Sloped walls with a flat 45° face, and diagonal wall lines (t36)

- New Sloped wall piece: a half-block triangle in any wall material, at half a wall's cost.
  Dragging walls or slopes at about 45° lays a diagonal line; the drag picks the slope's
  orientation and T flips or turns it.
- Each slope fills one cell past its corner, so a diagonal run is sealed against grains and water.
- New test/t_slopes.js: a slope funnel passes 400/400 sand (square steps 379/400).

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

test/t_slopes.js

@@ -0,0 +1,90 @@
+// Sloped walls: flow, sealed joints, building, refunds and persistence.
+const { load, suite, flatWorld, rect, count, ticks } = require('./harness');
+const { run } = load();
+const { check, done } = suite();
+function fresh() { flatWorld(run, 240, 192, 176); run('AMB.fill(20);temp.fill(20);'); }
+function funnel(sloped, material) {
+  fresh();
+  run(`for (let k=0;k<12;k++) {
+    placeBlock(${sloped ? 'BP_SLOPE_BL' : 'BP_WALL'}, RSTONE, 12+k, 12+k, true);
+    placeBlock(${sloped ? 'BP_SLOPE_BR' : 'BP_WALL'}, RSTONE, 36-k, 12+k, true);
+  }`);
+  rect(run, 80, 20, 119, 29, material);
+  ticks(run, 1800);
+  const out = count(run, material, 0, 96, 239, 175);
+  check(`${sloped ? 'slope' : 'square'} funnel conserves 400 grains`, count(run, material) === 400);
+  return out;
+}
+const sand = run('SAND'), water = run('WATER');
+const slopeOut = funnel(true, sand), squareOut = funnel(false, sand);
+check('all sand leaves the sloped funnel', slopeOut === 400, slopeOut);
+check('square steps retain sand', squareOut < 400, squareOut);
+check('all water leaves the sloped funnel', funnel(true, water) === 400);
+for (const material of ['GRAVEL', 'CUORE', 'LDIRT']) check(`${material} slides down`, funnel(true, run(material)) === 400);
+fresh();
+run('for (let k=0;k<12;k++) placeBlock(BP_SLOPE_BL,RSTONE,12+k,12+k,true); spawnBar(BARCU,52,35);');
+ticks(run, 600);
+check('bars slide off the slope', run('ents.length === 1 && ents[0].iy > 96'), run('ents.map(e=>[e.ix,e.iy])'));
+for (let c = 15; c <= 18; c++) {
+  fresh();
+  run(`bagAdd(RSTONE,100,true); bagAdd(BARCU,10,true);`);
+  const before = run('bag[RSTONE]');
+  run(`placeBlock(${c},RSTONE,20,20);`);
+  check(`slope ${c} costs half a wall`, before-run('bag[RSTONE]') === 8);
+  check(`slope ${c} has its triangle`, run('blockIntegrity(20*BW+20)') === 10);
+  run(`undoRecord('cut',()=>cutRegion(80,80,83,83)); undoLast();`);
+  check(`undo restores orientation ${c}`, run(`blockP[20*BW+20] === ${c}`));
+  check(`copy and flip preserve material and mirror ${c}`, run(`(()=>{ const bp=flipBlueprint(copyRegion(80,80,83,83)); return bp.blocks[0][2] === ${15+((c-15)^1)} && bp.blocks[0][3]===RSTONE; })()`));
+  run(`const snap${c}=serializeWorld(); deserializeWorld(snap${c}.meta,snap${c}.buffers);`);
+  check(`save restores orientation ${c}`, run(`blockP[20*BW+20] === ${c} && blockIntegrity(20*BW+20)===10`));
+  run(`pasteGhost(copyRegion(80,80,83,83),24,20); bot.x=96;bot.y=80;ghostTick();`);
