Function execute_shell_with_capture 

pub async fn execute_shell_with_capture(
    env: &Arc<dyn ExecutionEnv>,
    command: &str,
    options: ShellCaptureOptions<'_>,
) -> Result<ShellCaptureResult, ExecutionError>

Mirrors executeShellWithCapture. Drives env.exec with on_stdout/on_stderr callbacks that fold into [CaptureState], spills to a temp file in a post-stream pass, and returns the terminal ShellCaptureResult.