"technical solution could reduce this risk, so that any attempt to make an illegal weapon alerted the authorities, and the equipment would cease to function"

No way to do so.

The 80% completed receivers are the example of that. BY LAW, they are NOT firearms, and cannot be controlled. At SOME point in the manufacturing process, they become controlled items- Just stop ONE step short and finish it up by hand.

I think that the criminals who would make illegal firearms are as smart ( or smarter) than the ones proposing the laws about them