takeSnapshot

Returns a snapshot of currently-measured items suitable for round- tripping through state storage (sessionStorage, history, etc.) and passing back as initialMeasurementsCache on remount. Pair with the current scrollOffset to restore exact scroll position after navigation.

Only items the consumer has actually rendered (and thus measured) appear in the snapshot; unmeasured items will fall back to estimateSize on restore. Returns an empty array if no items have been measured.