Wino Mail is a native Windows mail client (Windows 10 1809+ / Windows 11) replacing the deprecated Windows Mail & Calendar. It's **transitioning from UWP to WinUI 3** - always work with WinUI projects (Wino.Mail.WinUI), never edit the deprecated Wino.Mail UWP project.
## Build and Development Commands
```bash
# Open solution
# WinoMail.slnx is the main solution file (VS 2022+)
- If a WinUI build only reports `XamlCompiler.exe exited with code 1`, rerun with the diagnostic logging command above and inspect the terminal output plus `winui-build.log` for real `WMC`/`WMC1121`/binding diagnostics before guessing
-`x:Bind` does not implicitly convert `double` to `GridLength`; when binding `RowDefinition.Height` or `ColumnDefinition.Width`, use a `XamlHelpers` method such as `DoubleToGridLength(...)`
- For `ComboBox` controls in XAML, never use `DisplayMemberPath` or `SelectedValuePath`; use a typed `ItemTemplate` and bind `SelectedItem` explicitly, preferably with `x:Bind`
- Putting authentication validation, token refresh, account API calls, settings serialization/deserialization, or preference-application logic into ViewModels instead of the corresponding service
- For dependency properties in WinUI code, always prefer `[GeneratedDependencyProperty]` from CommunityToolkit over manual `DependencyProperty.Register(...)` declarations.
- When a `[RelayCommand]` needs enable/disable logic, prefer the command's `CanExecute` over binding `Button.IsEnabled` in XAML; use `[NotifyCanExecuteChangedFor]` on dependent properties and call `NotifyCanExecuteChanged()` explicitly when non-generated state affects the command.
- In ViewModels, update all UI-bound properties/collections via `ExecuteUIThread(...)` (especially after awaited calls and any use of `ConfigureAwait(false)`).
-`ConfigureAwait(false)` continues execution on a background thread. Any UI-bound property change, `INotifyPropertyChanged` notification, collection mutation, or similar UI-facing state update after that point must be marshaled back with `ExecuteUIThread(...)` or the appropriate dispatcher call, otherwise the app can crash.
- Messenger messages are raised from a background thread by default, while UI control event handlers such as `Button.Click` start on the UI thread. Be deliberate when combining dispatcher usage with `ConfigureAwait(false)` so post-await UI updates always return to the UI thread.
- ViewModels should only handle UI interaction/state and delegate business logic to services; account-management work belongs in `WinoAccountProfileService`, and preferences import/export/apply logic belongs in `PreferencesService`.
- Never create pure C# controls or controls that heavily manipulate UI structure from `.cs` files. Define controls in XAML and keep UI composition in XAML.
- Never add XAML-backed UI controls to `.xaml.cs`. If a view has XAML, all control declarations, flyouts, templates, and visual composition belong in the `.xaml` file; keep `.xaml.cs` limited to event handling and view glue.
- Never subscribe to framework events like `Loaded`, `Unloaded`, or input events from constructors in `.xaml.cs` for XAML-backed controls and pages; wire them directly in XAML instead.
