src/NexusReader.Application/Abstractions/Persistence/IEbookRepository.cs

@@ -23,6 +23,11 @@ public interface IEbookRepository
     /// </summary>
     void AddEbook(Ebook ebook);
 
+    /// <summary>
+    /// Finds an ebook by its unique identifier.
+    /// </summary>
+    Task<Ebook?> FindByIdAsync(Guid id, CancellationToken cancellationToken = default);
+
     /// <summary>
     /// Persists all staged changes to the underlying store.
     /// </summary>

src/NexusReader.Application/Abstractions/Persistence/IQuizResultRepository.cs

@@ -0,0 +1,25 @@
+using NexusReader.Domain.Entities;
+
+namespace NexusReader.Application.Abstractions.Persistence;
+
+/// <summary>
+/// Abstraction for QuizResult and related User entity lookup.
+/// Defined in the Application layer to maintain Clean Architecture isolation.
+/// </summary>
+public interface IQuizResultRepository
+{
+    /// <summary>
+    /// Finds a user by ID to extract tenant context.
+    /// </summary>
+    Task<NexusUser?> FindUserByIdAsync(string userId, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Adds a new quiz result to the database.
+    /// </summary>
+    void AddQuizResult(QuizResult quizResult);
+
+    /// <summary>
+    /// Persists all staged changes to the repository.
+    /// </summary>
+    Task<int> SaveChangesAsync(CancellationToken cancellationToken = default);
+}

src/NexusReader.Application/Commands/Library/IngestEbookCommandHandler.cs

@@ -1,6 +1,8 @@
 using FluentResults;
+using System.Linq;
 using MediatR;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
 using NexusReader.Application.Abstractions.Messaging;
 using NexusReader.Application.Abstractions.Persistence;
 using NexusReader.Application.Abstractions.Services;
@@ -79,15 +81,37 @@ public class IngestEbookCommandHandler : IRequestHandler<IngestEbookCommand, Res
             // 4. Trigger asynchronous background processing and vector indexing
             _ = Task.Run(async () =>
             {
+                using var scope = _scopeFactory.CreateScope();
+                var logger = scope.ServiceProvider.GetRequiredService<ILogger<IngestEbookCommandHandler>>();
+                var broadcaster = scope.ServiceProvider.GetRequiredService<ISyncBroadcaster>();
                 try
                 {
-                    using var scope = _scopeFactory.CreateScope();
                     var mediator = scope.ServiceProvider.GetRequiredService<IMediator>();
-                    await mediator.Send(new ProcessEbookCommand(ebook.Id, request.UserId, request.TenantId));
+                    var result = await mediator.Send(new ProcessEbookCommand(ebook.Id, request.UserId, request.TenantId));
+                    if (result.IsFailed)
+                    {
+                        var errorMsg = string.Join("; ", result.Errors.Select(e => e.Message));
+                        logger.LogError("[IngestEbook] Background ebook processing failed for Ebook {EbookId}: {Error}", ebook.Id, errorMsg);
+                        await broadcaster.BroadcastIngestionProgressAsync(
+                            request.UserId,
+                            $"Błąd indeksowania: {errorMsg}",
+                            1.0);
+                    }
                 }
-                catch (Exception)
+                catch (Exception ex)
                 {
-                    // Swallowed to prevent ThreadPool crashes
+                    logger.LogError(ex, "[IngestEbook] Exception during background ebook processing for Ebook {EbookId}", ebook.Id);
+                    try
+                    {
+                        await broadcaster.BroadcastIngestionProgressAsync(
+                            request.UserId,
+                            $"Błąd krytyczny podczas przetwarzania e-booka: {ex.Message}",
+                            1.0);
+                    }
+                    catch
+                    {
+                        // Ignore broadcast failures to prevent crashes
+                    }
                 }
             });
 

src/NexusReader.Application/Commands/Library/ProcessEbookCommand.cs

@@ -5,8 +5,8 @@ using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
 using NexusReader.Application.Abstractions.Messaging;
+using NexusReader.Application.Abstractions.Persistence;
 using NexusReader.Application.Abstractions.Services;
-using NexusReader.Data.Persistence;
 
 namespace NexusReader.Application.Commands.Library;
 
