UserMainPage.razor

@page "/__main"
@using Microsoft.JSInterop
@using System.Runtime.Loader
@using Try.UserComponents
@using TryMudBlazor.Client.Services
@inject IJSRuntime JSRuntime
@inject UserComponentsAssemblyService AssemblyService
@implements IAsyncDisposable

<MudDialogProvider FullWidth="true" MaxWidth="MaxWidth.ExtraSmall" />
<MudSnackbarProvider />

<DynamicComponent Type="@_type" />

@code {
    private Type _type = typeof(__Main);
    private AssemblyLoadContext _loadContext;
    private readonly Lazy<DotNetObjectReference<UserMainPage>> _ref;

    public UserMainPage()
    {
        _ref = new Lazy<DotNetObjectReference<UserMainPage>>(CreateDotNetObject());
    }

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender)
        {
            await JSRuntime.InvokeVoidAsync("Try.registerHotReload", _ref.Value);
        }
    }

    [JSInvokable]
    public async Task HotReload()
    {
        try
        {
            var base64 = await JSRuntime.InvokeAsync<string>("sessionStorage.getItem", "TryMudBlazor.UserComponentsDllBase64");
            if (base64 == null)
            {
                // sessionStorage was cleared (e.g. crash recovery) — fall back to a full reload
                // so loadBootResource picks up the safe static DLL.
                await JSRuntime.InvokeVoidAsync("Try.requestFullReload", "/__main");
                return;
            }

            var bytes = Convert.FromBase64String(base64);

            // Swap to a fresh collectible context; previous one becomes eligible for GC
            // once Blazor disposes the old component instance below.
            var previousContext = _loadContext;
            _loadContext = new AssemblyLoadContext(name: null, isCollectible: true);
            var assembly = _loadContext.LoadFromStream(new MemoryStream(bytes));
            previousContext?.Unload();

            // UserStartup requires DI re-registration — fall back to full iframe reload
            if (assembly.GetType("UserStartup") is not null ||
                assembly.GetType("Try.UserComponents.UserStartup") is not null)
            {
                await JSRuntime.InvokeVoidAsync("Try.requestFullReload", "/__main");
                return;
            }

            var newType = assembly.GetType("Try.UserComponents.__Main");
            if (newType is not null)
            {
                // Update the Router's AdditionalAssemblies before rendering the new __Main
                // so that any NavigateTo calls inside it can resolve user-defined @page routes.
                await AssemblyService.UpdateAssemblyAsync(assembly);
                _type = newType;
                await InvokeAsync(StateHasChanged);
            }
        }
        catch
        {
            await JSRuntime.InvokeVoidAsync("Try.requestFullReload", "/__main");
        }
    }

    public async ValueTask DisposeAsync()
    {
        if (_ref.IsValueCreated)
        {
            await JSRuntime.InvokeVoidAsync("Try.unregisterHotReload");
            _ref.Value.Dispose();
        }
        _loadContext?.Unload();
    }

    private DotNetObjectReference<UserMainPage> CreateDotNetObject() => DotNetObjectReference.Create(this);
}