/**
 * Reading a HALF-EXTENT size prop that may carry pixels.
 *
 * A shape's size props are half-extents in canvas-height units, and a user may switch one to
 * absolute pixels — at which point the prop value becomes a `DimensionalValue` carrying the FULL
 * pixel size (the same number the Design Editor's px chip shows), not the half. A `computeBounds` /
 * `writeBounds` pair therefore has to normalize before it can do arithmetic, and it has to do so
 * IDENTICALLY on both sides or a resize round-trip drifts.
 *
 * Trapezoid had this as a local closure shared between its two bounds callbacks. It lives here so
 * the next `computeBounds` shape that grows px-capable size props can reuse the exact reading rule
 * rather than re-deriving the ÷2 (which is the easy half to get wrong).
 *
 * NOT adopted by Ring or Blob: neither handles px size props at all today (both read
 * `props.<size> as number`), so pointing them at this helper would ADD px support — a behaviour
 * change, not an extraction. Left for whenever that support is wanted deliberately.
 */
/**
 * Normalize a half-extent size prop to half-UV (canvas-height units).
 *
 * - `{value, unit: 'px'}` → the value is the FULL pixel size, so `value / (2 · canvasHeight)`.
 * - any other `{value: number}` → already the half-UV value (this is Trapezoid's original rule: a
 *   value object whose unit is anything but `'px'`, including missing, is read as UV).
 * - a plain number → already the half-UV value.
 * - anything else → `fallback` (the prop's default), never NaN.
 *
 * "Never NaN" is checked, not assumed: a non-finite numeric value (a dynamic prop resolving to NaN
 * mid-frame) and a px read against a zero or non-finite `canvasHeight` (the frame before the canvas
 * has been measured) both fall back rather than poisoning the bounds arithmetic downstream. The
 * `fallback` itself is normalized at the boundary too (→ 0.5, a half-canvas half-extent), so the
 * promise holds even for a caller that computes its fallback — every call site today passes a
 * literal, making that branch unreachable, but the contract shouldn't depend on it.
 */
export declare function halfUvFromProp(value: unknown, canvasHeight: number, fallback: number): number;
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