`message_id` value indicating next message not current one?

[xec-abailey]

Been working on a custom langfuse filter and noticed that the message_id metadata entry is not indicating the current message but the next message.

Example:

INLET:

OUTLET:

As you can see, the message_id value that was sent with the initial user message is now the assistant's message id on outlet. It's unclear to me why this is the case

Thanks!