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fix(langchain): propagate run name as trace name #1743

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fix(langchain): propagate run name as trace name #1743

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2 changes: 1 addition & 1 deletion langfuse/langchain/CallbackHandler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -594,7 +594,7 @@ def on_chain_start(
session_id=parsed_trace_attributes.get("session_id", None),
tags=parsed_trace_attributes.get("tags", None),
metadata=parsed_trace_attributes.get("metadata", None),
trace_name=parsed_trace_attributes.get("trace_name", None),
trace_name=parsed_trace_attributes.get("trace_name", span_name),

@greptile-apps greptile-apps Bot Jul 8, 2026

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P2 When serialized carries no name information and the name kwarg is absent, get_langchain_run_name returns the sentinel string "<unknown>". With this change, "<unknown>" will now be propagated as the explicit trace name (it is non-None, so propagate_attributes won't filter it out and will write it into the OTel context). Before this PR the None default caused the trace_name attribute to be omitted entirely. Consider guarding against the sentinel so the pre-existing "no-name" behaviour is preserved for that edge case.

Suggested change
trace_name=parsed_trace_attributes.get("trace_name", span_name),
trace_name=parsed_trace_attributes.get(
"trace_name",
span_name if span_name != "<unknown>" else None,
),
Prompt To Fix With AI 
This is a comment left during a code review.
Path: langfuse/langchain/CallbackHandler.py
Line: 597

Comment:
When `serialized` carries no name information and the `name` kwarg is absent, `get_langchain_run_name` returns the sentinel string `"<unknown>"`. With this change, `"<unknown>"` will now be propagated as the explicit trace name (it is non-`None`, so `propagate_attributes` won't filter it out and will write it into the OTel context). Before this PR the `None` default caused the `trace_name` attribute to be omitted entirely. Consider guarding against the sentinel so the pre-existing "no-name" behaviour is preserved for that edge case.

```suggestion
                    trace_name=parsed_trace_attributes.get(
                        "trace_name",
                        span_name if span_name != "<unknown>" else None,
                    ),
```

How can I resolve this? If you propose a fix, please make it concise.

)

root_run_state = self._get_root_run_state(run_id)
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23 changes: 22 additions & 1 deletion tests/unit/test_langchain.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
import importlib
from contextvars import copy_context
from unittest.mock import patch
from unittest.mock import MagicMock, patch
from uuid import uuid4

import pytest
Expand Down Expand Up @@ -276,6 +276,27 @@ def test_root_chain_exports_when_end_runs_in_copied_context(
otel_context.detach(context_token)


def test_root_chain_propagates_run_name_as_default_trace_name():
handler = CallbackHandler()
run_id = uuid4()
propagation_context_manager = MagicMock()

with patch.object(
callback_handler_module,
"propagate_attributes",
return_value=propagation_context_manager,
) as mock_propagate:
handler.on_chain_start(
{"id": ["langgraph", "Pregel"]},
{"messages": ["hello"]},
run_id=run_id,
name="my-agent",
)

mock_propagate.assert_called_once()
assert mock_propagate.call_args.kwargs["trace_name"] == "my-agent"


def test_control_flow_errors_use_default_level_and_keep_status_message(
langfuse_memory_client, get_span, monkeypatch
):
Expand Down