Wow great discussion! The only thing I can think of to add that hasn't been specifically called out already (if someone did and I missed it from skimming let me know) is that sneak attack is precision damage. So while both harm and sneak attack deal negative energy damage, harm deals "spell damage" with its own subset of rules and sneak attack deal "precision damage" with its own subset of rules. So I would lean a bit toward SA not falling under the the 1hp limitation.
That said, it looks to me like there is no clearly defined RAW answer and just another point in the rules where you need DM adjudication.