Entry point `Program.Main` builds an `AppBuilder` configured with `UsePlatformDetect`, `LogToTrace`, and `UseReactiveUI`; `App.OnFrameworkInitializationCompleted` creates the root `MainWindow` with a `MainWindowViewModel` and wires it into `Assistant.Engine.MainWindow`. The module is loaded as a plugin by the core engine: `Engine.Install` (in the `Assistant` namespace) loads `ClassicAssist.Shared.dll` via `Assembly.LoadFile`, subscribes to `Options.SaveEvent`/`LoadEvent` to serialize/deserialize every `BaseViewModel` implementing `ISettingProvider`, then calls `LoadUI`. `LoadUI` branches on `SEngine.GetPlatformType()`: on Unix it starts the Avalonia app on a background thread; otherwise it calls `SetupWithoutStarting()` so the core can set `SEngine.Dispatcher = new AvaloniaDispatcher(Dispatcher.UIThread)` and `SEngine.UIInvoker = new AvaloniaUIInvoker(...)` before showing windows. `AvaloniaUIInvoker` implements `IUIInvoker` using reflection to construct `Window` subclasses by name, exposing `Invoke`, `InvokeDialog<T>`, `GetHueAsync`, and clipboard access through `IClipboard`. Views live under `Views/` (root windows plus `Agents/` tabbed sub-views), each paired with a `.axaml.cs` code-behind; reusable widgets are in `Controls/` (e.g. `GroupBox` extending `HeaderedContentControl` with a XAML theme); shared helpers (`Misc/`) provide behaviors, value converters, and the `AvaloniaMessageBoxProvider`. Dependencies flow one-way: this module depends on `ClassicAssist.Shared`, `ClassicAssist.Data`, `ClassicAssist.Misc`, and `ClassicAssist.UI.ViewModels`; the core never references Avalonia types directly — it only sees the `IDispatcher`/`IUIInvoker`/`IMessageBoxProvider` abstractions.