Now, when loading present items, they're inserted into the data source
immediately along with a gap. If the user taps Jump to Present, then a
new snapshot _with only the present items_ will be applied (which allows
infinite scrolling to work properly when they scroll back down) and the
view scrolled-to-top. Tapping Go Back, then, applies the original
snapshot (i.e., the current one from when Jump to Present was tapped)
and restores the scroll position.
Shadowfacts
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