The step-down schema epoch is set and cleared under step_down_lock, but no epoch reader acquires that lock. Schema/publication readers are ordered by the schema lock; timestamp-setting validation reads the epoch under the global transaction lock. The step-down lock therefore adds no epoch-reader synchronization, and its comments misleadingly imply atomic timestamp/epoch observation by those readers.

Move the epoch set/clear operations outside step_down_lock, preserving their existing surrounding locks and atomic accesses. Keep timestamp synchronization unchanged and update the lock/epoch comments.