Function build_agent 

pub async fn build_agent(
    intent: &str,
    generator: &dyn TurnGenerator,
    executor: &WorktreeExecutor,
    cfg: &BuildAgentConfig,
) -> BuildAgentOutcome

Generate an agent spec from intent, run its scenarios, and repair until they pass. Tool names the model invents that aren’t in available_tools are dropped (the allowlist can only contain real tools).