What is the __CHECKFIX1436934 environment variable?
It comes from launch services, specifically this binary

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/LaunchServices


and that environment variable seems to be inherited by many processes, as you can see with ps -Efax

1436934 looks like the number of digits in recent Apple "radar" bug numbers, so perhaps it refers to some value used internally for testing.