static LOCK_STATE_PREV: AtomicU8Expand description
Encoded previous lock state for the transition logger:
0 = unknown / haven’t seen yet (the initial value)
1 = last seen as Some(false) (confidently unlocked)
2 = last seen as Some(true) (confidently locked)
Option<bool> directly is what we want logically, but we need an
atomic so the run-loop closure can mutate the previous-state
across ticks without locking. AtomicU8 is the smallest fit.