Sorry if this sounds overly simplistic regarding the question posed originally, but I think it’s simpler to answer by treating the issue of C”Y as one would food allergies. Hence, it’s incumbent on both the host and the guest to discuss the issue and come up with a plan for the visit that doesn’t overly impose on either the host nor the guest.
To some degree it’s less an issue of kashrus than of mẹnschlichkeit.