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fix: add CONTROL_FLOW_EXCEPTION_TYPES check to on_tool_error, on_retriever_error, and on_llm_error #1514

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fix: add CONTROL_FLOW_EXCEPTION_TYPES check to on_tool_error, on_retriever_error, and on_llm_error #1514

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fix: add CONTROL_FLOW_EXCEPTION_TYPES check to on_tool_error, on_retr…
vishnumishra Feb 9, 2026
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Merge branch 'main' into fix/control-flow-exception-check-in-error-ha…
vishnumishra Feb 9, 2026
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fix: use DEFAULT level and preserve status_message for control-flow e…
vishnumishra Feb 9, 2026
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Merge branch 'main' into fix/control-flow-exception-check-in-error-ha…
vishnumishra Feb 9, 2026
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vishnumishra Feb 17, 2026
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35 changes: 29 additions & 6 deletions langfuse/langchain/CallbackHandler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -255,12 +255,20 @@ def on_retriever_error(
self._log_debug_event(
"on_retriever_error", run_id, parent_run_id, error=error
)
if any(isinstance(error, t) for t in CONTROL_FLOW_EXCEPTION_TYPES):
level = None
else:
level = "ERROR"
Comment on lines +256 to +259
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@greptile-apps greptile-apps Bot Feb 9, 2026

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Control-flow errors lose status

When error is a LangGraph control-flow exception, this sets level=None and also clears status_message (status_message=str(error) if level else None). That removes any indication in the observation that the run ended due to an interrupt/command, which makes these observations look “successfully ended” but empty. If the goal is only to avoid ERROR, consider keeping a non-error status message (or setting a neutral level like "DEFAULT") so users can still see why the run stopped.

Also appears in on_tool_error and on_llm_error (CallbackHandler.py:814-830, CallbackHandler.py:1016-1032).

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@vishnumishra vishnumishra Feb 9, 2026 •
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A user looking at traces can't distinguish between "tool completed normally" and tool was interrupted for human-in-the-loop

However, this is the exact same pattern on_chain_error already uses (line 583-596), which has been shipping and working. So the behavior is consistent across all four handlers

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You're right that this is a real UX problem. When we set level=None and status_message=None, control-flow interruptions become invisible in traces.

Looking at the code, I can see that on_chain_error (lines ~583-605) sets both level=None AND clears the status message for control-flow exceptions:

status_message=str(error) if level else None  # ← This clears the message when level=None!

This PR applies the same pattern to on_tool_error, on_retriever_error, and on_llm_error, which means control-flow interruptions will have no visible status indication in traces.

The problem: Users can't distinguish between:

  1. Tool completed successfully → level=None, status_message=None
  2. Tool interrupted for human-in-the-loop → level=None, status_message=None (same!)

Suggested fix: Keep the status message but use a neutral level like "DEFAULT" or "WARNING" instead of None, so the interruption reason is visible but not marked as an error:

if any(isinstance(error, t) for t in CONTROL_FLOW_EXCEPTION_TYPES):
    level = "DEFAULT"
    status_message = f"Control flow: {str(error)}"
else:
    level = "ERROR"
    status_message = str(error)

observation = self._detach_observation(run_id)

if observation is not None:
    observation.update(
        level=cast(
            Optional[Literal["DEBUG", "DEFAULT", "WARNING", "ERROR"]],
            level,
        ),
        status_message=status_message,
        ...
    )

This preserves visibility of interrupts/handoffs while avoiding the red ERROR badge. The same pattern should be applied to on_chain_error for consistency across all error handlers.

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@vishnumishra vishnumishra Feb 9, 2026 •
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I have updated the PR, with the required changes.


observation = self._detach_observation(run_id)

if observation is not None:
observation.update(
level="ERROR",
status_message=str(error),
level=cast(
Optional[Literal["DEBUG", "DEFAULT", "WARNING", "ERROR"]],
level,
),
status_message=str(error) if level else None,
input=kwargs.get("inputs"),
cost_details={"total": 0},
).end()
Expand Down Expand Up @@ -803,12 +811,20 @@ def on_tool_error(
) -> Any:
try:
self._log_debug_event("on_tool_error", run_id, parent_run_id, error=error)
if any(isinstance(error, t) for t in CONTROL_FLOW_EXCEPTION_TYPES):
level = None
else:
level = "ERROR"

observation = self._detach_observation(run_id)

if observation is not None:
observation.update(
status_message=str(error),
level="ERROR",
level=cast(
Optional[Literal["DEBUG", "DEFAULT", "WARNING", "ERROR"]],
level,
),
status_message=str(error) if level else None,
input=kwargs.get("inputs"),
cost_details={"total": 0},
).end()
Expand Down Expand Up @@ -997,13 +1013,20 @@ def on_llm_error(
) -> Any:
try:
self._log_debug_event("on_llm_error", run_id, parent_run_id, error=error)
if any(isinstance(error, t) for t in CONTROL_FLOW_EXCEPTION_TYPES):
level = None
else:
level = "ERROR"

generation = self._detach_observation(run_id)

if generation is not None:
generation.update(
status_message=str(error),
level="ERROR",
level=cast(
Optional[Literal["DEBUG", "DEFAULT", "WARNING", "ERROR"]],
level,
),
status_message=str(error) if level else None,
input=kwargs.get("inputs"),
cost_details={"total": 0},
).end()
Expand Down