The harness

for step in 0..max_steps() {
    let response = llm.chat(&messages, &schemas, &notify, &on_delta).await?;

    if response.tool_calls.is_empty() {
        let checks = verify::run(engine, question, &response.content, &evidence);
        return Ok(finish_with(
            engine, response.content, evidence, usage, checks, emit,
        ));
    }

    messages.push(ChatMessage::Assistant {
        content: response.content.clone(),
        tool_calls: response.tool_calls.clone(),
    });

    // The production code handles exact duplicates separately, then joins
    // non-duplicate calls and stitches them back into call order.
    let outcomes = join_all(
        response
            .tool_calls
            .iter()
            .map(|call| run_tool_call(engine, registry, call)),
    )
    .await;

    for (call, (item, llm_text)) in response.tool_calls.iter().zip(outcomes) {
        emit(AskEvent::ToolEnd { item: Box::new(item.clone()) });
        evidence.push(item);
        messages.push(ChatMessage::Tool {
            call_id: call.id.clone(),
            name: call.name.clone(),
            content: llm_text,
        });
    }

    trim_history(&mut messages);
}