Runtime Safety Monitor 2D: Anomaly Detection & Fallback Switch

A wheeled robot patrols between two docks past a restricted zone using a potential-field policy whose hazard-avoidance gain degrades as you raise the perception-drift slider — modelling a sensor or perception fault rather than a hard-coded bug. An independent runtime monitor never inspects the policy itself; it only tracks how far the robot's actual trajectory diverges from a verified-safe reference ("ghost") running in parallel, folding that divergence into an EWMA anomaly score. Cross the tunable trip threshold for a debounce window of consecutive frames and the monitor hands control to the reference policy's own commands until the score settles back down — the same detect-and-switch pattern used by runtime-verification shields and supervisory watchdogs guarding learned robot controllers in the field. This top-down 2D rendition draws the exact same planar potential-field dynamics as the 3D version — the physics here was never anything but two-dimensional (x/z position, no vertical motion) — plus a live strip-chart of the anomaly score so you can watch the trip/release cycle unfold over time.