- Add RegionPrepass data model for frontmatter/structured_insert/body classification
- Add PDF visual container detection (filled rects) for sidebar detection
- Add Box N and keyword-based sidebar anchor detection
- Add column-aware block expansion for mixed sidebar clusters
- Add _container_text from PDF text blocks for cross-column truncation
- Add degraded-mode heading level normalization with font size clustering
- Merge adjacent structured_insert blocks into single callout
- Fix metadata enrichment from Literature-hub note frontmatter for old papers
- Fix heading hierarchy using span font-size clusters when available
- Add real-paper regression harness (TSCKAVIS, CAQNW9Q2, A8E7SRVS, K7R8PEKW)
- Add body retention, heading, metadata, and callout acceptance tests
- 219 passed, 4 control guards passed
