Namespace metadata column by output column name

- Changes metadata column from fixed 'olmocr_metadata' to '{output_column}_metadata'
- Allows multiple OCR runs on same dataset with different column names
- Handles existing columns by removing and overwriting with warning
- Enables workflow: process same dataset with different models/settings

Example:
--output-column markdown → markdown_metadata
--output-column olmocr2 → olmocr2_metadata

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

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

olmocr2-vllm.py

@@ -323,9 +323,10 @@ def main(
     logger.info(f"Processing {len(ds)} samples")
     logger.info(f"Output will be written to column: {output_column}")
 
-    # Set column names
-    metadata_column_name = "olmocr_metadata"
+    # Set column names - namespace metadata by output column to avoid conflicts
+    metadata_column_name = f"{output_column}_metadata"
     inference_info_column = "inference_info"
+    logger.info(f"Metadata will be written to column: {metadata_column_name}")
 
     # Initialize LLM
     logger.info(f"Initializing vLLM with model: {model}")
@@ -365,7 +366,15 @@ def main(
             all_metadata.append(json.dumps(metadata))
 
     # Add results to dataset
+    # Check if columns already exist and handle appropriately
+    if output_column in ds.column_names:
+        logger.warning(f"Column '{output_column}' already exists, it will be overwritten")
+        ds = ds.remove_columns([output_column])
     ds = ds.add_column(output_column, all_outputs)
+
+    if metadata_column_name in ds.column_names:
+        logger.warning(f"Column '{metadata_column_name}' already exists, it will be overwritten")
+        ds = ds.remove_columns([metadata_column_name])
     ds = ds.add_column(metadata_column_name, all_metadata)
 
     # Add inference information