@@ -18,20 +18,20 @@ public record ProcessEbookCommand(
 
 public class ProcessEbookCommandHandler : IRequestHandler<ProcessEbookCommand, Result<bool>>
 {
-    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;
+    private readonly IEbookRepository _ebookRepository;
     private readonly IKnowledgeService _knowledgeService;
     private readonly IEpubExtractor _epubExtractor;
     private readonly ISyncBroadcaster _broadcaster;
     private readonly ILogger<ProcessEbookCommandHandler> _logger;
 
     public ProcessEbookCommandHandler(
-        IDbContextFactory<AppDbContext> dbContextFactory,
+        IEbookRepository ebookRepository,
         IKnowledgeService knowledgeService,
         IEpubExtractor epubExtractor,
         ISyncBroadcaster broadcaster,
         ILogger<ProcessEbookCommandHandler> logger)
     {
-        _dbContextFactory = dbContextFactory;
+        _ebookRepository = ebookRepository;
         _knowledgeService = knowledgeService;
         _epubExtractor = epubExtractor;
         _broadcaster = broadcaster;
@@ -46,8 +46,7 @@ public class ProcessEbookCommandHandler : IRequestHandler<ProcessEbookCommand, R
         {
             await _broadcaster.BroadcastIngestionProgressAsync(request.UserId, "Wyszukiwanie e-booka w bazie danych...", 0.05, cancellationToken);
 
-            using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
-            var ebook = await dbContext.Ebooks.FindAsync(new object[] { request.EbookId }, cancellationToken);
+            var ebook = await _ebookRepository.FindByIdAsync(request.EbookId, cancellationToken);
             if (ebook == null)
             {
                 _logger.LogError("[ProcessEbook] Ebook not found in database: {EbookId}", request.EbookId);
@@ -122,7 +121,7 @@ public class ProcessEbookCommandHandler : IRequestHandler<ProcessEbookCommand, R
 
             // Mark the ebook as ready
             ebook.IsReadyForReading = true;
-            await dbContext.SaveChangesAsync(cancellationToken);
+            await _ebookRepository.SaveChangesAsync(cancellationToken);
 
             _logger.LogInformation("[ProcessEbook] Ingestion and vector indexing completed for: {Title}", ebook.Title);
             

src/NexusReader.Application/Commands/Quiz/SubmitQuizResultCommandHandler.cs

@@ -1,25 +1,22 @@
 using FluentResults;
-using Microsoft.EntityFrameworkCore;
 using NexusReader.Application.Abstractions.Messaging;
-using NexusReader.Data.Persistence;
+using NexusReader.Application.Abstractions.Persistence;
 using NexusReader.Domain.Entities;
 
 namespace NexusReader.Application.Commands.Quiz;
 
 public sealed class SubmitQuizResultCommandHandler : ICommandHandler<SubmitQuizResultCommand>
 {
-    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;
+    private readonly IQuizResultRepository _quizResultRepository;
 
-    public SubmitQuizResultCommandHandler(IDbContextFactory<AppDbContext> dbContextFactory)
+    public SubmitQuizResultCommandHandler(IQuizResultRepository quizResultRepository)
     {
-        _dbContextFactory = dbContextFactory;
+        _quizResultRepository = quizResultRepository;
     }
 
     public async Task<Result> Handle(SubmitQuizResultCommand request, CancellationToken cancellationToken)
     {
-        using var context = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
-
-        var user = await context.Users.FirstOrDefaultAsync(u => u.Id == request.UserId, cancellationToken);
+        var user = await _quizResultRepository.FindUserByIdAsync(request.UserId, cancellationToken);
         if (user == null)
         {
             return Result.Fail("User not found.");
@@ -36,8 +33,8 @@ public sealed class SubmitQuizResultCommandHandler : ICommandHandler<SubmitQuizR
             CompletedDate = DateTime.UtcNow
         };
 
-        context.QuizResults.Add(quizResult);
-        await context.SaveChangesAsync(cancellationToken);
+        _quizResultRepository.AddQuizResult(quizResult);
+        await _quizResultRepository.SaveChangesAsync(cancellationToken);
 
