After feedback on my concept, I began work on my playable prototype. I decided to go with greyboxing in Unreal Engine so that I could program the key mechanics and players could get a preliminary sense on how the complete game will play. This prototype also allows me to receive feedback on the controls, visuals, and other areas relating to game feel, which is important for me to polish. I've attached a video walkthrough of my prototype, where I showcase NPC interaction, moving books between the shelf and the book cart, recognition of a properly complete bookshelf, and a staircase that blocks the book cart. Working on this prototype really helped me figure out my next steps for developing the game, which are building the rest of the library, creating UI, and refining my main mechanics.