feat: Add relay ping and lock message destination

lib/providers/connection_provider.dart

@@ -47,6 +47,23 @@ class PingResult {
   });
 }
 
+/// Result of a relay ping (trace path) operation
+class RelayPingResult {
+  final bool success;
+  final int durationMs;
+  final double snrThere;
+  final double snrBack;
+  final int hopCount;
+
+  const RelayPingResult({
+    required this.success,
+    required this.durationMs,
+    required this.snrThere,
+    required this.snrBack,
+    required this.hopCount,
+  });
+}
+
 /// Scanned device with RSSI information
 class ScannedDevice {
   final BluetoothDevice device;
@@ -172,6 +189,8 @@ class ConnectionProvider with ChangeNotifier {
       MessageDeliveryTracker();
   final PingTracker _pingTracker = PingTracker();
   final Map<String, Future<PingResult>> _pendingSmartPings = {};
+  final Map<int, Completer<RelayPingResult>> _pendingRelayPings = {};
+  final Map<int, int> _relayPingStartTimes = {};
 
   // Expose room login states
   Map<String, RoomLoginState> get roomLoginStates =>
@@ -631,6 +650,10 @@ class ConnectionProvider with ChangeNotifier {
       notifyListeners();
     };
 
+    service.onTraceDataReceived = (nonce, hopCount, snrThere, snrBack) {
+      _handleTraceDataReceived(nonce, hopCount, snrThere, snrBack);
+    };
+
     service.onTxActivity = () {
       _txActivity = true;
       notifyListeners();
@@ -2036,6 +2059,88 @@ class ConnectionProvider with ChangeNotifier {
     }
   }
 
+  /// Ping a relay/repeater using trace path (command 36).
+  /// Returns RTT, SNR there/back, and hop count.
+  Future<RelayPingResult> pingRelay(Contact contact) async {
+    if (!_activeService.isConnected) {
+      return const RelayPingResult(
+        success: false, durationMs: 0, snrThere: 0, snrBack: 0, hopCount: 0,
+      );
+    }
+
+    final nonce = Random().nextInt(0xFFFFFFFF);
+    final completer = Completer<RelayPingResult>();
+    _pendingRelayPings[nonce] = completer;
+    _relayPingStartTimes[nonce] = DateTime.now().millisecondsSinceEpoch;
+
+    // Map ContactType to hop type: chat=0, repeater=1, room=2, sensor=3
+    int hopType;
+    switch (contact.type) {
+      case ContactType.chat:
+        hopType = 0;
+        break;
+      case ContactType.repeater:
+        hopType = 1;
+        break;
+      case ContactType.room:
+        hopType = 2;
+        break;
+      case ContactType.sensor:
+        hopType = 3;
+        break;
+      default:
+        hopType = 0;
+    }
+
+    // Timeout after 10 seconds
+    final timer = Timer(const Duration(seconds: 10), () {
+      _pendingRelayPings.remove(nonce);
+      _relayPingStartTimes.remove(nonce);
+      if (!completer.isCompleted) {
+        completer.complete(const RelayPingResult(
+          success: false, durationMs: 0, snrThere: 0, snrBack: 0, hopCount: 0,
+        ));
+      }
+    });
+
+    try {
+      await _activeService.sendTracePath(
+        nonce: nonce,
+        hopType: hopType,
+        contactPublicKey: contact.publicKey,
+      );
+      final result = await completer.future;
+      timer.cancel();
+      return result;
+    } catch (e) {
+      timer.cancel();
+      _pendingRelayPings.remove(nonce);
+      _relayPingStartTimes.remove(nonce);
+      return const RelayPingResult(
+        success: false, durationMs: 0, snrThere: 0, snrBack: 0, hopCount: 0,
+      );
+    }
+  }
+
+  void _handleTraceDataReceived(
+    int nonce, int hopCount, double snrThere, double snrBack,
+  ) {
+    final completer = _pendingRelayPings.remove(nonce);
+    final startTime = _relayPingStartTimes.remove(nonce);
+    if (completer != null && !completer.isCompleted) {
+      final durationMs = startTime != null
+          ? DateTime.now().millisecondsSinceEpoch - startTime
+          : 0;
+      completer.complete(RelayPingResult(
+        success: true,
+        durationMs: durationMs,
+        snrThere: snrThere,
+        snrBack: snrBack,
+        hopCount: hopCount,
+      ));
+    }
+  }
+
   String _publicKeyToHex(Uint8List publicKey) {
     return publicKey.map((b) => b.toRadixString(16).padLeft(2, '0')).join('');
   }

lib/screens/messages_tab.dart

@@ -148,11 +148,13 @@ class _MessagesTabState extends State<MessagesTab> {
   TextRange? _activeMentionRange;
   String _mentionQuery = '';
   List<Contact> _mentionSuggestions = const [];
+  ContactsProvider? _contactsProvider;
 
   // Message destination state
   String _destinationType =
       MessageDestinationPreferences.destinationTypeChannel;
   Contact? _selectedRecipient;
+  bool _isDestinationLocked = false;
 
   // Region scope state
   String? _channelRegionScopeName;
@@ -183,13 +185,9 @@ class _MessagesTabState extends State<MessagesTab> {
     super.initState();
     _textController.addListener(_handleComposerChanged);
     _focusNode.addListener(_handleFocusChanged);
-    // Load saved message destination
-    _loadSavedDestination();
     _loadVoiceSettings();
     _loadAllChannelRegionScopes();
-    WidgetsBinding.instance.addPostFrameCallback((_) {
-      _checkForNavigationRequest();
-    });
+    _scheduleDestinationSync();
   }
 
