Realtime only: put new items straight at the top of the column. Resolves
to how many were added, or null when this column can't (it then falls
back to checkForNew() and the "new" pill).
Resolves to how many items showNew() would add or move to the top.
ProtectedinsertProtectedmatchesWhether a post belongs in this column: undefined when only the server can tell.
ProtectedmayWhether a new discussion's first post might belong here: false rules it out.
ProtectednewerA new reply that certainly belongs here is inserted from the payload; one that certainly doesn't is ignored; only undecidable ones ask the server. A new discussion's first post isn't in its Started payload, so a column that may want it asks.
ProtectedprepareRuns once before the first load, for columns whose params need looking up.
ProtectedrefillFor a prune() that takes posts out: the next page fills an emptied column.
ProtectedremoveProtectedshowsProtectedsnapshot
A newest-first column of comments, backed by its own PostListState, so any post filter the API understands works. Post ids only grow, so the newest id on screen is the key for asking "anything newer?".