Tiny World Mesh Terrain Sculptor

A self-contained, opt-in landscape designer in engine/world/46-mesh-terrain.js. Lay a fine voxel grid over the home board, paint per-voxel materials, and pull/push voxels up and down. The result is flat-topped voxel blocks, not a smooth/curved surface, and it stays that way — Apply keeps the block mesh as the terrain instead of baking into per-tile setCell.

The model is per-voxel blocks (not a smooth heightfield)