   Future<void> _loadVoiceSettings() async {
@@ -203,11 +201,13 @@ class _MessagesTabState extends State<MessagesTab> {
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
-    // Reload saved destination and check for navigation request whenever dependencies change
-    WidgetsBinding.instance.addPostFrameCallback((_) {
-      _loadSavedDestination();
-      _checkForNavigationRequest();
-    });
+    final contactsProvider = context.read<ContactsProvider>();
+    if (!identical(_contactsProvider, contactsProvider)) {
+      _contactsProvider?.removeListener(_handleContactsChanged);
+      _contactsProvider = contactsProvider;
+      _contactsProvider?.addListener(_handleContactsChanged);
+    }
+    _scheduleDestinationSync();
   }
 
   @override
@@ -216,6 +216,7 @@ class _MessagesTabState extends State<MessagesTab> {
     _channelReadTimer?.cancel();
     _voiceStreamSub?.cancel();
     _voiceRecorder.dispose();
+    _contactsProvider?.removeListener(_handleContactsChanged);
     _focusNode.removeListener(_handleFocusChanged);
     _textController.dispose();
     _focusNode.dispose();
@@ -228,13 +229,37 @@ class _MessagesTabState extends State<MessagesTab> {
     super.didUpdateWidget(oldWidget);
     if (oldWidget.isActive != widget.isActive) {
       _syncChannelAutoReadTimer(context.read<MessagesProvider>());
+      if (widget.isActive) {
+        _scheduleDestinationSync();
+      }
     }
   }
 
-  void _checkForNavigationRequest() {
+  void _scheduleDestinationSync() {
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      _synchronizeDestinationState();
+    });
+  }
+
+  void _handleContactsChanged() {
+    if (!mounted) return;
+    _scheduleDestinationSync();
+  }
+
+  Future<void> _synchronizeDestinationState() async {
+    if (!mounted) return;
     final messagesProvider = context.read<MessagesProvider>();
     final targetMessageId = messagesProvider.targetMessageId;
     final targetDestinationType = messagesProvider.targetDestinationType;
+    final targetRecipientPublicKeyHex =
+        messagesProvider.targetRecipientPublicKeyHex;
+
+    await _restoreDestinationState(
+      overrideType: targetDestinationType,
+      overrideRecipientPublicKeyHex: targetRecipientPublicKeyHex,
+    );
+
+    if (!mounted) return;
 
     if (targetMessageId != null) {
       _scrollToMessage(targetMessageId);
@@ -242,11 +267,8 @@ class _MessagesTabState extends State<MessagesTab> {
     }
 
     if (targetDestinationType != null) {
-      _applyPendingDestination(
-        type: targetDestinationType,
-        recipientPublicKeyHex: messagesProvider.targetRecipientPublicKeyHex,
-      );
       messagesProvider.clearDestinationNavigation();
+      _focusNode.requestFocus();
     }
   }
 
@@ -447,56 +469,91 @@ class _MessagesTabState extends State<MessagesTab> {
     _updateCharacterCount();
   }
 
-  /// Load saved message destination from preferences
-  Future<void> _loadSavedDestination() async {
+  Future<void> _restoreDestinationState({
+    String? overrideType,
+    String? overrideRecipientPublicKeyHex,
+  }) async {
+    final lockedDestination =
+        await MessageDestinationPreferences.getLockedDestination();
     final savedDestination =
         await MessageDestinationPreferences.getDestination();
-
-    if (savedDestination == null || !mounted) {
-      // Default to public channel
-      return;
-    }
-
-    final type = savedDestination['type']!;
-    final publicKey = savedDestination['publicKey'];
-
-    setState(() {
-      _destinationType = type;
-    });
-
-    // If it's a contact or room, try to find it in the contacts list
-    if (publicKey != null && mounted) {
-      final contactsProvider = context.read<ContactsProvider>();
-      final contact = contactsProvider.contacts.where((c) {
-        return c.publicKeyHex == publicKey;
-      }).firstOrNull;
-
-      if (contact != null) {
-        setState(() {
-          _selectedRecipient = contact;
-        });
-      } else {
-        // Contact/room not found, fallback to public channel
-        debugPrint(
-          '⚠️ [MessagesTab] Saved recipient not found, falling back to public channel',
-        );
-        setState(() {
-          _destinationType =
+    final effectiveType =
+        overrideType ??
+        lockedDestination?['type'] ??
+        savedDestination?['type'] ??
         MessageDestinationPreferences.destinationTypeChannel;
-          _selectedRecipient = null;
+    final effectivePublicKeyHex =
+        overrideRecipientPublicKeyHex ??
+        lockedDestination?['publicKey'] ??
+        savedDestination?['publicKey'];
+    if (!mounted) return;
+    final contactsProvider = context.read<ContactsProvider>();
+    final recipient = _resolveDestinationRecipient(
+      contactsProvider,
+      effectiveType,
+      effectivePublicKeyHex,
+    );
+    final allowsEmptyRecipient =
+        effectiveType == MessageDestinationPreferences.destinationTypeAll ||
+        (effectiveType == MessageDestinationPreferences.destinationTypeChannel &&
+            effectivePublicKeyHex == null);
+    final shouldFallbackToPublicChannel =
+        recipient == null && !allowsEmptyRecipient;
+    final destinationType = shouldFallbackToPublicChannel
+        ? MessageDestinationPreferences.destinationTypeChannel
+        : effectiveType;
+    final selectedRecipient = shouldFallbackToPublicChannel ? null : recipient;
+    final shouldClearSavedDestination =
+        lockedDestination == null &&
+        overrideType == null &&
+        shouldFallbackToPublicChannel &&
+        savedDestination != null;
+
+    if (!mounted) return;
+
+    setState(() {
+      _isDestinationLocked = lockedDestination != null;
+      _destinationType = destinationType;
+      _selectedRecipient = selectedRecipient;
     });
+
+    if (shouldClearSavedDestination) {
       await MessageDestinationPreferences.clearDestination();
     }
-    }
 
