Navigation

INavigator is host-agnostic. UseFrameNavigation is the only Avalonia host: login → replace-root → push on a Plugin.Avalonia.MVVMExpress.Controls.Frame named NavigationHost. AvaloniaFrameNavigator hops to IMainThread before constructing a view. There is no UseShell.

• URI stack on the Frame host: Current, Stack, ModalStack, CanGoBack, History, GoBackAsync, PopToRootAsync, ReplaceAsync, ResetAsync / ReplaceRootAsync, PushModalAsync / PopModalAsync.
• ResetAsync clears the Frame journal so Back cannot return to login. It does not keep the old journal and Push a new root.
• Modal views open as owned Window instances — not a second Frame overlay.
• UseAuth<TChallenge>() wraps GuardedNavigator. Register IAuthState yourself (Playground uses DemoAuthState). There is no UseSecureSessionAuth() host helper in 1.0.
• One INavigator per IWindowContext. A second Window gets its own navigator.
• ViewModels never call Frame.Navigate or show a dialog statically. IMainThread is the only marshal API.

Add Plugin.Avalonia.MVVMExpress.Navigation and call UseFrameNavigation(). Typed args use a record and IAcceptNavArgs<T>.Accept. URI / dictionary args use IAcceptNavQuery.

public sealed record ProductDetailsArgs(int ProductId);

public sealed class ProductDetailsViewModel : PageViewModel,
    IAcceptNavArgs<ProductDetailsArgs>, IAcceptNavQuery
{
    private int _productId;

    public void Accept(ProductDetailsArgs args) => _productId = args.ProductId;

    public void Accept(IReadOnlyDictionary<string, object> query)
    {
        if (query.TryGetValue(nameof(ProductDetailsArgs.ProductId), out var raw)
            && int.TryParse(Convert.ToString(raw), out var id))
        {
            _productId = id;
        }
    }
}

await Navigator.NavigateToAsync<ProductDetailsViewModel, ProductDetailsArgs>(
    new ProductDetailsArgs(product.Id), ct);

await Navigator.NavigateToAsync(
    "details",
    new Dictionary<string, object> { ["ProductId"] = product.Id },
    cancellationToken: ct);

builder.Services.UseAvaloniaMvvmExpress(o => o
    .UseFrameNavigation((nav, _) => nav
        .Map<LoginViewModel, LoginPage>("login")
        .Map<HomeViewModel, HomePage>("home")
        .Map<DetailsViewModel, DetailsPage>("details"))
    .UseDialogs()
    .UseAuth<LoginViewModel>());

await Navigator.ResetAsync<HomeViewModel>(); // replace-root after login
await Navigator.NavigateToAsync<DetailsViewModel, DetailsArgs>(new(id));

if (pages.CanGoBack)
    await pages.GoBackAsync();
await pages.PopToRootAsync();
await pages.ReplaceRootAsync<HomeViewModel>();