Bake window derives itself: %-knob fold, declick pad, Gate held to exhaustion, preview velocity; Hold is the one knob a loop needs

src/core/instrument/ui/bake_hold.h

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+#pragma once
+// bake_hold — how one radial knob addresses the note-length ladder: the Hold control's
+// normalized [0,1] position mapped onto a Division and back. The ladder and its picker order
+// are musical_division's; nothing about them is restated here.
+
+#include "core/instrument/note/musical_division.h"
+
+namespace reasampler::instrument::ui {
+
+// [0,1] across the ladder in picker order (shortest rung first). Out-of-range or non-finite
+// input clamps to an end rather than wrapping — a knob cannot express anything else.
+note::Division bakeHoldFromNorm(double norm);
+
+// The inverse: the position that reproduces `hold` exactly, so a knob painted from a stored
+// value and then released without moving cannot shift it a rung.
+double bakeHoldNorm(note::Division hold);
+
+}  // namespace reasampler::instrument::ui