     _enforceMessageByteLimit();
-
-    // Load region scope for channel destinations
     await _loadRegionScope();
   }
 
+  Contact? _resolveDestinationRecipient(
+    ContactsProvider contactsProvider,
+    String type,
+    String? publicKeyHex,
+  ) {
+    if (publicKeyHex == null) {
+      return null;
+    }
+
+    final candidates = switch (type) {
+      MessageDestinationPreferences.destinationTypeChannel =>
+        contactsProvider.channels,
+      MessageDestinationPreferences.destinationTypeRoom => contactsProvider.rooms,
+      MessageDestinationPreferences.destinationTypeContact =>
+        contactsProvider.chatContacts,
+      _ => contactsProvider.contacts,
+    };
+
+    return candidates.where((contact) {
+      return contact.publicKeyHex == publicKeyHex;
+    }).firstOrNull;
+  }
+
   /// Show recipient selector bottom sheet
   void _showRecipientSelector() {
+    if (_isDestinationLocked) {
+      return;
+    }
+
     final contactsProvider = context.read<ContactsProvider>();
     final messagesProvider = context.read<MessagesProvider>();
 
@@ -552,7 +609,11 @@ class _MessagesTabState extends State<MessagesTab> {
   }
 
   /// Handle recipient selection
-  Future<void> _onRecipientSelected(String type, Contact? recipient) async {
+  Future<void> _onRecipientSelected(
+    String type,
+    Contact? recipient, {
+    bool persistSelection = true,
+  }) async {
     setState(() {
       _destinationType = type;
       _selectedRecipient = recipient;
@@ -565,11 +626,12 @@ class _MessagesTabState extends State<MessagesTab> {
     // Load region scope for channel destinations
     await _loadRegionScope();
 
-    // Save to preferences
+    if (persistSelection) {
       await MessageDestinationPreferences.setDestination(
         type,
         recipientPublicKey: recipient?.publicKeyHex,
       );
+    }
 
     // Show confirmation toast
     if (!mounted) return;
@@ -620,23 +682,6 @@ class _MessagesTabState extends State<MessagesTab> {
     });
   }
 
-  Future<void> _applyPendingDestination({
-    required String type,
-    String? recipientPublicKeyHex,
-  }) async {
-    Contact? recipient;
-    if (recipientPublicKeyHex != null) {
-      final contactsProvider = context.read<ContactsProvider>();
-      recipient = contactsProvider.contacts.where((contact) {
-        return contact.publicKeyHex == recipientPublicKeyHex;
-      }).firstOrNull;
-    }
-
-    await _onRecipientSelected(type, recipient);
-    if (!mounted) return;
-    _focusNode.requestFocus();
-  }
-
   void _insertReplyMention(String displayName, {TextRange? replacementRange}) {
     final trimmedName = displayName.trim();
     if (trimmedName.isEmpty) return;
@@ -746,7 +791,11 @@ class _MessagesTabState extends State<MessagesTab> {
       }
     }
 
-    await _onRecipientSelected(destinationType, recipient);
+    await _onRecipientSelected(
+      destinationType,
+      recipient,
+      persistSelection: !_isDestinationLocked,
+    );
     if (!mounted) return;
     if ((message.isChannelMessage || recipient?.isRoom == true) &&
         senderDisplayName != null &&
@@ -2442,6 +2491,7 @@ class _MessagesTabState extends State<MessagesTab> {
                   bottomPadding: composerBottomPadding,
                   destinationLabel: _getDestinationLabel(),
                   destinationAvatar: _buildDestinationAvatar(context),
+                  destinationLocked: _isDestinationLocked,
                   mentionSuggestions: _mentionSuggestions,
                   mentionQuery: _mentionQuery,
                   onMentionSelected: _selectMention,

lib/screens/settings_screen.dart

@@ -25,6 +25,7 @@ import '../services/update_checker_service.dart';
 import '../services/voice_bitrate_preferences.dart';
 import '../services/image_preferences.dart';
 import '../services/route_hash_preferences.dart';
+import '../services/message_destination_preferences.dart';
 import '../services/image_codec_service.dart';
 import '../services/developer_mode_service.dart';
 import '../services/notification_service.dart';
@@ -60,6 +61,8 @@ class SettingsScreen extends StatefulWidget {
 }
 
 class _SettingsScreenState extends State<SettingsScreen> {
+  static const String _publicChannelPublicKeyHex =
+      '0000000000000000000000000000000000000000000000000000000000000000';
   late AppThemeMode _selectedTheme;
   late Locale? _selectedLocale;
   PackageInfo? _packageInfo;
@@ -91,6 +94,10 @@ class _SettingsScreenState extends State<SettingsScreen> {
   bool _muteForegroundNotifications = true;
   bool _isDeveloperModeEnabled = false;
   bool _profilesEnabled = false;
+  bool _messageDestinationLockEnabled = false;
+  String _messageDestinationLockType =
+      MessageDestinationPreferences.destinationTypeChannel;
+  String? _messageDestinationLockPublicKey = _publicChannelPublicKeyHex;
   DateTime? _onlineTraceCacheUpdatedAt;
   bool _isClearingOnlineTraceCache = false;
   int _versionTapCount = 0;
@@ -114,6 +121,7 @@ class _SettingsScreenState extends State<SettingsScreen> {
     _loadOnlineTraceCacheStatus();
     _loadMapPreferences();
     _loadNotificationPreferences();
+    _loadMessageDestinationLock();
   }
 
   @override
@@ -184,6 +192,94 @@ class _SettingsScreenState extends State<SettingsScreen> {
     });
   }
 
