This week in Cursor + .NET — 7 rules (week ending August 02, 2026)

A weekly digest from the Agentic Architect persistence kit: 7 senior C#/.NET rules for engineers keeping Cursor honest across sessions.

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 6: TimeProvider Injection

Sun 02 Aug

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.

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Rule 5: Minimal API Groups

Sat 01 Aug

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.

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Rule 4: Validator Enforcement

Fri 31 Jul

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.

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Rule 3: Structured Logging

Thu 30 Jul

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.

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Rule 2: Persistence Boundaries

Wed 29 Jul

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.

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Rule 1: The Result Pattern

Tue 28 Jul

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.

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Rule 25: ActivitySource for OpenTelemetry

Mon 27 Jul

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.

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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.

• 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/.