feat(shared): add getPretextFontString formatter

src/shared/lib/utils/getPretextFontString/getPretextFontString.test.ts

@@ -0,0 +1,15 @@
+import {
+    describe,
+    expect,
+    it,
+} from 'vitest';
+import { getPretextFontString } from './getPretextFontString';
+
+describe('getPretextFontString', () => {
+    it('formats weight, px size and quoted family for pretext/canvas', () => {
+        expect(getPretextFontString(400, 48, 'Inter')).toBe('400 48px "Inter"');
+    });
+    it('preserves fractional sizes and quotes multi-word family names', () => {
+        expect(getPretextFontString(700, 12.5, 'PT Serif')).toBe('700 12.5px "PT Serif"');
+    });
+});

src/shared/lib/utils/getPretextFontString/getPretextFontString.ts

@@ -0,0 +1,16 @@
+/**
+ * Formats a font config into the string `@chenglou/pretext` and the Canvas 2D
+ * `font` property both expect: `weight sizepx "family"`.
+ *
+ * ponytail: deliberate copy of widgets/ComparisonView/lib's version — ADR-0002
+ * keeps the shelved morph tool untouched, so we don't move its util. Three lines
+ * is cheaper to duplicate than to refactor frozen code.
+ *
+ * @param weight - Numeric font weight (e.g. 400).
+ * @param sizePx - Font size in pixels.
+ * @param fontName - The font family name.
+ * @returns A formatted font string: `weight sizepx "fontName"`.
+ */
+export function getPretextFontString(weight: number, sizePx: number, fontName: string): string {
+    return `${weight} ${sizePx}px "${fontName}"`;
+}

src/shared/lib/utils/index.ts

@@ -18,6 +18,7 @@ export { clampNumber } from './clampNumber/clampNumber';
 export { cn } from './cn';
 export { debounce } from './debounce/debounce';
 export { getDecimalPlaces } from './getDecimalPlaces/getDecimalPlaces';
+export { getPretextFontString } from './getPretextFontString/getPretextFontString';
 export { getSkeletonWidth } from './getSkeletonWidth/getSkeletonWidth';
 export { roundToStepPrecision } from './roundToStepPrecision/roundToStepPrecision';
 export { smoothScroll } from './smoothScroll/smoothScroll';