Why did the alien-god give us emotions?

The alien-god does not act rationally.... The origin of emotion ultimately seems like the result of random chance.

Emotions are likely as useless as other things the alien-god gave us, things like eyes and livers and kidneys and sex-drives and fight-or-flight responses.

Emotions appear to drive social cooperation at least between mammals. Human partnership with dogs is mediated and cemented by emotions, I think only someone who has spent no time with dogs could disagree with this observation. Emotions and their expressions are common enough between humans and dogs that they probably exist across, at least, a broad swath of mammals.

Just two examples of what emotions get us: 1) pair-bonding leading to effective partnership at raising our extremely needy young, and 2) a nearly irresistibly powerful impetus to get the hell away from scary animals, especially if they surprise us at night. Pretty clearly, both of these are quite useful to our survival and so these emotions would have been developed by natural selection for fitness, just as the kidney's ability to clean blood and they eye's ability to focus would have been.