Aspexia Rugatonn needed to check over Cayden Cailean's oracle anyways.
As long as she has to visit, goes the reasoning, she might as well visit Keltham right after he gets morning spells and run Spell Gauge over him to avoid further surprises. You need an unreasonably high caster circle to get all of the spells of a fourth-circle cleric with high Wisdom, lowest first as Spell Gauge does, so yes, Aspexia Rugatonn.
As long as she's doing that, she might as well use her personal Detect Thoughts tool, which adopts the user's strength for purposes of determining Will saves of the target, on Keltham.
Aspexia informs the 'scholar' of what Keltham is trying. She doesn't bother explaining who's sending the message; the agent doesn't need the distraction. Also, somebody had better have been on the ball about matching writing styles very perfectly with real archives, or else they're going to have to fake all the other archives Keltham ever looks at.