[xperiandri]

Summary

This pull request adds instructions and configuration for AI coding agents (GitHub Copilot, Claude Code and others), so that they build, test and change the extension the way the project expects. The extension code and the project files do not change; the only converted file is the solution, which moves from the .sln to the .slnx format (see below).

What is added

• .github/copilot-instructions.md is the single source of the project instructions: the build and test commands, the layout of the repository, how the adornments are created and refreshed, the shared static state that the resource loading touches, and the rules for Visual Studio extensions. It also tells agents to leave the parts that belong to the original author alone: the sponsorship message, the telemetry and the signing of the release build. CLAUDE.md and AGENTS.md point to it.
• .github/agents/vs-extension-expert.agent.md is a custom agent for the extension code (it refers to the instructions and the skills), and .github/prompts/create-pr-description.prompt.md is a prompt that writes pull request descriptions.
• .github/skills/ holds six Visual Studio extension skills (handling-async-threading, handling-extension-errors, adding-editor-adornments, listening-text-view-events, adding-options-settings, handling-solution-events), copied unchanged from madskristensen/vs-agent-plugins at commit e971073e2163d4bc66d3e455e102c316e01c94c6. That repository is licensed under Apache-2.0, and its license text is included next to the skills. .claude/settings.json lets Claude Code offer the whole catalogue of that repository as a plugin.
• .mcp.json lists the GitHub and Microsoft Learn MCP servers. .claude/scripts/github-mcp-headers.ps1 gives the GitHub server the token that Git Credential Manager already stores, because that server does not support the OAuth registration that Claude Code needs. Claude Code asks for approval before it starts a server of a project.
• .github/workflows/copilot-setup-steps.yml restores the packages for the Copilot coding agent. It runs on windows-2022, like the existing build, because the extension targets Visual Studio 2022.
• Directory.Build.targets creates .claude/skills as a junction to .github/skills when Visual Studio loads the project (a command-line build skips it), and .gitignore excludes the junction. .mcp.json and Directory.Build.targets are added to the solution items.

The nine commits can be reviewed one by one.

About the location of the solution

The solution is already in the repository root, which is the layout that Visual Studio needs for .mcp.json: Visual Studio reads the repository-level MCP configuration from the folder of the solution, and Claude Code reads it from the root of the repository.

Why the solution is converted to .slnx

The last commit converts StringResourceVisualizer.sln to StringResourceVisualizer.slnx with dotnet sln migrate. The projects and the solution items are the same, and the file has 11 lines instead of 38. The format is XML, easy to read and edit, and designed to reduce merge conflicts; dotnet new sln creates it by default since .NET 10. The project ids are the ones of the old solution (Visual Studio adds them to a .slnx otherwise).

The price is the tooling: building a .slnx needs the .NET SDK 9.0.200 or later, or MSBuild from Visual Studio or Build Tools 17.13 or later (the minimum that Microsoft states), so a Visual Studio 2022 older than 17.13 cannot open the solution. The build workflow, which used to find the only .sln in the folder by itself, names the new file now, and so do the setup steps and the instructions. The commit is the last one and independent of the others: without it the repository keeps the .sln, and everything else works.

Verification

• A full rebuild before the change and after the last commit, through the .slnx, gives no errors, the same 26 distinct warnings and a VSIX of the same size (4,848,348 bytes). The machine that prepared this change has no .NET Framework 4.8.1 targeting pack, so the build used the MSBuild of Visual Studio 2026 with -p:TargetFrameworkVersion=v4.8.
• The 4 tests pass before and after the change.
• The change does not touch code, so the extension was not run in the Experimental instance.
• CI: the workflows of this repository wait for the approval of a maintainer on this pull request. The same commits ran in a fork: Copilot Setup Steps passes, and Build builds the .slnx on windows-2022, runs the tests and uploads the VSIX, and then fails in its step Publish Test Results: the third-party action EnricoMi/publish-unit-test-result-action/windows@v2 finds no Python interpreter on the image (No python3 interpreter found; the message of the action suggests actions/setup-python). That step fails in the same way on the unchanged code of main (run in the fork), so this change does not cause it, and it is not fixed here.

🤖 Generated with Claude Code

[xperiandri]

Closing in favor of two smaller pull requests with the same content: #53 (.slnx) and #54 (instructions and configuration for AI coding agents, which replaces this pull request). #54 is stacked on #53; the modernization steps that follow are #55 to #58.