Three sites compared f32 q_gap values via partial_cmp().unwrap() — any
NaN q_gap would panic the snapshot swap-out / best-pointer paths on the
training hot path. Replaced with partial_cmp().unwrap_or(Ordering::Equal)
and tightened the outer Option unwrap to expect() with the invariant text
(len >= MAX_SNAPSHOTS guarantees a worst element exists).
e508475f3c