OCR/openspec/changes/fix-table-column-alignment/tasks.md

1. Core Algorithm Implementation

1.1 Table Column Corrector Module

• 1.1.1 Create table_column_corrector.py service file
• 1.1.2 Implement ColumnAnchor dataclass for header column ranges
• 1.1.3 Implement build_column_anchors() to extract header column X-ranges
• 1.1.4 Implement calculate_x_overlap() utility function
• 1.1.5 Implement correct_cell_column() for single cell correction
• 1.1.6 Implement correct_table_columns() main entry point

1.2 HTML Cell Extraction

• 1.2.1 Implement parse_table_html_with_positions() to extract cells with row/col
• 1.2.2 Implement cell-to-cellbox matching using IoU
• 1.2.3 Handle colspan/rowspan in header detection

1.3 Vertical Fragment Merging

• 1.3.1 Implement detect_vertical_fragments() to find narrow text blocks
• 1.3.2 Implement should_merge_blocks() adjacency check
• 1.3.3 Implement merge_vertical_fragments() main function
• 1.3.4 Integrate merged blocks back into table structure

2. Configuration

2.1 Settings

• 2.1.1 Add table_column_correction_enabled: bool = True
• 2.1.2 Add table_column_correction_threshold: float = 0.5
• 2.1.3 Add vertical_fragment_merge_enabled: bool = True
• 2.1.4 Add vertical_fragment_aspect_ratio: float = 0.3

3. Integration

3.1 Pipeline Integration

• 3.1.1 Add correction step in pdf_generator_service.py before table rendering
• 3.1.2 Pass corrected HTML to existing table rendering logic
• 3.1.3 Add diagnostic logging for corrections made

3.2 Error Handling

• 3.2.1 Handle tables without headers gracefully
• 3.2.2 Handle empty/malformed cell_boxes
• 3.2.3 Fallback to original structure on correction failure

4. Testing

4.1 Unit Tests

• 4.1.1 Test build_column_anchors() with various header configurations
• 4.1.2 Test correct_cell_column() with known column shift cases
• 4.1.3 Test merge_vertical_fragments() with vertical text samples
• 4.1.4 Test edge cases: empty tables, single column, no headers

4.2 Integration Tests

• 4.2.1 Test with scan.pdf Table 7 (the problematic case)
• 4.2.2 Test with tables that have correct alignment (no regression)
• 4.2.3 Visual comparison of corrected vs original output

5. Documentation

• 5.1 Add inline code comments explaining correction algorithm
• 5.2 Update spec with new table column correction requirement
• 5.3 Add logging messages for debugging