Agent Instructions

Language and Framework

This project uses C# 14 and .NET 10. Always prefer features from these versions over older alternatives.

Code Style

Always use extension blocks over extension methods. Lines must never exceed 80 characters. Each class must be in its own file. Prefer primary constructors over traditional constructors. Always use init over set for properties. Always use is null and is not null instead of == null and != null.

For record declarations, each parameter must be on its own line with the opening parenthesis alone on the first line:

public record ItemDto(
    int Id,
    string Name,
    string Description);

For method declarations and calls with more than one parameter, the first parameter stays on the same line as the method name. Each additional parameter goes on its own line:

public Task<ItemDto?> UpdateAsync(int id,
    ItemDto item);

logger.LogExceptionInMiddleware(ex.Message,
    ex);

For HTTP handler return types, expand generic type arguments onto separate indented lines:

private static async Task<
    Results<
        Ok<ItemDto>,
        NotFound>
    > UpdateItem(int id,
    UpdateItemRequest request,
    IItemService service)

Method chaining is fine when each call is short and reads naturally. When chains are long, break each call onto its own line:

var result = items
    .Where(x => x.IsActive)
    .OrderBy(x => x.Name)
    .Select(x => new ItemDto(x.Id, x.Name));

Locals

Always use var for local variables. The editorconfig enforces csharp_style_var_elsewhere = true:warning, which combined with TreatWarningsAsErrors makes explicit types a build error for locals.

Usings

Never add using directives at the top of individual C# files. Always add them to GlobalUsings.cs instead.

DTOs

DTOs must be records and placed in the Dtos directory. Never use default parameter values in records. The multi-parameter rule applies — each property on its own line regardless of count:

public record ItemDto(
    int Id,
    string Name,
    string Description);