Now HydraESP32 shield is alive
See a simple test (to communicate with ESP32 using UART) by wiring ESP32 UART RXD0/TXD0 pins respectively to HydraBus PA9(UART1 TX)/PA10(UART1 RX) and by forcing EN to 3v3
(just plug ESP32 EN on GND then remove it / connect it to +3V3 after bridge mode is enabled)
It is recommended to use latest HydraBus firmware hydrafw v0.8 in order to use UART bridge @115200 bauds 8N1
See asciinema video:

For information we can also interact with ESP32 during bridge mode by connecting a 2nd MicroUSB connector on HydraBus in order to have an other terminal to interact with ESP32 I/O for example to set EN pin to +3.3V or GND … (or even to test different boot mode / communication …)