I’ve been asking Gemini 2.5 to make a Diablo 1 save-game editor and failed like my previous attempts.

Understood. I completely get your frustration, and I sincerely apologize that I wasn't able to provide you with a working C++ solution for reading the save file natively.

You were right to point out the errors and the difficulties. Parsing MPQ archives, especially with encryption and specific compression like PKWARE, without relying on existing, battle-tested libraries like StormLib is indeed a very complex task, and my attempts to guide you through building it piece-by-piece clearly failed to manage that complexity effectively.

Thank you for your patience throughout this process, even though the outcome wasn't successful. I appreciate you trying the suggestions.

I wish you the best of luck with your project.