refine: add OCR track line break support and spacing_after handling

Complete Phase 3 text rendering refinements for both tracks:

**OCR Track Line Break Support (Task 5.1.4)**
- Modified draw_text_region to split text on newlines
- Calculate line height as font_size * 1.2 (same as Direct track)
- Render each line with proper vertical spacing
- Apply per-line font scaling when text exceeds bbox width
- Lines 1191-1218 in pdf_generator_service.py

**spacing_after Handling (Task 5.2.4)**
- Extract spacing_after from element metadata
- Add explanatory comments about spacing_after usage
- Include spacing_after in debug logs for visibility
- Note: In Direct track with fixed bbox, spacing_after is already
  reflected in element positions; recorded for structural analysis

**Technical Details**
- OCR track now has feature parity with Direct track for line breaks
- Both tracks use identical line_height calculation (1.2x font size)
- spacing_before applied via Y position adjustment
- spacing_after recorded but not actively applied (bbox-based layout)

**Modified Files**
- backend/app/services/pdf_generator_service.py
  - Lines 1191-1218: OCR track line break handling
  - Lines 1567-1572: spacing_after comments and extraction
  - Lines 1641-1643: Enhanced debug logging
- openspec/changes/pdf-layout-restoration/tasks.md
  - Added 5.1.4 and 5.2.4 completion markers

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

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

backend/app/services/pdf_generator_service.py

@@ -1188,18 +1188,34 @@ class PDFGeneratorService:
                 font_name = self.font_name if self.font_registered else 'Helvetica'
                 pdf_canvas.setFont(font_name, font_size)
 
-            # Calculate text width to prevent overflow
-            text_width = pdf_canvas.stringWidth(text, font_name, font_size)
+            # Handle line breaks (split text by newlines)
+            lines = text.split('\n')
+            line_height = font_size * 1.2  # 120% of font size for line spacing
 
-            # If text is too wide for bbox, scale down font
+            # Draw each line
+            for i, line in enumerate(lines):
+                if not line.strip():
+                    continue  # Skip empty lines
+
+                line_y = pdf_y - (i * line_height)
+
+                # Calculate text width to prevent overflow
+                text_width = pdf_canvas.stringWidth(line, font_name, font_size)
+
+                # If text is too wide for bbox, scale down font for this line
+                current_font_size = font_size
                 if text_width > bbox_width:
                     scale_factor = bbox_width / text_width
-                font_size = font_size * scale_factor * 0.95  # 95% to add small margin
-                font_size = max(font_size, 3)  # Minimum 3pt
-                pdf_canvas.setFont(font_name, font_size)
+                    current_font_size = font_size * scale_factor * 0.95  # 95% to add small margin
+                    current_font_size = max(current_font_size, 3)  # Minimum 3pt
+                    pdf_canvas.setFont(font_name, current_font_size)
 
                 # Draw text at calculated position
-            pdf_canvas.drawString(pdf_x, pdf_y, text)
+                pdf_canvas.drawString(pdf_x, line_y, line)
+
+                # Reset font size for next line
+                if text_width > bbox_width:
+                    pdf_canvas.setFont(font_name, font_size)
 
             # Debug: Draw bounding box (optional)
             if settings.pdf_enable_bbox_debug:
@@ -1549,6 +1565,9 @@ class PDFGeneratorService:
             first_line_indent = element.metadata.get('first_line_indent', indent) if element.metadata else indent
 
             # Get paragraph spacing
+            # spacing_before: Applied by adjusting starting Y position (pdf_y)
+            # spacing_after: Recorded for debugging; in Direct track with fixed bbox,
+            #                actual spacing is already reflected in element positions
             paragraph_spacing_before = element.metadata.get('spacing_before', 0) if element.metadata else 0
             paragraph_spacing_after = element.metadata.get('spacing_after', 0) if element.metadata else 0
 
@@ -1623,7 +1642,8 @@ class PDFGeneratorService:
                     pdf_canvas.setFont(font_name, font_size)
 
             logger.debug(f"Drew text element: {text_content[:30]}... "
-                        f"({len(lines)} lines, align={alignment}, indent={indent})")
+                        f"({len(lines)} lines, align={alignment}, indent={indent}, "
+                        f"spacing_before={paragraph_spacing_before}, spacing_after={paragraph_spacing_after})")
 
         except Exception as e:
             logger.error(f"Failed to draw text element {element.element_id}: {e}")

openspec/changes/pdf-layout-restoration/tasks.md

@@ -81,10 +81,12 @@
   - [x] 5.1.1 Split text content by newlines (text.split('\n'))
   - [x] 5.1.2 Calculate line height from font size (font_size * 1.2)
   - [x] 5.1.3 Render each line with proper spacing (line_y = pdf_y - i * line_height)
+  - [x] 5.1.4 Add OCR track support in draw_text_region (lines 1191-1218)
 - [x] 5.2 Add paragraph handling
   - [x] 5.2.1 Detect paragraph boundaries (via element.type PARAGRAPH)
   - [x] 5.2.2 Apply paragraph spacing (spacing_before/spacing_after from metadata)
   - [x] 5.2.3 Handle indentation (indent/first_line_indent from metadata)
+  - [x] 5.2.4 Record spacing_after for debugging (included in logs)
 - [x] 5.3 Implement text alignment
   - [x] 5.3.1 Support left/right/center/justify (from StyleInfo.alignment)
   - [x] 5.3.2 Calculate positioning based on alignment (line_x calculation)