         return Result.Ok();
     }

src/NexusReader.Application/Queries/User/GetUserProfileQueryHandler.cs

@@ -18,14 +18,15 @@ public class GetUserProfileQueryHandler : IRequestHandler<GetUserProfileQuery, R
     public async Task<Result<UserProfileDto>> Handle(GetUserProfileQuery request, CancellationToken cancellationToken)
     {
         using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
-        var profile = await dbContext.Users
+        
+        var userRaw = await dbContext.Users
             .Where(u => u.Id == request.UserId)
-            .Select(u => new UserProfileDto
+            .Select(u => new
             {
                 Email = u.Email ?? string.Empty,
                 UserId = u.Id,
                 AITokensUsed = u.AITokensUsed,
-                TenantId = u.TenantId != null && u.TenantId.Length == 36 ? new Guid(u.TenantId) : Guid.Empty,
+                TenantIdString = u.TenantId,
                 Plan = u.SubscriptionPlan != null ? new SubscriptionPlanDto
                 {
                     Id = u.SubscriptionPlan.Id,
@@ -33,12 +34,17 @@ public class GetUserProfileQueryHandler : IRequestHandler<GetUserProfileQuery, R
                     AITokenLimit = u.SubscriptionPlan.AITokenLimit,
                     MonthlyPrice = u.SubscriptionPlan.MonthlyPrice
                 } : new SubscriptionPlanDto(),
-                AverageQuizScore = u.QuizResults.Any(q => q.TotalQuestions > 0) 
-                    ? (int)u.QuizResults.Where(q => q.TotalQuestions > 0).Average(q => (double)q.Score / q.TotalQuestions * 100) 
-                    : 0,
+                QuizResults = u.QuizResults.Select(q => new
+                {
+                    q.Score,
+                    q.TotalQuestions,
+                    q.Id,
+                    q.Topic,
+                    q.Percentage,
+                    q.CompletedDate
+                }).ToList(),
                 DisplayName = u.DisplayName,
                 BooksReadCount = u.Ebooks.Count(),
-                ConceptsMappedCount = dbContext.KnowledgeUnits.Count(k => k.TenantId == u.TenantId || k.TenantId == "global" || string.IsNullOrEmpty(k.TenantId)),
                 LastReadBook = u.Ebooks.OrderByDescending(e => e.LastReadDate).Select(e => new LastReadBookDto
                 {
                     Id = e.Id,
@@ -55,26 +61,6 @@ public class GetUserProfileQueryHandler : IRequestHandler<GetUserProfileQuery, R
                     Description = e.Description,
                     IsReadyForReading = e.IsReadyForReading
                 }).FirstOrDefault(),
-                RecentQuizzes = u.QuizResults.OrderByDescending(q => q.CompletedDate).Take(5).Select(q => new QuizResultDto
-                {
-                    Id = q.Id,
-                    Topic = q.Topic,
-                    Score = q.Score,
-                    TotalQuestions = q.TotalQuestions,
-                    Percentage = q.Percentage,
-                    CompletedDate = q.CompletedDate
-                }).ToList(),
-                MappedConcepts = dbContext.KnowledgeUnits
-                    .Where(k => k.TenantId == u.TenantId || k.TenantId == "global" || string.IsNullOrEmpty(k.TenantId))
-                    .OrderByDescending(k => k.CreatedAt)
-                    .Take(6)
-                    .Select(k => new MappedConceptDto
-                    {
-                        Id = k.Id,
-                        Type = k.Type.ToString(),
-                        Content = k.Content
-                    })
-                    .ToList(),
                 Roles = dbContext.UserRoles
                     .Where(ur => ur.UserId == u.Id)
                     .Join(dbContext.Roles, ur => ur.RoleId, r => r.Id, (ur, r) => r.Name!)
@@ -82,11 +68,59 @@ public class GetUserProfileQueryHandler : IRequestHandler<GetUserProfileQuery, R
             })
             .FirstOrDefaultAsync(cancellationToken);
 
-        if (profile == null)
+        if (userRaw == null)
         {
             return Result.Fail("Profile not found.");
         }
 
+        var tenantId = userRaw.TenantIdString;
+        var mappedConcepts = await dbContext.KnowledgeUnits
+            .Where(k => k.TenantId == tenantId || k.TenantId == "global" || string.IsNullOrEmpty(k.TenantId))
+            .OrderByDescending(k => k.CreatedAt)
+            .Take(6)
+            .Select(k => new MappedConceptDto
+            {
+                Id = k.Id,
+                Type = k.Type.ToString(),
+                Content = k.Content
+            })
+            .ToListAsync(cancellationToken);
+
+        var conceptsMappedCount = await dbContext.KnowledgeUnits
+            .CountAsync(k => k.TenantId == tenantId || k.TenantId == "global" || string.IsNullOrEmpty(k.TenantId), cancellationToken);
+
+        int averageQuizScore = 0;
+        var validQuizzes = userRaw.QuizResults.Where(q => q.TotalQuestions > 0).ToList();
+        if (validQuizzes.Count > 0)
+        {
+            averageQuizScore = (int)(validQuizzes.Average(q => (double)q.Score / q.TotalQuestions) * 100);
+        }
+
+        var profile = new UserProfileDto
+        {
+            Email = userRaw.Email,
+            UserId = userRaw.UserId,
+            AITokensUsed = userRaw.AITokensUsed,
+            TenantId = userRaw.TenantIdString != null && userRaw.TenantIdString.Length == 36 ? new Guid(userRaw.TenantIdString) : Guid.Empty,
+            Plan = userRaw.Plan,
+            AverageQuizScore = averageQuizScore,
+            DisplayName = userRaw.DisplayName,
+            BooksReadCount = userRaw.BooksReadCount,
+            ConceptsMappedCount = conceptsMappedCount,
+            LastReadBook = userRaw.LastReadBook,
+            RecentQuizzes = userRaw.QuizResults.OrderByDescending(q => q.CompletedDate).Take(5).Select(q => new QuizResultDto
+            {
+                Id = q.Id,
+                Topic = q.Topic,
+                Score = q.Score,
+                TotalQuestions = q.TotalQuestions,
+                Percentage = q.Percentage,
+                CompletedDate = q.CompletedDate
+            }).ToList(),
+            MappedConcepts = mappedConcepts,
+            Roles = userRaw.Roles
+        };
+
         return Result.Ok(profile);
     }
 }

src/NexusReader.Infrastructure/DependencyInjection.cs

@@ -120,6 +120,7 @@ public static class DependencyInjection
 
         // Fix #1: Ebook repository (scoped, matches AppDbContext lifetime)
         services.AddScoped<IEbookRepository, EbookRepository>();
+        services.AddScoped<IQuizResultRepository, QuizResultRepository>();
 
