Module hover_stabilizer 

Hover jitter stabilization using CUSUM change-point detection.

Eliminates hover flicker when the pointer jitters around widget boundaries while maintaining responsiveness for intentional target changes.

Algorithm

The stabilizer uses a simplified CUSUM (Cumulative Sum) change-point detector:

• Track signed distance d_t to current target boundary (positive = inside)
• Compute cumulative sum: S_t = max(0, S_{t-1} + d_t - k) where k is drift allowance
• Switch target only when S_t > h (threshold) indicating strong evidence of intent

A hysteresis band around boundaries prevents oscillation from single-cell jitter.

Invariants

1. Hover target only changes when evidence exceeds threshold
2. Single-cell jitter sequences do not cause target flicker
3. Intentional crossing (steady motion) triggers switch within ~2 frames
4. No measurable overhead (<2%) on hit-test pipeline

Failure Modes

• If hit-test returns None consistently, stabilizer holds last known target
• If threshold is too high, responsiveness degrades (tune via config)
• If drift allowance is too low, jitter causes accumulation (tune k parameter)

Evidence Ledger

In debug mode, the stabilizer logs:

• CUSUM score at each update
• Hysteresis state (inside band vs. outside)
• Target switch events with evidence values

Structs

HoverStabilizer

Stateful hover stabilizer that prevents jitter-induced target flicker.

HoverStabilizerConfig

Configuration for hover jitter stabilization.