Outdoor terrain cell (retail CLandCell) synthesized on demand from a
landblock's TerrainSurface. Factory Synthesize() samples four quad
corners to establish Z bounds; PointInCell() tests the 24 m XY quad
in world-local space. BuildingCellId stub is null (Stage 2).
2/2 tests RED→GREEN.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
