route and frontier ask for the grid once per plan and fall back to the window
when there is none. With it: one plan crosses a whole map, GO WARP / GO OUT /
GO ROUTE route to their warp or connection tile rather than to the nearest tile
of an edge that reads Unknown, a tile-pair wall is planned around instead of
being learned by walking into it, and the frontier is the nearest unstood
walkable tile anywhere on the map instead of the nearest one on screen.
