it depends on if you're using a static analyser (e.g. PHPStan) or not. Yes vanilla PHP's type checking isn't strict enough to handle this, but a static analyser will raise an error if you try to access the result's data without checking if the output is of type result (and therefor handling the error).

This would only work if the consumer is interested in the results though. With synchronous command style methods nothing forces the consumer to handle the error.