So this differs from m_isBrightnessAvailable in that m_serviceRegistered can be set at the beginning of onServiceRegistered(), rather than at the end of it when the whole thing is already stood up? Very well then, that looks robust enough to me. No objections.
I'd be in favor of squashing both commits, because adding just the first one without the second one introduces a certain kind of unreliability (even though it fixes another, more common kind).