Kendall Jenner Working Hard Before Theft

Kendall Jenner left her house Wednesday around noon to shoot 'KUWTK' scenes with her mom ... oblivious to the $200k nightmare she was about to endure.

Kendall and Kris Jenner headed into Whizin Market Square in Agoura Hills around 1:30 PM for lunch with Kourtney Kardashian -- just another casual day at the office.

That all changed about 12 hours later when, as TMZ first reported ... a bunch of her jewelry went missing from her Hollywood Hills home. Police believe it was an inside job.