To avoid the binary search making it trivial, maybe just tell you which guesses are correct and which other guesses match a value somewhere, like yellow letters in wordle. I think that would be more interesting but I have only played it in my head so the error margin could be significant. Of the top of my head I would use the lesser digits to search the space systematically while making the major digits match the color as best I could. Still it is fun as is and I have added it to my window of daily puzzle tabs.