+  Future<void> _loadMessageDestinationLock() async {
+    final lockedDestination =
+        await MessageDestinationPreferences.getLockedDestination();
+    if (!mounted) return;
+
+    setState(() {
+      _messageDestinationLockEnabled = lockedDestination != null;
+      _messageDestinationLockType =
+          lockedDestination?['publicKey'] == null
+          ? MessageDestinationPreferences.destinationTypeChannel
+          : lockedDestination?['type'] ??
+                MessageDestinationPreferences.destinationTypeChannel;
+      _messageDestinationLockPublicKey =
+          lockedDestination?['publicKey'] ?? _publicChannelPublicKeyHex;
+    });
+  }
+
+  List<Contact> _messageDestinationLockOptions(
+    ContactsProvider contactsProvider,
+  ) {
+    final channels = List<Contact>.from(contactsProvider.channels)
+      ..sort((a, b) {
+        if (a.isPublicChannel != b.isPublicChannel) {
+          return a.isPublicChannel ? -1 : 1;
+        }
+        return a.displayName.toLowerCase().compareTo(
+          b.displayName.toLowerCase(),
+        );
+      });
+    final rooms = List<Contact>.from(contactsProvider.rooms)
+      ..sort(
+        (a, b) => a.displayName.toLowerCase().compareTo(
+          b.displayName.toLowerCase(),
+        ),
+      );
+
+    return [...channels, ...rooms];
+  }
+
+  String _messageDestinationLockLabel(BuildContext context, Contact contact) {
+    final name = contact.isChannel
+        ? contact.getLocalizedDisplayName(context)
+        : contact.displayName;
+    return contact.isRoom ? 'Room: $name' : 'Channel: $name';
+  }
+
+  String _messageDestinationLockTypeForContact(Contact contact) {
+    return contact.isRoom
+        ? MessageDestinationPreferences.destinationTypeRoom
+        : MessageDestinationPreferences.destinationTypeChannel;
+  }
+
+  String? _selectedMessageDestinationLockValue(List<Contact> destinations) {
+    final currentValue = _messageDestinationLockPublicKey;
+    if (currentValue != null &&
+        destinations.any((contact) => contact.publicKeyHex == currentValue)) {
+      return currentValue;
+    }
+
+    return destinations.isEmpty ? null : destinations.first.publicKeyHex;
+  }
+
+  Future<void> _setMessageDestinationLock({
+    required bool enabled,
+    String? type,
+    String? recipientPublicKey,
+  }) async {
+    final nextType = type ?? _messageDestinationLockType;
+    final nextRecipientPublicKey =
+        recipientPublicKey ??
+        _messageDestinationLockPublicKey ??
+        _publicChannelPublicKeyHex;
+
+    await MessageDestinationPreferences.setLockedDestination(
+      enabled: enabled,
+      type: nextType,
+      recipientPublicKey: enabled ? nextRecipientPublicKey : null,
+    );
+
+    if (!mounted) return;
+
+    setState(() {
+      _messageDestinationLockEnabled = enabled;
+      _messageDestinationLockType = nextType;
+      _messageDestinationLockPublicKey = nextRecipientPublicKey;
+    });
+  }
+
   Future<void> _handleVersionTap() async {
     if (_isDeveloperModeEnabled) {
       await DeveloperModeService.setEnabled(false);
@@ -1430,6 +1526,90 @@ class _SettingsScreenState extends State<SettingsScreen> {
                 },
               ),
             ),
+            SwitchListTile(
+              secondary: const Icon(Icons.lock_outline),
+              title: const Text('Lock messages to one channel or room'),
+              subtitle: const Text(
+                'Keep the Messages tab and composer fixed on one destination. Direct messages from Contacts still open as usual.',
+              ),
+              value: _messageDestinationLockEnabled,
+              onChanged: (value) async {
+                final contactsProvider = context.read<ContactsProvider>();
+                final options = _messageDestinationLockOptions(
+                  contactsProvider,
+                );
+                final selectedPublicKey =
+                    _selectedMessageDestinationLockValue(options) ??
+                    _publicChannelPublicKeyHex;
+                final selectedContact = options.where((contact) {
+                  return contact.publicKeyHex == selectedPublicKey;
+                }).firstOrNull;
+
+                await _setMessageDestinationLock(
+                  enabled: value,
+                  type: selectedContact == null
+                      ? MessageDestinationPreferences.destinationTypeChannel
+                      : _messageDestinationLockTypeForContact(selectedContact),
+                  recipientPublicKey: selectedPublicKey,
+                );
+              },
+            ),
+            Consumer<ContactsProvider>(
+              builder: (context, contactsProvider, child) {
+                final options = _messageDestinationLockOptions(
+                  contactsProvider,
+                );
+                final selectedValue =
+                    _selectedMessageDestinationLockValue(options);
+
+                return Padding(
+                  padding: const EdgeInsets.fromLTRB(16, 12, 16, 16),
+                  child: DropdownButtonFormField<String>(
+                    key: ValueKey(selectedValue),
+                    initialValue: selectedValue,
+                    isExpanded: true,
+                    decoration: const InputDecoration(
+                      labelText: 'Locked channel or room',
+                      prefixIcon: Icon(Icons.forum_outlined),
+                      border: OutlineInputBorder(),
+                    ),
+                    items: [
+                      for (final contact in options)
+                        DropdownMenuItem<String>(
+                          value: contact.publicKeyHex,
+                          child: Text(
+                            _messageDestinationLockLabel(context, contact),
+                            overflow: TextOverflow.ellipsis,
+                          ),
+                        ),
+                    ],
+                    onChanged:
+                        _messageDestinationLockEnabled && options.isNotEmpty
+                        ? (value) async {
+                            if (value == null) {
+                              return;
+                            }
+
+                            final selectedContact = options.where((contact) {
+                              return contact.publicKeyHex == value;
+                            }).firstOrNull;
+                            if (selectedContact == null) {
+                              return;
+                            }
+
+                            await _setMessageDestinationLock(
+                              enabled: true,
+                              type: _messageDestinationLockTypeForContact(
+                                selectedContact,
+                              ),
+                              recipientPublicKey: value,
+                            );
+                          }
+                        : null,
+                  ),
+                );
+              },
+            ),
             ListTile(
               leading: const Icon(Icons.delete_sweep, color: Colors.red),
               title: const Text(

