Wow this is pretty fun! The combos started to make sense once I played for a little while. After getting comfortable with the mechanic I started developing strategies like just sending extra carts away even for no points, which was satisfying to figure out. Generally really easy to get what is going on once you remember the combos. It crashed on me a couple of times, but other times I was able to finish games.
Great job! I could imagine playing this on my phone