Provides CommunityFeedContext. It fetches the feed once a component watches it, for the signed-in user alone. The socket's messages don't carry a feed's lines, an upvote's naming neither its dump nor its voter, so each one that may change the feed has it fetched again, and the server's query stays the one place that decides what the feed holds. A change that comes while nothing watches is caught up with on the next watch.