         // Fix #2: SignalR broadcaster (scoped, wraps IHubContext which is itself a singleton wrapper)
         services.AddScoped<ISyncBroadcaster, SignalRSyncBroadcaster>();

src/NexusReader.Infrastructure/Persistence/EbookRepository.cs

@@ -46,6 +46,12 @@ internal sealed class EbookRepository : IEbookRepository
         _context.Ebooks.Add(ebook);
     }
 
+    /// <inheritdoc />
+    public async Task<Ebook?> FindByIdAsync(Guid id, CancellationToken cancellationToken = default)
+    {
+        return await _context.Ebooks.FindAsync(new object[] { id }, cancellationToken);
+    }
+
     /// <inheritdoc />
     public Task<int> SaveChangesAsync(CancellationToken cancellationToken = default)
         => _context.SaveChangesAsync(cancellationToken);

src/NexusReader.Infrastructure/Persistence/QuizResultRepository.cs

@@ -0,0 +1,37 @@
+using Microsoft.EntityFrameworkCore;
+using NexusReader.Application.Abstractions.Persistence;
+using NexusReader.Data.Persistence;
+using NexusReader.Domain.Entities;
+
+namespace NexusReader.Infrastructure.Persistence;
+
+/// <summary>
+/// EF Core implementation of <see cref="IQuizResultRepository"/>.
+/// </summary>
+internal sealed class QuizResultRepository : IQuizResultRepository
+{
+    private readonly AppDbContext _context;
+
+    public QuizResultRepository(AppDbContext context)
+    {
+        _context = context;
+    }
+
+    /// <inheritdoc />
+    public async Task<NexusUser?> FindUserByIdAsync(string userId, CancellationToken cancellationToken = default)
+    {
+        return await _context.Users.FirstOrDefaultAsync(u => u.Id == userId, cancellationToken);
+    }
+
+    /// <inheritdoc />
+    public void AddQuizResult(QuizResult quizResult)
+    {
+        _context.QuizResults.Add(quizResult);
+    }
+
+    /// <inheritdoc />
+    public Task<int> SaveChangesAsync(CancellationToken cancellationToken = default)
+    {
+        return _context.SaveChangesAsync(cancellationToken);
+    }
+}

src/NexusReader.Infrastructure/Services/KnowledgeService.cs

@@ -35,6 +35,7 @@ public class KnowledgeService : IKnowledgeService
     private readonly IDriver _neo4jDriver;
     private const string PromptVersion = "1.7";
     private static readonly ConcurrentDictionary<string, Lazy<Task<Result<KnowledgePacket>>>> _activeRequests = new();
+    private static readonly SemaphoreSlim _collectionSemaphore = new(1, 1);
 
     public KnowledgeService(
         IChatClient chatClient,
@@ -454,6 +455,7 @@ public class KnowledgeService : IKnowledgeService
 
     private async Task EnsureCollectionExistsAsync(string collectionName, CancellationToken cancellationToken = default)
     {
+        await _collectionSemaphore.WaitAsync(cancellationToken);
         try
         {
             var exists = await _qdrantClient.CollectionExistsAsync(collectionName, cancellationToken);
@@ -474,7 +476,19 @@ public class KnowledgeService : IKnowledgeService
         }
         catch (Exception ex)
         {
-            _logger.LogError(ex, "[KnowledgeService] Error ensuring Qdrant collection '{CollectionName}' exists.", collectionName);
+            if (ex.Message.Contains("already exists", StringComparison.OrdinalIgnoreCase) || 
+                (ex.InnerException != null && ex.InnerException.Message.Contains("already exists", StringComparison.OrdinalIgnoreCase)))
+            {
+                _logger.LogInformation("[KnowledgeService] Qdrant collection '{CollectionName}' was already created by another thread.", collectionName);
+            }
+            else
+            {
+                _logger.LogError(ex, "[KnowledgeService] Error ensuring Qdrant collection '{CollectionName}' exists.", collectionName);
+            }
+        }
+        finally
+        {
+            _collectionSemaphore.Release();
         }
     }
 
@@ -575,8 +589,9 @@ public class KnowledgeService : IKnowledgeService
                 );
                 searchResult = response.ToList();
             }
-            catch (Exception)
+            catch (Exception ex)
             {
+                _logger.LogWarning(ex, "[KnowledgeService] Qdrant search failed during GetRelevantContextAsync. Returning empty search results.");
                 searchResult = new List<Qdrant.Client.Grpc.ScoredPoint>();
             }
 
