docs: archive enable-doc-orientation-detection proposal

Feature implementation completed and tested successfully.
- PP-StructureV3 orientation detection enabled
- Page dimensions correctly swapped for 90°/270° rotations
- Output PDF now displays landscape content correctly

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

openspec/changes/archive/2025-12-11-enable-doc-orientation-detection/specs/ocr-processing/spec.md

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+# ocr-processing Specification Delta
+
+## ADDED Requirements
+
+### Requirement: Document Orientation Detection
+
+The system SHALL detect and correct document orientation for scanned PDFs where the content orientation differs from PDF page metadata.
+
+#### Scenario: Portrait PDF with landscape content is corrected
+- **GIVEN** a PDF with portrait page dimensions (width < height)
+- **AND** the scanned content is rotated 90° (landscape scan in portrait page)
+- **WHEN** PP-StructureV3 processes the image with `use_doc_orientation_classify=True`
+- **THEN** the system SHALL detect rotation angle as "90" or "270"
+- **AND** the output PDF page dimensions SHALL be swapped (width ↔ height)
+- **AND** all text elements SHALL be correctly positioned in the rotated coordinate space
+
+#### Scenario: Landscape PDF with portrait content is corrected
+- **GIVEN** a PDF with landscape page dimensions (width > height)
+- **AND** the scanned content is rotated 90° (portrait scan in landscape page)
+- **WHEN** PP-StructureV3 processes the image
+- **THEN** the system SHALL detect rotation angle as "90" or "270"
+- **AND** the output PDF page dimensions SHALL be swapped
+- **AND** all text elements SHALL be correctly positioned
+
+#### Scenario: Upside-down content is corrected
+- **GIVEN** a scanned document that is upside down (180° rotation)
+- **WHEN** PP-StructureV3 processes the image
+- **THEN** the system SHALL detect rotation angle as "180"
+- **AND** page dimensions SHALL NOT be swapped (orientation is same, just flipped)
+- **AND** text elements SHALL be correctly positioned after internal rotation
+
+#### Scenario: Correctly oriented documents remain unchanged
+- **GIVEN** a PDF where page metadata matches actual content orientation
+- **WHEN** PP-StructureV3 processes the image
+- **THEN** the system SHALL detect rotation angle as "0"
+- **AND** page dimensions SHALL remain unchanged
+- **AND** processing SHALL proceed normally without dimension adjustment
+
+#### Scenario: Rotation angle is captured from PP-StructureV3 results
+- **GIVEN** PP-StructureV3 is configured with `use_doc_orientation_classify=True`
+- **WHEN** processing completes
+- **THEN** the system SHALL extract rotation angle from `doc_preprocessor_res.label_names`
+- **AND** include `detected_rotation` in the OCR result metadata
+- **AND** log the detected rotation for debugging
+
+#### Scenario: Dimension adjustment happens before PDF generation
+- **GIVEN** OCR processing detects rotation angle of "90" or "270"
+- **WHEN** creating the UnifiedDocument for PDF generation
+- **THEN** the Page dimensions SHALL use adjusted (swapped) width and height
+- **AND** OCR coordinates SHALL be used directly (already in rotated space)
+- **AND** no additional coordinate transformation is needed
+
+### Requirement: Orientation Detection Configuration
+
+The system SHALL provide configuration for enabling/disabling document orientation detection.
+
+#### Scenario: Orientation detection is enabled by default
+- **GIVEN** default configuration settings
+- **WHEN** OCR track processing runs
+- **THEN** `use_doc_orientation_classify` SHALL be `True`
+- **AND** PP-StructureV3 SHALL perform document orientation classification
+
+#### Scenario: Orientation detection can be disabled
+- **GIVEN** `use_doc_orientation_classify` is set to `False` in configuration
+- **WHEN** OCR track processing runs
+- **THEN** the system SHALL NOT perform orientation detection
+- **AND** page dimensions SHALL be based on original image dimensions
+- **AND** this maintains backward compatibility for controlled environments
+
+## MODIFIED Requirements
+
+### Requirement: Layout Model Selection (Modified)
+
+The system SHALL apply document orientation detection before layout detection regardless of the selected layout model.
+
+#### Scenario: Orientation detection works with all layout models
+- **GIVEN** a user selects any layout model (chinese, default, cdla)
+- **WHEN** OCR processing runs with `use_doc_orientation_classify=True`
+- **THEN** orientation detection SHALL be applied regardless of layout model choice
+- **AND** orientation detection happens in Stage 1 (preprocessing) before layout detection (Stage 3)