Fetch an HTTP or HTTPS URL through MoonBit's policy-visible HTTP client.Supports -s/--silent, -S/--show-error, -f/--fail, and-o/--output, plus --idle-timeout SECONDS (default 30, positivefractional values accepted). Progress is written to stderr. -s suppressesprogress and errors, while -sS restores errors without restoring progress.Progress updates are throttled and use a single terminal status line.With -f, HTTP 400 and later responses fail with the actual status in thediagnostic. It does not invoke a host curl executable; redirects,uploads, and arbitrary request methods are intentionally outside this firstpolicy-focused implementation.