DEV Community: Agentic Architect

This week in Cursor + .NET — 6 rules (week ending June 28, 2026)

Agentic Architect — Sun, 28 Jun 2026 11:58:43 +0000

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.

6 daily senior rules

Rule 21: Channels for Producer Consumer

Sun 28 Jun

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.

What reviewers see	What production sees
Clean diff, idiomatic C#	Tracking overhead, stale scoped state, ignored cancellation
Green CI	Incidents that are hard to trace back to a specific PR
"We have analyzers"	Warnings buried in the IDE or not enforced on merge

Tool / plan	Price	What you actually get
Cursor Pro	approx £16/mo ($20; £12.60/mo billed annually)	$20 of included API usage, unlimited Tab completions, unlimited Auto mode. Monthly credit pool with overage.
Cursor Ultra (top tier)	approx £158/mo ($200; £126/mo annually)	$400 of included API usage and roughly 20x the Pro agent limits. Same frontier model access as Pro.
GitHub Copilot Pro	approx £8/mo ($10)	Code completions and Next Edit Suggestions stay unlimited and free. 1,500 monthly AI credits (1,000 base + 500 flex) cover agent mode, chat, CLI and PR review.
GitHub Copilot Pro+	approx £31/mo ($39)	7,000 monthly AI credits (3,900 base + 3,100 flex) and wider model choice. Completions are still free and unlimited.
GitHub Copilot Business	approx £15/user/mo ($19)	Org policy controls, audit and seat management pooled across the org, plus IP indemnity on the business plan.

Task	Reach for	Why
Inline completion while typing in Visual Studio	Copilot	Native IDE integration, already licensed
Add the same field + constructor + DI registration across 12 services	Cursor	Agentic cascade in one prompt; Copilot edits line by line
Port a controller to Minimal API + tests + run them	Cursor	Iterate-until-tests-pass is Cursor's home turf
Org-wide policy, audit, IP indemnity	Copilot Business	Org policy controls and indemnity on the business plan
Pin house style so the AI stops regressing it	Cursor	Directory-scoped `.mdc` rules + Learning Log

The Drift	What Cursor Does	What the Rules Do
throw instead of Result	Cursor defaults to try/catch/throw in controllers — ignores your Result convention set 6 months ago	arch-core.mdc blocks throw in controllers. dotnet-di.mdc requires Result through your pipeline.
Captive DI dependencies	AI injects a Scoped DbContext into a Singleton cache service — compiles fine, explodes at runtime	dotnet-di.mdc catches the lifetime mismatch during generation and blocks the suggestion.
Missing AsNoTracking()	Cursor generates reads that track every entity — memory balloons, queries slow	ef-core-reads.mdc enforces AsNoTracking() on all query-only operations.
Hallucination spiral	AI invents IOrderRepository.FindByLegacyCode(), code doesn't compile, AI invents another method to fix it	bug-breaker.mdc detects 3+ failed attempts on the same file, forces a re-read, and asks you.

Tool	Plan	Cost	What you actually get
Cursor	Pro	$20/mo (~£16)	Sonnet/Opus access, Composer, MCP, 500 fast requests
JetBrains Rider	Personal annual	$159/yr (~£125)	Rider only, all updates
JetBrains All Products	Personal annual	$289/yr (~£230)	Rider + DataGrip + WebStorm + ReSharper + 9 more
Both (typical senior)	Cursor Pro + Rider	~$33/mo (~£26)	Single seat, both tools, no compromise

Task	Reach for	Why
Renaming a public type used in 80 files	Rider	Symbol-aware refactor, won't miss xUnit fixtures or attribute references
Adding the same field + constructor + DI registration across 12 services	Cursor	Agentic loop with Composer; Rider can't iterate on intent
Async call-stack debugging into a NuGet package	Rider	Decompiled-source stepping; Cursor relies on the VS Code debugger
Porting a controller to Minimal API + tests + Swagger doc	Cursor	Multi-file edit + iterate-until-tests-pass; pure prompt territory
Inspecting why a Scoped service is captured by a Singleton	Rider	`dotnet-di.mdc` in Cursor catches it post-hoc; Rider catches it on hover
Wiring a new MCP server that queries your local SQLite	Cursor	Rider doesn't speak MCP yet

