This week in Cursor + .NET — 6 rules + 1 essay (week ending June 07, 2026)

#csharp #dotnet #ai #cursor

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.

New essays this week

Cursor vs GitHub Copilot for C#/.NET in 2026: which to pay for

Tue 02 Jun · .NET tooling

Real pricing, where each one wins on agentic .NET edits, where each one loses, and a straight verdict on which to pay for.

6 daily senior rules

Rule 24: ValueTask Only When Justified

Sat 06 Jun

ValueTask is a perf optimisation for hot paths that often return synchronously. It is not a drop-in for Task. Cursor swaps them around without thinking. Flag ValueTask returns and ask whether the method is actually mostly synchronous. If not, revert to Task.

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Rule 23: No Bool Flag Parameters

Fri 05 Jun

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

Thu 04 Jun

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

Wed 03 Jun

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

Tue 02 Jun

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

Mon 01 Jun

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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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.