Toolhead USB + RPMsg “mcu” connections unstable across RESTART/SAVE_CONFIG; propose Katapult bootloaders + restart ordering/waits

[mshrem]

After RESTART / FIRMWARE_RESTART / SAVE_CONFIG, Klipper often fails to reconnect:

• Sometimes main mcu (/dev/ttyRPMSG0) drops: Lost communication with MCU 'mcu' and dmesg shows rpmsg_create_channel failed / already exist.
• Sometimes toolhead mcu hotend drops or re-enumerates: /dev/ttyACM0 disappears or becomes ttyACM1, and occasionally shows up as usb-ShenZhenCBD_STM32_Virtual_ComPort_* (seems like stock/bootloader mode), causing mcu 'hotend': Unable to connect.

Current workaround is brute-force:

service klipper-firmware-dsp restart
service klipper-firmware-toolhead restart   # works but reflashes every time

Request

1. Recommended restart ordering/waits so Save/Restart is reliable (RPMsg + toolhead USB).
2. How to flash Katapult on bed/toolhead MCUs for Centauri (James mentioned using it) so the toolhead doesn’t fall back to stock CDC identity after resets.

I can provide dmesg / klippy.log snippets if needed.