Blizzard really screwed up on this one in my opinion. The stormheim attack should have been viewed as a declaration of war. I don't think there is a way around that. It's an offical alliance army attacking an offical horde army. I can't think of an example in history or on Azeroth where that doesn't count for some reason like "but some guy thought..".
But then we get a book full of Silvanas and Anduin and both of them still seem to think that we aren't at war. Everything is still in cold war status and the reasons we get for why the war needs to be fought is stuff like: because "we can't have a missile base in range of our captitol" and "I want to use Stormwind as a source for undead babies".
At which point you can't really use that attack as a reason for the attack anymore and we go back to "because Silvanas is evil and paranoid".
So, yeah - in a world, where Blizzard would have a better cordinated writing team, you could totaly justify an attack on Teldrassil. But in this world, nothing that happened is actually used as the justification to attack.
(to your other stuff: Jaina was before the armistice and also the king told her no and she obeyed. The Silithus events are just unofficial spy stuff (also the book made it sound like the Horde was the attacker, but I'm not sure). The Calia event has the same problem as the Stormheim attack. They could have used that as a justification, but they let Silvanas and Anduin come together and talk about it and it's declared that it isn't viewed as a continuation of the war.)
I haven't played the ptr or beta stuff, yet, so I might be missing something from there.