Changes held in one step are applied in the order the chat shows them, so
"undo all" walks them back newest first. A page put back is checked against
the digest of the page as the change left it, so a save to another page no
longer blocks the undo; restore_book_page takes these digests as an option and
keeps the whole book check without them. The book card counts the user's own
photos, the preview tool describes itself per role, a copy into another trip
names no places, a held vacay toggle says up front whether it can be taken
back, and a viewer's Studio prompt names none of the design's tools.
The Studio draws the page on request and uploads it once, each provider gets
the image where it expects it, and a refusal falls back to the text
description. No image is stored.
Maurice