Pid.scale(k) set self.k as persistent state, mutated from outside the class and never reset in reset(), so a stale scale factor could survive a state-transition reset. Replace it with a plain scale=1.0 argument on Pid.process(), and have temp_controller.py/temp_controller_smith.py compute the heat-rate-overshoot compensation factor themselves and pass it through process_pid() each tick instead of mutating pid_hold's state. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>