On startup we don't want to block input during the initial refresh (it
should be possible to press, say, `4` to jump to the commits panel right
after startup without a delay), and we also want panels to show their
contents as soon as possible; it doesn't matter so much that it's not in
sync, we go from empty to populated here. However, when switching repos
it can be confusing that some panels that are slow to update still show
the old repo's data while others already show the new one's data, so
update the UI only when everything is ready, and also block input to
prevent accidentally trying to act on the old, stale data.