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#MechanicalEngineers: How would one do a box with slots for two "keys" where exactly of them *must* always stay inserted? Basically a mechanical XOR.

I need something like this for a (door) key management system:

You want a key? Fine, you can only take it if you insert your name tag to unlock the key. When you put the key back, you get your name tag back.

The inserts would preferrably need to be without too sharp corners for pocket-friendlyness