What problem does it solve? Upgrading a project from .NET 8 to .NET 9 introduces dozens of breaking changes across the compiler, runtime, ASP.NET Core, EF Core, and SDK tooling. Manually tracking down every build error, new obsoletion warning, and silent behavioral change is error-prone and time-consuming. ## Core Features & Use Cases - Systematic Migration Workflow: Guides a six-step process from project assessment and TargetFramework update through build error resolution, behavioral change review, infrastructure updates, and final verification. - Breaking Change Reference Library: Ships ten detailed reference documents covering C# 13 compiler changes, core libraries, ASP.NET Core 9, EF Core 9, cryptography, serialization, networking, WinForms/WPF, containers, and deployment, loaded on demand based on project type. - Concrete Fix Guidance: Provides before/after code fixes for high-impact issues such as BinaryFormatter removal, params span overload resolution, SYSLIB0054-SYSLIB0057 obsoletions, EF Core pending-model-changes exceptions, and HttpClientFactory handler changes. - Use Case: A team upgrades their ASP.NET Core + EF Core service to net9.0 and hits build errors plus a runtime exception from Migrate(). The skill identifies the applicable breaking changes, supplies exact fixes, and updates the Dockerfile and CI pipeline for .NET 9. ## Quick Start Migrate my .NET 8 solution to .NET 9 and fix all resulting build errors and breaking changes.
