fix(langfuse_otel): keep a caller trace user that the metadata mapping already wrote in its logged form

litellm/integrations/langfuse/langfuse_otel.py

@@ -267,7 +267,8 @@ class LangfuseOtelLogger(OpenTelemetry):
     def _set_trace_user_attribute(span: Span, kwargs: Mapping[str, object]) -> None:
         caller: Final = caller_trace_controls(kwargs).user_id
         if caller is not None:
-            safe_set_attribute(span, LangfuseSpanAttributes.TRACE_USER_ID.value, caller)
+            if caller != LangfuseOtelLogger._mapped_caller_trace_user_id(kwargs):
+                safe_set_attribute(span, LangfuseSpanAttributes.TRACE_USER_ID.value, caller)
             return
         slp: Final[Mapping[str, object]] = as_str_mapping(kwargs.get("standard_logging_object")) or MappingProxyType({})
         slp_metadata: Final[Mapping[str, object]] = as_str_mapping(slp.get("metadata")) or MappingProxyType({})
@@ -279,6 +280,13 @@ class LangfuseOtelLogger(OpenTelemetry):
         if end_user:
             safe_set_attribute(span, LangfuseSpanAttributes.TRACE_USER_ID.value, str(end_user))
 
+    @staticmethod
+    def _mapped_caller_trace_user_id(kwargs: Mapping[str, object]) -> str | None:
+        """The caller trace user that `_set_metadata_attributes` already wrote from the header or `metadata`."""
+        request: Final[Mapping[str, object]] = as_str_mapping(kwargs.get("litellm_params")) or MappingProxyType({})
+        mapped_sources: Final = {key: request.get(key) for key in ("metadata", "proxy_server_request")}
+        return caller_trace_controls({"litellm_params": mapped_sources}).user_id
+
     @staticmethod
     def _get_langfuse_otel_host() -> str | None:
         """

tests/integration/observability/test_langfuse_otel_identity_edges.py

@@ -150,7 +150,7 @@ def test_langfuse_otel_list_body_user_does_not_crash(gateway: Gateway, tmp_path:
         _subsequent_request_still_lands(candidate, collector, batches, model)
 
 
-def test_langfuse_otel_integer_trace_user_id_does_not_crash(gateway: Gateway, tmp_path: Path) -> None:
+def test_langfuse_otel_integer_trace_user_id_keeps_its_integer_form(gateway: Gateway, tmp_path: Path) -> None:
     marker: Final = uuid.uuid4().hex
     with (
         wire_server(lambda request: _upstream_reply_for(request, _marker_from_body(request))) as provider,
@@ -163,11 +163,26 @@ def test_langfuse_otel_integer_trace_user_id_does_not_crash(gateway: Gateway, tm
         assert response.status_code == 200, response.text
         batches: Final[list[bytes]] = []
         attributes: Final = _await_generation(collector, batches, marker)
-        assert attributes.get("user.id") in ("123", f"end-user-{marker}"), attributes
-        assert attributes.get("session.id") is None, attributes
+        assert _identity(attributes) == {"user.id": 123, "session.id": None}, attributes
         _subsequent_request_still_lands(candidate, collector, batches, model)
 
 
+def test_langfuse_otel_list_trace_user_id_keeps_its_json_form(gateway: Gateway, tmp_path: Path) -> None:
+    marker: Final = uuid.uuid4().hex
+    with (
+        wire_server(lambda request: _upstream_reply_for(request, _marker_from_body(request))) as provider,
+        wire_server(_sink) as collector,
+        _langfuse_proxy(gateway, tmp_path, collector.url) as candidate,
+        candidate.scenario() as scenario,
+    ):
+        model: Final = scenario.model(model="openai/gpt-4o-mini", api_base=provider.url + "/v1")
+        response: Final = _end_user_request(candidate, model, marker, metadata={"trace_user_id": ["caller-1"]})
+        assert response.status_code == 200, response.text
+        batches: Final[list[bytes]] = []
+        attributes: Final = _await_generation(collector, batches, marker)
+        assert _identity(attributes) == {"user.id": '["caller-1"]', "session.id": None}, attributes
+
+
 def test_langfuse_otel_null_metadata_still_maps_the_end_user(gateway: Gateway, tmp_path: Path) -> None:
     marker: Final = uuid.uuid4().hex
     with (

tests/unit/integrations/test_langfuse_otel.py

@@ -1137,6 +1137,24 @@ class TestLangfuseOtelTraceIdentity:
         identity, _ = self._identity(self._kwargs(slp_metadata={"user_api_key_user_id": "internal-1"}))
         assert identity == {"user.id": None, "session.id": None}
 
+    def test_non_string_caller_trace_user_id_keeps_its_metadata_form(self):
+        listed, _ = self._identity(
+            self._kwargs(
+                slp_metadata={"user_api_key_end_user_id": "end-1"},
+                request_metadata={"trace_user_id": ["caller-1"]},
+            )
+        )
+        numbered, _ = self._identity(
+            self._kwargs(
+                slp_metadata={"user_api_key_end_user_id": "end-1"},
+                request_metadata={"trace_user_id": 123},
+            )
+        )
+        assert (listed, numbered) == (
+            {"user.id": '["caller-1"]', "session.id": None},
+            {"user.id": 123, "session.id": None},
+        )
+
     def test_logged_end_user_lands_in_user_id_without_a_metadata_copy(self):
         identity, _ = self._identity(self._kwargs(slp_extra={"end_user": "end-1"}))
         assert identity == {"user.id": "end-1", "session.id": None}