UpdateOTW

Stream a firmware image from a Modbus RTU master to a slave over a half-duplex RS485 bus, and the slave reboots into it. Two register-array state machines (UpdateOTW_Master sender, UpdateOTW_Slave receiver) — your code keeps doing the Modbus, the library only reads/writes a small register window. Non-blocking (one frame per tick), so the device keeps running while it updates, with deferred apply. Per-chunk CRC16 plus full-image CRC32, automatic retry with patient back-off, and free rollback via the ESP32 Update library. No external dependencies.