Document automatic migration for project.json in Visual Studio 2026 (#3478)

Author: Copilot

docs/archive/project-json.md

@@ -42,15 +42,35 @@ The [`project.lock.json`](#projectlockjson) file (described below) is also used
 
 ## Migrate project.json to PackageReference
 
-The migration between project.json and PackageReference is straightforward. The easiest way to do it to use the built-in migrator in the latest Visual Studio 2022, Update 14.
+The migration between project.json and PackageReference is straightforward.
+
+### Automatic migration in Visual Studio 2026
+
+Visual Studio 2026 and later automatically migrates project.json projects to PackageReference when you open a solution containing project.json projects.
+The migration happens at solution load time:
+
+1. Open a solution containing project.json projects in Visual Studio 2026 or later.
+1. Visual Studio automatically detects project.json files and migrates them to PackageReference format.
+1. To check migration status, open the [Output Window](/visualstudio/ide/output-window) and select Show output from "Package Manager".
+You should see messages like "Migrating project.json project..." followed by "Migration Succeeded" for each project.
+Any errors will appear in the Error List.
+1. A backup of the original project file and project.json file is created in a `Backup` folder in the root of the project directory.
+1. The migration converts all package dependencies to PackageReference format in the project file.
+
+
+### Manual migration in Visual Studio 2022
+
+For Visual Studio 2022 and earlier, you can use the built-in migrator:
 
 1. Load the project.json project in Visual Studio.
 1. Go to the solution explorer of the project.json project and find the dependencies node.
-1. Click `Migrate project.json to PackageReference...`!
+1. Right-click and select `Migrate project.json to PackageReference...`
 
 ![Migrating from project.json to PackageReference](media/project-json-migrator.png)
 
-Alternatively, you may use the [dotnet migrate](/dotnet/core/tools/dotnet-migrate), or do the migration manually by taking all of the content from the project.json file and replacing it with the equivalent [PackageReference syntax](../consume-packages/Package-References-in-Project-Files.md).
+### Alternative migration methods
+
+Alternatively, you may use the [dotnet migrate](/dotnet/core/tools/dotnet-migrate) command-line tool, or do the migration manually by taking all of the content from the project.json file and replacing it with the equivalent [PackageReference syntax](../consume-packages/Package-References-in-Project-Files.md).
 
 ## Dependencies
 

docs/reference/errors-and-warnings/NU1016.md

@@ -21,9 +21,13 @@ Managing packages with project.json is deprecated. Migrate to PackageReference.
 
 [Migrate your project from project.json to PackageReference](../../archive/project-json.md#migrate-projectjson-to-packagereference).
 
-In Visual Studio 2026 or newer, your project.json project will be automatically migrated.
+**Visual Studio 2026 or later:**
 
-In Visual Studio 2022, you need to use the [built-in migrator](../../archive/project-json.md#migrate-projectjson-to-packagereference).
+Your project.json project will be automatically migrated to PackageReference when you open the solution. Visual Studio will create a backup of the original files in a `Backup` folder in the project directory.
+
+**Visual Studio 2022:**
+
+You need to use the built-in migrator:
 
 1. Open your project.json project in Visual Studio
 1. In Solution Explorer, find the project's Dependencies node