refactor(motion): extraer useEnVista, compartido por las ilustraciones

lib/__tests__/motion.test.tsx

@@ -0,0 +1,24 @@
+import { render } from '@testing-library/react';
+import { describe, it, expect } from 'vitest';
+import { useEnVista } from '@/lib/motion';
+
+function Sonda() {
+  const { ref, enVista, reduced } = useEnVista();
+  return <svg ref={ref} data-en-vista={String(enVista)} data-reducido={String(reduced)} />;
+}
+
+describe('useEnVista', () => {
+  it('hands back a ref to attach, plus the two flags a drawing needs', () => {
+    const { container } = render(<Sonda />);
+    const svg = container.querySelector('svg');
+    expect(svg).toHaveAttribute('data-en-vista');
+    expect(svg).toHaveAttribute('data-reducido');
+  });
+
+  it('starts out not-yet-in-view so drawings do not skip their entrance', () => {
+    const { container } = render(<Sonda />);
+    // jsdom's IntersectionObserver stub never fires, so this also pins the
+    // safe default: nothing claims to be visible until the observer says so.
+    expect(container.querySelector('svg')).toHaveAttribute('data-en-vista', 'false');
+  });
+});

lib/motion.ts

@@ -1,4 +1,4 @@
-import { useEffect, useState } from 'react';
+import { useEffect, useRef, useState } from 'react';
 import type { Variants } from 'framer-motion';
 
 // EaseOutExpo — smooth editorial deceleration
@@ -30,6 +30,34 @@ export function usePrefersReducedMotion() {
   return reduced;
 }
 
+// Shared "draw once when scrolled into view" wiring for the SVG illustrations.
+// Returns the ref to attach, whether the element has been seen, and the
+// reduced-motion flag the caller needs anyway to pick its render branch.
+// Observes nothing under reduced motion — those branches render statically.
+export function useEnVista(umbral = 0.4) {
+  const reduced = usePrefersReducedMotion();
+  const ref = useRef<SVGSVGElement>(null);
+  const [enVista, setEnVista] = useState(false);
+
+  useEffect(() => {
+    const el = ref.current;
+    if (!el || reduced) return;
+    const observer = new IntersectionObserver(
+      ([entry]) => {
+        if (entry.isIntersecting) {
+          setEnVista(true);
+          observer.unobserve(el);
+        }
+      },
+      { threshold: umbral },
+    );
+    observer.observe(el);
+    return () => observer.disconnect();
+  }, [reduced, umbral]);
+
+  return { ref, enVista, reduced };
+}
+
 // Pass to <motion.*> as motion-reduced guard. When reduced, variants resolve to visible immediately.
 export const motionProps = (reduced: boolean) =>
   reduced