A lookup that reveals a target's position and cancels concealment spells like Subterfuge outright.
Waiting with the primed gate, Elle messages Carl about a weird notification: someone had searched her location, and it canceled out her Subterfuge spell. She notes she has to wait a minute before she can recast.
The timing is not coincidental. Within seconds, multiple enemy dots appear on Carl's map, all teleported directly onto Elle's position and the portal — Prince Stalwart and the War Mages who will kill him. The location search was the mechanical key that unlocked the ambush.
The counter-stealth tool that exposed the gate site.