Thanee said:To me the question is not about suspicion or awareness, but at what point combat starts and how the situation is at this point. It doesn't matter what was before.
That is, after the door has been opened. At this point, both sides are aware of each other, so both sides get to act. Therefore, I'd not consider surprise in this scenario.
The spectre has the option to surprise the party, because it can sense them, but then it would have to actively do this, not just wait for them to open the door. At this point it forfeits that advantage and has to roll initiative like everyone else, because it is merely reacting to the party's actions now.
So, basically, the encounter starts with the spectre becoming aware of the party, but combat only starts after the door is opened. The spectre could do all sorts of things in the meantime (not ready, of course), but that won't speed up its reactions, once the door opens. Everyone is on the same level in that moment.
The assassin is around the corner. He has Detect Magic up, so he knows the exact position of his target. The target walks past the corner, the assassin gets a standard action for a) being aware and b) his target being unaware: according to RAW.
So, he stops concentrating on his Detect Magic spell (free action) and fires his bow (standard action).
According to a philosophy that you cannot initiate combat until the target gets into position (e.g. opens the door, whatever) and once he gets into position, he is always entitled to automatically spot his opponent, the assassin in this case would not get a surprise round.
The assassin is watching his target slowly come into view and is ready. His opponent is clueless, but suddenly becomes the Flash. To me, this is not reasonable.
Even giving the target a Spot roll is really not that reasonable unless the DC is real high or unless the target is somewhat suspicious.
But, getting rid of the surprise round completely in the Spectre case is like getting rid of it completely in this Assassin case.
An alternative in the Spectre case is to give the PC who opens the door a moderate DC Spot roll and the other PCs a real high DC Spot roll. That way, some of them have a chance to act on the Surprise round, but only the PC who opened the door has a good chance of acting on the Surprise round.