lib/services/message_destination_preferences.dart

@@ -5,6 +5,12 @@ import 'package:shared_preferences/shared_preferences.dart';
 class MessageDestinationPreferences {
   static const String _destinationTypeKey = 'message_destination_type';
   static const String _recipientPublicKeyKey = 'message_recipient_public_key';
+  static const String _lockedDestinationEnabledKey =
+      'message_locked_destination_enabled';
+  static const String _lockedDestinationTypeKey =
+      'message_locked_destination_type';
+  static const String _lockedRecipientPublicKeyKey =
+      'message_locked_recipient_public_key';
 
   /// Destination types
   static const String destinationTypeAll = 'all';
@@ -12,6 +18,10 @@ class MessageDestinationPreferences {
   static const String destinationTypeContact = 'contact';
   static const String destinationTypeRoom = 'room';
 
+  static bool isLockableDestinationType(String type) {
+    return type == destinationTypeChannel || type == destinationTypeRoom;
+  }
+
   /// Get the saved destination configuration
   /// Returns a map with 'type' and optional 'publicKey'
   /// Returns null if no preference is saved (defaults to public channel)
@@ -53,6 +63,53 @@ class MessageDestinationPreferences {
     await prefs.remove(_recipientPublicKeyKey);
   }
 
+  /// Get the saved locked destination configuration.
+  /// Returns null when the lock is disabled.
+  static Future<Map<String, String>?> getLockedDestination() async {
+    final prefs = await SharedPreferences.getInstance();
+    final isEnabled = prefs.getBool(_lockedDestinationEnabledKey) ?? false;
+
+    if (!isEnabled) {
+      return null;
+    }
+
+    final savedType =
+        prefs.getString(_lockedDestinationTypeKey) ?? destinationTypeChannel;
+    final type = isLockableDestinationType(savedType)
+        ? savedType
+        : destinationTypeChannel;
+    final publicKey = prefs.getString(_lockedRecipientPublicKeyKey);
+
+    return {'type': type, 'publicKey': ?publicKey};
+  }
+
+  static Future<void> setLockedDestination({
+    required bool enabled,
+    String type = destinationTypeChannel,
+    String? recipientPublicKey,
+  }) async {
+    final prefs = await SharedPreferences.getInstance();
+
+    await prefs.setBool(_lockedDestinationEnabledKey, enabled);
+
+    if (!enabled) {
+      await prefs.remove(_lockedDestinationTypeKey);
+      await prefs.remove(_lockedRecipientPublicKeyKey);
+      return;
+    }
+
+    final sanitizedType = isLockableDestinationType(type)
+        ? type
+        : destinationTypeChannel;
+    await prefs.setString(_lockedDestinationTypeKey, sanitizedType);
+
+    if (recipientPublicKey != null) {
+      await prefs.setString(_lockedRecipientPublicKeyKey, recipientPublicKey);
+    } else {
+      await prefs.remove(_lockedRecipientPublicKeyKey);
+    }
+  }
+
   /// Get display name for destination type
   static String getDestinationTypeName(String type) {
     switch (type) {

lib/widgets/contacts/contact_tile.dart

@@ -11,6 +11,7 @@ import '../../providers/contacts_provider.dart';
 import '../../providers/map_provider.dart';
 import '../../providers/messages_provider.dart';
 import '../../providers/sensors_provider.dart';
+import '../../services/location_tracking_service.dart';
 import '../../services/message_destination_preferences.dart';
 import 'contact_route_dialog.dart';
 import 'contact_trace_sheet.dart';
@@ -529,6 +530,16 @@ class ContactTile extends StatelessWidget {
             _showNeighbours(context, contact);
           },
         ),
+      if (contact.type == ContactType.repeater ||
+          contact.type == ContactType.room)
+        _ContactSheetAction(
+          icon: Icons.network_ping,
+          label: 'Ping',
+          onTap: () async {
+            Navigator.pop(context);
+            _pingRelay(context, contact);
+          },
+        ),
       if (!contact.isPublicChannel)
         _ContactSheetAction(
           icon: Icons.edit_outlined,
@@ -664,6 +675,18 @@ class ContactTile extends StatelessWidget {
     );
   }
 
