fix(langchain): set cost to zero on errors

[hassiebp]

Important

Set cost_details to zero on errors in CallbackHandler.py to prevent incorrect cost reporting.

• Error Handling:
  • Set cost_details to {"total": 0} in on_retriever_error(), on_chain_error(), on_tool_error(), and on_llm_error() in CallbackHandler.py to ensure cost is zero on errors.

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Disclaimer: Experimental PR review

Greptile Summary

Updated On: 2025-09-08 11:41:11 UTC

This PR addresses cost calculation handling in the Langchain integration's CallbackHandler when errors occur. The change appears to modify the CallbackHandler.py file to set cost details to zero when exceptions or errors are encountered during LLM operations.

PR Description Notes:

• The PR description is missing, making it difficult to understand the specific issue being addressed or the rationale behind the change
• No linked GitHub issue or discussion is referenced, which goes against the contributing guidelines

The modification likely prevents incorrect cost calculations from being recorded when LLM calls fail, ensuring that failed operations don't contribute misleading cost metrics to traces. This change fits into Langfuse's broader cost tracking functionality by providing more accurate cost attribution when errors occur in Langchain-integrated workflows.

Confidence score: 0/5

• This PR is not ready to merge due to missing context and potential compliance issues
• Score reflects lack of PR description, missing issue reference, and insufficient information to assess the technical implementation
• Pay close attention to the CallbackHandler.py file and require proper documentation before proceeding

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)

[greptile-apps]

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[ellipsis-dev]

Good: cost_details set to {"total": 0} on retriever errors. Consider extracting the literal to a constant if used in multiple error handlers.