Checklist v4 from contracts: step 31, each wheel by hand

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

lib/main.dart

@@ -5,6 +5,7 @@ import 'package:flutter/material.dart';
 
 import 'link/boundary.dart';
 import 'link/net.dart';
+import 'link/reading.dart';
 import 'pages/link_test.dart';
 import 'shell.dart';
 import 'shell_scope.dart';
@@ -24,6 +25,14 @@ Future<void> main() async {
   final usb = UsbLink();
   await usb.bindFor(Uri.parse(defaultUrl));
   final boundary = Boundary(defaultUrl)..start();
+  // The sun, for auto dark/bright: the car's position while GNSS has one.
+  boundary.addListener(() {
+    final lat = Reading.of(boundary, 'gnss_lat');
+    final lon = Reading.of(boundary, 'gnss_lon');
+    if (!lat.dim && !lon.dim && lat.number != null && lon.number != null) {
+      themes.setPosition(lat.number!, lon.number!);
+    }
+  });
   final linkTest = LinkTest(usb);
   // Development hook: `am start ... --es linktest [dl:|bi:]<label>[@<host>]` runs the test
   // (`dl:` the download series, `bi:` burst latency against idle gaps), on the gateway's host unless one is given.