WhatsApp / Slack / Facebook / Twitter previews showed nothing useful for
shared gallery links — the SPA's stub index.html has no OG tags and the
meta-injection in DynamicFavicon happens at runtime, which crawlers
never see (they don't execute JS).
Add a backend OG handler at /og/gallery/:slug that returns minimal HTML
with proper og:* and twitter:* meta sourced from the event row + branding
settings (event name, formatted date, welcome_message excerpt as
description, configured logo as the preview image, FRONTEND_URL-based
canonical). Honours slug redirects so renamed galleries still get rich
previews.
Wire crawler detection in both nginx configs (production and dev) — UA
match against the standard list (facebookexternalhit, WhatsApp, Slackbot,
Twitterbot, Discordbot, LinkedInBot, etc.) triggers an internal
rewrite to /og/gallery/:slug, while humans fall through to the SPA via
try_files. The OG endpoint is also wired into the native-install SPA
fallback in server.js for setups that bypass nginx.
The OG image is intentionally the brand logo, not a gallery photo —
crawlers fetch it without auth, and password-protected gallery photos
must not leak via share previews.
Paul Nothaft
5275621fcd