This week in Cursor + .NET — 5 rules + 4 essays (week ending May 24, 2026)

*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](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/).* ## New essays this week ### [Teach Cursor Result<T> instead of throwing](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/04-cursor-result-not-throw.html) _Thu 21 May · C# patterns_ Stop the AI from undoing your Result/ErrorOr error model with throw and null on every new prompt. ### [Seven words that stop Cursor hallucination loops](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/03-cursor-hallucination-loop-breaker.html) _Wed 20 May · Cursor rules_ The correction spiral — and the circuit-breaker rule that ends it before you type the stop phrase. ### [The Scoped→Singleton DI bug your AI just suggested (and how to catch it)](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/02-scoped-singleton-di-bug.html) _Tue 19 May · .NET DI_ The .NET lifetime bug that ships to production silently — and the one Cursor rule that catches it before merge. ### [The Context Tax: Why every Cursor session costs you 15 minutes](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/01-the-context-tax.html) _Mon 18 May · Architecture_ The hidden cost senior engineers pay every morning — and a four-rule architecture for eliminating it. ## 5 daily senior rules ### Rule 11: Rethrow, Don't throw ex _Sun 24 May_ 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. [→ Permalink on the blog](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/#2026-05-24) ### Rule 10: AsNoTracking for Reads _Sat 23 May_ 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. [→ Permalink on the blog](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/#2026-05-23) ### Rule 9: Scoped Capture in Singleton _Fri 22 May_ 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. [→ Permalink on the blog](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/#2026-05-22) ### Rule 8: CancellationToken Propagation _Thu 21 May_ 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. [→ Permalink on the blog](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/#2026-05-21) ### Rule 2: Persistence Boundaries _Wed 20 May_ 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. [→ Permalink on the blog](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/#2026-05-20) --- ## Try one rule before you trust the whole kit The free **[`arch-core-lite.mdc`](https://github.com/agenticstandardcontact-byte/agentic-architect/blob/main/arch-core-lite.mdc?utm_source=devto&utm_medium=weekly_digest&utm_campaign=free_sample)** 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 £19.99. - **Free sample:** [`arch-core-lite.mdc` on GitHub](https://github.com/agenticstandardcontact-byte/agentic-architect/blob/main/arch-core-lite.mdc?utm_source=devto&utm_medium=weekly_digest&utm_campaign=free_sample) - **Full kit (£19.99, one-time):** [Agentic Architect on Gumroad](https://agenticarchitect.gumroad.com/l/dotnet-persistence-kit?utm_source=devto&utm_medium=weekly_digest&utm_campaign=paid_kit) - **Daily rules feed:** [https://agenticstandardcontact-byte.github.io/agentic-architect/blog/](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/?utm_source=devto&utm_medium=weekly_digest&utm_campaign=blog_index) Canonical home for everything in this digest: [https://agenticstandardcontact-byte.github.io/agentic-architect/blog/](https://agenticstandardcontact-byte.github.io/agentic-architect/blog/).