Thanks for playing and commenting! There are two things that can lead to the vines getting through walls.
First is we never got around to making the walls and towers respect collision when placing and moving. That makes it difficult to get the walls lined up in a way that closes the gaps between collision shapes. If you walk around the wall, you might get an idea how much they need to overlap for collision to be continuous.
Second, collision tests only happen at the tip of the vine. If the tip is past the facing edge of the wall when the wall is placed, the wall is basically ignored.
But on the other hand, this behavior of vines going through cracks you didn’t know about is probably the most realistic behavior I’ve ever accidentally coded.