Indices of the CURRENT items array whose item is skip-listed.
The pager settled on index: promote, demote, recycle, prefill.
Settling the page that is already active (updateItems re-runs this when
the host's list grows) only refills the window — it never re-promotes,
so a page the viewer paused stays paused, and the page-level callbacks
(onActiveItemChanged / onNearEnd) fire once per settled page.
Test seam: how one pooled player is built (unit tests hand in fakes).