ai-agents-prompt-placeholder-h-when-using-langfuse-sdk-s-getlangchainprompt-with--e5ae535d

THEN Update the Langfuse JS/TS SDK to version 4.2.0 or later, which fixes the issue by correctly converting unresolved placeholders to Langchain MessagesPlaceholder objects. If updating is not immediately possible, manually transform the output by mapping objects containing variableName and optional fields to the expected { type: 'placeholder', name: 'variableName' } format 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);