Function call 

pub async fn call(
    name: &str,
    agent: Arc<dyn TextAgent>,
    state: &State,
) -> Result<String, AgentError>

Invoke agent synchronously: run it to completion, write its result to {name}:result (or its error to {name}:error), and return the result.

This is the Mode::Call lowering. It uses the same {name}:result convention as BackgroundAgentDispatcher::dispatch, so sync and async invocations are observed identically.