Bluesky does not hydrate link cards server-side, so build the app.bsky.embed.external embed at publish time: detect the first URL, scrape its OpenGraph metadata, and re-upload the og:image as the card thumb. Works for web, API and MCP. Adds a posts/link-preview endpoint so the editor renders the card live. The thumb download is SSRF-guarded and does not follow redirects.
