"It feels like it does nothing" is indistinguishable from "it does nothing",
and at 24fps a lead of 1 is 42ms - small enough to reasonably doubt. So the
shift is now provable and visible rather than taken on trust:
- shiftIndex is a pure exported function with assertions covering identity,
both directions, and clamping at each end
- the frame label always shows the mouth frame, not only when shifted, so the
number can be watched diverging from f; non-zero leads also report in ms
- the slider readout carries an explicit + sign
- the stabilised pane draws the unshifted contour as a dark-green ghost when a
lead is set, so the offset is something you can see
Also: leadIndex called opts() on every invocation - ~14 DOM reads, once per
strip thumbnail, so ~1000 per redraw at 74 frames. It reads a cached scalar now.
The "different pose" assertion checks the whole track rather than one pair:
synthetic poses hold for nine-frame beats, so a single pair can legitimately be
identical while the shift works correctly.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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