fix(langchain): token detach exceptions in async contexts

[hassiebp]

Important

Fixes token detachment exceptions in async contexts in CallbackHandler.py by modifying _detach_observation() and introducing _get_parent_observation() for improved observation handling.

• Behavior:
  • Fixes token detachment exceptions in async contexts by modifying _detach_observation() in CallbackHandler.py to use _RUNTIME_CONTEXT.detach() and handle exceptions.
  • Introduces _get_parent_observation() to retrieve parent observation, used in on_chain_start(), on_tool_start(), on_retriever_start(), and __on_llm_action().
• Functions:
  • Replaces self.client.start_observation() with self._get_parent_observation(parent_run_id).start_observation() in on_chain_start(), on_tool_start(), on_retriever_start(), and __on_llm_action().
• Imports:
  • Adds import for _RUNTIME_CONTEXT from opentelemetry.context and Langfuse from langfuse._client.client.

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Disclaimer: Experimental PR review

Greptile Summary

Updated On: 2025-09-01 14:56:28 UTC

This PR fixes critical issues with LangChain async callback handling in the Langfuse Python SDK, specifically addressing token detach exceptions and observation nesting problems in async contexts like LangGraph.

The changes introduce two key improvements to the CallbackHandler.py file:

1. Proper Parent-Child Observation Relationships: A new _get_parent_observation() helper method is added that correctly resolves parent observations for nested tracing scenarios. Instead of always attaching child observations to the root client, this method checks if a parent run ID exists in the self.runs dictionary and returns the appropriate parent observation. This ensures that traces maintain proper hierarchical structure rather than appearing as flat, disconnected observations.

2. Safer Context Token Detaching: The token detaching logic is enhanced with exception handling that directly uses _RUNTIME_CONTEXT.detach() instead of relying on OpenTelemetry's context management. This prevents exceptions that commonly occur in async scenarios where context tokens are created in one async task/thread but detached in another.

These changes integrate with Langfuse's existing tracing infrastructure by maintaining compatibility with all observation types (LangfuseAgent, LangfuseChain, LangfuseGeneration, etc.) while fixing the async context issues that were causing runtime errors. The solution preserves tracing data integrity while eliminating exceptions that were disrupting async LangChain workflows.

PR Description Notes:

• The PR description is missing entirely (null), which makes it difficult to understand the context and rationale for these changes without examining the code diff directly.

Confidence score: 4/5

• This PR addresses well-defined async context issues with targeted fixes that maintain backward compatibility
• Score reflects solid technical approach but lacks comprehensive testing evidence and proper PR documentation
• Pay close attention to the new parent observation resolution logic and exception handling in async contexts

Context used:

Rule - Open a GitHub issue or discussion first before submitting PRs to explain the rationale and necessity of the proposed changes, as required by the contributing guide. (link)

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