Page-turn placement is out of scope for the web lesson surface but directly applies to Gradus's print/export (scoreGifts) pipeline

Page turns should never fall in the middle of a phrase if avoidable, and a performer needs enough rest (a bar or more, or a held note) immediately before a turn to physically turn the page — this only matters for paginated, printed output, not a single continuously-scrolling web SVG.

Ross, The Art of Music Engraving (page-turn placement is a dedicated topic — avoid turns mid-phrase, prefer turns at rests or long notes); Gould, Behind Bars (same, framed around performer practicality).

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.