open-graph-share-seo-geo

How to make a page unfurl reliably in iMessage, WhatsApp, Slack, Discord, LinkedIn, and X; surface to search engines via sitemap.xml + robots.txt; and stay legible to generative engines (GEO), including the llms.txt standard for LLM corpus ingest. Use when adding or debugging OpenGraph / Twitter Card metadata, picking an OG image format, choosing where to host the image, fixing pages that "won't unfurl", auditing share previews, scaffolding /llms.txt and /llms-full.txt, or adding @astrojs/sitemap + robots.txt to a splash or marketing site. Encodes the JPEG-over-WebP rule, the ImageKit content-negotiation gotcha, the absolute-URL requirement, the og:image:type-must-match-bytes invariant, the cache-busting recipe for forcing a re-unfurl, the prose-in-markdown source-of-truth pattern for llms.txt, and the sitemap filter that keeps non-HTML routes (llms.txt, 404) out of the search-engine index.