DEV Community: Agentic Architect

This week in Cursor + .NET — 6 rules (week ending June 28, 2026)

6 daily senior rules

Rule 21: Channels for Producer Consumer

Rule 20: Source-Generated JSON Serialisation

Rule 19: NetArchTest for Boundaries

Rule 18: WebApplicationFactory for Integration Tests

Rule 17: ConfigureAwait false in Libraries

Rule 15: Records for Value Objects, Classes for Entities

Try one rule before you trust the whole kit

This week in Cursor + .NET — 7 rules (week ending June 21, 2026)

7 daily senior rules

Rule 14: Sealed By Default

Rule 13: Strongly-Typed IDs

Rule 12: IOptionsSnapshot Over Raw Config

Rule 11: Rethrow, Don't throw ex

Rule 10: AsNoTracking for Reads

Rule 9: Scoped Capture in Singleton

Rule 8: CancellationToken Propagation

Try one rule before you trust the whole kit

This week in Cursor + .NET — 7 rules (week ending June 14, 2026)

7 daily senior rules

Rule 7: IHttpClientFactory Discipline

Rule 6: TimeProvider Injection

Rule 5: Minimal API Groups

Rule 4: Validator Enforcement

Rule 3: Structured Logging

Rule 2: Persistence Boundaries

Rule 1: The Result Pattern

Try one rule before you trust the whole kit

The AI-generated C# that passes review and breaks in production

The pattern

Five regressions I keep seeing

1. EF Core read paths without AsNoTracking()

2. Captive dependency (scoped service in a singleton)

3. Dropped CancellationToken

4. Swallowed exception

5. Task.Run over blocking I/O

Why review misses them

Why IDE warnings aren't enough (maybe)

Two questions for you

This week in Cursor + .NET — 7 rules + 1 essay (week ending June 07, 2026)

New essays this week

7 daily senior rules

Rule 25: ActivitySource for OpenTelemetry

Rule 24: ValueTask Only When Justified

Rule 23: No Bool Flag Parameters

Rule 22: BackgroundService Over Task.Run

Rule 21: Channels for Producer Consumer

Rule 20: Source-Generated JSON Serialisation

Rule 19: NetArchTest for Boundaries

Try one rule before you trust the whole kit

Cursor vs GitHub Copilot for C#/.NET in 2026: which to pay for

This week in Cursor + .NET — 6 rules + 3 essays (week ending May 31, 2026)

New essays this week

6 daily senior rules

Rule 18: WebApplicationFactory for Integration Tests

Rule 17: ConfigureAwait false in Libraries

Rule 16: async void Outside Event Handlers

Rule 15: Records for Value Objects, Classes for Entities

Rule 14: Sealed By Default

Rule 12: IOptionsSnapshot Over Raw Config

Try one rule before you trust the whole kit

How to use Cursor AI with Entity Framework Core (without blowing up your database)

How to stop Cursor AI forgetting your .NET architecture (the $9 fix)

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Cursor vs JetBrains Rider for C#/.NET in 2026: which to pay for

1. Open the same solution root in both

2. Add scoped Cursor rules (or grab arch-core-lite.mdc free)

3. Seed a Learning Log Cursor will re-read on session start

Learning Log

ADR-001 - Result over throw for business failures

ADR-002 - Scoped lifetime for DbContext, never captured by Singletons

ADR-003 - AsNoTracking on every read-only IQueryable

4. Commit the conventions

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

New essays this week

1. EF Core read paths without `AsNoTracking()`

3. Dropped `CancellationToken`

5. `Task.Run` over blocking I/O