The threshold was written boot-only, so a firmware that clears
charge_control_end_threshold on unplug would silently lose the cap
until the next reboot. Add a services.udev rule on the mains adapter
(ATTR{type}=="Mains", vendor-neutral) that restarts the oneshot via
systemctl --no-block on every AC state change. Uses restart (not
try-restart) so it re-applies even if the boot run was inactive.
Eval-verified: rule present when the charge limit is on, absent when
off; downstream-template-system still evaluates.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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