A working Duende IdentityServer 8.0.9 example on .NET 10 — the server with EF stores, a client-credentials client, an MVC code-flow client and a JWT-protected API — quoted from a public repo you can run.
Same model, three tools, one migration — measured. What Copilot's upgrade agent, plain Claude Code, and a guarded setup actually delivered, warts included.
Why every C# coding agent needs compiler-grade context, the nine tool methods worth exposing, and the design rules that keep a Roslyn MCP server fast.
A complete, copy-pasteable CLAUDE.md for .NET 10 + Aspire + EF Core 10 — annotated section by section, with the reasoning behind every rule.
AI agents amplify whole-program reasoning, and only a monolith gives them a whole program. The engineering case for the unfashionable architecture.
