Report the running firmware USB mode without disturbing logging

src/helpers/CommonCLI.cpp

@@ -5,6 +5,7 @@
 #include <helpers/sensors/SolarXiaoPower.h>
 #include <helpers/LedSettings.h>
 #include <Arduino.h>
+#include "UsbMode.h"
 #include "CarrierTools.h"
 #include "PacketFileLoggingConfig.h"
 #include "CommonCLI.h"
@@ -3553,6 +3554,7 @@ bool CommonCLI::handleUDPBridgeCommand(uint32_t sender_timestamp,
 void CommonCLI::handleCommand(uint32_t sender_timestamp, char* command, char* reply) {
     PrefsSaveReplyGuard save_reply(_prefs_save_failures, reply);
     mesh::cli::normalizeCommandVerb(command);
+    if (mesh::handleUsbModeCommand(command, reply, 160, Serial)) return;
 #if MESH_ENABLE_HOST_KISS
     if (mesh::hostkiss::handleCommand(command, reply, 157, sender_timestamp == 0)) return;
 #endif

src/helpers/UsbLogging.cpp

@@ -1303,7 +1303,8 @@ void noteUsbConsoleCommand(const char* command) {
   if (command == nullptr || isUsbPacketLoggingAlways()
       || hasDedicatedUsbLoggingPort() || isUsbLoggingPacketStream()) return;
   while (*command == ' ' || *command == '\t' || *command == '\r' || *command == '\n') ++command;
-  if (*command == 0 || isUsbLoggingStatsCommand(command)) return;
+  if (*command == 0 || isUsbLoggingStatsCommand(command)
+      || isUsbModeDetectionCommand(command)) return;
   for (const unsigned char* p = reinterpret_cast<const unsigned char*>(command); *p; ++p) {
     if ((*p < 32 && *p != '\t') || *p >= 127) return;
   }

src/helpers/UsbLoggingClientActivity.h

@@ -11,6 +11,22 @@ namespace mesh {
 // not identify a particular application or prove MQTT/disk health.
 constexpr uint32_t USB_LOGGING_CLIENT_LEASE_MS = 15UL * 60UL * 1000UL;
 
+// Firmware detection is passive even before the role strips an optional
+// two-byte Companion request prefix or normalizes an uppercase GET verb.
+// Unlike stats polling, this query must not establish a logging-reader lease.
+inline bool isUsbModeDetectionCommand(const char* command) {
+  if (!command) return false;
+  while (*command == ' ' || *command == '\t') ++command;
+  if (command[0] && command[1] && command[2] == '|' && command[3]) {
+    command += 3;
+    while (*command == ' ' || *command == '\t') ++command;
+  }
+  return (command[0] == 'g' || command[0] == 'G')
+      && (command[1] == 'e' || command[1] == 'E')
+      && (command[2] == 't' || command[2] == 'T')
+      && strcmp(command + 3, " usb.mode") == 0;
+}
+
 inline bool isUsbLoggingStatsCommand(const char* command) {
   if (!command) return false;
   while (*command == ' ' || *command == '\t') ++command;

src/helpers/UsbMode.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+#include <type_traits>
+
+namespace mesh {
+
+// Describe the primary Serial backend selected by this application build,
+// not its board name, host port name, USB VID/PID or optional logging CDC.
+// Include after Arduino.h. The caller supplies decltype(Serial), after any
+// board-specific alias is visible, so a custom primary UART cannot inherit a
+// native-USB claim merely because the unused USB peripheral has those flags.
+template <typename SerialType>
+inline const char* usbModeName() {
+#if defined(ESP32) || defined(ESP32_PLATFORM)
+  if (std::is_same<SerialType, HardwareSerial>::value) return "uart";
+  #if defined(ARDUINO_USB_CDC_ON_BOOT) && ARDUINO_USB_CDC_ON_BOOT
+    #if defined(ARDUINO_USB_MODE) && ARDUINO_USB_MODE == 1
+      if (std::is_same<SerialType, HWCDC>::value) return "hardware-cdc-jtag";
+    #elif defined(ARDUINO_USB_MODE) && ARDUINO_USB_MODE == 0
+      if (std::is_same<SerialType, USBCDC>::value) return "tinyusb";
+    #endif
+  #endif
+#elif defined(NRF52_PLATFORM) && defined(USE_TINYUSB)
+  if (std::is_same<SerialType, Adafruit_USBD_CDC>::value) return "tinyusb";
+#endif
+  return "unknown";
+}
+
+inline bool isUsbModeCommand(const char* command) {
+  return command != nullptr && strcmp(command, "get usb.mode") == 0;
+}
+
+// Read-only, bounded and independent of diagnostic/logging build flags.
+// No setter: changing a USB backend requires installing another application.
+template <typename SerialType>
+inline bool handleUsbModeCommand(const char* command, char* reply,
+                                 size_t capacity, const SerialType&) {
+  if (!isUsbModeCommand(command) || reply == nullptr || capacity == 0) return false;
+  snprintf(reply, capacity, "usb.mode %s", usbModeName<SerialType>());
+  return true;
+}
+
+}  // namespace mesh