twitter:card type is explicitly set

Without an explicit twitter:card tag, Twitter/X selects the card type automatically based on available OG tags. This fallback produces inconsistent results: pages with large hero images may get a summary card (small thumbnail) instead of summary_large_image, and the card format can differ between share events as Twitter's heuristics change. The twitter:card type determines whether your link preview shows a prominent full-width image or a small inline thumbnail. Per the Twitter Cards spec, explicit configuration is the only way to guarantee card format. A page that should render with a large image card but falls back to a summary card shows a thumbnail that competes poorly in image-forward social feeds.

Set twitter:card in the root layout as a default, then override per content type where needed:

// app/layout.tsx
export const metadata: Metadata = {
  twitter: {
    card: 'summary_large_image',
  },
}

The summary_large_image type is appropriate for most content pages. Override with summary on utility pages like /login, /settings, and /404 where a large image card is not appropriate. This single root layout addition is the minimum required to pass this check.