+  void _pingRelay(BuildContext context, Contact contact) {
+    showModalBottomSheet(
+      context: context,
+      isScrollControlled: true,
+      backgroundColor: Theme.of(context).colorScheme.surface,
+      shape: const RoundedRectangleBorder(
+        borderRadius: BorderRadius.vertical(top: Radius.circular(16)),
+      ),
+      builder: (context) => _PingRelaySheet(contact: contact),
+    );
+  }
+
   void _showDeleteConfirmation(
     BuildContext context,
     Contact contact, {
@@ -2325,3 +2348,181 @@ class _MappedNeighbour {
     required this.location,
   });
 }
+
+/// Bottom sheet for pinging a relay/repeater with history and distance.
+class _PingRelaySheet extends StatefulWidget {
+  final Contact contact;
+
+  const _PingRelaySheet({required this.contact});
+
+  @override
+  State<_PingRelaySheet> createState() => _PingRelaySheetState();
+}
+
+class _PingRelaySheetState extends State<_PingRelaySheet> {
+  bool _pinging = false;
+  final List<RelayPingResult> _history = [];
+
+  @override
+  void initState() {
+    super.initState();
+    _doPing();
+  }
+
+  Future<void> _doPing() async {
+    setState(() => _pinging = true);
+    final connectionProvider = context.read<ConnectionProvider>();
+    final result = await connectionProvider.pingRelay(widget.contact);
+    if (!mounted) return;
+    setState(() {
+      _pinging = false;
+      _history.insert(0, result);
+    });
+  }
+
+  String? _distanceText() {
+    final location = widget.contact.displayLocation;
+    if (location == null) return null;
+    final currentPosition =
+        LocationTrackingService().currentPosition;
+    if (currentPosition == null) return null;
+    final meters = Geolocator.distanceBetween(
+      currentPosition.latitude,
+      currentPosition.longitude,
+      location.latitude,
+      location.longitude,
+    );
+    if (meters < 1000) return '${meters.round()} m';
+    if (meters < 10000) return '${(meters / 1000).toStringAsFixed(2)} km';
+    return '${(meters / 1000).toStringAsFixed(1)} km';
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final displayName = widget.contact.displayName;
+    final distance = _distanceText();
+
+    return SafeArea(
+      child: Padding(
+        padding: const EdgeInsets.fromLTRB(16, 12, 16, 16),
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            Center(
+              child: Container(
+                width: 40,
+                height: 4,
+                decoration: BoxDecoration(
+                  color: theme.dividerColor,
+                  borderRadius: BorderRadius.circular(2),
+                ),
+              ),
+            ),
+            const SizedBox(height: 14),
+            Row(
+              children: [
+                Expanded(
+                  child: Text(
+                    'Ping $displayName',
+                    style: theme.textTheme.titleLarge,
+                  ),
+                ),
+                FilledButton.icon(
+                  onPressed: _pinging ? null : _doPing,
+                  icon: _pinging
+                      ? const SizedBox(
+                          width: 16,
+                          height: 16,
+                          child: CircularProgressIndicator(
+                            strokeWidth: 2,
+                            color: Colors.white,
+                          ),
+                        )
+                      : const Icon(Icons.refresh, size: 18),
+                  label: Text(_pinging ? 'Pinging...' : 'Ping Again'),
+                ),
+              ],
+            ),
+            if (distance != null) ...[
+              const SizedBox(height: 4),
+              Text(
+                'Distance: $distance',
+                style: theme.textTheme.bodySmall,
+              ),
+            ],
+            const SizedBox(height: 12),
+            if (_history.isEmpty && _pinging)
+              const Padding(
+                padding: EdgeInsets.symmetric(vertical: 24),
+                child: Center(child: CircularProgressIndicator()),
+              )
+            else if (_history.isEmpty)
+              Padding(
+                padding: const EdgeInsets.symmetric(vertical: 24),
+                child: Center(
+                  child: Text(
+                    'No results yet',
+                    style: theme.textTheme.bodyMedium,
+                  ),
+                ),
+              )
+            else
+              ConstrainedBox(
+                constraints: const BoxConstraints(maxHeight: 300),
+                child: ListView.separated(
+                  shrinkWrap: true,
+                  itemCount: _history.length,
+                  separatorBuilder: (_, _) => const Divider(height: 1),
+                  itemBuilder: (context, index) {
+                    final r = _history[index];
+                    final seq = _history.length - index;
+                    if (!r.success) {
+                      return ListTile(
+                        dense: true,
+                        leading: CircleAvatar(
+                          radius: 14,
+                          backgroundColor: theme.colorScheme.error,
+                          child: Text(
+                            '$seq',
+                            style: const TextStyle(
+                              color: Colors.white,
+                              fontSize: 11,
+                              fontWeight: FontWeight.bold,
+                            ),
+                          ),
+                        ),
+                        title: const Text('Timeout'),
+                        subtitle: const Text('No response received'),
+                      );
+                    }
+                    return ListTile(
+                      dense: true,
+                      leading: CircleAvatar(
+                        radius: 14,
+                        backgroundColor: Colors.green,
+                        child: Text(
+                          '$seq',
+                          style: const TextStyle(
+                            color: Colors.white,
+                            fontSize: 11,
+                            fontWeight: FontWeight.bold,
+                          ),
+                        ),
+                      ),
+                      title: Text('${r.durationMs} ms'),
+                      subtitle: Text(
+                        'SNR there: ${r.snrThere.toStringAsFixed(1)} dB  '
+                        'SNR back: ${r.snrBack.toStringAsFixed(1)} dB',
+                      ),
+                    );
+                  },
+                ),
+              ),
+          ],
+        ),
+      ),
+    );
+  }
+}

lib/widgets/messages/messages_composer.dart

@@ -19,6 +19,7 @@ class MessagesComposer extends StatelessWidget {
   final double bottomPadding;
   final String destinationLabel;
   final Widget destinationAvatar;
+  final bool destinationLocked;
   final List<Contact> mentionSuggestions;
   final String mentionQuery;
   final ValueChanged<Contact> onMentionSelected;
@@ -44,6 +45,7 @@ class MessagesComposer extends StatelessWidget {
     required this.bottomPadding,
     required this.destinationLabel,
     required this.destinationAvatar,
+    required this.destinationLocked,
     required this.mentionSuggestions,
     required this.mentionQuery,
     required this.onMentionSelected,
@@ -118,10 +120,13 @@ class MessagesComposer extends StatelessWidget {
                           ],
                           const SizedBox(width: 8),
                           Expanded(
-                            child: _DestinationSelector(
+                            child: _DestinationPill(
                               destinationLabel: destinationLabel,
                               destinationAvatar: destinationAvatar,
-                              onTap: onShowRecipientSelector,
+                              isLocked: destinationLocked,
+                              onTap: destinationLocked
+                                  ? null
+                                  : onShowRecipientSelector,
                             ),
                           ),
                         ],
@@ -297,25 +302,27 @@ class _ComposerActionButton extends StatelessWidget {
   }
 }
 
