This week in Cursor + .NET — 7 rules (week ending September 13, 2026)

A weekly digest from the Agentic Architect persistence kit: 7 senior C#/.NET rules for engineers keeping Cursor honest across sessions.

Every weekday a single, opinionated rule for senior C#/.NET engineers using Cursor. Here's the full week in one read — canonical posts live on the Agentic Architect blog.

7 daily senior rules

Rule 23: No Bool Flag Parameters

Sun 13 Sep

SendEmail(string to, bool isHtml) should be SendHtmlEmail and SendPlainEmail. Bool flags hide branching that belongs in the type system. Flag any method signature with two or more bool parameters as a refactor candidate.

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Rule 22: BackgroundService Over Task.Run

Sat 12 Sep

Long-running work in ASP.NET Core goes in a BackgroundService, not Task.Run inside a controller. Cursor will happily fire Task.Run and call it "async work" — your request thread will die mid-execution and you'll never know why. Catch Task.Run outside test code and propose a hosted service.

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Rule 21: Channels for Producer Consumer

Fri 11 Sep

System.Threading.Channels beats BlockingCollection and beats roll-your-own queue plus SemaphoreSlim. The AI reaches for ConcurrentQueue every time and stitches it together by hand. A rule that detects producer/consumer patterns and proposes Channel will save you a class.

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Rule 20: Source-Generated JSON Serialisation

Thu 10 Sep

Reflection-based System.Text.Json is fine for prototypes. For hot paths and AOT, use JsonSerializable source generation. Cursor never thinks of this on its own — add a rule that flags new DTO classes and asks whether they should be source-generated.

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Rule 19: NetArchTest for Boundaries

Wed 09 Sep

Architectural rules belong in tests, not in code review. Encode them as NetArchTest assertions ("no class in Domain references EntityFrameworkCore") and they fail your build instead of your standup. Add the corresponding test whenever a new layer or project is introduced.

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Rule 18: WebApplicationFactory for Integration Tests

Tue 08 Sep

In-memory EF Core providers lie. Use WebApplicationFactory with Testcontainers (SQL Server, Postgres) for real integration coverage. Cursor defaults to UseInMemoryDatabase — it passes locally and ships the bug to production. Flag the in-memory provider in test projects.

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Rule 17: ConfigureAwait false in Libraries

Mon 07 Sep

Library code (non-ASP.NET) should ConfigureAwait false on every awaited Task. ASP.NET Core code should not. Cursor mixes the two contexts in the same solution. Detect the project type and enforce the right default.

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Try one rule before you trust the whole kit

The free arch-core-lite.mdc is one drop-in Cursor rule that ends the morning re-explanation ritual. Install in 60 seconds, see whether Cursor actually remembers your DI lifetimes, and decide for yourself whether the full kit is worth £9.00.

• Free sample: arch-core-lite.mdc on GitHub
• Full kit (£9.00, one-time): Agentic Architect Kit
• Daily rules feed: https://agentic-architect.dev/blog/

Canonical home for everything in this digest: https://agentic-architect.dev/blog/.