Magnets was the answer, as it turns out. For locking the tool, good alignment is necessary. I had planned for, but forgotten to put, magnets on the coupling screws to help the tool positioning. It does a "click" now when taken from the rack and then the lock can be closed.

I posted a video here:

Apologies for vertical orientation, I was too excited!

Next steps: Working on the software stack to go from layered svg to mutli-tool gcode.