/** * ======================================================================================== * @file Prefetcher.tsx - client component for background route prefetching * ======================================================================================== * @description * - silently fetches RSC payloads for all navigation routes into the Next.js router cache * - uses requestIdleCallback and sequential queueing to avoid blocking the main thread * - aborts if the user has data saver enabled or is on a slow connection * @see src/modules/nav/Panel.tsx */"use client";import { useEffect } from "react";import { useRouter } from "next/navigation";export default function Prefetcher({ urls }: { urls: string[] }) {  const router = useRouter();  useEffect(() => {    // 1. Guards    // If the browser doesn't support requestIdleCallback, degrade gracefully by doing nothing.    if (typeof window === "undefined" || !("requestIdleCallback" in window)) return;    // Respect user bandwidth constraints    // eslint-disable-next-line @typescript-eslint/no-explicit-any    const conn = (navigator as any).connection;    if (conn) {      if (conn.saveData) return;      if (["slow-2g", "2g", "3g"].includes(conn.effectiveType)) return;    }    // 2. Queue State    let isCancelled = false;    const queue = [...urls];    // 3. Execution    // Process exactly one URL per idle frame to avoid blocking rendering    const processQueue = (deadline: IdleDeadline) => {      if (isCancelled || queue.length === 0) return;      // As long as we have idle time remaining, pop the next URL and prefetch it      while (deadline.timeRemaining() > 0 && queue.length > 0) {        const url = queue.shift();        if (url) {          router.prefetch(url);        }      }      // If there are still items left, request the next idle frame      if (queue.length > 0) {        requestIdleCallback(processQueue);      }    };    // Wait 3 seconds to let the initial page load settle before stealing bandwidth    const timer = setTimeout(() => {      if (!isCancelled) {        requestIdleCallback(processQueue);      }    }, 3000);    return () => {      isCancelled = true;      clearTimeout(timer);    };  }, [urls, router]);  return null; // pure behavior, no UI}