angular-ui/ui-router ? reverse-engineered prompt

Build me an AngularJS routing library for single page apps that makes navigation feel simple and flexible.

I want app pages to be organized as a tree of states, so I can define nested views, move between states, and have the browser URL stay in sync with what the user is seeing. It should support deep linking, so someone can bookmark or share a URL and land right on the right screen. I also want state transitions to feel reliable, like a controlled switch from one app view to another, instead of a bunch of fragile route rules.

Please set it up so it works as a reusable client side library for AngularJS 1.x, with clear documentation or examples for getting started. If you need to check current docs or best practices online while building it, go ahead.