@@ -594,7 +609,10 @@ public class KnowledgeService : IKnowledgeService
                             summary = sumObj?.ToString();
                         }
                     }
-                    catch {}
+                    catch (JsonException ex)
+                    {
+                        _logger.LogWarning(ex, "[KnowledgeService] Failed to deserialize metadata JSON in RelevantContext mapping.");
+                    }
                 }
                 var text = string.IsNullOrEmpty(summary) ? content : $"{content}: {summary}";
                 return new RelevantContext 
@@ -747,7 +765,10 @@ public class KnowledgeService : IKnowledgeService
                     {
                         metadata = JsonSerializer.Deserialize<Dictionary<string, object>>(metaVal.StringValue);
                     }
-                    catch {}
+                    catch (JsonException ex)
+                    {
+                        _logger.LogWarning(ex, "[KnowledgeService] Failed to deserialize metadata JSON in search library mapping.");
+                    }
                 }
 
                 var dto = new SemanticSearchResultDto
@@ -871,6 +892,8 @@ public class KnowledgeService : IKnowledgeService
             {
                 using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
                 var units = await dbContext.KnowledgeUnits
+                    .Include(u => u.Ebook)
+                        .ThenInclude(e => e.Author)
                     .Where(u => u.TenantId == tenantId && (ebookId == null || u.EbookId == ebookId))
                     .ToListAsync(cancellationToken);
                 guidMap = units.ToDictionary(u => GetDeterministicGuid(u.Id).ToString(), u => u);
@@ -916,7 +939,10 @@ public class KnowledgeService : IKnowledgeService
                                         summary = sumObj?.ToString();
                                     }
                                 }
-                                catch { }
+                                catch (JsonException jsonEx)
+                                {
+                                    _logger.LogWarning(jsonEx, "[KnowledgeService] Failed to deserialize metadata JSON for unit {UnitId} in AskQuestionAsync source hydration.", sourceUnit.Id);
+                                }
                             }
                             sourceText = string.IsNullOrEmpty(summary) ? sourceUnit.Content : $"{sourceUnit.Content}: {summary}";
                         }
@@ -954,7 +980,10 @@ public class KnowledgeService : IKnowledgeService
                                                         summary = sumObj?.ToString();
                                                     }
                                                 }
-                                                catch { }
+                                                catch (JsonException jsonEx)
+                                                {
+                                                    _logger.LogWarning(jsonEx, "[KnowledgeService] Failed to deserialize metadata JSON for unit {UnitId} in AskQuestionAsync target hydration.", targetUnit.Id);
+                                                }
                                             }
                                             targetText = string.IsNullOrEmpty(summary) ? targetUnit.Content : $"{targetUnit.Content}: {summary}";
                                         }
@@ -986,7 +1015,10 @@ public class KnowledgeService : IKnowledgeService
                                         summary = sumObj?.ToString();
                                     }
                                 }
-                                catch { }
+                                catch (JsonException jsonEx)
+                                {
+                                    _logger.LogWarning(jsonEx, "[KnowledgeService] Failed to deserialize metadata JSON for unit {UnitId} in fallback AskQuestionAsync.", sourceUnit.Id);
+                                }
                             }
                             sourceText = string.IsNullOrEmpty(summary) ? sourceUnit.Content : $"{sourceUnit.Content}: {summary}";
                         }
@@ -1082,19 +1114,6 @@ public class KnowledgeService : IKnowledgeService
                         {
                             citation.Author = unit.Ebook.Author.Name;
                         }
-                        else if (unit.EbookId.HasValue)
-                        {
-                            try
-                            {
-                                using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
-                                var eb = await dbContext.Ebooks.Include(e => e.Author).FirstOrDefaultAsync(e => e.Id == unit.EbookId.Value, cancellationToken);
-                                if (eb?.Author != null)
-                                {
-                                    citation.Author = eb.Author.Name;
-                                }
-                            }
-                            catch { }
-                        }
 
                         if (!string.IsNullOrEmpty(unit.MetadataJson))
                         {
@@ -1106,7 +1125,10 @@ public class KnowledgeService : IKnowledgeService
                                     citation.PageNumber = pageVal;
                                 }
                             }
-                            catch { }
+                            catch (JsonException ex)
+                            {
+                                _logger.LogWarning(ex, "[KnowledgeService] Failed to deserialize metadata JSON for unit {UnitId} in AskQuestionAsync citation mapping.", unit.Id);
+                            }
                         }
                     }
                 }

src/NexusReader.UI.Shared/Components/Atoms/NexusSearchBox.razor

@@ -1,7 +1,9 @@
 @namespace NexusReader.UI.Shared.Components.Atoms
 @using System.Text.RegularExpressions
+@using MediatR
 @using NexusReader.Application.DTOs.AI
-@inject IKnowledgeService KnowledgeService
+@using NexusReader.Application.Queries.Library
+@inject IMediator Mediator
 @inject IReaderNavigationService NavService
 @inject IReaderInteractionService InteractionService
 @inject NavigationManager NavManager
@@ -100,6 +102,7 @@
     private bool _isLoading;
     private string? _searchError;
     private bool _isDropdownOpen;
+    private bool _disposed;
     
     private CancellationTokenSource? _searchCts;
 
