Detect newspaper-style two-column layouts (dense independent text
flows) and emit columns sequentially instead of Y-interleaving them.
This fixes academic papers where column text was being merged across
columns at the same Y position.
Key changes:
- Add is_newspaper_layout() heuristic (≥15 lines/col, >50% Y-collision)
- Add split_column_stragglers() to separate core column clusters from
header remnants and per-word items that landed in column buckets
- Filter wide items (>60% page width) from column detection histogram
so full-width text doesn't fill the gutter and prevent detection
- Emit: above spanning → core columns sequentially → column stragglers
sequentially → below spanning items
- Fix markdown paragraph break to detect backward Y jumps (y_gap.abs())
so sequential columns on the same page get proper paragraph breaks
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
