The link-card cache stored a LinkCardMetadata object, which does not round-trip through the Redis cache driver — a cache hit came back as __PHP_Incomplete_Class and 500'd the preview endpoint. Cache the plain array (toArray) and rebuild the DTO via a new fromArray(). Primitives round-trip cleanly through every driver. The cache test now asserts a primitive is stored and a hit reconstructs the DTO; the array cache driver used in tests hid the bug because it never serializes.
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.
