Tag geometry-built children with `userData.__fromGeometry` so
rebuilds don't dispose React-mounted hosted children (the
item-disappears-on-shelf bug).
- Previews must clone materials before mutating them when the kind's
builder caches at module scope.
- Host kinds need a `children: z.array(...).default([])` field on their
schema (and a migration patch for older scenes).
`tools.md` — three new move/placement pitfalls:
- Disable raycast on the moved mesh during drag, otherwise it captures
the ray and starves `grid:move` → commits land at the stale start.
- Commit handlers listen to `grid:click` AND every `${kind}:click` to
catch clicks that land on neighbouring 3D geometry first.
- Move tools must preserve the node's actual `rotation[1]` in
`useLiveTransforms` — hardcoding 0 makes the node un-rotate mid-drag.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
