feat(nav): 17.3 - a map in square tiles (nav_tiled, nav_tile_build; a tile must be a whole number of cells or its seams never join, and the shim refuses one that is not; 64-bit polygon refs for 16384 tiles), ground as a NavGround with boulders as convex footprints, one save format for one tile or many, and nav_random_near - a reachable point from the caller's seed, bit-identical on the Mac and the PC. 10 tests on both

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.nav/state.ludic

@@ -7,9 +7,10 @@ export const NAV_KINDS: int = 3
 export const NAV_CORNERS: int = 256   # a path's corners at most; a longer one is cut there
 
 # what a mesh is built for: its voxels (cell across, cell high) and its walker (height, radius,
-# the step it takes whatever its gradient, the steepest ground it walks, degrees)
+# the step it takes whatever its gradient, the steepest ground it walks, degrees). A tile must be a
+# whole number of cells across, or its seams never join: 0.25 m is 256 to a 64 m tile
 export property NavConfig {
-  cell: float = 0.3
+  cell: float = 0.25
   cell_h: float = 0.2
   height: float = 1.8
   radius: float = 0.35
@@ -17,6 +18,21 @@ export property NavConfig {
   slope: float = 45.0
 }
 
+# what a mesh is built from: v holds nv points (x, y, z) and t nt triangles (three indices each);
+# area a byte per triangle, 0 not walkable and 1..62 a kind of ground; cyl nc cylinders (x, y, z,
+# r, h) and foot nf floats of convex footprints (n, n points x z, ymin, ymax) nothing stands in
+export property NavGround {
+  v: []float = null
+  nv: int = 0
+  t: []int = null
+  nt: int = 0
+  area: []byte = null
+  cyl: []float = null
+  nc: int = 0
+  foot: []float = null
+  nf: int = 0
+}
+
 export state NavState {
   nv_meshes: []pointer = nv_none()
   nv_out: []float = floats(NAV_CORNERS * 3)