C# Backend Engineering

Quick Reference

Decision	Default	Notes
Runtime	.NET 10 + C# 14 (LTS, GA Nov 2025, supported through ~Nov 2028)	.NET 8 LTS ends Nov 10, 2026 — verify current dates at dotnet support policy; treat continued .NET 8 targeting as a tracked migration, not a comfortable steady state
API style	Minimal API for new endpoints	Controllers for large CQRS surface with many filters/action results
Persistence (SQL, write-heavy)	EF Core	Use Dapper when query shapes are complex and hand-tuned SQL wins
Persistence (SQL, query-heavy)	Dapper	Pair with EF Core for write path if aggregates exist
Persistence (document)	MongoDB driver	Use when schema variability is genuine, not habitual
Background worker	`IHostedService` / `BackgroundService`	Add lease, graceful shutdown, and poison-message handling from day one
Resilience	`Microsoft.Extensions.Resilience` (Polly v8)	Standard pipeline: retry → circuit breaker → timeout
OpenAPI	Built-in ASP.NET Core OpenAPI (`Microsoft.AspNetCore.OpenApi`)	Do not add Swashbuckle unless repo already uses it

Route other tasks:

NUnit fixture design, WireMock/Testcontainers setup, or flake reduction → $qa-testing-nunit
nuke/Build.cs, CI target sequencing, or artifact publication → $ops-nuke-cicd
Legacy ILogger or Serilog rewrite automation → $dev-structured-logs