@@ -140,15 +143,18 @@
     {
         _isLoading = true;
         _searchError = null;
-        await InvokeAsync(StateHasChanged);
+        if (!_disposed)
+        {
+            await InvokeAsync(StateHasChanged);
+        }
 
         try
         {
             var authState = await AuthStateProvider.GetAuthenticationStateAsync();
             var tenantId = authState.User.FindFirst("TenantId")?.Value ?? "global";
 
-            var result = await KnowledgeService.SearchLibrarySemanticallyAsync(SearchValue, tenantId, Limit, token);
-            if (token.IsCancellationRequested) return;
+            var result = await Mediator.Send(new SearchLibrarySemanticallyQuery(SearchValue, tenantId, Limit), token);
+            if (token.IsCancellationRequested || _disposed) return;
 
             if (result.IsSuccess)
             {
@@ -164,7 +170,7 @@
         }
         catch (Exception ex)
         {
-            if (!token.IsCancellationRequested)
+            if (!token.IsCancellationRequested && !_disposed)
             {
                 _results.Clear();
                 _searchError = "Wystąpił nieoczekiwany błąd podczas wyszukiwania.";
@@ -173,7 +179,7 @@
         }
         finally
         {
-            if (!token.IsCancellationRequested)
+            if (!token.IsCancellationRequested && !_disposed)
             {
                 _isLoading = false;
                 await InvokeAsync(StateHasChanged);
@@ -291,6 +297,7 @@
         IsFocused = false;
         // Delay slightly to allow click handlers on result cards to execute
         await Task.Delay(200);
+        if (_disposed) return;
         _isDropdownOpen = false;
         StateHasChanged();
     }
@@ -305,29 +312,35 @@
 
     private string HighlightQueryWords(string text, string query)
     {
-        if (string.IsNullOrWhiteSpace(text) || string.IsNullOrWhiteSpace(query))
-            return text;
+        if (string.IsNullOrWhiteSpace(text))
+            return string.Empty;
+
+        var escapedText = System.Net.WebUtility.HtmlEncode(text);
+
+        if (string.IsNullOrWhiteSpace(query))
+            return escapedText;
 
         var words = query.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)
                          .Where(w => w.Length > 2)
                          .Select(Regex.Escape);
 
         if (!words.Any())
-            return text;
+            return escapedText;
 
         var pattern = "(" + string.Join("|", words) + ")";
         try
         {
-            return Regex.Replace(text, pattern, "<mark class=\"search-highlight\">$1</mark>", RegexOptions.IgnoreCase);
+            return Regex.Replace(escapedText, pattern, "<mark class=\"search-highlight\">$1</mark>", RegexOptions.IgnoreCase);
         }
         catch
         {
-            return text;
+            return escapedText;
         }
     }
 
     public void Dispose()
     {
+        _disposed = true;
         _searchCts?.Cancel();
         _searchCts?.Dispose();
     }

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

@@ -142,6 +142,7 @@
     private LocalEpubMetadata? Metadata { get; set; }
     private string? ErrorMessage { get; set; }
     private byte[]? _epubBytes;
+    private bool _disposed;
     
     // Allow up to 50 MB
     private const long MaxFileSize = 50 * 1024 * 1024;
@@ -154,23 +155,30 @@
 
     private async Task HandleIngestionProgress(string message, double progress)
     {
+        if (_disposed) return;
         if (!IsIndexing) return;
 
         IngestionStatusMessage = message;
         IngestionProgressPercent = progress;
         
-        await InvokeAsync(StateHasChanged);
+        if (!_disposed)
+        {
+            await InvokeAsync(StateHasChanged);
+        }
 
         if (progress >= 1.0)
         {
             // Give the user a moment to see the completion message
             await Task.Delay(2500);
             
