Chat host

A desktop messenger is one persistent window, in-place tabs, a filterable inbox, and a thread on the Frame stack. Bind SectionHostView to the host ViewModel — do not write visibility flippers in code-behind. Auth and forms stay on FormViewModel / IAuthState / UseAuth.

builder.Services.UseAvaloniaMvvmExpress(o => o
    .UseFrameNavigation((nav, _) => nav
        .Map<LoginViewModel, LoginPage>("login")
        .Map<ChatHostViewModel, ChatHostPage>("chats")
        .Map<ChatThreadViewModel, ChatThreadPage>("thread"))
    .UseDialogs()
    .UseAuth<LoginViewModel>());

await Navigator.ResetAsync<ChatHostViewModel>();
await Navigator.NavigateToAsync<ChatThreadViewModel, ChatNavArgs>(new(id));

public sealed class ChatHostViewModel : SectionHostViewModel
{
    public ChatHostViewModel()
    {
        Inbox = Add("chats", new ChatInboxViewModel(seed));
        Add("updates", new ChatInboxViewModel([]));
    }

    public ChatInboxViewModel Inbox { get; }
}

// Bind SectionHostView. DataContext is the host; Current is the visible child.