System.Text.Json emitted both "@type" and a bare "Type" because the attribute was only on the abstract base member. Adds regression assertions for all node types.
Escape </>& in JSON-LD body to kill script-breakout; byArtist now uses the release artist; detail-page not-found branches emit noindex; default robots gated to Production via a PersistentState SeoEnvironment bridge.
One presentational SeoHead renders the full OG/Twitter/JSON-LD head surface at prerender via typed schema.org builders. Per-medium release schema, config-sourced canonicals, 404 noindex. Zero CMS change.