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/PROJECT_MAP.md

@@ -260,19 +260,19 @@ Pipes, pumps and outlets: each joined line holds one liquid as a count, not as g
 - functions: sideOf, pipeClosedSide, pipeJoins, rebuildPipes, pipeNetOf, pipeTakeShare, faceCell, pumpDraw, outletPour, pipesTick
 - variables: PIPE_CAP, PUMP_RATE, OUTLET_RATE, PUMP_MAX_T, SIDE_V, PUMP_V, OUTLET_V, pipeNets, pipeNetAt, pipesDirty
 
-### src/sim/machine-tick.js (155 lines)
+### src/sim/machine-tick.js (156 lines)
 Per-tick machine work: steam engines, fans, belts, filters, screw conveyors (machinesTick).
 - functions: engineIntake, fanBlow, machinesTick
 
-### src/sim/conveyors.js (197 lines)
+### src/sim/conveyors.js (193 lines)
 How belts, filters and screw conveyors move what is on or in them. What rests on a belt or filter rides along: the whole stack standing on the carrying surface steps one cell toward d together (belts run front of the line first, so the way ahead is clear). If a powder grain is blocked, the load above it stands still and the belt slips underneath. A filter's own material drops through it instead, unless it is already full.
 - functions: conveyorStep, carryColumn, beltDrain, launchGrain, rebuildFilters, filterCarry, carryBeltsAndFilters, setFilter, filterRun, roomFor, screwSpread, screwIntake, diagonalScrewNext
 - variables: CARRY_DEPTH, filterR, filterL, filtersDirty
 
-### src/sim/slope-conveyors.js (66 lines)
-Cleats are moving barriers, not material cells. A cleat supports a finite pocket; the bare face never holds grains.
-- functions: cleatFoot, pocketDepth, slopeCleatsTick, screenNudge, wakeCleatLoad
-- variables: CLEAT_SPACING, CLEAT_HEIGHT, CLEAT_REACH, SCREEN_NUDGE_TICKS, cleatCarrying, cleatChunks, cleatMask, cleatCells, slopePhase
+### src/sim/slope-conveyors.js (220 lines)
+Cleats are rubber ribs standing up from a sloped belt's face, one every CLEAT_SPACING face cells. Loose grains treat them as solid (cleatMask). Nothing grips the bare face: grains slide down it until a cleat stops them. Each belt step moves every cleat one face cell along the belt, and the rib pushes whatever is in its way ahead of it, so the pocket in front rides along while anything heaped above the rib is left to roll back. If a rib can't push its way, its whole run stalls.
+- functions: ribMove, cleatFoot, ribCells, slopeFaceAt, pushRow, scoop, pocketRoom, advanceCleat, slopeRunKey, slopeCleatsTick, rebuildCleatMask, expelFromRib, screenNudge, wakeCleatLoad
+- variables: CLEAT_SPACING, CLEAT_HEIGHT, CLEAT_REACH, SCREEN_NUDGE_TICKS, cleatChunks, cleatMask, cleatCells, slopePhase, ribLog
 
 ### src/sim/blocks.js (219 lines)
 Building blocks: placing, integrity, removing, lines and rectangles of blocks.
@@ -366,7 +366,7 @@ Drawing only: the face stays on its simulation cells; the band hangs below it.
 - functions: slopeBeltConnections, flatBeltCaps, prepareSlopeBelts, slopeBeltSegment, slopeBeltCorner, slopeBeltShape, slopeBeltAt, slopeBeltColor, screenLoaded, slopeWallShape, slopeWallAt, slopeDetailAt, slopePreviewCleat
 - variables: slopeBeltJoins, slopeBeltHalo, beltCaps, slopeAcross, slopeAlong, slopeDistance, slopeWallOwner
 
-### src/render/world.js (456 lines)
+### src/render/world.js (458 lines)
 Scale colour without changing the smooth-look class.
 - functions: fogColor, diagonalScrewJoins, diagonalScrewShape, diagonalScrewBlock, drawWorld
 - variables: SCREW_CLASS, diagonalJoins, diagonalAcross, diagonalAlong, diagonalCap
@@ -384,7 +384,7 @@ Smooth look: WebGL setup, texture uploads, drawing and adaptive resolution.
 - functions: smCompile, smoothAvailable, smUpload, smoothDraw, smoothPace
 - variables: SM, smBytes
 
-### src/render/slope-belt-shader.js (99 lines)
+### src/render/slope-belt-shader.js (109 lines)
 Smooth slope shading, kept beside the shared CPU geometry in slope-belts.js.
 - variables: SM_SLOPE_HELPERS, SM_SLOPE_DRAW
 
@@ -566,6 +566,7 @@ The frame loop and boot.
 - `tools/scenes/silo.js`: Run after clear-sky.js; leave paused so the open gate keeps its demonstration charge.
 - `tools/scenes/slope-conveyors.js`: Loaded sidewall conveyor and screen. Use --js 'slopeScene(false)' (belt) or 'slopeScene(true)' (screen).
 - `tools/scenes/stone-uses.js`: The stone and sand machines: a half-full silo with its gate open over a belt, a stone cutter fed with rubble, and cut stone and glass brick walls. Run clear-sky.js first, e.g. python3 tools/shot.py /tmp/stone.png --setup tools/scenes/clear-sky.js --js "$(cat tools/scenes/stone-uses.js)" --ticks 240 --zoom 7
+- `tools/scenes/t-screen-joint.js`: Downhill screen whose outlet belt sits level with its last block (the jam the owner saw).
 - `tools/scenes/t33-ground.js`: Paused dug pocket: copper ore, rubble and dirt against stone, granite and dirt. Use --js "..." to set daylight or R.lens after this setup; CAM frames the pocket.
 - `tools/scenes/t35-diagonal.js`: Run after clear-sky.js: a belt takes sand from a pile, up a diagonal screw to an upper belt.
 - `tools/scenes/t35-joins.js`: Run after clear-sky.js. Paused, empty pipes make casing, flights and mouths easy to inspect.