Cleats really hold and push their pockets (t42 feedback)

Nothing carries the load on a slope but the ribs: each belt step every
rib moves one face cell and pushes the grains in its way, the layer on
the belt is only dragged by friction that gravity beats on 45 degrees,
and heaped grains roll back. Ribs never pass through grains or into
machines; a run that can't push stalls. The foot of an uphill run
scoops the feed into pockets. Ribs drawn as rubber bars in both looks.

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

docs/DESIGN.md

@@ -417,7 +417,7 @@ above, including:
   only loaded screens shake. Empty moving cleats must let chunks sleep. Keep pocket transport,
   uphill throughput near 71 grains/s and exact sorting unchanged.
 
-- **Sidewall belts with moving cleats (t42, 2026-10-26).** To replace the old full-column
+- **Sidewall belts with moving cleats (t42, 2026-10-26; physics replaced by the entry below).** To replace the old full-column
   grip, use moving barrier lines rather than material cells: the barrier mask blocks normal
   powder movement without overwriting grains, terrain or parts. Cleats stand perpendicular
   to the face, spaced 8 horizontal face cells apart and 6 grains tall (integer normal reach
@@ -449,6 +449,19 @@ above, including:
   belt and the animation stopped on everything affected, and belts limited to a realistic
   load depth instead of carrying 96-grain stacks. Not built yet.
 
+- **Cleats really push their pockets (t42 feedback, 2026-10-26).** The owner found the first
+  cleats passed through heavy loads while the material climbed as before, and wants cleats that
+  hold the material and drag it up. Now nothing carries the load on a slope but the ribs and a
+  friction drag on the layer touching the belt (which gravity beats on 45°, so loose grains slide
+  back until a rib holds them). Each belt step every rib moves one face cell and pushes the
+  grains in its way ahead of it; whatever is heaped above the rib is left to roll back. A rib
+  never moves into a grain, never crosses a machine, and stops short of anything built. If any
+  rib of a run can't push its way, the whole run stalls that step and every move is undone (the
+  stall t45 will show). At the foot of an uphill run, each rib coming up around the end roller
+  scoops what lies on the feeding belt behind it into its pocket, like a real boot section.
+  Measured: about 80-86 grains/s uphill under a heavy feed (flat 90); downhill about 38, since
+  the top only feeds a layer two grains deep onto the face.
+
 ## Ideas not built yet
 
 - **Concrete**, as a stronger wall material from rubble.