This week in Cursor + .NET — 3 rules + 4 essays (week ending May 22, 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. ## 3 daily senior rules ### 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/).