Offline Protection is Exploitable

[Deantwo]

So if the game can recognize that an empire has attacked another as the "war policy" mechanic suggests, then why couldn't that be the trigger to cease protections as well.

If it was a mistake then "oops" .. that's where diplomacy comes into play.

Cease protections for how long? What you are suggesting doesn't make much sense. You might have to read up on how the current offline protection (AKA "noncombatant") mechanic works before continuing this discussion.
See: hazeron.com/wiki/Noncombatant