[VS 2026] Go to Definition for tag helpers not working

I was very happy to read in the VS 2026 release notes that there is finally support for Go to Definition for tag helpers.

The [Visual Studio Insiders release notes](https://learn.microsoft.com/en-us/visualstudio/releases/vs18/release-notes-insiders) says:

> Leveraging new capabilities from cohosting, you can now navigate to the definitions of ASP.NET Core MVC Tag Helpers and their attributes directly from Razor files. Hitting F12 (or Ctrl+Click) on a Tag Helper (e.g. an or any MVC Tag Helper usage) will jump to its source definition. This long-requested feature makes it much easier to explore and understand Tag Helpers in your projects.

So I created a new solution (MVC, .NET 10, Identity with individual user accounts), build it, and pressed F12 on `asp-page` in `Hello @User.Identity?.Name!`

But that doesn't work. So I checked the settings and I enabled "Use Roslyn Cohost server for Razor", restarted, and it sill doesn't work.

Added a custom tag helper: still doesn't work.

@davidwengier Am I doing something wrong?