Function run_agent_loop 

pub async fn run_agent_loop(
    prompts: Vec<AgentMessage>,
    context: AgentContext,
    config: AgentLoopConfig,
    emit: Arc<dyn AgentEmitter>,
    stream_fn: StreamFn,
) -> Result<NewMessages, AgentError>

Run an agent loop starting from a new prompt. Mirrors TS runAgentLoop.

Emits agent_start, turn_start, then message_start/message_end for each prompt, then drives [run_loop]. Returns the messages produced.