fix: fix rerank model runner usage (#19008)

api/core/rag/rerank/rerank_model.py

@@ -52,6 +52,7 @@ class RerankModelRunner(BaseRerankRunner):
         rerank_documents = []
 
         for result in rerank_result.docs:
+            if score_threshold is None or result.score >= score_threshold:
                 # format document
                 rerank_document = Document(
                     page_content=result.text,
@@ -62,4 +63,5 @@ class RerankModelRunner(BaseRerankRunner):
                     rerank_document.metadata["score"] = result.score
                     rerank_documents.append(rerank_document)
 
-        return rerank_documents
+        rerank_documents.sort(key=lambda x: x.metadata.get("score", 0.0), reverse=True)
+        return rerank_documents[:top_n] if top_n else rerank_documents