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Pages with two side-by-side vocabulary columns separated by a vertical black line are now split into independent sub-zones before row/column detection. Each sub-zone gets its own rows, preventing misalignment from different heading rhythms. - _detect_vertical_dividers(): finds pipe word_boxes at consistent x positions spanning >50% of zone height - _split_zone_at_vertical_dividers(): creates left/right PageZone objects with layout_hint and vsplit_group metadata - Column union skips vsplit zones (independent column sets) - Frontend renders vsplit zones side by side via flex layout - PageZone gets layout_hint + vsplit_group fields Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>