get isCacheStale() {
    if (!fs.existsSync(this.cacheFileExpiryPath)) return true;
    const cachedAt = fs.readFileSync(this.cacheFileExpiryPath, "utf8");
    return Date.now() - cachedAt > ContextWindowFinder.expiryMs;
  }
Checks if the cache is stale by checking if the cache file exists and if the cache file is older than the expiry time.
@returns {boolean}