-class _DestinationSelector extends StatelessWidget {
+class _DestinationPill extends StatelessWidget {
   final String destinationLabel;
   final Widget destinationAvatar;
-  final VoidCallback onTap;
+  final bool isLocked;
+  final VoidCallback? onTap;
 
-  const _DestinationSelector({
+  const _DestinationPill({
     required this.destinationLabel,
     required this.destinationAvatar,
-    required this.onTap,
+    required this.isLocked,
+    this.onTap,
   });
 
   @override
   Widget build(BuildContext context) {
-    return Material(
-      color: Colors.transparent,
-      child: InkWell(
-        borderRadius: BorderRadius.circular(20),
-        onTap: onTap,
-        child: Ink(
+    final content = Ink(
+      key: ValueKey(
+        isLocked
+            ? 'messages_composer_destination_locked'
+            : 'messages_composer_destination_selector',
+      ),
       height: 40,
       decoration: BoxDecoration(
         color: Theme.of(context).colorScheme.surface,
@@ -341,6 +348,7 @@ class _DestinationSelector extends StatelessWidget {
                 ),
               ),
             ),
+            if (!isLocked)
               Icon(
                 Icons.expand_more_rounded,
                 size: 18,
@@ -349,7 +357,18 @@ class _DestinationSelector extends StatelessWidget {
           ],
         ),
       ),
-        ),
+    );
+
+    if (onTap == null) {
+      return Material(color: Colors.transparent, child: content);
+    }
+
+    return Material(
+      color: Colors.transparent,
+      child: InkWell(
+        borderRadius: BorderRadius.circular(20),
+        onTap: onTap,
+        child: content,
       ),
     );
   }

pubspec.lock

@@ -826,11 +826,9 @@ packages:
   meshcore_client:
     dependency: "direct main"
     description:
-      path: "."
-      ref: a0deff8
-      resolved-ref: a0deff80fcbca974f0e18fe47971b76bec583109
-      url: "https://github.com/dz0ny/meshcore_client.git"
-    source: git
+      path: "../meshcore_client"
+      relative: true
+    source: path
     version: "0.1.0"
   meta:
     dependency: transitive

pubspec.yaml

@@ -42,9 +42,7 @@ dependencies:
 
   # MeshCore BLE protocol client
   meshcore_client:
-    git:
-      url: https://github.com/dz0ny/meshcore_client.git
-      ref: a0deff8
+    path: ../meshcore_client
 
