ai-agents-langchain-prompt-pla-when-using-getlangchainprompt-with-unresolved-plac-035c73d5

THEN Upgrade to Langfuse JS SDK v4.2.0 or later to fix the output format, or manually transform unresolved placeholder objects to { type: 'placeholder', name: msg.variableName } before passing to ChatPromptTemplate.fromMessages.

const rawMessages = langfusePrompt.getLangchainPrompt();
const fixedMessages = rawMessages.map(msg => {
  if (msg.variableName && typeof msg.optional === "boolean") {
    return { type: "placeholder", name: msg.variableName };
  }
  return msg;
});
const langchainPrompt = ChatPromptTemplate.fromMessages(fixedMessages);