Two findings, one a bug and one the real cause.
Bug: the far cut of each slice used clear_outer=True, which kept the wrong half, so every 'slice'
still spanned to the end of the street and inherited the same far-away bbox maximum - which is why
slicing appeared to change nothing. Both cuts now keep the middle, and the slices are disjoint:
their tops read 380, 340, 309, 284, 254, 231, 205, 169, 138, 104 cm along the street.
Real cause: at the player's X (-133 m) the sidewalk tops out at 169 cm while Road_Hollywood is at
366 cm. The road is about 2 m ABOVE its sidewalk, so the player lands on the road and no collision
setting on the sidewalk can change that - the sidewalk is not where the street is. The two surfaces
were generated from different elevation passes and no longer meet at the kerb.
That is site-pipeline data, not placement. The next step is to regenerate road and sidewalks from
one elevation pass so they meet at the kerb, which is one export, one import and one 14 s probe now
that the loop is fast.
The ground measurement was the slowest part of every iteration: the game ran until the shell's
timeout because nothing told it to stop. -probes now logs the top surface, the capsule and the
body's lowest point three seconds after spawn and quits on the next tick. A run went from minutes
to 13.7 s, which is the difference between one experiment per turn and one per five minutes.
Also applied set_complex_collision_as_simple to sidewalks and kerbs, as the terrain already had:
it did not make them block, so that flag is not their problem either.
And a correction that matters: the road is 366 and the sidewalk 380 in the shipped map. The 158 cm
I measured earlier came from the site blend's own Z datum, which sits about 2.2 m below the map's
because the terrain was added after that blend was written. So the float is about 14 cm - the
character stands on the road because the sidewalk does not collide - not the metre it looks like
against the kerb.
The site exporter now splits sidewalks and kerbs into ~20 m pieces
(SEGMENTED / SEGMENT_M in Art/blender/site/export_site_fbx.py), 56 slices in all, so each has a
bounding box that means something where it stands instead of reporting the highest point on a
279 m slope. They import and stage (63 site meshes in the demo map).
The hypothesis behind it is dead, and that is the useful part: with the invisible sidewalk
stopgap retired, the player now falls to Road_Hollywood at 366 - the slices do not block either.
So the 279 m aspect ratio was never the cause; a 20 m slice of the same mesh fails identically.
The sidewalk geometry itself is what does not collide, and the next place to look is its shape -
an open surface with no volume, inverted winding or zero-thickness triangles - not the import
flags and not the size.
The stopgap retirement stands: the player walks on the road, which is real geometry that does
collide, rather than on an invisible ledge.
zwitschi