G. Luger Patent #639,414
 

SAFETY DEVICE FOR FIREARMS, Patented Dec. 19, 1899

I found the reference to this in Ian Hogg's "German Handguns" and looked up the patent on a whim...

I was surprised to find that the illustration showed the roller-toggle link of the Borchardt mated with the flat mainspring of the early Lugers...

Was this model ever produced???

As far as is known, no example of that mechanism was ever produced. It is thought that this patent was actually generated to protect a forthcoming design feature but never implemented in the form shown.