foil wrap is not used for the most part on oil quench or water quench steels
most makers i know leave a bit of extra thickness on the blade before heat treat and then grind clean
alot of production knife makers grind there blanks full hard and not even part ground before heat treat (shaped yes but not beveled )
for the more simple steels 10xx and the like the quench from temp is only around 1500 ish and soak times are short so decarb may not be a big deal
not like when i do SS at 2050f for a 30 min soak. with out foil there would be nothing left of the blade to use