Copilot instructions

1---
2description: 'C# and .NET specific coding instructions for production code.'
3applyTo: '**.cs, **.csx'
4---
5 
6# C# / .NET Instructions
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8> Auto-loads when editing C# files. For comprehensive standards, load the skill.
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10**Skill**: [.github/skills/languages/csharp/SKILL.md](../skills/languages/csharp/SKILL.md)
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12## Key Rules
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14- Use file-scoped namespaces
15- Use primary constructors where appropriate (.NET 8+)
16- Prefer `record` for DTOs and immutable types
17- Enable nullable reference types (`<Nullable>enable</Nullable>`)
18- PascalCase for classes/methods/properties, _camelCase for private fields
19- Always use `Async` suffix for async methods
20- Use `ConfigureAwait(false)` in library code
21- Never use `.Result` or `.Wait()` -- always await
22- Catch specific exceptions, re-throw with `throw;`
23- xUnit for tests, Arrange-Act-Assert pattern
24- Name tests: `MethodName_Scenario_ExpectedResult`
25 
26## Critical Rules (Embedded -- Always Active)
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28### Security
29- Validate/sanitize ALL inputs at controller/endpoint boundaries
30- Use EF Core parameterized queries or Dapper `@param` syntax -- NEVER string concatenation
31- Secrets via `IConfiguration` + Azure Key Vault -- NEVER hardcode
32- Use `[Authorize]` attribute on all non-public endpoints
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34### Testing
35- 80%+ code coverage required
36- Pyramid: 70% unit (`xUnit`), 20% integration (`WebApplicationFactory`), 10% e2e
37- AAA pattern (Arrange-Act-Assert) in every test
38- Use `Verify` or `FluentAssertions` for readable assertions
39 
40### Error Handling
41- Catch specific exceptions (`InvalidOperationException`, `ArgumentNullException`, etc.)
42- Re-throw with `throw;` (not `throw ex;`) to preserve stack trace
43- Use `ILogger<T>` with structured logging and correlation IDs
44- Implement `IAsyncDisposable` for async resource cleanup
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