Thank you!
I looked at all the footage of the demo that I could find, and replicated it in my "demake" (I don't think it's technically a demake lol). I never saw anyone unlock that door so yes, it's intentional. I also don't think I saw anyone use any charms or upgrade the nail. And I felt the demake was too small for upgrades to really make sense to implement. As for other missing features such as abilities (I think the silk spear at least was in the demo), I simply didn't feel like implementing them lol. If you're thinking of audio too, I tried making some sound effects with some free online tool, but it just didn't sound right and I gave up.