https://agentic-architect.dev/blog/ One practical Cursor + C#/.NET pattern per day. Field notes from building a stateful AI partner for production .NET codebases. en-gb https://agentic-architect.dev/blog/04-cursor-result-not-throw.html https://agentic-architect.dev/blog/04-cursor-result-not-throw.html Thu, 21 May 2026 20:00:00 +0000 Keep Cursor on Result/ErrorOr when your team already rejected throw-based control flow. https://agentic-architect.dev/blog/03-cursor-hallucination-loop-breaker.html https://agentic-architect.dev/blog/03-cursor-hallucination-loop-breaker.html Wed, 20 May 2026 08:00:00 +0000 Break the correction spiral — seven words, or a circuit-breaker .mdc rule. https://agentic-architect.dev/blog/02-scoped-singleton-di-bug.html https://agentic-architect.dev/blog/02-scoped-singleton-di-bug.html Tue, 19 May 2026 08:00:00 +0000 The .NET lifetime bug that ships silently — and the Cursor rule that catches it before merge. https://agentic-architect.dev/blog/01-the-context-tax.html https://agentic-architect.dev/blog/01-the-context-tax.html Mon, 18 May 2026 08:00:00 +0000 The hidden cost senior engineers pay every morning — and a four-rule architecture for eliminating it. https://agentic-architect.dev/blog/#2026-05-20 daily-rule-2026-05-20 Wed, 20 May 2026 09:00:00 +0000 Never let the AI write database logic in your Controllers. Enforce a strict boundary where all IQueryable access stays in the Infrastructure layer. This keeps your business logic "pure" and readable for the LLM. https://agentic-architect.dev/blog/#2026-05-21 daily-rule-2026-05-21 Thu, 21 May 2026 09:00:00 +0000 Every async method in your codebase should accept and forward a CancellationToken. Make it a rule that any new async signature without one is flagged. Stops the AI from quietly losing cancellation half-way down a call chain. https://agentic-architect.dev/blog/#2026-05-22 daily-rule-2026-05-22 Fri, 22 May 2026 09:00:00 +0000 The single most expensive .NET runtime bug: a Singleton holding a Scoped service. Cursor cheerfully writes this without warning. Audit constructor parameters of any class registered as Singleton — if any are typically Scoped (DbContext, repositories, MediatR sender), flag it before merge. https://agentic-architect.dev/blog/#2026-05-23 daily-rule-2026-05-23 Sat, 23 May 2026 09:00:00 +0000 Every read-only EF Core query should call AsNoTracking. Add a rule that recognises query methods returning DTOs (not entities) and inserts the call. Cursor never does this by default and your read perf degrades silently across releases. https://agentic-architect.dev/blog/#2026-05-24 daily-rule-2026-05-24 Sun, 24 May 2026 09:00:00 +0000 throw ex resets the stack trace. throw preserves it. Cursor gets this wrong about 40 percent of the time when generating catch blocks. Rewrite any naked throw ex to throw unless the exception has been explicitly wrapped. https://agentic-architect.dev/blog/#2026-05-25 daily-rule-2026-05-25 Mon, 25 May 2026 09:00:00 +0000 Business code should never call IConfiguration directly. Strongly-typed IOptions or IOptionsSnapshot bindings only. The AI loves to "just grab the config value" — refuse it and force a settings class with validation attributes. https://agentic-architect.dev/blog/#2026-05-27 daily-rule-2026-05-27 Wed, 27 May 2026 09:00:00 +0000 Mark every class sealed unless inheritance is explicitly planned. Stops Cursor inventing accidental inheritance hierarchies "for flexibility." Small but measurable virtual-call perf wins too. https://agentic-architect.dev/blog/#2026-05-28 daily-rule-2026-05-28 Thu, 28 May 2026 09:00:00 +0000 Value objects (Money, Address, Coordinates) should be records. Entities with identity (Order, Customer) should be classes with an Id. Cursor mixes these constantly. A rule that classifies based on the presence or absence of an identity property keeps the distinction honest. https://agentic-architect.dev/blog/#2026-05-29 daily-rule-2026-05-29 Fri, 29 May 2026 09:00:00 +0000 async void is a deadlock and unhandled-exception trap everywhere except UI event handlers. The AI uses it routinely for "fire and forget" — wrong answer every time. Flag it on sight. https://agentic-architect.dev/blog/#2026-05-30 daily-rule-2026-05-30 Sat, 30 May 2026 09:00:00 +0000 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. https://agentic-architect.dev/blog/#2026-05-31 daily-rule-2026-05-31 Sun, 31 May 2026 09:00:00 +0000 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. https://agentic-architect.dev/blog/#2026-06-01 daily-rule-2026-06-01 Mon, 01 Jun 2026 09:00:00 +0000 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. https://agentic-architect.dev/blog/#2026-06-02 daily-rule-2026-06-02 Tue, 02 Jun 2026 09:00:00 +0000 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. https://agentic-architect.dev/blog/#2026-06-03 daily-rule-2026-06-03 Wed, 03 Jun 2026 09:00:00 +0000 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. https://agentic-architect.dev/blog/#2026-06-04 daily-rule-2026-06-04 Thu, 04 Jun 2026 09:00:00 +0000 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. https://agentic-architect.dev/blog/#2026-06-05 daily-rule-2026-06-05 Fri, 05 Jun 2026 09:00:00 +0000 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. https://agentic-architect.dev/blog/#2026-06-06 daily-rule-2026-06-06 