+            if (_disposed) return;
+
             // Now close the modal and navigate to the book
             if (IngestedBookId != Guid.Empty)
             {
                 var bookId = IngestedBookId;
                 await InvokeAsync(async () => {
+                    if (_disposed) return;
                     await CloseModal();
                     ReaderNavigation.NavigateToBook(bookId);
                 });
@@ -227,10 +235,12 @@
             using var stream = file.OpenReadStream(MaxFileSize);
             using var memoryStream = new MemoryStream();
             await stream.CopyToAsync(memoryStream);
+            if (_disposed) return;
             _epubBytes = memoryStream.ToArray();
             
             memoryStream.Position = 0;
             var result = await MetadataExtractor.ExtractMetadataAsync(memoryStream);
+            if (_disposed) return;
 
             if (result.IsSuccess)
             {
@@ -245,12 +255,18 @@
         catch (Exception ex)
         {
             Logger.LogError(ex, "Error uploading EPUB");
-            ErrorMessage = $"An unexpected error occurred: {ex.Message}";
+            if (!_disposed)
+            {
+                ErrorMessage = $"An unexpected error occurred: {ex.Message}";
+            }
         }
         finally
         {
-            IsParsing = false;
-            StateHasChanged();
+            if (!_disposed)
+            {
+                IsParsing = false;
+                StateHasChanged();
+            }
         }
     }
 
@@ -273,10 +289,12 @@
             );
 
             var response = await Http.PostAsJsonAsync("api/library/ingest", request);
+            if (_disposed) return;
 
             if (response.IsSuccessStatusCode)
             {
                 var result = await response.Content.ReadFromJsonAsync<IngestResult>();
+                if (_disposed) return;
                 if (result != null)
                 {
                     IngestedBookId = result.Id;
@@ -297,12 +315,18 @@
         catch (Exception ex)
         {
             Logger.LogError(ex, "Error during ingestion");
-            ErrorMessage = "Failed to save book to library. Please try again.";
-            IsIngesting = false;
+            if (!_disposed)
+            {
+                ErrorMessage = "Failed to save book to library. Please try again.";
+                IsIngesting = false;
+            }
         }
         finally
         {
-            StateHasChanged();
+            if (!_disposed)
+            {
+                StateHasChanged();
+            }
         }
     }
 
@@ -310,6 +334,7 @@
 
     public async ValueTask DisposeAsync()
     {
+        _disposed = true;
         SyncService.OnIngestionProgressReceived -= HandleIngestionProgress;
         // Clear the large byte array so it is eligible for GC even if the component is cached.
         _epubBytes = null;

src/NexusReader.Web.Client/Program.cs

@@ -50,6 +50,7 @@ builder.Services.AddSingleton<IDbContextFactory<AppDbContext>>(new ThrowingDbCon
 builder.Services.AddSingleton<IEmbeddingGenerator<string, Embedding<float>>>(new ThrowingEmbeddingGenerator());
 builder.Services.AddSingleton<IBookStorageService>(new ThrowingBookStorageService());
 builder.Services.AddSingleton<IEbookRepository>(new ThrowingEbookRepository());
+builder.Services.AddSingleton<IQuizResultRepository>(new ThrowingQuizResultRepository());
 builder.Services.AddSingleton<ISyncBroadcaster>(new ThrowingSyncBroadcaster());
 builder.Services.AddSingleton<IEpubExtractor>(new ThrowingEpubExtractor());
 
@@ -89,6 +90,16 @@ public class ThrowingEbookRepository : IEbookRepository
     public Task<Author?> FindAuthorByNameAsync(string name, CancellationToken cancellationToken = default) => throw new NotSupportedException(ErrorMessage);
     public void AddAuthor(Author author) => throw new NotSupportedException(ErrorMessage);
     public void AddEbook(Ebook ebook) => throw new NotSupportedException(ErrorMessage);
+    public Task<Ebook?> FindByIdAsync(Guid id, CancellationToken cancellationToken = default) => throw new NotSupportedException(ErrorMessage);
+    public Task<int> SaveChangesAsync(CancellationToken cancellationToken = default) => throw new NotSupportedException(ErrorMessage);
+}
+
+public class ThrowingQuizResultRepository : IQuizResultRepository
+{
+    private const string ErrorMessage = "QuizResult repository operations are not supported in the WASM client. Use the API endpoint for data access.";
+
+    public Task<NexusUser?> FindUserByIdAsync(string userId, CancellationToken cancellationToken = default) => throw new NotSupportedException(ErrorMessage);
+    public void AddQuizResult(QuizResult quizResult) => throw new NotSupportedException(ErrorMessage);
     public Task<int> SaveChangesAsync(CancellationToken cancellationToken = default) => throw new NotSupportedException(ErrorMessage);
 }
 

tests/NexusReader.Application.Tests/Commands/SubmitQuizResultCommandHandlerTests.cs

@@ -5,53 +5,46 @@ using FluentAssertions;
 using Microsoft.Data.Sqlite;
 using Microsoft.EntityFrameworkCore;
 using Moq;
+using NexusReader.Application.Abstractions.Persistence;
 using NexusReader.Application.Commands.Quiz;
 using NexusReader.Data.Persistence;
 using NexusReader.Domain.Entities;
+using NexusReader.Infrastructure.Persistence;
 using Xunit;
 
 namespace NexusReader.Application.Tests.Commands;
 
