generate-reorder-variant-poperties now validates the main instances and
the variant container, but only when the reorder changed something, so
a no-op still returns the same changes. Add tests that corrupt a main
instance or the container and expect a validation error.
AI-assisted-by: claude-opus-5-5
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>