   # Codec2 ultra-low-bitrate speech codec (FFI plugin)
   codec2_flutter:

test/screens/messages_tab_test.dart

@@ -13,6 +13,7 @@ import 'package:meshcore_sar_app/providers/map_provider.dart';
 import 'package:meshcore_sar_app/providers/messages_provider.dart';
 import 'package:meshcore_sar_app/providers/voice_provider.dart';
 import 'package:meshcore_sar_app/screens/messages_tab.dart';
+import 'package:meshcore_sar_app/services/message_destination_preferences.dart';
 import 'package:meshcore_sar_app/services/voice_codec_service.dart';
 import 'package:meshcore_sar_app/services/voice_player_service.dart';
 import 'package:provider/provider.dart';
@@ -208,4 +209,227 @@ void main() {
     connectionProvider.dispose();
     channelsProvider.dispose();
   });
+
+  testWidgets(
+    'locks messages tab to the configured channel and removes the selector affordance',
+    (tester) async {
+      final lockedChannel = buildContact(
+        name: '#ops',
+        type: ContactType.channel,
+        secondByte: 2,
+      );
+      SharedPreferences.setMockInitialValues({
+        'message_locked_destination_enabled': true,
+        'message_locked_destination_type':
+            MessageDestinationPreferences.destinationTypeChannel,
+        'message_locked_recipient_public_key': lockedChannel.publicKeyHex,
+      });
+
+      final connectionProvider = ConnectionProvider();
+      final contactsProvider = ContactsProvider();
+      final messagesProvider = MessagesProvider();
+      final mapProvider = MapProvider();
+      final drawingProvider = DrawingProvider();
+      await messagesProvider.initialize();
+      await drawingProvider.initialize();
+      final channelsProvider = ChannelsProvider()..initializePublicChannel();
+      final voiceProvider = VoiceProvider(
+        codec: VoiceCodecService(),
+        player: VoicePlayerService(),
+      );
+      final imageProvider = ip.ImageProvider();
+      final appProvider = AppProvider(
+        connectionProvider: connectionProvider,
+        contactsProvider: contactsProvider,
+        messagesProvider: messagesProvider,
+        drawingProvider: drawingProvider,
+        channelsProvider: channelsProvider,
+        voiceProvider: voiceProvider,
+        imageProvider: imageProvider,
+      );
+
+      contactsProvider.addContacts([lockedChannel]);
+      messagesProvider.addMessage(
+        Message(
+          id: 'public-message',
+          messageType: MessageType.channel,
+          pathLen: 1,
+          textType: MessageTextType.plain,
+          senderTimestamp: 1700000200,
+          text: 'Public chatter',
+          receivedAt: DateTime.now(),
+          channelIdx: 0,
+        ),
+      );
+      messagesProvider.addMessage(
+        Message(
+          id: 'locked-message',
+          messageType: MessageType.channel,
+          pathLen: 1,
+          textType: MessageTextType.plain,
+          senderTimestamp: 1700000201,
+          text: 'Ops chatter',
+          receivedAt: DateTime.now(),
+          channelIdx: 2,
+        ),
+      );
+
+      await tester.pumpWidget(
+        MultiProvider(
+          providers: [
+            ChangeNotifierProvider.value(value: connectionProvider),
+            ChangeNotifierProvider.value(value: contactsProvider),
+            ChangeNotifierProvider.value(value: messagesProvider),
+            ChangeNotifierProvider.value(value: mapProvider),
+            ChangeNotifierProvider.value(value: drawingProvider),
+            ChangeNotifierProvider.value(value: channelsProvider),
+            ChangeNotifierProvider.value(value: voiceProvider),
+            ChangeNotifierProvider.value(value: imageProvider),
+            ChangeNotifierProvider.value(value: appProvider),
+          ],
+          child: MaterialApp(
+            localizationsDelegates: AppLocalizations.localizationsDelegates,
+            supportedLocales: AppLocalizations.supportedLocales,
+            home: const Scaffold(body: MessagesTab(isActive: true)),
+          ),
+        ),
+      );
+
+      await tester.pumpAndSettle();
+
+      expect(find.text('Ops chatter'), findsOneWidget);
+      expect(find.text('Public chatter'), findsNothing);
+      expect(
+        find.byKey(const ValueKey('messages_composer_destination_locked')),
+        findsOneWidget,
+      );
+      expect(
+        find.byKey(const ValueKey('messages_composer_destination_selector')),
+        findsNothing,
+      );
+
+      appProvider.dispose();
+      voiceProvider.dispose();
+      imageProvider.dispose();
+      drawingProvider.dispose();
+      mapProvider.dispose();
+      messagesProvider.dispose();
+      contactsProvider.dispose();
+      connectionProvider.dispose();
+      channelsProvider.dispose();
+    },
+  );
+
+  testWidgets(
+    'contact navigation temporarily overrides the lock while keeping the selector hidden',
+    (tester) async {
+      final directContact = buildContact(
+        name: 'Tim',
+        type: ContactType.chat,
+        secondByte: 9,
+      );
+      SharedPreferences.setMockInitialValues({
+        'message_locked_destination_enabled': true,
+        'message_locked_destination_type':
+            MessageDestinationPreferences.destinationTypeChannel,
+      });
+
+      final connectionProvider = ConnectionProvider();
+      final contactsProvider = ContactsProvider();
+      final messagesProvider = MessagesProvider();
+      final mapProvider = MapProvider();
+      final drawingProvider = DrawingProvider();
+      await messagesProvider.initialize();
+      await drawingProvider.initialize();
+      final channelsProvider = ChannelsProvider()..initializePublicChannel();
+      final voiceProvider = VoiceProvider(
+        codec: VoiceCodecService(),
+        player: VoicePlayerService(),
+      );
+      final imageProvider = ip.ImageProvider();
+      final appProvider = AppProvider(
+        connectionProvider: connectionProvider,
+        contactsProvider: contactsProvider,
+        messagesProvider: messagesProvider,
+        drawingProvider: drawingProvider,
+        channelsProvider: channelsProvider,
+        voiceProvider: voiceProvider,
+        imageProvider: imageProvider,
+      );
+
+      contactsProvider.addContacts([directContact]);
+      messagesProvider.addMessage(
+        Message(
+          id: 'public-message',
+          messageType: MessageType.channel,
+          pathLen: 1,
+          textType: MessageTextType.plain,
+          senderTimestamp: 1700000300,
+          text: 'Public chatter',
+          receivedAt: DateTime.now(),
+          channelIdx: 0,
+        ),
+      );
+      messagesProvider.addMessage(
+        Message(
+          id: 'direct-message',
+          messageType: MessageType.contact,
+          senderPublicKeyPrefix: directContact.publicKey.sublist(0, 6),
+          pathLen: 1,
+          textType: MessageTextType.plain,
+          senderTimestamp: 1700000301,
+          text: 'Direct chatter',
+          receivedAt: DateTime.now(),
+        ),
+      );
+      messagesProvider.navigateToDestination(
+        MessageDestinationPreferences.destinationTypeContact,
+        recipientPublicKeyHex: directContact.publicKeyHex,
+      );
+
+      await tester.pumpWidget(
+        MultiProvider(
+          providers: [
+            ChangeNotifierProvider.value(value: connectionProvider),
+            ChangeNotifierProvider.value(value: contactsProvider),
+            ChangeNotifierProvider.value(value: messagesProvider),
+            ChangeNotifierProvider.value(value: mapProvider),
+            ChangeNotifierProvider.value(value: drawingProvider),
+            ChangeNotifierProvider.value(value: channelsProvider),
+            ChangeNotifierProvider.value(value: voiceProvider),
+            ChangeNotifierProvider.value(value: imageProvider),
+            ChangeNotifierProvider.value(value: appProvider),
+          ],
+          child: MaterialApp(
+            localizationsDelegates: AppLocalizations.localizationsDelegates,
+            supportedLocales: AppLocalizations.supportedLocales,
+            home: const Scaffold(body: MessagesTab(isActive: true)),
+          ),
+        ),
+      );
+
+      await tester.pumpAndSettle();
+
+      expect(find.text('Direct chatter'), findsOneWidget);
+      expect(find.text('Public chatter'), findsNothing);
+      expect(
+        find.byKey(const ValueKey('messages_composer_destination_locked')),
+        findsOneWidget,
+      );
+      expect(
+        find.byKey(const ValueKey('messages_composer_destination_selector')),
+        findsNothing,
+      );
+
+      appProvider.dispose();
+      voiceProvider.dispose();
+      imageProvider.dispose();
+      drawingProvider.dispose();
+      mapProvider.dispose();
+      messagesProvider.dispose();
+      contactsProvider.dispose();
+      connectionProvider.dispose();
+      channelsProvider.dispose();
+    },
+  );
 }