5-task TDD plan: TerrainSurface (outdoor heightmap Z + cell ID),
CellSurface (indoor floor polygon projection via barycentric interp),
PhysicsEngine (top-level resolver with step-height + cell transitions),
GameWindow integration (populate from streaming), and roadmap update.
~16 new unit tests with fake data. No dat files or rendering needed.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>