Final answer:
The built-in fail-safe for a robot is an Emergency stop button, which provides an immediate means to halt the robot in case of an emergency by cutting off power.
Step-by-step explanation:
The built-in fail-safe for a robot that would ensure its immediate and safe shutdown in case of a malfunction or emergency is an Emergency stop button. This button is designed to be easily accessible and when activated, it will immediately cut off power to the robot, halting all operations. It's considered a passive safety feature because it requires user intervention to be effective. Other options, like redundant backup power and remote control, are additional safety or control features but do not serve as a direct means of halting the robot in response to a failure or emergency. Learning from mistakes is a type of adaptive intelligence or learning capability that helps a robot improve over time but isn't necessarily a safety mechanism.