I recently encountered the sentence 「あなたに嬉しくなって欲しい」, which means “I want you to be happy.” Why is に used to mark “you”? If you rephrase the sentence as 「あなたが嬉しくなることが欲しい」, the meaning still comes through but the に drops out. So why is the に used in the first variation? Do similar patterns exist for Vstemたい and/or other adjectives?
Think of て欲しい as a version of てもらいたい. For example:
"I want my teacher to teach me calculus." Or more literally, "I want to receive the favor of my teacher teaching me calculus."
The person doing the favor is marked with に. Same with て欲しい. In both of these expressions, you're probably not used to seeing the "giver" marked with a particle, because they're more often just addressed directly to that person.