RE of lghub_agent.arm64 revealed that LGHUB's service-layer handler
for 0x0618 HeadsetBatterySaverMode
(on_headset_battery_saver_set_handler @ 0x100c21790) compares the
requested new state against its cached current state and ONLY invokes
the devio SetEcoModeState write on a genuine transition. Wire format
is confirmed 0/1 (canonical doc correct); the G522 firmware rejects
no-op writes with device-specific NACK 0x0B.
BooleanValidator's prepare_write already contains the "skip if same as
current" branch — it just fires only when current_value is supplied,
which requires needs_current_value=True. For default-mask (0xFF)
validators, needs_current_value defaults to False so Setting.write
skips the pre-read and prepare_write gets current_value=None.
HeadsetEcoMode now builds its validator explicitly and forces
needs_current_value=True so Setting.write reads first, compares in
prepare_write, and skips redundant writes — matching LGHUB exactly.
Same fix may apply to other Centurion boolean features whose firmware
rejects no-op writes, but leaving those unchanged until observed.
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