I have come across this in a previous job. We requested that the subcontractor provided suitable edge protection by using scaffold towers to the front of the wall, behind was the embankment in which they were building up the wall thus no edge protection required behind them. Make sure the scaffold tower(s) are correctly erected, secured with base plates to flat stable surface and outriggers. Cannot remember the exact height the wall went to as we came off site before completion due to recession!!

Is this a vertical or a "stepped" gabion?

Surely that will depend on whether or not you can get a solid base to attach to, from my recognition the gabion baskets are wire and filled with loose stone (which are not all same size)laid flat, which I don't think would give a suitable secure base for hand rail. Forgive me if I am wrong!