Improve USB disconnection handling and add payload length validation for USB frames

android/app/src/main/kotlin/com/meshcore/meshcore_open/MainActivity.kt

@@ -105,8 +105,12 @@ class MainActivity : FlutterActivity() {
                     "connect" -> handleUsbConnect(call, result)
                     "write" -> handleUsbWrite(call, result)
                     "disconnect" -> {
-                        closeUsbConnection()
+                        usbIoExecutor.execute {
-                        result.success(null)
+                            closeUsbConnection()
+                            mainHandler.post {
+                                result.success(null)
+                            }
+                        }
                     }
                     else -> result.notImplemented()
                 }

lib/services/usb_serial_frame_codec.dart

@@ -6,6 +6,13 @@ const int usbSerialHeaderLength = 3;
 const int usbSerialMaxPayloadLength = 172;
 
 Uint8List wrapUsbSerialTxFrame(Uint8List payload) {
+  if (payload.length > usbSerialMaxPayloadLength) {
+    throw ArgumentError.value(
+      payload.length,
+      'payload.length',
+      'USB serial payload exceeds $usbSerialMaxPayloadLength bytes',
+    );
+  }
   final packet = Uint8List(usbSerialHeaderLength + payload.length);
   packet[0] = usbSerialTxFrameStart;
   packet[1] = payload.length & 0xff;