Function resolve_call_output_path_at 

pub(crate) fn resolve_call_output_path_at(
    history: &[Message],
    call_id: &str,
    base: impl FnOnce() -> PathBuf,
) -> Option<PathBuf>

resolve_call_output_path with the base named, so the composition can be exercised against a scratch tree without writing the process env.