fix: fix reindex not working due to unnecessary dupe check (open-webui#20857)

* Update retrieval.py

* Update knowledge.py

* Update retrieval.py

* Update knowledge.py

Author: Classic298

backend/open_webui/routers/retrieval.py

@@ -1425,8 +1425,16 @@ def _get_docs_info(docs: list[Document]) -> str:
         if result is not None and result.ids and len(result.ids) > 0:
             existing_doc_ids = result.ids[0]
             if existing_doc_ids:
-                log.info(f"Document with hash {metadata['hash']} already exists")
-                raise ValueError(ERROR_MESSAGES.DUPLICATE_CONTENT)
+                # Check if the existing document belongs to the same file
+                # If same file_id, this is a re-add/reindex - allow it
+                # If different file_id, this is a duplicate - block it
+                existing_file_id = None
+                if result.metadatas and result.metadatas[0]:
+                    existing_file_id = result.metadatas[0][0].get("file_id")
+                
+                if existing_file_id != metadata.get("file_id"):
+                    log.info(f"Document with hash {metadata['hash']} already exists")
+                    raise ValueError(ERROR_MESSAGES.DUPLICATE_CONTENT)
 
     if split:
         if request.app.state.config.ENABLE_MARKDOWN_HEADER_TEXT_SPLITTER: