Add GitHub Copilot instructions

[Copilot]

Configures repository-level instructions for GitHub Copilot as per best practices, while preserving existing AGENTS.md documentation.

Changes

• Added .github/copilot-instructions.md: Provides quick-reference guidance for Copilot including:

  • Technology stack (C#/.NET 10.0, ASP.NET Core Minimal APIs, NUnit)
  • Essential build/test commands
  • Key code conventions (3-space indentation, _camelCase private fields, snake_case test methods)
  • Repository-specific patterns (OAuth2 grant type handlers, endpoint organization)
  • Reference to custom C# Expert agent

• Preserved AGENTS.md: Existing comprehensive guidelines remain unchanged. New Copilot instructions reference this file for detailed specifications.

The instructions file acts as a concise entry point for Copilot while maintaining the detailed AGENTS.md as the canonical reference for contributors.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• gh.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>✨ Set up Copilot instructions</issue_title>
<issue_description>Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository.

</issue_description>

<agent_instructions>The repo already has an AGENTS.md file, can this be preserved as much as possible?</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes ✨ Set up Copilot instructions #60

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