fix(preview): derive signals from OSM controls

scripts/build-area.js

@@ -253,6 +253,11 @@ function reimportGpkg(area) {
 function buildBlenderScene(area) {
   ensureFile(blenderExecutable(area), "Blender executable");
   ensureFile(path.join(repoRoot, "blender", "generate_scene.py"), "Blender scene generator");
+  // Traffic signal anchors are derived from the current OSM input plus the
+  // normalized stop-line/intersection layers. Regenerate them for every
+  // Blender build so partial runs cannot reuse a stale signal topology after
+  // the source OSM has changed.
+  writeTrafficSignals(area);
   ensureFile(area.outputs.trafficSignals, "Traffic signal anchors");
   fs.mkdirSync(path.dirname(area.outputs.blend), { recursive: true });
   fs.mkdirSync(path.dirname(area.outputs.render), { recursive: true });
@@ -527,6 +532,7 @@ function writeTrafficSignals(area) {
   const signals = readTrafficSignals(
     path.join(area.outputs.geojsonDir, "vehicle_stop_lines.geojson"),
     path.join(area.outputs.geojsonDir, "intersection_surface.geojson"),
+    area.input,
   );
   fs.writeFileSync(area.outputs.trafficSignals, `${JSON.stringify(signals, null, 2)}\n`);
   console.log(`Traffic signals: ${signals.signals.length} anchors in ${area.outputs.trafficSignals}`);