Loose walls slump to a natural slope instead of eroding layer by layer (t93)

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

tools/scenes/t93-pile-collapse.js

@@ -0,0 +1,22 @@
+// Left to right: 40x20 walls of sand, mixed rubble, and rubble with 20% clay.
+// Capture at --ticks 0 and --ticks 180, --zoom 3 --no-light --freeze.
+{
+  const left = Math.max(4, SX - 400), floor = SY + 40;
+  const rubble = [RSTONE, CUORE, FEORE, LDIRT];
+  for (let x = left; x < left + 390; x++) {
+    surfY[x] = floor; dirtY[x] = floor + 8;
+    for (let y = floor - 90; y < floor + 8; y++) {
+      bgm[y * W + x] = 0;
+      setCell(y * W + x, y >= floor ? STONE : EMPTY, 20, y >= floor ? F_NAT : 0);
+    }
+  }
+  for (let pile = 0; pile < 3; pile++) {
+    const start = left + 60 + pile * 120;
+    for (let y = floor - 40; y < floor; y++) for (let x = start; x < start + 20; x++) {
+      const m = pile === 0 ? SAND : pile === 2 && (x + y) % 5 === 0 ? LCLAY : rubble[(x + y) % 4];
+      setCell(y * W + x, m, 20, 0);
+    }
+  }
+  updateRoof();
+  window.CAM = [left + 195, floor - 24];
+}