I’d probably go something like ^. Increase the difficulty by a level or 3, depending on circumstances.
If you wanted to get a little hand-wavy, maybe you could do some sort of Realm check, Eg: use Empathy skill/bonus for an Essence trap (probably the majority of magical traps imho) to see if the thief maybe “feels” something odd?
But you could argue a case the thief does the physical stuff and wouldn’t have a chance of perceiving something magical.
Or maybe there’s runes/sigils on the door/chest they recognize as being real/legit magical symbols, so it’s likely magically trapped.
So it kinda depends on how *you* want it to play out as to whether you you wave a hand and manufacture a reason it either doesn’t work, does work, or works but is difficult. Personally I’d go the 3rd option. Partly because if you have a spellcaster with Detection spells, it works kinda around the other way - magic is easier to dismiss, but the physical is harder. So that seems nicely “balanced”, for me.
Also might depend on the nature of the trap - ie: does the trap need to be specifically disarmed, or does it only go off if there’s a failed attempt to open/fiddle the lock. Generally I’d guess the former, but the latter might be relevant sometimes.