Sliding-window scan over single-char digit input events. A run of NUMPAD_RUN_MIN (4) consecutive digit events whose pairwise IATs are all ≤ NUMPAD_FAST_IAT_S (50ms) → detected. Otherwise → not_detected. Skips below NUMPAD_MIN_TYPED_CHARS (50) typed chars. Confidence cap 0.50 per the registry's weak-signal flag.