One instanced terrain draw

The terrain proposal drew the whole visible ground as one instanced draw: every tile the same small grid, displaced in the vertex stage by a height texture array the workers stream into, with an indirection table from a tile's key to its layer.

Why deferred: A tile per mesh is simpler to stream, since a tile's arrays become a geometry as they arrive, and the view holds a few dozen tiles, each sharing one material and one index buffer. That is within the engine's budget of tens of draws, and the shadow cascades cull most tiles for themselves.

Revisit when: the terrain's draws show in a frame's cost on the lowest tier, or a region's view holds so many tiles that the draws leave the tens.