fix: pass preprocessing parameters from start_task to OCR service

The preprocessing_mode and preprocessing_config parameters were not
being passed from the start_task endpoint through to the OCR service:
- Add preprocessing_mode and preprocessing_config to process_task_ocr()
- Extract preprocessing options from ProcessingOptions in start_task()
- Convert string/dict to proper PreprocessingModeEnum/PreprocessingConfig
- Pass converted parameters to ocr_service.process() and process_image()

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

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

backend/app/routers/tasks.py

@@ -73,7 +73,9 @@ def process_task_ocr(
     use_dual_track: bool = True,
     force_track: Optional[str] = None,
     language: str = 'ch',
-    layout_model: Optional[str] = "chinese"
+    layout_model: Optional[str] = "chinese",
+    preprocessing_mode: Optional[str] = "auto",
+    preprocessing_config: Optional[dict] = None
 ):
     """
     Background task to process OCR for a task with dual-track support.
@@ -90,6 +92,8 @@ def process_task_ocr(
         force_track: Force specific track ('ocr' or 'direct')
         language: OCR language code
         layout_model: Layout detection model ('chinese', 'default', 'cdla')
+        preprocessing_mode: Preprocessing mode ('auto', 'manual', 'disabled')
+        preprocessing_config: Manual preprocessing config dict (contrast, sharpen, binarize)
     """
     from app.core.database import SessionLocal
     from app.models.task import Task
@@ -101,6 +105,20 @@ def process_task_ocr(
     try:
         logger.info(f"Starting OCR processing for task {task_id}, file: {filename}")
         logger.info(f"Processing options: dual_track={use_dual_track}, force_track={force_track}, lang={language}")
+        logger.info(f"Preprocessing options: mode={preprocessing_mode}, config={preprocessing_config}")
+
+        # Convert preprocessing parameters to proper types
+        preprocess_mode_enum = None
+        preprocess_config_obj = None
+        if preprocessing_mode:
+            preprocess_mode_enum = PreprocessingModeEnum(preprocessing_mode)
+        if preprocessing_config:
+            from app.schemas.task import PreprocessingContrastEnum
+            preprocess_config_obj = PreprocessingConfig(
+                contrast=PreprocessingContrastEnum(preprocessing_config.get("contrast", "clahe")),
+                sharpen=preprocessing_config.get("sharpen", True),
+                binarize=preprocessing_config.get("binarize", False)
+            )
 
         # Get task directly by database ID (bypass user isolation for background task)
         task = db.query(Task).filter(Task.id == task_db_id).first()
@@ -148,7 +166,9 @@ def process_task_ocr(
                 output_dir=result_dir,
                 use_dual_track=use_dual_track,
                 force_track=force_track,
-                layout_model=layout_model
+                layout_model=layout_model,
+                preprocessing_mode=preprocess_mode_enum,
+                preprocessing_config=preprocess_config_obj
             )
         else:
             # Fall back to traditional processing (no force_track support)
@@ -157,7 +177,9 @@ def process_task_ocr(
                 lang=language,
                 detect_layout=True,
                 output_dir=result_dir,
-                layout_model=layout_model
+                layout_model=layout_model,
+                preprocessing_mode=preprocess_mode_enum,
+                preprocessing_config=preprocess_config_obj
             )
 
         # Calculate processing time
@@ -744,6 +766,17 @@ async def start_task(
         layout_model = options.layout_model.value if options.layout_model else "chinese"
         logger.info(f"Using layout model: {layout_model}")
 
+        # Extract preprocessing options
+        preprocessing_mode = options.preprocessing_mode.value if options.preprocessing_mode else "auto"
+        preprocessing_config = None
+        if options.preprocessing_config:
+            preprocessing_config = {
+                "contrast": options.preprocessing_config.contrast.value,
+                "sharpen": options.preprocessing_config.sharpen,
+                "binarize": options.preprocessing_config.binarize
+            }
+        logger.info(f"Preprocessing: mode={preprocessing_mode}, config={preprocessing_config}")
+
         # Get task details
         task = task_service.get_task_by_id(
             db=db,
@@ -790,11 +823,13 @@ async def start_task(
             use_dual_track=use_dual_track,
             force_track=force_track,
             language=language,
-            layout_model=layout_model
+            layout_model=layout_model,
+            preprocessing_mode=preprocessing_mode,
+            preprocessing_config=preprocessing_config
         )
 
         logger.info(f"Started OCR processing task {task_id} for user {current_user.email}")
-        logger.info(f"Options: dual_track={use_dual_track}, force_track={force_track}, lang={language}, layout_model={layout_model}")
+        logger.info(f"Options: dual_track={use_dual_track}, force_track={force_track}, lang={language}, layout_model={layout_model}, preprocessing={preprocessing_mode}")
         return task
 
     except HTTPException: