### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

## Describe the bug

When calling the LLM interface wrapped by LiteLLM and passing a custom `trace_id` via `extra_body.metadata`, the custom trace ID fails to take effect in Langfuse\. Langfuse still generates a default random trace ID instead of using the manually specified custom `trace_id`\.

I followed the official LiteLLM advanced configuration documentation to set the `trace_id` parameter in metadata, but the configuration does not work as expected\.

### Steps to Reproduce

1. Configure Langfuse callback for LiteLLM and complete environment variable initialization

2. Use the OpenAI client to request the LiteLLM proxy interface

3. Pass custom `trace_id` and`generation_name` via `extra_body.metadata`

4. Check trace records in Langfuse OSS, the custom trace ID is not applied

![](https://private-user-images.githubusercontent.com/31612743/613052496-e370cdbb-df26-4f85-8319-127fbdc8c6f4.png?jwt=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJnaXRodWIuY29tIiwiYXVkIjoicmF3LmdpdGh1YnVzZXJjb250ZW50LmNvbSIsImtleSI6ImtleTUiLCJleHAiOjE3ODI0MzUx…