Provided by CommunityFeedProvider through CommunityFeedContext.
feed: CommunityFeed | null
Null until it is fetched, which waits for a first watch, and always for a visitor: the feed is for signed-in users.
watch: () => () => void
Says a component is showing the feed, until the returned call. The feed
is fetched, and kept up to date, only while one is: most styles show it
nowhere. useCommunityFeed calls it.