AgentX: Instructions file for GitHub Copilot

C# / .NET Instructions

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Skill: .github/skills/languages/csharp/SKILL.md

Key Rules

• Use file-scoped namespaces
• Use primary constructors where appropriate (.NET 8+)
• Prefer record for DTOs and immutable types
• Enable nullable reference types (<Nullable>enable</Nullable>)
• PascalCase for classes/methods/properties, _camelCase for private fields
• Always use Async suffix for async methods
• Use ConfigureAwait(false) in library code
• Never use .Result or .Wait() -- always await
• Catch specific exceptions, re-throw with throw;
• xUnit for tests, Arrange-Act-Assert pattern
• Name tests: MethodName_Scenario_ExpectedResult

Critical Rules (Embedded -- Always Active)

Security

• Validate/sanitize ALL inputs at controller/endpoint boundaries
• Use EF Core parameterized queries or Dapper @param syntax -- NEVER string concatenation
• Secrets via IConfiguration + Azure Key Vault -- NEVER hardcode
• Use [Authorize] attribute on all non-public endpoints

Testing

• 80%+ code coverage required
• Pyramid: 70% unit (xUnit), 20% integration (WebApplicationFactory), 10% e2e
• AAA pattern (Arrange-Act-Assert) in every test
• Use Verify or FluentAssertions for readable assertions

Error Handling

• Catch specific exceptions (InvalidOperationException, ArgumentNullException, etc.)
• Re-throw with throw; (not throw ex;) to preserve stack trace
• Use ILogger<T> with structured logging and correlation IDs
• Implement IAsyncDisposable for async resource cleanup