<!-- SOLID CITY · part 2806 -->
Idx), width: 7.6, furniture: 'bench' });
    var nodeY = probeB2.stations[0].y;
    var bB1 = buildOne('B1', ROAD_DEFS[1].slice(0, headIdx + 1), 'bench', null, nodeY, null, null, { width: 5.6, over: 30 });
    var headSt = bB1.stations[bB1.stations.length - 1];
    var bB2 = buildOne('B2', ROAD_DEFS[1].slice(headIdx), 'bench', headSt.y, null, null, { width: 5.6, over: 30 });
    var hBC = surfSt(bB2, 945, -1487.5);
    buildOne('C', ROAD_DEFS[2], 'bench', hBC.y, null, hBC);
    // the spur is hosted by THE PAD: a junction is a level place,
    // and a guest leaving it should be held to the pad's own
    // plane — not to the arrival pitch of whichever road happened
    // to be built first. (Its host was the climb's last station,
    // and when the climb's line moved, the spur's first metres
    // were clamped to a falling plane: a 72% kink at the seam.)
    var headPad = { x: 915, z: -1285, y: headSt.y, grade: 0, bank: 0, fx: 0, fz: 1, rx: 1, rz: 0 };
    buildOne('S', ROAD_DEFS[3], 'bench', headSt.y, null, headPad);
    var hA = surfSt(bB1, 430, -1065);
    buildOne('A1', ROAD_DEFS[0].slice(1).reverse(), 'street', null, hA.y);
    buildOne('A2', [[430, -1065], [640, -1005]], 'street', hA.y, null, hA);
    apronAt(915, -1285, headSt);
    apronAt(945, -1487.5, hBC);
    apronAt(430, -1065, hA);
    // THE CLEARANCE OF SURFACES: the drive reads VOID at a
    // sample when the HIGHEST standing triangle there rises
    // above the world's gate — the road's own profile plus 1.6.
    // Where benches braid, an upper road's shoulder can be that
    // highest triangle over a lower road's line, and the lower
    // road is voided beneath a surface it cannot use. The law
    // therefore strikes the ARGMAX ONLY: the single highest
    // triangle at each voided sample, pass after pass, until no
    // centreline sample of any road is voided by a road's own
    // triangles. Nothing else is struck — a triangle that merely
    // rises over a neighbour's line is a bench, and benches are
    // the country these roads are built in. Struck triangles
    // remain in the eye; they are removed from the standing only.
    (function clearSurfaces() {
      var tris = [];
      for (var i = triBase; i < standTris.length; i += 9) {
        tris.push({ i: i, cx: (standTris[i] + standTris[i + 3] + standTris[i + 6]) / 3, cz: (standTris[i + 2] + standTris[i + 5] + standTris[i + 8]) / 3, drop: false });
      }
      var cell = 16, grid = {};
      tris.forEach(function (t) { var k = Math.floor(t.cx / cell) + ':' + Math.floor(t.cz / cell); (grid[k] = grid[k] || []).push(t); });
      function triYAtLocal(x, z) {
        var best = -Infinity, arg = null;
        var bx = Math.floor(x / cell), bz = Math.floor(z / cell);
        for (var a2 = -1; a2 <= 1; a2++) for (var b2 = -1; b2 <= 1; b2++) {
          var list = grid[(bx + a2) + ':' + (bz + b2)]; if (!list) continue;
          for (var q = 0; q < list.length; q++) {
            var t = list[q]; if (t.drop) continue;
            var ax = standTris[t.i], ay = standTris[t.i + 1], az = standTris[t.i + 2], bxx = standTris[t.i + 3], by = standTris[t.i + 4], bzz = standTris[t.i + 5], cx2 = standTris[t.i + 6], cy = standTris[t.i + 7], cz2 = standTris[t.i + 8];
            var d = (bzz - cz2) * (ax - cx2) + (cx2 - bxx) * (az - cz2);
            if (Math.abs(d) < 1e-9) continue;
            var w0 = ((bzz - cz2) * (x - cx2) + (cx2 - bxx) * (z - cz2)) / d;
            var w1 = ((cz2 - az) * (x - cx2) + (ax - cx2) * (z - cz2)) / d;
            var w2 = 1 - w0 - w1;
            if (w0 < -0.02 || w1 < -0.02 || w2 < -0.02) continue;
            var y = w0 * ay + w1 * by + w2 * cy;
            if (y > best) { best = y; arg = t; }
          }
        }
        return arg ? { y: best, t: arg } : null;
      }
      var samples = apronSamples.slice();
      Object.keys(smithRoads).forEach(function (nm) {
        var sts = smithRoads[nm].stations;
        for (var i2 = 0; i2 < sts.length - 1; i2++) {
          var A = sts[i2], B = sts[i2 + 1];
          var segLen = Math.hypot(B.x - A.x, B.z - A.z), n = Math.max(1, Math.round(segLen / 0.5));
          for (var j = 0; j <= n; j++) { var t2 = j / n; samples.push([A.x + (B.x - A.x) * t2, A.z + (B.z - A.z) * t2, A.y + (B.y - A.y) * t2]); }
        }
      });
      for (var pass = 0; pass < 4; pass++) {
        var struck = 0;
        for (var si = 0; si < samples.length; si++) {
          var sm = samples[si], hit = triYAtLocal(sm[0], sm[1]);
          if (hit && hit.y - sm[2] > 1.6) { hit.t.drop = true; struck++; }
        }
        if (!struck) break;
      }
      var kept = standTris.slice(0, triBase);
      tris.forEach(function (t) { if (t.drop) return; for (var v = 0; v < 9; v++) kept.push(standTris[t.i + v]); });
      standTris.length = 0;
      for (var w = 0; w < kept.length; w++) standTris.push(kept[w]);
    })();
    // street lights along the smith's stations: one every ~63 m of
    // travel, alter