Function user_brain_enabled 

pub fn user_brain_enabled() -> bool

v0.4.1: returns true when the user brain is enabled.

KIMETSU_USER_BRAIN=0 / false / off / no disables it (case-insensitive). Anything else, including unset, leaves it enabled by default — the “brain follows you between projects” pitch only works if the user opts OUT, not opts IN.