feat: MeshCore SAR - Flutter BLE mesh radio companion app

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

lib/services/message_destination_preferences.dart

@@ -0,0 +1,71 @@
+import 'package:shared_preferences/shared_preferences.dart';
+
+/// Service for managing message destination preferences
+/// Stores the last selected recipient (channel, contact, or room) for sending messages
+class MessageDestinationPreferences {
+  static const String _destinationTypeKey = 'message_destination_type';
+  static const String _recipientPublicKeyKey = 'message_recipient_public_key';
+
+  /// Destination types
+  static const String destinationTypeChannel = 'channel';
+  static const String destinationTypeContact = 'contact';
+  static const String destinationTypeRoom = 'room';
+
+  /// Get the saved destination configuration
+  /// Returns a map with 'type' and optional 'publicKey'
+  /// Returns null if no preference is saved (defaults to public channel)
+  static Future<Map<String, String>?> getDestination() async {
+    final prefs = await SharedPreferences.getInstance();
+    final type = prefs.getString(_destinationTypeKey);
+
+    if (type == null) {
+      return null; // Use default (public channel)
+    }
+
+    final publicKey = prefs.getString(_recipientPublicKeyKey);
+
+    return {
+      'type': type,
+      if (publicKey != null) 'publicKey': publicKey,
+    };
+  }
+
+  /// Save the selected destination
+  /// [type] - one of: destinationTypeChannel, destinationTypeContact, destinationTypeRoom
+  /// [recipientPublicKey] - hex string of recipient's public key (required for contact/room)
+  static Future<void> setDestination(
+    String type, {
+    String? recipientPublicKey,
+  }) async {
+    final prefs = await SharedPreferences.getInstance();
+
+    await prefs.setString(_destinationTypeKey, type);
+
+    if (recipientPublicKey != null) {
+      await prefs.setString(_recipientPublicKeyKey, recipientPublicKey);
+    } else {
+      await prefs.remove(_recipientPublicKeyKey);
+    }
+  }
+
+  /// Clear the saved destination (resets to default public channel)
+  static Future<void> clearDestination() async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.remove(_destinationTypeKey);
+    await prefs.remove(_recipientPublicKeyKey);
+  }
+
+  /// Get display name for destination type
+  static String getDestinationTypeName(String type) {
+    switch (type) {
+      case destinationTypeChannel:
+        return 'Channel';
+      case destinationTypeContact:
+        return 'Contact';
+      case destinationTypeRoom:
+        return 'Room';
+      default:
+        return 'Unknown';
+    }
+  }
+}