feat: implement cross-device reading progress synchronization using SignalR and remove legacy quiz generation services.

src/NexusReader.UI.Shared/Components/Organisms/ReaderCanvas.razor

@@ -10,6 +10,7 @@
 @inject IReaderNavigationService NavigationService
 @inject KnowledgeCoordinator Coordinator
 @inject IReaderInteractionService InteractionService
+@inject ISyncService SyncService
 
 <div class="reader-canvas @(ThemeService.IsLightMode ? "theme-light" : "theme-dark")">
     @if (ViewModel == null)
@@ -77,6 +78,11 @@
 
     protected override async Task OnAfterRenderAsync(bool firstRender)
     {
+        if (firstRender)
+        {
+            await SyncService.InitializeAsync();
+        }
+
         if (ViewModel != null && !_isJsInitialized)
         {
             _isJsInitialized = true;
@@ -109,6 +115,23 @@
     public void HandleBlockReached(string blockId, string content)
     {
         Coordinator.OnBlockReached(blockId, content);
+        
+        // Debounce sync update (simple version: every 5 seconds or on a timer)
+        _ = SyncService.UpdateProgressAsync(blockId);
+    }
+
+    private void HandleSyncProgressReceived(string blockId, DateTime timestamp)
+    {
+        // For now, let's just scroll to the node if it's in the current view, 
+        // or just log it. Usually, we should prompt the user.
+        Console.WriteLine($"[Sync] Received progress from another device: {blockId} at {timestamp}");
+        
+        // Simple auto-scroll if it's newer than what we have (we don't track our own timestamp yet, 
+        // but we can assume incoming syncs are from other active devices)
+        _ = InvokeAsync(async () => {
+             await ScrollToNodeAsync(blockId);
+             StateHasChanged();
+        });
     }
 
     [JSInvokable]
@@ -196,5 +219,6 @@
         InteractionService.OnScrollToBlockRequested -= HandleScrollRequested;
         InteractionService.OnHighlightBlockRequested -= HandleHighlightRequested;
         InteractionService.OnTextSelected -= HandleTextSelected;
+        SyncService.OnProgressReceived -= HandleSyncProgressReceived;
     }
 }

src/NexusReader.UI.Shared/NexusReader.UI.Shared.csproj

@@ -13,6 +13,7 @@
     <PackageReference Include="Microsoft.AspNetCore.Components.Web" Version="10.0.7" />
     <PackageReference Include="MediatR" Version="12.1.1" />
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.7" />
+    <PackageReference Include="Microsoft.AspNetCore.SignalR.Client" Version="10.0.7" />
   </ItemGroup>
 
   <ItemGroup>

src/NexusReader.UI.Shared/Services/ISyncService.cs

@@ -0,0 +1,11 @@
+using FluentResults;
+
+namespace NexusReader.UI.Shared.Services;
+
+public interface ISyncService
+{
+    Task<Result> InitializeAsync();
+    Task<Result> UpdateProgressAsync(string pageId);
+    event Action<string, DateTime> OnProgressReceived;
+    Task DisposeAsync();
+}

src/NexusReader.UI.Shared/Services/SyncService.cs

@@ -0,0 +1,112 @@
+using FluentResults;
+using Microsoft.AspNetCore.SignalR.Client;
+using NexusReader.Application.Abstractions.Services;
+using System.Net.Http;
+
+namespace NexusReader.UI.Shared.Services;
+
+public class SyncService : ISyncService, IAsyncDisposable
+{
+    private readonly HttpClient _httpClient;
+    private readonly INativeStorageService _storageService;
+    private readonly IPlatformService _platformService;
+    private HubConnection? _hubConnection;
+    private bool _isInitialized;
+    private CancellationTokenSource? _debounceCts;
+
+    public event Action<string, DateTime>? OnProgressReceived;
+
+    public SyncService(
+        HttpClient httpClient,
+        INativeStorageService storageService,
+        IPlatformService platformService)
+    {
+        _httpClient = httpClient;
+        _storageService = storageService;
+        _platformService = platformService;
+    }
+
+    public async Task<Result> InitializeAsync()
+    {
+        if (_isInitialized) return Result.Ok();
+
+        var tokenResult = await _storageService.GetSecureString("nexus_auth_token");
+        if (tokenResult.IsFailed) return Result.Fail("Not authenticated");
+
+        var baseUrl = _httpClient.BaseAddress?.ToString() ?? "http://localhost:5000/";
+        var hubUrl = new Uri(new Uri(baseUrl), "synchub").ToString();
+
+        _hubConnection = new HubConnectionBuilder()
+            .WithUrl(hubUrl, options =>
+            {
+                options.AccessTokenProvider = () => Task.FromResult<string?>(tokenResult.Value);
+            })
+            .WithAutomaticReconnect()
+            .Build();
+
+        _hubConnection.On<string, DateTime>("ProgressUpdated", (pageId, timestamp) =>
+        {
+            OnProgressReceived?.Invoke(pageId, timestamp);
+        });
+
+        try
+        {
+            await _hubConnection.StartAsync();
+            _isInitialized = true;
+            return Result.Ok();
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(ex.Message);
+        }
+    }
+
+    private string? _lastSentPageId;
+
+    public async Task<Result> UpdateProgressAsync(string pageId)
+    {
+        if (pageId == _lastSentPageId) return Result.Ok();
+        
+        // Proper trailing-edge debounce
+        _debounceCts?.Cancel();
+        _debounceCts = new CancellationTokenSource();
+        var token = _debounceCts.Token;
+
+        _ = Task.Run(async () =>
+        {
+            try
+            {
+                await Task.Delay(2000, token);
+                
+                if (!_isInitialized) await InitializeAsync();
+                
+                if (_hubConnection?.State == HubConnectionState.Connected)
+                {
+                    await _hubConnection.SendAsync("UpdateProgress", pageId, token);
+                    _lastSentPageId = pageId;
+                }
+            }
+            catch (TaskCanceledException) { /* Ignored, user kept scrolling */ }
+            catch (Exception ex)
+            {
+                Console.WriteLine($"[SyncService] Error sending progress: {ex.Message}");
+            }
+        }, token);
+
+        return Result.Ok();
+    }
+
+    public async Task DisposeAsync()
+    {
+        _debounceCts?.Cancel();
+        if (_hubConnection != null)
+        {
+            await _hubConnection.DisposeAsync();
+        }
+    }
+
+    async ValueTask IAsyncDisposable.DisposeAsync()
+    {
+        await DisposeAsync();
+    }
+}