Height-3 case pins the halfSpan clamp itself (height-4 passed pre-fix too); dropped the vacuous tall-rect mirror since min() is symmetric and wide already discriminates.
Aligns inKnobFace's hit radius with computeKnob's draw-side min(w,h) rule and adds a non-square-rect test; clamps halfSpan for degenerate waveform bands with a test; fixes stale docs/comments and annotates an uncommitted perf measurement.
The waveform column's vertical extents move to pure component_geometry so the shared
primitive stops being untested; PlaySeconds hoists into a header-only play_seconds target.
kWaveformOversample set to 1 (was 4) — overbinning produced byte-identical pixels because columnMinMax exact partition already makes the draw gap-free. Comments credit columnMinMax, not oversampling.
daniel