Deepest level the SSE budget wanted to refine to this frame (whether or not
tiles were available there). If deepestRendered ≪ deepestWanted, refinement
is blocked — by availability or by tiles still streaming, not by PIXEL ERROR.
True if some tile this frame wanted to refine (SSE over budget) but had no
available children — refinement capped by the layer.json available data.
Diagnostic: true if an availability-capped tile WOULD have had children under
the opposite y-convention (TMS vs native). A true here is the smoking gun for
the availability y-flip bug → flip the convention in isAvailable.
Tiles refined this frame purely to satisfy the neighbor LOD-balance (2:1) constraint — not because their own pixel error was over budget. High values mean the camera is near many LOD boundaries; zero means screen-space error alone already produced a balanced quadtree. Only meaningful when TerrainTileset.balanceLod is on.
Deepest tile level actually drawn this frame.