I’m running micro-ROS on an STM32G474RE (NUCLEO-G474RE) with FreeRTOS (STM32CubeIDE / CubeMX integration) over UART to the micro-ROS agent.
The firmware boots and the executor loop runs (LED heartbeat works), but no subscription callback ever triggers, even for a simple topic like std_msgs/msg/Int32.
```
export ROS_DOMAIN_ID=<id>
ros2 run micro_ros_agent micro_ros_agent serial --dev /dev/ttyACM0 -b 115200 -v6
```
```
export ROS_DOMAIN_ID=<id>
ros2 topic pub -r 5 /mcu/test std_msgs/msg/Int32 "{data: 1}"
```
ros2 topic echo on the host shows messages, but the MCU callback never fires. I also tried different QoS and longer spin_some() timeouts.
Question: can this happen if I print debug logs (printf/UART) on the same UART used for micro-ROS transport, or are there other common causes on STM32G4?
