On a local strategy "+" adds a copy of the page on screen; on a cloud
strategy it added a blank page, because the server keeps item ids unique
across every strategy. The new cloud page now gets a copy of every item
and lineup as the canvas draws them, each under a copy id that keeps its
root, so turning to the page glides rather than fades. Images have their
pictures copied first (images:copyAsset); one that can't be copied yet is
left out and the "+" caller says so. The page opens once the copies land,
waiting at most three seconds. A copied stroke now counts as its original
when deciding whether the drawing layer changes between pages.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>