Print spread (Letter landscape) opens one sheet with both visible topics scaled to fit half of an 11″×8.5″ page — best for desktop printing two trim pages at once. Print left / Print right prints a single mockup at true 6in × 9in trim (each file sets @page { size: 6in 9in }). Choose Save as PDF if needed. If the dialog ignores page size, use Open in tab. Run npm run book:sync-mockups after editing HTML under book/mockups/topics/.