Add or modify a wire/protocol type in the AG-UI .NET SDK AGUI.Abstractions package — a new event, message, or content-part type, the AOT source-gen serializer context, or a polymorphic JSON converter, keeping it AOT-safe, JSON-wire-compatible with the TypeScript reference, and PublicAPI-clean. USE FOR: adding an AG-UI event type, adding a message role or input-content type, editing AGUIJsonSerializerContext, editing BaseEventJsonConverter / AGUIMessageJsonConverter / AGUIInputContentJsonConverter, fixing PublicAPI.Unshipped analyzer build failures on protocol types, wire-format round-trip serialization. DO NOT USE FOR: writing integration/SSE tests (use agui-dotnet-integration-tests), server hosting/endpoint code, or non-Abstractions packages.