fix(messages): keep the provider out of a shared logger's litellm_params on native messages calls

Python's messages handler only records custom_llm_provider in model_call_details. The native adapter also wrote it into litellm_params after every provider result, and the proxy reuses one logger across router hops, so a fallback hop's pre_call log showed the provider where Python shows null.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013FDwtkaNTifWAP4W7JZavE

litellm-rust/crates/callbacks-legacy-python/src/adapter.rs

@@ -525,7 +525,11 @@ impl LegacyLogging {
             .getattr("litellm_params")?
             .cast_into::<PyDict>()?
             .copy()?;
-        params.set_item("custom_llm_provider", &facts.provider.provider)?;
+        if self.operation != LoggingOperation::Messages {
+            // Python's Messages handler hands the provider to the logger beside its params, never
+            // in them, and the proxy's logger carries over to the next fallback hop.
+            params.set_item("custom_llm_provider", &facts.provider.provider)?;
+        }
         crate::python::Logging::Update.call(
             py,
             (
@@ -1142,6 +1146,52 @@ assert logger.update['custom_llm_provider'] == 'edenai', logger.update
         });
     }
 
+    #[rstest]
+    #[case::messages(crate::LoggingOperation::Messages, false)]
+    #[case::ocr(crate::LoggingOperation::Ocr, true)]
+    fn result_ready_puts_the_provider_in_the_logged_params_except_for_messages(
+        #[case] operation: crate::LoggingOperation,
+        #[case] in_params: bool,
+    ) {
+        Python::initialize();
+        Python::attach(|py| {
+            let locals = namespace(py, PAYLOAD_LOGGER);
+            run(
+                py,
+                &locals,
+                c"
+logger.litellm_params = {}
+logger.optional_params = {}
+logger.model_call_details = {}
+logger._provider_reported_cost = None
+",
+            );
+            let mut logging = LegacyLogging {
+                logger: Some(PythonLogger::new(local(&locals, "logger").unbind())),
+                operation,
+                ..legacy_call(py, &locals, false)
+            };
+            let facts = litellm_host::interceptors::ExecutionFacts {
+                provider: litellm_host::interceptors::ProviderIdentity {
+                    model: "native-test".into(),
+                    provider: "anthropic".into(),
+                },
+                cost: litellm_host::interceptors::Cost::Deferred,
+                source: litellm_host::interceptors::ResultSource::Provider,
+            };
+            logging.result_ready(py, &facts).unwrap();
+            locals.set_item("in_params", in_params).unwrap();
+            run(
+                py,
+                &locals,
+                c"
+assert logger.update['custom_llm_provider'] == 'anthropic', logger.update
+assert ('custom_llm_provider' in logger.update['litellm_params']) is in_params, logger.update
+",
+            );
+        });
+    }
+
     const DOCUMENT: &str = "data:application/pdf;base64,YWJj";
     const EDITED: &str = "data:application/pdf;base64,ZWRpdGVk";
 

tests/test_litellm_rust/messages/test_callbacks.py

@@ -10,14 +10,15 @@ from pydantic import TypeAdapter
 import litellm
 from litellm.integrations.argilla import ArgillaLogger
 from litellm.integrations.custom_logger import CustomLogger
+from litellm.litellm_core_utils.litellm_logging import Logging
 from litellm.types.integrations.argilla import ArgillaItem
 from litellm.types.utils import ModelResponse, StandardLoggingPayload
-from tests.test_litellm_rust.messages.data import BAD_REQUEST, MESSAGES_RESPONSE, RATE_LIMITED, call
+from tests.test_litellm_rust.messages.data import BAD_REQUEST, MESSAGES_RESPONSE, RATE_LIMITED, REQUEST, call
 from tests.test_litellm_rust.support.callback_recorder import HookRecorder, RecordingLogger, request_body
 from tests.test_litellm_rust.support.isolation import rebound
 from tests.test_litellm_rust.support.recording_server import RecordingServer, ResponseSpec, relaxed
 from tests.test_litellm_rust.support.results import response_id, with_id
-from tests.test_litellm_rust.support.routing import assert_served_natively
+from tests.test_litellm_rust.support.routing import CALL_ID, assert_served_natively
 
 pytestmark = pytest.mark.requires_rust_extension
 
@@ -110,6 +111,33 @@ async def test_pre_api_call_sees_the_wire_body(server: RecordingServer) -> None:
     assert request_body(pre_call) == server.requests[0].body
 
 
+@pytest.mark.asyncio
+async def test_pre_api_call_of_a_retried_call_keeps_the_provider_out_of_the_litellm_params(
+    server: RecordingServer,
+) -> None:
+    recorder: Final = RecordingLogger()
+    logging_obj: Final = Logging(
+        model=REQUEST["model"],
+        messages=[],
+        stream=False,
+        start_time=datetime.now(),
+        call_type="anthropic_messages",
+        litellm_call_id=CALL_ID,
+        function_id=CALL_ID,
+        dynamic_input_callbacks=[recorder],
+    )
+
+    await call(server, litellm_logging_obj=logging_obj)
+    await call(server, litellm_logging_obj=logging_obj)
+
+    pre_calls: Final = recorder.wait_for("log_pre_api_call", count=2)
+
+    assert_served_natively(server, count=2)
+    for pre_call in pre_calls:
+        assert isinstance(pre_call.kwargs, dict)
+        assert "custom_llm_provider" not in _OBJECT.validate_python(pre_call.kwargs["litellm_params"])
+
+
 @pytest.mark.asyncio
 async def test_pre_api_call_edits_reach_the_provider(server: RecordingServer) -> None:
     class Edit(CustomLogger):