Constant MAX_SCENE_GRIDS 

pub const MAX_SCENE_GRIDS: u32 = 16;

Maximum number of grids the shader’s per-grid camera uniform array can hold. The scene-demo has 12 (1 ground + 1 ship + 10 markers); 16 leaves headroom for a future +4 without re-cooking the shader. The runtime check rejects scenes that overflow.