Serial bus No. 3: Configure peers over Serial Bus

[JensOgorek]

Motivation

When configuring ESP32 nodes over the serial bus, there was no easy way to send a complete .liz script to a remote node. Additionally, if a broken script was deployed to a bus node (or a script without SerialBus configuration), the node would become unreachable and require physical USB access to fix.

Implementation

Remote configuration via serial bus (configure.py)

• Added --serial-bus NODE_ID argument
• Wraps each command in bus.send(NODE_ID, "...") to forward to remote node
• Waits for reboot and verifies checksum via bus echo relay

Automatic bus backup (main/utils/bus_backup.cpp)

• When a SerialBus is created, its config (pins, baud, uart, node_id) is saved to NVS
• On boot, if startup fails to create a SerialBus but backup config exists:
  • Looks for existing Serial with matching pins (reuses if found)
  • Otherwise finds a free UART and creates a new Serial
  • Creates a backup SerialBus to keep the node reachable
• Added core.delete_bus_backup() to remove the saved config

Progress

• The implementation is complete.
• Tested on hardware.
• Documentation has been added.