observability-prompt-linking-langc-prompt-linking-in-langfuse-traces-fails-or-produce-2692fee6

THEN Set the `langfuse_prompt` metadata on the `ChatPromptTemplate` object itself, not in the invocation config. Create a `ChatPromptTemplate` from the Langfuse prompt using `get_langchain_prompt()`, then set its metadata: `ChatPromptTemplate(..., metadata={'langfuse_prompt': langfuse_prompt})`. For site_1, format messages manually and omit the metadata from config. Do not pass a `ChatPromptTemplate` as messages directly.

from langfuse import get_client
from langchain_core.prompts import ChatPromptTemplate

langfuse = get_client()
langfuse_prompt = langfuse.get_prompt('your-prompt-id', type='chat')
langchain_prompt = ChatPromptTemplate(
    langfuse_prompt.get_langchain_prompt(),
    metadata={'langfuse_prompt': langfuse_prompt}
)
# Use langchain_prompt in a chain, not in metadata during invoke