Function drain_formatted 

pub fn drain_formatted<Attachment>(
    buffer: &InterjectionBuffer<Attachment>,
    sanitize_text: impl Fn(String) -> String,
) -> Vec<FormattedInterjection<Attachment>>

Drain buffer, framing each entry as a synthetic user message (FIFO, one message per entry, never merged). sanitize_text runs on the raw text first (hosts strip artifacts like image placeholder paths; pass std::convert::identity if none).