I rewrote an old offline BIP39 seed generator after realizing how many bad design decisions I'd originally made

A couple of month ago I put together a small offline BIP39 seed generator as a personal project. It worked, but after looking at it again recently I realized there were quite a few things I'd do differently today.

Instead of patching the old code, I decided to rewrite it from scratch and focus on keeping the implementation simple, transparent and easy to review.

The current version includes:

• Mandatory OS CSPRNG
• Optional supplemental entropy (manual input, dice rolls and timer jitter)
• HKDF-SHA512 for entropy mixing
• BIP39 checksum validation
• Interactive mnemonic verification
• Built-in self-test
• Automated test suite
• Windows and Linux support
• GitHub Actions CI

I'm deliberately not claiming it's the "most secure" seed generator or anything like that. My goal was to build an offline tool with conservative design choices and code that's straightforward to inspect.

If anyone has experience with BIP39, cryptography or secure software in general, I'd really appreciate a code review or any suggestions for improvement. I'd rather hear criticism now than discover a mistake later.

Repository:
https://github.com/shadowbipnode/Seed-Phrase-Generator-with-Multi-Source-Entropy