@jos_mosa No, there is no failsafe for "stupid" moves; on another machine, such a move may be perfectly valid. Generally tools are free to move around in the space defined by M208, once homed. On IDEX machines, you usually set each carriage up as a separate tool, and one gets parked while the other is printing. You can also set them up for simultaneous 'duplicate' and 'mirror' mode printing. In these modes you usually set them to use half the bed area each (and possibly less in mirror mode) so the carriages don't crash. See https://docs.duet3d.com/User_manual/Machine_configuration/Configuration_IDEX#configuring-tools
We are working on separate gcode streams for RRF, so it's possible that each carriage could move independently (though they will always have to be synchronised in Y), but it would still be advisable to limit the print area of each tool to half the bed.
Ian