This is precisely the reason they wrote the stealth rules with natural language... in the hopes that the DM reading it would make a ruling that was just common sense. Rather than flipping through 57 different pages of all the different books trying to parse "Well, if A does B and C is in position for D, then according to page 500 X should mean that Y is Z and thus A gets surprise but not Sneak Attack, but C with the Alert feat would get Surprise and Sneak Attack..." blah blah blah. This is another corner case out of the thousands that apply to hiding and stealth, and which would probably have gotten missed had they tried to write airtight stealth rules like everyone wants them to. So they just put it in the DM's hands.
A bunch of spiders show up literally from out of nowhere and attack the party immediately. You're the DM, just make a ruling. Hell, if THEY can't Surprise a party member, then who the heck ever can?!?
A bunch of spiders show up literally from out of nowhere and attack the party immediately. You're the DM, just make a ruling. Hell, if THEY can't Surprise a party member, then who the heck ever can?!?
