When PaddleOCR fails to detect a standalone 'Figure N' / 'FIGURE N'
heading (rendered in a bold/small-caps font that the OCR engine doesn't
read), the caption body is captured as figure_caption_candidate but
lacks the figure number prefix. The new _recover_figure_heading_prefix()
function checks the PDF text layer (via existing page_pdf_lines_by_page
infrastructure — no extra PDF open) and prepends the heading.
Key logic:
- Scans PDF text lines on the same page for 'Figure N' headings
- Confirms by checking if the NEXT PDF line (by y-order) shares ≥15
chars of common prefix with the OCR caption candidate text
- Only runs when _extract_figure_number() returns None (no figure
number in existing caption text)
- Integrated into build_figure_inventory() before _is_formal_legend()
check, so recovered captions enter the legend matching pool
Fixes 'FIGURE 1' loss in 5S7UI34M and 'FIGURE 5' loss in HQAQBSBP.
372 figure tests pass.
- _TABLE_PREFIX_PATTERN in ocr_roles.py, ocr_signatures.py, ocr_tables.py
now matches Table I/II/III and Table S1/S2
- _extract_table_number and _extract_marker_signature parse Roman numbers
- figure_title generic fallback checks table prefix before figure caption
- ocr_families.py adds early table-prefix guard before reference family
