Function publish_chunk 

fn publish_chunk(
    broker: &Broker,
    scope: &str,
    source_block_id: &str,
    request_id: &str,
    event: &AgentEvent,
    done: bool,
)

Publish one EVENT_BTW_ANSWER_CHUNK. See mps::EVENT_BTW_ANSWER_CHUNK’s own doc comment for the payload shape and scope-string contract.