+  check(`paste builds orientation ${c}`, run(`blockP[20*BW+24]===${c} && blockV[20*BW+24]===RSTONE`));
+  run('removeBlock(24,20);removeBlock(20,20)');
+  check(`slope ${c} refunds half a wall`, run('bag[RSTONE]') === before);
+  run(`placeBlock(${c},BARCU,20,20);removeBlock(20,20);`);
+  check(`metal slope ${c} refunds one bar`, run('bag[BARCU]') === 10);
+}
+check('wall diagonal snaps within 30 percent', run('JSON.stringify(blockLine(2,3,7,7,true))') === JSON.stringify([[2,3],[3,4],[4,5],[5,6],[6,7],[7,8]]));
+check('belts stay straight', run('blockLine(2,3,7,8).every(p=>p[1]===3)'));
+check('drag chooses below or above and ignores drag reversal', run('slopeCode(5,5,0)===15 && slopeCode(-5,-5,0)===15 && slopeCode(5,-5,0)===16 && slopeCode(5,5,2)===18 && slopeCode(5,-5,2)===17'));
+// Probe every open cell along both sides, including all eleven joints. A grain may
+// leave an end, so measure crossing only within the interior of the diagonal run.
+for (let c = 15; c <= 18; c++) for (const m of ['SAND', 'WATER']) for (const side of [-1, 1]) {
+  fresh();
+  const descending = c === 15 || c === 18;
+  run(`for(let k=0;k<12;k++) placeBlock(${c},RSTONE,12+k,${descending ? '12+k' : '23-k'},true);`);
+  const leaked = run(`(()=>{
+    const sideAt=(x,y)=>${descending ? 'y-x' : 'x+y-143'};
+    let leaks=0, probes=0;
+    for(let y=52;y<92;y++) for(let x=52;x<92;x++) {
+      const i=y*W+x, d=sideAt(x,y);
+      if(mat[i]!==EMPTY || Math.sign(d)!==${side} || Math.abs(d)>2) continue;
+      setCell(i,${m},20,0); probes++;
+      // Exercise the real movement functions repeatedly without letting grains escape an end.
+      for(let k=0;k<20 && mat[i]===${m};k++) { tickStamp++; ${m === 'WATER' ? 'liquid(i,x,y,WATER)' : 'powder(i,x,y,SAND)'}; }
+      for(let yy=y;yy<=y+1;yy++) for(let xx=x-32;xx<=x+32;xx++) {
+        if(xx<0 || xx>=W)continue;
+        const j=yy*W+xx;
+        if(mat[j]===${m}) { if(Math.sign(sideAt(xx,yy))===${-side}) leaks++; setCell(j,EMPTY,20,0); }
+      }
+    }
+    return [leaks,probes];
+  })()`);
+  check(`slope ${c} seals ${m} from side ${side}`, leaked[0] === 0 && leaked[1] > 0, leaked);
+}
+for (const c of [15, 16]) {
+  fresh();
+  run(`for(let k=0;k<12;k++) placeBlock(${c},RSTONE,12+k,${c === 15 ? '12+k' : '23-k'},true);spawnBar(BARCU,${c === 15 ? 52 : 136},35);`);
+  ticks(run,600);
+  check(`bars reach the bottom of slope ${c}`,run('ents.length===1 && ents[0].iy>96'));
+}
+for(const c of [15,16,17,18]) {
+  fresh();
+  check(`slope ${c} supports every wall material`,run(`WALL_LIST.every((v,k)=>{ const bx=4+k*3;bagAdd(v,16,true);const before=bag[v];if(placeBlock(${c},v,bx,20))return false;removeBlock(bx,20);return bag[v]===before; })`));
+}
+fresh();
+run('placeBlock(BP_SLOPE_BL,RSTONE,20,20,true);placeBlock(BP_WALL,RSTONE,20,21,true);removeBlock(20,21);');
+check('removing an adjoining square wall restores the slope seal',run('mat[slopeSeal(BP_SLOPE_BL,20,20)]===STONE'));
+run('removeBlock(20,20)');
+check('removal leaves no free seal grains behind',count(run,run('STONE'),80,80,83,87)===0);
+done();