The site editor has a built-in routing approach that is a bit fragile and hard to scale to the next steps of the Admin Redesign project. It is time to look at it and refactor it to both address its immediate shortcomings (bugs and maintainability) and provide a solid base for the next steps (extensibility, new pages)...

The solution needs to address the following requirements:

• Creating and maintaining routes today is not easy at all. You have to include code in very different places (sidebar routing, multiple sync hooks, and router.js file), we should have a coherent way to define routes.
• There's a lot of bugs when navigating in the site editor due to lingering arguments in the url... Having a consistent API for routing and links will help us address these bugs holistically
• Ultimately, we'd like to split the "routing/shell" of the site editor from its content (the different routes) in order to be able to build multiple site editor like experiences.
• We'd like a simple routing API that we can open later for third-parties (probably starting as a private API as we work through things)