feat: add node deep link handling to DeepLinkService

Adds `deflockapp://node?id=<nodeId>` deep link support: parses the node
ID, fetches the OSM node via the public API, and delivers it via an
`onNodeDeepLink` callback for HomeScreen to register. Includes URL
parsing unit tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/services/deep_link_service.dart

@@ -1,9 +1,13 @@
 import 'dart:async';
+import 'dart:convert';
 import 'package:app_links/app_links.dart';
 import 'package:flutter/material.dart';
+import 'package:http/http.dart' as http;
+import 'package:latlong2/latlong.dart';
 
 import '../models/node_profile.dart';
 import '../models/operator_profile.dart';
+import '../models/osm_node.dart';
 import 'profile_import_service.dart';
 import 'operator_profile_import_service.dart';
 import '../screens/profile_editor.dart';
@@ -16,6 +20,9 @@ class DeepLinkService {
 
   late AppLinks _appLinks;
   StreamSubscription<Uri>? _linkSubscription;
+
+  /// Callback for HomeScreen to receive node deep links
+  void Function(OsmNode node)? onNodeDeepLink;
   
   /// Initialize deep link handling (sets up stream listener only)
   Future<void> init() async {
@@ -45,6 +52,9 @@ class DeepLinkService {
       case 'profiles':
         _handleProfilesLink(uri);
         break;
+      case 'node':
+        _handleNodeLink(uri);
+        break;
       case 'auth':
         // OAuth links are handled by flutter_web_auth_2
         debugPrint('[DeepLinkService] OAuth link handled by flutter_web_auth_2');
@@ -71,6 +81,58 @@ class DeepLinkService {
     }
   }
   
+  /// Handle node deep link: `deflockapp://node?id=<nodeId>`
+  Future<void> _handleNodeLink(Uri uri) async {
+    final idStr = uri.queryParameters['id'];
+    final nodeId = int.tryParse(idStr ?? '');
+    if (nodeId == null) {
+      _showError('Invalid node link: missing or invalid ID');
+      return;
+    }
+
+    final node = await _fetchNodeById(nodeId);
+    if (node == null) {
+      _showError('Node $nodeId not found');
+      return;
+    }
+
+    if (onNodeDeepLink != null) {
+      onNodeDeepLink!(node);
+    } else {
+      debugPrint('[DeepLinkService] No node deep link handler registered');
+    }
+  }
+
+  /// Fetch an OSM node by ID from the OpenStreetMap API
+  Future<OsmNode?> _fetchNodeById(int nodeId) async {
+    try {
+      final url = Uri.parse('https://api.openstreetmap.org/api/0.6/node/$nodeId.json');
+      final response = await http.get(url);
+      if (response.statusCode != 200) return null;
+
+      final json = jsonDecode(response.body);
+      final elements = json['elements'] as List?;
+      if (elements == null || elements.isEmpty) return null;
+
+      final e = elements[0];
+      final tags = <String, String>{};
+      if (e['tags'] != null) {
+        (e['tags'] as Map<String, dynamic>).forEach((k, v) {
+          tags[k] = v.toString();
+        });
+      }
+
+      return OsmNode(
+        id: e['id'] as int,
+        coord: LatLng((e['lat'] as num).toDouble(), (e['lon'] as num).toDouble()),
+        tags: tags,
+      );
+    } catch (e) {
+      debugPrint('[DeepLinkService] Failed to fetch node $nodeId: $e');
+      return null;
+    }
+  }
+
   /// Handle profile-related deep links
   void _handleProfilesLink(Uri uri) {
     final segments = uri.pathSegments;

test/deep_link_service_test.dart

@@ -0,0 +1,26 @@
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('Node deep link URL parsing', () {
+    test('extracts node ID from valid link', () {
+      final uri = Uri.parse('deflockapp://node?id=1234567890');
+      expect(uri.host, 'node');
+      expect(uri.queryParameters['id'], '1234567890');
+    });
+
+    test('returns null for missing id param', () {
+      final uri = Uri.parse('deflockapp://node');
+      expect(uri.queryParameters['id'], isNull);
+    });
+
+    test('returns null for empty id param', () {
+      final uri = Uri.parse('deflockapp://node?id=');
+      expect(uri.queryParameters['id'], '');
+    });
+
+    test('returns null for non-numeric id', () {
+      final uri = Uri.parse('deflockapp://node?id=abc');
+      expect(int.tryParse(uri.queryParameters['id'] ?? ''), isNull);
+    });
+  });
+}