Resting faces steeper than the angle of repose topple: blown sand towers collapse (t93)

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

test/pile-blow.js

@@ -0,0 +1,21 @@
+// Shared reproduction: continuously blow plain bagged sand straight above a stationary bot.
+function pileBlowSetup() {
+  pileCutWorld();
+  for (let x=0;x<W;x++) { surfY[x]=480; dirtY[x]=490; }
+  computeAmbient();
+  for(let y=0;y<H;y++)for(let x=0;x<W;x++) {
+    const i=y*W+x;mat[i]=y>=480?STONE:EMPTY;flags[i]=y>=480?F_NAT:0;temp[i]=AMB[y];
+  }
+  bot.x=384-bot.w/2;bot.y=330-bot.h/2;bot.vx=bot.vy=0;
+  bag[SAND]=40000;bagTotal=40000;updateRoof();
+}
+function pileBlowStroke() { toolBlow(383.5,250,6,SAND); }
+function pileBlowProfile() {
+  let cliff=0,previous=0,grains=0,height=0;
+  for(let x=0;x<W;x++) {
+    let y=0;while(y<480&&mat[y*W+x]!==SAND)y++;
+    const h=480-y;cliff=Math.max(cliff,Math.abs(h-previous));previous=h;height=Math.max(height,h);
+    for(;y<480;y++)if(mat[y*W+x]===SAND)grains++;
+  }
+  return {cliff,height,grains,flying:flyers.length,bag:bagTotal,awake:awake.filter(v=>v).length};
+}