Function agent_loop_continue 

pub fn agent_loop_continue(
    messages: Vec<AgentMessage>,
    system_prompt: String,
    config: AgentLoopConfig,
    cancellation_token: CancellationToken,
) -> Pin<Box<dyn Stream<Item = AgentEvent> + Send>>

Resume an agent loop from existing messages.

Resumes from existing messages (no new prompt), calls the loop. Returns a stream of AgentEvent values.