Added a -profile probe: one downward trace every 20 m along the street at the player's Y, naming
the surface each time. It settles the question the bounding boxes could not:
x=-14336..-2336 z=366 Road_Hollywood (flat)
x=-336 z=302 Road_Hollywood
x=1664 z=5 Terrain_DEM
The road is FLAT at 366 cm across the demo block, while the sidewalk slices follow the DEM and
descend 380 -> 104 cm. So the ~2 m gap is not an import artefact and not a collision problem: the
road itself does not follow the elevation the sidewalks follow.
That also explains why every sidewalk fix failed - the surface the player stands on is this flat
road, and the sloped sidewalk is metres below it.
Next: how rows is built in Art/blender/street/street_mesh.py. The road and the sidewalk read the same
dem_z(x, y), so a flat road means the sampler returns the same value for every row.