The iPad Messenger app unfurls a share link on-device (fetches + renders the OG tags itself),
but messenger.com desktop shows only what Facebook's server-side scraper cached — which is
pickier. Add og:image:secure_url (public HTTPS) and og:image:type=image/jpeg for our poster so
the card renders even when the scraper won't sniff the bytes. Reachability/stale-cache is a
separate, live-diagnosis step.