Mitre route corners and run routes into the buildings

Route ribbons were built from independent segments, each extended half
a width past both ends and offset into its lane separately, so every
turn drew overlapping, brighter corners. Each route is now one strip
with mitred vertices shared by neighbouring segments (sharp reversals
fall back to the outgoing normal), and its along-distance is exact.

Routes also used to stop at the street door; both ends now continue
to the nearest point of the building's footprint and just inside, so
the path visibly meets the wall of the file it leaves and reaches.

webtest/nav.test.mjs

@@ -125,5 +125,27 @@ test('route ribbons keep right, so opposite directions on one street use separat
   assert.ok(ys(east).every(y => y > 0), `eastbound ribbon on +y: ${ys(east)}`);
   assert.ok(ys(west).every(y => y < 0), `westbound ribbon on -y: ${ys(west)}`);
   const along = []; for (let i = 4; i < east.length; i += 6) along.push(east[i]);
-  assert.ok(Math.max(...along) > 99 && Math.min(...along) < 0 && east[5] === 0 && west[5] === 2);
+  assert.ok(Math.max(...along) === 100 && Math.min(...along) === 0 && east[5] === 0 && west[5] === 2);
+});
+
+import { enterBuilding } from '../web/city.js';
+
+test('turns are mitred: consecutive segments share their corner edge instead of overlapping', () => {
+  const vertices = ribbonVertices([{ points: [[0, 0], [50, 0], [50, 40]], kind: 0 }], 1.3, .45, .8);
+  const at = i => [vertices[i * 6], vertices[i * 6 + 1]];
+  // Segment 1 ends with vertices 2 (right) and 5 (left); segment 2 starts with 6 (left) and 7 (right).
+  assert.deepEqual(at(2), at(7));
+  assert.deepEqual(at(5), at(6));
+  // The corner vertices sit on the diagonal offsets of the turn, not past the end of either segment.
+  const [rx, ry] = at(2);
+  assert.ok(Math.abs(rx - (50 - 1.45)) < 1e-9 && Math.abs(ry - 1.45) < 1e-9, `inner corner ${rx},${ry}`);
+  assert.equal(vertices.length / 6, 12, 'two quads, no extra caps');
+});
+
+test('route ends enter the building footprint', () => {
+  const b = { x: 10, y: 10, w: 20, h: 10 };
+  const [x, y] = enterBuilding([20, 4], b, .8);
+  assert.ok(x === 20 && Math.abs(y - 10.8) < 1e-9, `${x},${y}`);
+  const corner = enterBuilding([5, 5], b, 1);
+  assert.ok(corner[0] > 10 && corner[1] > 10 && corner[0] < 11 && corner[1] < 11);
 });