## ADDED Requirements

### Requirement: OCR Track Gap Filling with Raw OCR Regions

The system SHALL detect and fill gaps in PP-StructureV3 output by supplementing with Raw OCR text regions when significant content loss is detected.

#### Scenario: Gap filling activates when coverage is low
- **GIVEN** an OCR track processing task
- **WHEN** PP-StructureV3 outputs elements that cover less than 70% of Raw OCR text regions
- **THEN** the system SHALL activate gap filling
- **AND** identify Raw OCR regions not covered by any PP-StructureV3 element
- **AND** supplement these regions as TEXT elements in the output

#### Scenario: Coverage is determined by center-point and IoU
- **GIVEN** a Raw OCR text region with bounding box
- **WHEN** checking if the region is covered by PP-StructureV3
- **THEN** the region SHALL be considered covered if its center point falls inside any PP-StructureV3 element bbox
- **OR** if IoU with any PP-StructureV3 element exceeds 0.15 threshold
- **AND** regions not meeting either criterion SHALL be marked as uncovered

#### Scenario: Only TEXT elements are supplemented
- **GIVEN** uncovered Raw OCR regions identified for supplementation
- **WHEN** PP-StructureV3 has detected TABLE, IMAGE, FIGURE, FLOWCHART, HEADER, or FOOTER elements
- **THEN** the system SHALL NOT supplement regions that overlap with these structural elements
- **AND** only supplement regions as TEXT type to preserve structural integrity

#### Scenario: Supplemented regions meet confidence threshold
- **GIVEN** Raw OCR regions to be supplemented
- **WHEN** a region has confidence score below 0.3
- **THEN** the system SHALL skip that region
- **AND** only supplement regions with confidence >= 0.3

#### Scenario: Deduplication prevents repeated text
- **GIVEN** a Raw OCR region being considered for supplementation
- **WHEN** the region has IoU > 0.5 with any existing PP-StructureV3 TEXT element
- **THEN** the system SHALL skip that region to prevent duplicate text
- **AND** the original PP-StructureV3 element SHALL be preserved

#### Scenario: Reading order is recalculated after gap filling
- **GIVEN** supplemented elements have been added to the page
- **WHEN** assembling the final element list
- **THEN** the system SHALL recalculate reading order for the entire page
- **AND** sort elements by y0 coordinate (top to bottom) then x0 (left to right)
- **AND** ensure logical document flow is maintained

#### Scenario: Coordinate alignment with ocr_dimensions
- **GIVEN** Raw OCR processing may involve image resizing
- **WHEN** comparing Raw OCR bbox with PP-StructureV3 bbox
- **THEN** the system SHALL use ocr_dimensions to normalize coordinates
- **AND** ensure both sources reference the same coordinate space
- **AND** prevent coverage misdetection due to scale differences

#### Scenario: Supplemented elements have complete metadata
- **GIVEN** a Raw OCR region being added as supplemented element
- **WHEN** creating the DocumentElement
- **THEN** the element SHALL include page_number
- **AND** include confidence score from Raw OCR
- **AND** include original bbox coordinates
- **AND** optionally include source indicator for debugging

### Requirement: Gap Filling Track Isolation

The gap filling feature SHALL only apply to OCR track processing and SHALL NOT affect Direct or Hybrid track outputs.

#### Scenario: Gap filling only activates for OCR track
- **GIVEN** a document processing task
- **WHEN** the processing track is OCR
- **THEN** the system SHALL evaluate and apply gap filling as needed
- **AND** produce enhanced output with supplemented content

#### Scenario: Direct track is unaffected
- **GIVEN** a document processing task with Direct track
- **WHEN** the task is processed
- **THEN** the system SHALL NOT invoke any gap filling logic
- **AND** produce output identical to current Direct track behavior

#### Scenario: Hybrid track is unaffected
- **GIVEN** a document processing task with Hybrid track
- **WHEN** the task is processed
- **THEN** the system SHALL NOT invoke gap filling logic
- **AND** use existing Hybrid track processing pipeline

### Requirement: Gap Filling Configuration

The system SHALL provide configurable parameters for gap filling behavior.

#### Scenario: Gap filling can be disabled via configuration
- **GIVEN** gap_filling_enabled is set to false in configuration
- **WHEN** OCR track processing runs
- **THEN** the system SHALL skip all gap filling logic
- **AND** output only PP-StructureV3 results as before

#### Scenario: Coverage threshold is configurable
- **GIVEN** gap_filling_coverage_threshold is set to 0.8
- **WHEN** PP-StructureV3 coverage is 75%
- **THEN** the system SHALL activate gap filling
- **AND** supplement uncovered regions

#### Scenario: IoU thresholds are configurable
- **GIVEN** custom IoU thresholds configured:
  - gap_filling_iou_threshold: 0.2
  - gap_filling_dedup_iou_threshold: 0.6
- **WHEN** evaluating coverage and deduplication
- **THEN** the system SHALL use the configured values
- **AND** apply them consistently throughout gap filling process

#### Scenario: Confidence threshold is configurable
- **GIVEN** gap_filling_confidence_threshold is set to 0.5
- **WHEN** supplementing Raw OCR regions
- **THEN** the system SHALL only include regions with confidence >= 0.5
- **AND** filter out lower confidence regions