fix(vector_stores): reject MongoDB search params the provider cannot honour

filters was already refused, but ranking_options and rewrite_query were
accepted and then dropped. A caller asking for score_threshold 0.9 got results
scoring 0.5 with a 200 and no indication the threshold never ran, which is the
silent-wrong-answer case the filters check exists to prevent. Both now raise
the same 400 naming the parameter and what to do instead.

litellm/llms/mongodb/vector_stores/transformation.py

@@ -236,6 +236,17 @@ class MongoDBVectorStoreConfig(BaseDirectVectorStoreConfig):
                 "MongoDB vector store does not support the filters parameter yet. "
                 "Restrict the collection or the Atlas Vector Search index definition instead."
             )
+        if vector_store_search_optional_params.get("ranking_options") is not None:
+            raise config_error(
+                "MongoDB vector store does not support the ranking_options parameter yet. "
+                "Every result already carries the Atlas vectorSearchScore, so filter or re-rank "
+                "on that rather than having the threshold silently ignored."
+            )
+        if vector_store_search_optional_params.get("rewrite_query") is not None:
+            raise config_error(
+                "MongoDB vector store does not support the rewrite_query parameter. The query is "
+                "embedded exactly as sent; rewrite it before calling if you need that."
+            )
         limit: Final = cls._limit(vector_store_search_optional_params)
         search: Final = MappingProxyType(
             {

tests/test_litellm/llms/mongodb/vector_stores/test_mongodb_transformation.py

@@ -448,6 +448,30 @@ async def test_async_search_rejects_filters_rather_than_silently_ignoring_them()
         await _asearch(config, optional_params={"filters": {"genre": "sci-fi"}})
 
 
+def test_search_rejects_ranking_options_rather_than_silently_ignoring_them():
+    """A score_threshold that is quietly dropped is worse than an error: the caller asked for
+    results above 0.9, gets results scoring 0.5, and nothing says the threshold never ran."""
+    config, _, _ = _config()
+
+    with pytest.raises(BadRequestError, match="does not support the ranking_options parameter"):
+        _search(config, optional_params={"ranking_options": {"score_threshold": 0.9}})
+
+
+def test_search_rejects_rewrite_query_rather_than_silently_ignoring_it():
+    config, _, _ = _config()
+
+    with pytest.raises(BadRequestError, match="does not support the rewrite_query parameter"):
+        _search(config, optional_params={"rewrite_query": True})
+
+
+@pytest.mark.asyncio
+async def test_async_search_rejects_ranking_options_rather_than_silently_ignoring_them():
+    config, _, _ = _async_config()
+
+    with pytest.raises(BadRequestError, match="does not support the ranking_options parameter"):
+        await _asearch(config, optional_params={"ranking_options": {"score_threshold": 0.9}})
+
+
 @pytest.mark.parametrize("query", ["", "   ", "\n\t", []])
 def test_search_rejects_an_empty_query(query):
     config, _, _ = _config()