What is the absolute maximum salt-to-water ratio of a brine for Lacto-Fermentation
Fermented Fruits and Vegetables: A Global Perspective appears to be a good document. This chapter contains some information that will be helpful for you.  In section 5.6.3, it states:

At the highest concentrations of salt (about 60o salometer) the lactic fermentation ceases to function and if any acid is detected during brine storage it is acetic acid, presumably produced by acid-forming yeasts which are still active at this concentration of salt (Vaughn, 1985).

So, 60 degree salinity halts lactic fermentation. That's about 16% salt.