This week in Cursor + .NET — 7 rules (week ending September 06, 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. 7 daily senior rules Rule 16: async void Outside Event Handlers Sun 06 Sep 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. → Permalink on the blog Rule 15: Records for Value Objects, Classes for Entities Sat 05 Sep 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. → Permalink on the blog Rule 14: Sealed By Default Fri 04 Sep 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. → Permalink on the blog Rule 13: Strongly-Typed IDs Thu 03 Sep 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. → Permalink on the blog Rule 12: IOptionsSnapshot Over Raw Config Wed 02 Sep 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. → Permalink on the blog Rule 11: Rethrow, Don't throw ex Tue 01 Sep 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 Rule 10: AsNoTracking for Reads Mon 31 Aug 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 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/.