Feature 05 task 2: Core UI primitives (#34)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

web/src/test/hitArea.ts

@@ -0,0 +1,26 @@
+import { expect } from 'vitest'
+
+// Minimum tap target from the handoff's accessibility rules.
+export const MIN_HIT_AREA = 44
+
+function px(value: string): number {
+  return value.endsWith('px') ? Number.parseFloat(value) : 0
+}
+
+// The tap target an element's stylesheet guarantees: the larger of its
+// declared size and declared minimum size, per axis. jsdom does no layout, so
+// this reads the CSS Modules' computed values (Vitest runs with css: true).
+// A dimension the CSS leaves unsized counts as 0 and fails the check.
+export function hitArea(element: Element): { width: number; height: number } {
+  const style = getComputedStyle(element)
+  return {
+    width: Math.max(px(style.width), px(style.minWidth)),
+    height: Math.max(px(style.height), px(style.minHeight)),
+  }
+}
+
+export function expectMinHitArea(element: Element) {
+  const { width, height } = hitArea(element)
+  expect(width, 'hit area width').toBeGreaterThanOrEqual(MIN_HIT_AREA)
+  expect(height, 'hit area height').toBeGreaterThanOrEqual(MIN_HIT_AREA)
+}