Sloped belts hold their load with moving cleats (t42); sloped filters are downhill shaking screens (t43)

The magic grip is gone: cleats every 8 face cells, 6 grains tall, carry
pockets uphill (about 71 grains/s against 90 flat) and overflow rolls
back. Sloped filters always run downhill; grains travel by gravity and
a shake, and sorting stays exact. Drawing needs another pass.

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

src/sim/save.js

@@ -9,6 +9,7 @@ function serializeWorld() {
   const t16 = new Uint16Array(N);
   for (let i = 0; i < N; i++) { const v = (temp[i] + TOFF) * 16; t16[i] = v < 0 ? 0 : v > 65535 ? 65535 : v; }
   const meta = {
+    slopePhases: Array.from(slopePhase),
     v: SAVE_VERSION, seed: worldSeed, W, H, tick, surfBase, underD, shallowD, lapse, tOff: TOFF,
     saplings: saplings.map(s => [s.x, s.y, s.age, s.th, s.seed]),
     economy: { money, debt, earned, recent: Array.from(mkRecent, v => Math.round(v)), log: shipLog, orders, ordersDone, nextOrderT, orderSeq },
@@ -102,6 +103,7 @@ function deserializeWorld(meta, buffers) {
   if (!dock()) placeDock((W >> 1) + 34); // worlds from before the economy get their trade dock too
   ghostBlocks = new Map(meta.ghostBlocks || []); ghostMachines = meta.ghostMachines || []; ghostMolds = meta.ghostMolds || [];
   tick = meta.tick || 0;
+  if (meta.slopePhases) slopePhase.set(meta.slopePhases);
   updateRoof(); resetWeather();
   if (meta.weather) {
     const mw = meta.weather;
@@ -117,7 +119,7 @@ function deserializeWorld(meta, buffers) {
   seen = new Uint8Array(NMAT); meta.seen.forEach((v, k) => { if (k < NMAT) seen[k] = v; });
   ledger = meta.ledger || {};
   Object.assign(stats, meta.stats || {});
-  powerDirty = true; rebuildPower(); updateRoof();
+  powerDirty = true; rebuildPower(); slopeCleatsTick(false); updateRoof();
   if (!weather.base) weather.base = worldWater(); // older saves: take the water it has now as its starting amount
   if (!meta.specks) clearHardSpecks(true); // older saves: tidy away tiny specks of too-hard rock once
   rebuildPipes();