Hrmm. Tough call. I would agree with the "if the Cleric failed his Spot check" sentiment but with one particularly noteworthy point:
Were I DM, I would assign some significant bonuses in the Cleric's favor based on the situation.
A) The Cleric apparently has some reason to suspect the location of the Rogue and thus know to look for him. +5 circumstantial bonus
B) The Cleric has Darkvision which eliminates any potential concealment from poor lighting. +2 circumstance bonus for favorable conditions
C) The Rogue has to leave any cover or concealment for the last 2 squares of his movement before he can Sneak Attack, and the Stealth skill does not allow you to "hide in plain sight" (unless you have the class ability of the same name). The skill specifies that if someone is observing you "even casually", you cannot hide. However, I would be willing to grant the Rogue an opportunity to "get the drop" on the Cleric and attack him before the Cleric has time to react, but would award the Cleric an extra +2 circumstance bonus due to the Rogue having to expose himself before the attack can happen.
Thus, the Cleric would net a +9 (in all honesty, I would simply round this to +10) bonus to his check to foil the attempt. The Rogue would be better off, in my opinion, hiding and readying an attack once the Cleric comes within range, or use the Cleric's assumptions against him and attack from around the other side of the pillar. Or perhaps even hit the Cleric with a ranged weapon from his hiding spot in Position B.
My 2 cents.
HARRY DRESDEN — WIZARD
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