Add Copilot repository instructions

[Copilot]

Why make this change?

Per GitHub best practices, Copilot coding agent uses .github/copilot-instructions.md to understand repository context, conventions, and workflows. Without this, the agent lacks project-specific knowledge for optimal assistance.

What is this change?

Created .github/copilot-instructions.md containing:

• Project context: .NET 8 C# service supporting 6 database types (SQL Server, PostgreSQL, MySQL, Cosmos DB, etc.)
• Build/test commands: Database-specific test categories, dotnet format requirements, schema setup
• Code conventions: 4-space indent, LF endings, dotnet format enforcement, SQL query formatting per engine
• Security patterns: @env() syntax for connection strings, never commit secrets
• Project structure: Core/Auth/CLI/Service/GraphQLBuilder organization
• Common workflows: Config generation, local development setup, CLI usage

Key details for AI assistance:

• Integration tests require specific database schemas from src/Service.Tests/DatabaseSchema-<engine>.sql
• Config files use JSON with @env('var_name') for secrets
• Different SQL formatters per database engine (sqlformat.org for Postgres, poorsql.com for SQL Server/MySQL)

How was this tested?

• N/A - Documentation only, no code changes

Sample Request(s)

• N/A - Documentation only, no runtime behavior changes

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>

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

• Fixes ✨ Set up Copilot instructions #3089

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[Copilot]

Pull request overview

This PR adds comprehensive Copilot instructions to help GitHub Copilot understand the Data API builder (DAB) repository structure, conventions, and workflows. The new .github/copilot-instructions.md file provides detailed guidance about the .NET 8 C# service that supports 6 database types, build/test commands, code conventions, security practices, and common development workflows.

Changes:

• Added .github/copilot-instructions.md with comprehensive repository documentation including project overview, structure, build/test procedures, code style guidelines, and development workflows

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💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The API Types list includes "MCP" but the main README.md (lines 37-39) indicates MCP is "Coming soon" and not yet supported. While there is MCP code in the repository (src/Azure.DataApiBuilder.Mcp and tests in src/Service.Tests/Mcp), the documentation should be consistent. Either this should say "MCP (experimental)" or "MCP (preview)" or align with the official status in README.md.

[Copilot]

Inconsistent capitalization in section header. The previous two section headers are "### REST API" and "### GraphQL API" (with "API" capitalized), so this should be either "### MCP API" or maintain the pattern with "MCP Tools" as a distinct section name. Consider changing to "### MCP API" or "### MCP Tools" (capital T) for consistency.

Suggested change

	### MCP tools
	### MCP Tools

[Aniruddh25]

/azp run

[azure-pipelines]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.