It turns out password managers are tricky things, and even well known tools have bugs: washingtonpost.com/technology/2019...
Attempting to create one has unique challenges & covers a lot of ground, as you have noted, a brave effort :)
An interesting thing that happens in the security community is actively applying Kirchoff's Principle - submitting designs & code for review and cryptanalysis by others to find and fix the inevitable bugs before they have serious consequences, those who don't do this are usually viewed with some suspicion: selling snake oil perhaps; hiding flaws or backdoors for others to exploit. I would encourage you to do the same if you can - show us the source and we can provide more feedback :)
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