Constant Presence vs. Shifting Sands

[AutumnKing]

How would Constant Presence work against Shifting Sands?

Here's the scenario: PCs are facing off against an aggravating Acanthus who they have figured out has been using Shifting Sands to turn the table on them in previous scenes. This time, they are going after her with Constant Presence on. They face her and she invokes Shifting Sands.

Constant Presence "preserves its subject[s] against alterations to the timeline." Does that mean they remain in the same moment of time (the "present") but suddenly things change around them and they can assume the timeline has changed by looking around?

I'm assuming they don't get a "free ride" along with the shifting sands, remembering everything and getting to enjoy the benefits such as changing their actions.

Assuming that my hypothesis is correct, from the perspective of the time mage:
1) does she have a different interaction with them in the new (soon-to-be) past and then suddenly they appear back where they were in the previous timeline once they reach the present moment?
OR
2) do they vanish altogether from the intervening time that she rewrites and reappear at the end?

I appreciate your help!

[Scriptorian]

Constant Presence also says “ Any alteration to history through the action of time travel provokes a Clash of Wills. If the mage wins, the subject is treated as though she were returning from a trip to the past herself when history settles, safeguarding her against being rewritten.”

I think this means that the sand-shifted acanthus would have to be able to see and interact with the subjects’ past selves in order to attempt to alter their history, and it’s only in the attempt that the two spells come into conflict. So the way I’d run this is for the enemy mage to use Shifting Sands like normal, and then when they return to the present, roll the Clash between the two spells; if the enemy wins, the changes they made work as expected; if the cabal wins, they remain in the same state they were in when Shifting Sands was cast.

In other words: option 1, assuming the caster of Constant Presence wins the Clash.

Edit: if you wanted a result more similar to option 2, I think that could be achieved by a combined casting that added Shield of Chronos to the mix. (I don’t think Shield of Chronos would do anything against Shifting Sands by itself, since it only protects against viewing the subject through time, as opposed to actually traveling to their past.)

[Isator Levi]

I believe that with the usual way that time travel works, even if the Shifting Sands mage loses the Clash of Will their perspective will be that they did change things, they'll just fail to take. Correct usage of that might give a momentary tactical advantage.