Link unfurling service

Design a link-unfurling / URL-preview service for a chat app (Slack-like) that, when a user pastes a URL, fetches the page and shows a rich preview (title, description, image). Scale: ~30K URLs/sec at peak, many duplicate URLs (news links shared widely), target preview render <300ms when cached. Requirements: don't fetch the same URL repeatedly, handle slow/huge/malicious target sites without hanging or being abused as a proxy, and degrade gracefully when a site has no metadata.