Use to answer structural questions about a C#/.NET codebase that grep and LSP answer badly — public API surface, who implements an interface or derives from a base, what's undocumented, call/usage inventories. Write a throwaway read-only Roslyn program (a single-file `dotnet run query.cs` app) that parses the real syntax/semantic graph instead of text-matching. Roslyn knows the code; grep guesses.
