- A file with no `schema` key is read as schema 1, but every pier must have a
`ground` object, so a renamed field is refused instead of loading as empty.
- `schema` null or any other number is still refused.
- The project file keeps the normalised model and checks it with its own
check (checkStoredGroundModel), so a saved model reopens.
- Temporary: remove the no-schema branch once examples/out is regenerated.
Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>