BEHAVE-EXTRACTOR.md Phase B Step B.2. First principled
implementation — the prototype doesn't ship this primitive at all.
* _features/motor.py:motor_stability(ctx) emits one Observation
in {steady, variable, tremor}. Reuses ctx.typing_bursts from B.1.
* Tremor proxy: fraction of within-burst IATs below
TREMOR_FAST_FLOOR_S (30 ms — humans can't sustain sub-50 ms IATs).
≥ TREMOR_RATE_MIN (10%) sub-floor → tremor (double-press / motor
twitch / stuck-key).
* Otherwise median burst CV decides: < CV_STEADY_MAX → steady,
else → variable. Confidence 0.70 / 0.60 / 0.65.
* No typing bursts or fewer than 5 within-burst IATs → skip emit.
* Calibration grid widened to include motor.motor_stability; green
across all five shards.
Tests cover all three buckets + skip paths.
anti
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