Phase 1: road network and heat

Roads are a jittered 7x7 grid with ~a quarter of the edges thinned out, kept
connected. The loops are the point: "take a different road" is not a decision
without alternative routes.

Every metre driven adds heat to that segment; all roads shed it slowly. Crossing
a threshold escalates Clear -> Patrol -> Barricade -> Turret, each of which puts
real obstructions on the tarmac. Hysteresis stops a road on a boundary from
rebuilding its barricade every few seconds.

Level changes are deferred while the car is on the segment. Building a barricade
around the player would spawn a static collider inside the chassis, and the
player is meant to discover escalation by returning to a road, not by watching
it assemble behind them.

Checkpoint positions are seeded from the segment id, so a stretch of road always
fortifies in the same place — recognising it is part of learning the map.

Scenery now avoids the tarmac and the car spawns at a junction.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/render/scene.ts

@@ -60,6 +60,27 @@ export function createScene(model: WorldModel): SceneView {
   grid.position.y = 0.02;
   scene.add(grid);
 
+  // --- Roads ---
+  const roadMat = new THREE.MeshStandardMaterial({ color: 0x23262a, roughness: 1 });
+  const quad = new THREE.PlaneGeometry(1, 1).rotateX(-Math.PI / 2);
+  for (const s of model.roads.segments) {
+    const strip = new THREE.Mesh(quad, roadMat);
+    strip.scale.set(s.width, 1, s.length);
+    strip.position.set((s.ax + s.bx) / 2, 0.03, (s.az + s.bz) / 2);
+    strip.rotation.y = Math.atan2(s.bx - s.ax, s.bz - s.az);
+    strip.receiveShadow = true;
+    scene.add(strip);
+  }
+  // Discs fill the wedge-shaped gaps where segments meet at an angle.
+  const junction = new THREE.CircleGeometry(1, 20).rotateX(-Math.PI / 2);
+  for (const n of model.roads.nodes) {
+    const disc = new THREE.Mesh(junction, roadMat);
+    disc.scale.setScalar(4.5);
+    disc.position.set(n.x, 0.031, n.z);
+    disc.receiveShadow = true;
+    scene.add(disc);
+  }
+
   // --- Obstacles ---
   const blockMat = new THREE.MeshStandardMaterial({ color: 0x767c82, roughness: 0.9 });
   const crateMat = new THREE.MeshStandardMaterial({ color: 0xa9773f, roughness: 0.8 });