runner-images/.github/copilot-instructions.md

GitHub Copilot Instructions for Actions Runner Images Repository

Scope and goals

• This repository serves as the source for building GitHub Actions runner and Azure DevOps agent images for Windows, Ubuntu, and macOS. You can find exact versions in the Available Images section of README.md. Windows and Ubuntu images build on Azure infrastructure using Packer; macOS images use Anka virtualization.
• Emphasize best practices for contributing to open-source projects, including code style, commit messages, and pull request etiquette.
• Prefer clarity and correctness over creativity. If information is missing, ask clarifying questions or insert TODOs instead of guessing.

Code and command instructions

• Follow the code style guide in CONTRIBUTING.md for Bash and PowerShell scripts, including naming conventions, file structure, and indentation rules.
• Focus on re-using helpers when writing scripts. Windows, Linux and Ubuntu scripts have helper functions available to simplify installation and validation.
• Always confirm versions and installation paths against existing toolset files and installation scripts.

Output format

• Use GitHub Flavored Markdown only. Avoid raw HTML unless necessary.
• One H1 (#) per page, followed by logical, sequential headings (##, ###, …).
• Use fenced code blocks with language identifiers (```bash, ```json, ```yaml, etc.).
• Use blockquote callouts for notes:

  [!NOTE] Context or nuance
  [!TIP] Helpful hint
  [!WARNING] Risks or breaking changes
  [!IMPORTANT] Critical requirement for functionality

Style and tone

• Audience: Open-source contributors, GitHub Actions maintainers, and developers building custom runner images. Assume familiarity with CI/CD concepts, Packer, and basic infrastructure provisioning, but explain platform-specific details (Azure for Windows/Ubuntu, Anka for macOS) when relevant.
• Voice: Second person ("you"), active voice, imperative for operational steps.
• Be concise: short paragraphs and sentences. Prefer lists and step-by-steps, especially for operational procedures and troubleshooting.
• Use inclusive, accessible language. Avoid idioms, sarcasm, and culturally specific references.
• English: en-US (spelling, punctuation, and units).

Safety and integrity

• Do not expose sensitive credentials (API tokens, Azure subscription IDs, etc.) in code examples.
• Do not fabricate tool versions, installation paths, or software availability without verifying against toolset files or actual installation scripts.
• Always call out assumptions and limitations explicitly, especially for changes affecting runner image behavior or software availability.
• If ambiguous requests are made about image modifications, ask clarifying questions about target OS, tool versions, and compatibility requirements before proceeding.