> Would HN ever agree on a OS-level app-detection API for the browser? Never.

There already is one. It just asks the user whether it's okay before it tells the website, as you acknowledged: https://news.ycombinator.com/item?id=47664546

What you're arguing for is not good UX. It's lack of user privacy & control. You just think you're being hip or whatever for being blasé about it.

> There *already( is one. It just asks the user whether it's okay before it tells the website

The current implementation defines a way to launch (w/ the user's approval) but it lacks any signaling of success or failure of the request. Without such feedback, it falls short of being a detection API.