Returned by GET /api/remote/preview to the create form, which shows it before the
link is posted.
reached: boolean
False when the page couldn't be fetched. richContent is then a stub
holding the host name, and this flag is how the form tells a dead link
from a page with no preview.
richContent: RichContent | null
Null only for a link that doesn't parse, which the route rejects before fetching anyway.