Sat, 06 Jun 2026 09:00:00 +0000 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. https://agentic-architect.dev/blog/#2026-06-07 daily-rule-2026-06-07 Sun, 07 Jun 2026 09:00:00 +0000 Logs alone won't debug a distributed system. Add a static readonly ActivitySource per project and wrap every external call (DB, HTTP, queue) in StartActivity. Cursor never adds OTEL spans on its own — give it a rule that recognises external-call patterns and proposes the trace. https://agentic-architect.dev/blog/#2026-06-08 daily-rule-2026-06-08 Mon, 08 Jun 2026 09:00:00 +0000 Stop using nulls for flow control. Use a Result object to force Cursor to handle success and failure cases explicitly. This prevents 90% of AI-generated logic errors in Web APIs. https://agentic-architect.dev/blog/#2026-06-09 daily-rule-2026-06-09 Tue, 09 Jun 2026 09:00:00 +0000 Never let the AI write database logic in your Controllers. Enforce a strict boundary where all IQueryable access stays in the Infrastructure layer. This keeps your business logic "pure" and readable for the LLM. https://agentic-architect.dev/blog/#2026-06-10 daily-rule-2026-06-10 Wed, 10 Jun 2026 09:00:00 +0000 Enforce ILogger with structured templates. Never use string interpolation in logs. This ensures that when you feed logs back into Cursor for debugging, the AI recognizes the patterns immediately. https://agentic-architect.dev/blog/#2026-06-11 daily-rule-2026-06-11 Thu, 11 Jun 2026 09:00:00 +0000 Every MediatR Request must have a FluentValidation rule. Force the AI to check the validator before writing handler logic. This prevents "context rot" where the AI forgets your business constraints. https://agentic-architect.dev/blog/#2026-06-12 daily-rule-2026-06-12 Fri, 12 Jun 2026 09:00:00 +0000 Use MapGroup and EndPoints for .NET 9 services. It keeps the context window lean and focused, helping the AI provide more accurate code suggestions than it can with massive, bloated Controllers. https://agentic-architect.dev/blog/#2026-06-13 daily-rule-2026-06-13 Sat, 13 Jun 2026 09:00:00 +0000 Never let Cursor hardcode DateTime.Now or DateTime.UtcNow in business logic. Inject TimeProvider (or your own IClock) instead. This makes time deterministic for tests and stops the AI reaching for static APIs whenever it generates time-aware code. https://agentic-architect.dev/blog/#2026-06-14 daily-rule-2026-06-14 Sun, 14 Jun 2026 09:00:00 +0000 Refuse new HttpClient() in any generated code. Force Cursor to inject IHttpClientFactory or a typed client. The classic socket-exhaustion bug is exactly the kind of footgun an AI hands you without realising. https://agentic-architect.dev/blog/#2026-06-15 daily-rule-2026-06-15 Mon, 15 Jun 2026 09:00:00 +0000 Every async method in your codebase should accept and forward a CancellationToken. Make it a rule that any new async signature without one is flagged. Stops the AI from quietly losing cancellation half-way down a call chain. https://agentic-architect.dev/blog/#2026-06-16 daily-rule-2026-06-16 Tue, 16 Jun 2026 09:00:00 +0000 The single most expensive .NET runtime bug: a Singleton holding a Scoped service. Cursor cheerfully writes this without warning. Audit constructor parameters of any class registered as Singleton — if any are typically Scoped (DbContext, repositories, MediatR sender), flag it before merge. https://agentic-architect.dev/blog/#2026-06-17 daily-rule-2026-06-17 Wed, 17 Jun 2026 09:00:00 +0000 Every read-only EF Core query should call AsNoTracking. Add a rule that recognises query methods returning DTOs (not entities) and inserts the call. Cursor never does this by default and your read perf degrades silently across releases. https://agentic-architect.dev/blog/#2026-06-18 daily-rule-2026-06-18 Thu, 18 Jun 2026 09:00:00 +0000 throw ex resets the stack trace. throw preserves it. Cursor gets this wrong about 40 percent of the time when generating catch blocks. Rewrite any naked throw ex to throw unless the exception has been explicitly wrapped. https://agentic-architect.dev/blog/#2026-06-19 daily-rule-2026-06-19 Fri, 19 Jun 2026 09:00:00 +0000 Business code should never call IConfiguration directly. Strongly-typed IOptions or IOptionsSnapshot bindings only. The AI loves to "just grab the config value" — refuse it and force a settings class with validation attributes. https://agentic-architect.dev/blog/#2026-06-20 daily-rule-2026-06-20 Sat, 20 Jun 2026 09:00:00 +0000 OrderId as record struct OrderId(Guid Value) beats raw Guid everywhere. Stops the AI passing a CustomerId where an OrderId was expected — a bug the compiler can't catch with primitive obsession but catches instantly with domain primitives. https://agentic-architect.dev/blog/#2026-06-21 daily-rule-2026-06-21 Sun, 21 Jun 2026 09:00:00 +0000 Mark every class sealed unless inheritance is explicitly planned. Stops Cursor inventing accidental inheritance hierarchies "for flexibility." Small but measurable virtual-call perf wins too. https://agentic-architect.dev/blog/#2026-06-22 daily-rule-2026-06-22 Mon, 22 Jun 2026 09:00:00 +0000 Value objects (Money, Address, Coordinates) should be records. Entities with identity (Order, Customer) should be classes with an Id. Cursor mixes these constantly. A rule that classifies based on the presence or absence of an identity property keeps the distinction honest.