Keep hardware CDC packet log lines whole under congestion

src/helpers/SerialPacketLog.h

@@ -32,6 +32,17 @@ inline bool& serialLogPortSeen() {
 
 template <class T>
 bool serialLogEmit(T& out, const char* data, size_t len) {
+#if defined(ESP32_PLATFORM) && defined(ARDUINO_USB_CDC_ON_BOOT) && \
+    (ARDUINO_USB_CDC_ON_BOOT == 1) && defined(ARDUINO_USB_MODE) && \
+    (ARDUINO_USB_MODE == 1)
+  // The HWCDC logging view checks this complete record again under the shared
+  // producer guard. Never leave a line prefix behind when its host stalls.
+  const int space = out.availableForWrite();
+  if (space <= 0 || static_cast<size_t>(space) < len) return false;
+  if (out.write(reinterpret_cast<const uint8_t*>(data), len) != len) return false;
+  serialLogPortSeen() = true;
+  return true;
+#else
   if (out.availableForWrite() <= 0) return false;
 
   const uint32_t start = millis();
@@ -55,6 +66,7 @@ bool serialLogEmit(T& out, const char* data, size_t len) {
   }
   serialLogPortSeen() = true;
   return true;
+#endif
 }
 
 template <size_t CAP = SERIAL_LOG_LINE_MAX>

src/helpers/UsbLogging.cpp

@@ -513,6 +513,11 @@ static SingleAttemptNonBlockingStream guarded_esp32_hwcdc_port(
 static AtomicWholeRecordNonBlockingStream<11>
     guarded_esp32_hwcdc_mota_port(guarded_esp32_hwcdc_port);
 
+// Admit each complete packet log line under the same guard as CLI replies.
+// Short records can still use a smaller ring if the preferred allocation fails.
+static AtomicWholeRecordNonBlockingStream<640> guarded_esp32_hwcdc_logging_port(
+    guarded_esp32_hwcdc_port);
+
 static void serviceEsp32HwcdcTxKickExclusive(void*) {
   if (!esp32_hwcdc_tx_kick_pending.load(std::memory_order_acquire)
       || !canAccessEsp32Hwcdc(nullptr)) {
@@ -1393,7 +1398,7 @@ Stream& usbLoggingPort() {
   #if MESH_ESP32_TINYUSB_NONBLOCKING
     return buffered_esp32_tinyusb_logging_port;
   #elif MESH_ESP32_HWCDC_SESSION_GUARD
-    return guarded_esp32_hwcdc_port;
+    return guarded_esp32_hwcdc_logging_port;
   #elif defined(NRF52_PLATFORM)
     return nonblocking_primary_usb_logging_port;
   #else