Uphill runs share one cleat phase; no cleats downhill; pick slope bands

A piece added to a running sloped belt kept its own cleat phase, so at
the seam a rib could start just behind another and push its pocket into
it, stalling the whole run with only a few grains. Every block of a run
now takes the phase of the run's lower-left block.

Downhill sloped belts no longer have cleats: they carry like a flat belt
(90 grains/s, was 38) and draw only the sidewall.

Middle click on a sloped belt's band, where it is drawn into the empty
block beside it, now picks the belt.

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

docs/DESIGN.md

@@ -461,6 +461,10 @@ above, including:
   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.
+- **No cleats on downhill belts (t42 feedback, 2026-10-26).** The owner asked why a downhill
+  belt has cleats: on 45° the load slides anyway. A downhill sloped belt is now a plain belt with
+  a sidewall that carries at belt speed like a flat one (90 grains/s); only uphill runs have
+  ribs. A whole run also shares one cleat phase, so pieces added later line up with it.
 
 ## Ideas not built yet
 

docs/PROJECT_MAP.md

@@ -171,7 +171,7 @@ dist/, shots/         build output and screenshots (not committed)
 | Starter furnace designs | `src/sim/progress.js` (`STARTER_DESIGNS`, `smelterBlueprint`) |
 | Falling sand, liquids, gases | `src/sim/cells.js` |
 | Heat, melting, fire, reactions, alloys, steel | `src/sim/heat.js` |
-| Belts, filters, screw conveyors | `src/sim/conveyors.js`, `src/sim/slope-conveyors.js` (cleat barriers, pocket depth and screen nudges), `src/sim/machine-tick.js` |
+| Belts, filters, screw conveyors | `src/sim/conveyors.js`, `src/sim/slope-conveyors.js` (uphill cleat barriers and screen nudges), `src/sim/machine-tick.js` |
 | Fans | `src/sim/machine-tick.js` (`fanBlow`) |
 | Refiner, Stone cutter, Silo | `src/sim/processors.js` |
 | Pipes, pumps, outlets | `src/sim/pipes.js` |
@@ -264,14 +264,14 @@ Pipes, pumps and outlets: each joined line holds one liquid as a count, not as g
 Per-tick machine work: steam engines, fans, belts, filters, screw conveyors (machinesTick).
 - functions: engineIntake, fanBlow, machinesTick
 
-### src/sim/conveyors.js (193 lines)
+### src/sim/conveyors.js (194 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 (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
+### src/sim/slope-conveyors.js (230 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. Only uphill runs have cleats: downhill, the belt carries its load like a flat one.
+- functions: ribMove, cleatFoot, ribCells, slopeUphill, 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)
@@ -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 (109 lines)
+### src/render/slope-belt-shader.js (111 lines)
 Smooth slope shading, kept beside the shared CPU geometry in slope-belts.js.
 - variables: SM_SLOPE_HELPERS, SM_SLOPE_DRAW
 
@@ -471,7 +471,7 @@ Keyboard and mouse listeners.
 - functions: isTyping
 - variables: canvas
 
-### src/ui/actions.js (242 lines)
+### src/ui/actions.js (244 lines)
 What input does: overlays, F, pick, copy / cut / paste, undo, building and tool use each frame. Which overlays are on, shown as a coloured frame round the screen and a named badge
 - functions: updateOverlayUI, toggleLens, doInteract, pickUnderCursor, aimBlock, stampOrigin, selModeHeld, startPaste, stopSelectAndPaste, plural, piecesIn, doUndo, endRmbRecord, dragDirFor, blockLabel, primaryPress, primaryRelease, secondaryPress, toolTick
 - variables: ovShown

docs/agent-log.md

@@ -4,6 +4,23 @@ What agents have done, newest first. Add an entry for every piece of work: the d
 note or request it was for, what changed, the files touched, the tests run, and anything left
 open or not verified. Keep each entry short; the git history has the details.
 
+## 2026-10-26: t42 feedback: uphill stall at a seam, no cleats downhill, slope pick (Claude Code)
+
+- The owner's long uphill run stalled with a few grains, with a flashing seam between pieces 9
+  and 10. Cause: each block kept its own cleat phase, so a piece added to a running belt was out
+  of step; at the seam a rib started one or two cells behind another and pushed its pocket into
+  that rib's back, stalling the run for good. Every block of a run now takes the phase of the
+  run's lower-left block (`slopeCleatsTick`, memoised `slopeRunKey`).
+- Owner decision: downhill belts have no cleats. They carry like a flat belt (`carryColumn`) and
+  draw only the sidewall; ribs, friction drag and pushes are uphill only (`slopeUphill`).
+  `pushRow`'s downhill levelling is gone. Downhill now 90 grains/s (was 38).
+- Middle click on a sloped belt's band, where it is drawn into the empty block below, now picks
+  the belt (`pickUnderCursor` falls back to `slopeBeltAt`).
+- Tests: `t_slope_belts.js` adds pieces added 3/7/11/13 ticks later (13 stalled before) and the
+  band pick (fails without the fix); downhill floor back to 60; cleat checks uphill only.
+  `t_slope_belt_art.js` draws ribs on uphill runs. `python3 test/run_all.py --browser`: ALL
+  PASSED. Screenshots of an up-and-down run in both looks opened. Rebuilt dist.
+
 ## 2026-10-26: t42 feedback: cleats that really hold and push their load (Claude Code)
 
 - The owner saw ribs pass through heavy loads and the load climb as before. Rewrote the slope