handleChainStart in createLangChainCallbackHandler only read 4 of the 8 parameters
LangChain passes to the callback. The 8th argument, runName, carries the actual
node/run name (e.g. LangGraph node names), but the implementation never reached it.
chain.name is not a standard property on LangChain's Serialized type and is always
undefined, so every chain span fell back to 'unknown_chain' regardless of what the
actual chain or node was named.
The fix expands the signature to accept all 8 parameters and uses runName as the first
fallback before chain.name:
const chainName = runName || chain.name || 'unknown_chain';
This matches how handleLLMStart and handleChatModelStart already handle their
equivalent runName parameter (accepted but currently unused — chain spans are the
most impactful case since LangGraph passes node names there).
Note
The pull request "fix(langchain): use runName argument in handleChainStart to fix unknown_chain spans" was created by @priscilawebdev but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.
handleChainStartincreateLangChainCallbackHandleronly read 4 of the 8 parametersLangChain passes to the callback. The 8th argument,
runName, carries the actualnode/run name (e.g. LangGraph node names), but the implementation never reached it.
chain.nameis not a standard property on LangChain'sSerializedtype and is alwaysundefined, so every chain span fell back to'unknown_chain'regardless of what theactual chain or node was named.
The fix expands the signature to accept all 8 parameters and uses
runNameas the firstfallback before
chain.name:This matches how
handleLLMStartandhandleChatModelStartalready handle theirequivalent
runNameparameter (accepted but currently unused — chain spans are themost impactful case since LangGraph passes node names there).