fix(native-usb): isolate two-pair transport and hand off read status in IRQ

tools/switch2_usb_probe/tusb_config.h

@@ -27,6 +27,8 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
+// Returns the formatted length when queued, or -1 if the whole message cannot
+// fit. A diagnostic consumer may retry later; native logging never masks IRQs.
 int probe_debug_printf(const char* format, ...);
 #ifdef __cplusplus
 }