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/render/world.js

@@ -289,6 +289,12 @@ function drawWorld() {
         const color = slopeBeltColor(sb, x, y, anim, br, bgc, bb);
         r = color & 255; g = color >> 8 & 255; b = color >> 16 & 255;
       }
+      const slopeDetail = slopeDetailAt(i, x, y);
+      if (slopeDetail) {
+        r = slopeDetail === 1 ? 145 : slopeDetail === 3 ? 96 : 48;
+        g = slopeDetail === 1 ? 125 : slopeDetail === 3 ? 106 : 52;
+        b = slopeDetail === 1 ? 94 : slopeDetail === 3 ? 120 : 60;
+      }
       // incandescence
       if (T > 450 && m !== EMPTY && incand) {
         const gi = glowIndex(PH[m] === PH_SOLID ? T + nz * 0.9 : m === MAGMA ? T + Math.sin(x * 0.19 + y * 0.11 + anim * 0.03 + nz * 0.04) * 55 - 30 : T), w = GLOW_W[gi];
@@ -339,6 +345,7 @@ function drawWorld() {
             ((y - ((sb / BW) | 0) * BS + 8) << 16) | ((x - (sb % BW) * BS + 8) << 8);
           if (slopeArt) { r = fm ? COLR[fm] : 0; g = fm ? COLG[fm] : 0; b = fm ? COLB[fm] : 0; }
         }
+        if (slopeDetail) cl = 4;
         top = cl << 24;
         fpx[row + bx] = (tb ? 0xff000000 : 0) | (cl === 5 ? 0xff0000 : 0) | (cl === 3 ? 0xff00 : 0) | (cl === 1 && !builtForLight(i, x, y) ? 0xff : 0);
       }