CMD_MEASURE_ANTENNA_TUNING_HF requires a 1-byte mode arg (firmware rejects length!=1 with EINVARG) and returns the voltage as uint16, not uint32. tune() sent no arg (empty reply -> 0 mV) and parsed <I. Now sends mode 1/2/3 (START/MEASURE/STOP) and parses <H. Verified vs firmware appmain.c handler; C client reads the same ~15V on this firmware.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>