test(tcp): harden cancel-race handling and add coverage

- tighten late TCP connect error suppression to manual-cancel disconnecting/disconnected windows
- keep TCP handshake failures surfaced outside explicit cancel flow
- allow TcpScreen connect action when connector is scanning
- add connector-level tests for late-error suppression classifier
- add TcpScreen test covering connect from scanning state

lib/connector/meshcore_connector.dart

@@ -1059,10 +1059,14 @@ class MeshCoreConnector extends ChangeNotifier {
       await syncTime();
     } catch (error) {
       _appDebugLogService?.error('TCP connection error: $error', tag: 'TCP');
-      final tcpConnectNoLongerActive =
-          _activeTransport != MeshCoreTransportType.tcp ||
-          _state != MeshCoreConnectionState.connecting;
-      if (tcpConnectNoLongerActive) {
+      final tcpConnectCancelledBeforeHandshake =
+          shouldIgnoreLateTcpConnectError(
+            manualDisconnect: _manualDisconnect,
+            state: _state,
+            activeTransport: _activeTransport,
+            tcpManagerConnected: _tcpManager.isConnected,
+          );
+      if (tcpConnectCancelledBeforeHandshake) {
         _appDebugLogService?.info(
           'Ignoring late TCP connect error after cancellation/switch: state=$_state transport=$_activeTransport',
           tag: 'TCP',
@@ -1074,6 +1078,19 @@ class MeshCoreConnector extends ChangeNotifier {
     }
   }
 
+  @visibleForTesting
+  static bool shouldIgnoreLateTcpConnectError({
+    required bool manualDisconnect,
+    required MeshCoreConnectionState state,
+    required MeshCoreTransportType activeTransport,
+    required bool tcpManagerConnected,
+  }) {
+    return manualDisconnect &&
+        (state == MeshCoreConnectionState.disconnected ||
+            state == MeshCoreConnectionState.disconnecting) &&
+        (activeTransport != MeshCoreTransportType.tcp || !tcpManagerConnected);
+  }
+
   Future<void> connect(BluetoothDevice device, {String? displayName}) async {
     if (_state == MeshCoreConnectionState.connecting ||
         _state == MeshCoreConnectionState.connected) {

lib/screens/tcp_screen.dart

@@ -224,7 +224,11 @@ class _TcpScreenState extends State<TcpScreen> {
   }
 
   Future<void> _connectTcp() async {
-    if (_connector.state != MeshCoreConnectionState.disconnected) return;
+    if (_connector.state == MeshCoreConnectionState.connecting ||
+        _connector.state == MeshCoreConnectionState.connected ||
+        _connector.state == MeshCoreConnectionState.disconnecting) {
+      return;
+    }
 
     final host = _hostController.text.trim();
     final parsedPort = int.tryParse(_portController.text.trim());