-public class SubmitQuizResultCommandHandlerTests : IDisposable
+public class SubmitQuizResultCommandHandlerTests
 {
-    private readonly SqliteConnection _connection;
-    private readonly DbContextOptions<AppDbContext> _contextOptions;
-    private readonly Mock<IDbContextFactory<AppDbContext>> _dbContextFactoryMock;
+    private readonly Mock<IQuizResultRepository> _repositoryMock;
 
     public SubmitQuizResultCommandHandlerTests()
     {
-        _connection = new SqliteConnection("DataSource=:memory:");
-        _connection.Open();
-
-        _contextOptions = new DbContextOptionsBuilder<AppDbContext>()
-            .UseSqlite(_connection)
-            .Options;
-
-        using var context = new AppDbContext(_contextOptions);
-        context.Database.EnsureCreated();
-
-        _dbContextFactoryMock = new Mock<IDbContextFactory<AppDbContext>>();
-        _dbContextFactoryMock.Setup(f => f.CreateDbContextAsync(It.IsAny<CancellationToken>()))
-            .ReturnsAsync(() => new AppDbContext(_contextOptions));
+        _repositoryMock = new Mock<IQuizResultRepository>();
     }
 
     [Fact]
     public async Task Handle_WithValidRequest_PersistsQuizResultToDatabase()
     {
         // Arrange
-        using (var context = new AppDbContext(_contextOptions))
+        var user = new NexusUser
         {
-            var user = new NexusUser
-            {
-                Id = "user-abc",
-                UserName = "testuser",
-                Email = "test@example.com",
-                TenantId = "tenant-xyz",
-                SubscriptionPlanId = 1
-            };
-            context.Users.Add(user);
-            await context.SaveChangesAsync();
-        }
+            Id = "user-abc",
+            UserName = "testuser",
+            Email = "test@example.com",
+            TenantId = "tenant-xyz",
+            SubscriptionPlanId = 1
+        };
+
+        _repositoryMock.Setup(r => r.FindUserByIdAsync("user-abc", It.IsAny<CancellationToken>()))
+            .ReturnsAsync(user);
+
+        QuizResult? capturedQuizResult = null;
+        _repositoryMock.Setup(r => r.AddQuizResult(It.IsAny<QuizResult>()))
+            .Callback<QuizResult>(q => capturedQuizResult = q);
+
+        _repositoryMock.Setup(r => r.SaveChangesAsync(It.IsAny<CancellationToken>()))
+            .ReturnsAsync(1);
 
         var command = new SubmitQuizResultCommand(
             UserId: "user-abc",
@@ -60,29 +53,30 @@ public class SubmitQuizResultCommandHandlerTests : IDisposable
             TotalQuestions: 5
         );
 
-        var handler = new SubmitQuizResultCommandHandler(_dbContextFactoryMock.Object);
+        var handler = new SubmitQuizResultCommandHandler(_repositoryMock.Object);
 
         // Act
         var result = await handler.Handle(command, CancellationToken.None);
 
         // Assert
         result.IsSuccess.Should().BeTrue();
+        capturedQuizResult.Should().NotBeNull();
+        capturedQuizResult!.Topic.Should().Be("Sprawdzian: .NET 10");
+        capturedQuizResult.Score.Should().Be(4);
+        capturedQuizResult.TotalQuestions.Should().Be(5);
+        capturedQuizResult.TenantId.Should().Be("tenant-xyz");
 
-        using (var context = new AppDbContext(_contextOptions))
-        {
-            var quizResult = await context.QuizResults.FirstOrDefaultAsync(q => q.UserId == "user-abc");
-            quizResult.Should().NotBeNull();
-            quizResult!.Topic.Should().Be("Sprawdzian: .NET 10");
-            quizResult.Score.Should().Be(4);
-            quizResult.TotalQuestions.Should().Be(5);
-            quizResult.TenantId.Should().Be("tenant-xyz");
-        }
+        _repositoryMock.Verify(r => r.AddQuizResult(It.IsAny<QuizResult>()), Times.Once);
+        _repositoryMock.Verify(r => r.SaveChangesAsync(It.IsAny<CancellationToken>()), Times.Once);
     }
 
     [Fact]
     public async Task Handle_WithNonExistentUser_ReturnsFailureResult()
     {
         // Arrange
+        _repositoryMock.Setup(r => r.FindUserByIdAsync("non-existent", It.IsAny<CancellationToken>()))
+            .ReturnsAsync((NexusUser?)null);
+
         var command = new SubmitQuizResultCommand(
             UserId: "non-existent",
             Topic: "Sprawdzian: .NET 10",
@@ -90,7 +84,7 @@ public class SubmitQuizResultCommandHandlerTests : IDisposable
             TotalQuestions: 5
         );
 
-        var handler = new SubmitQuizResultCommandHandler(_dbContextFactoryMock.Object);
+        var handler = new SubmitQuizResultCommandHandler(_repositoryMock.Object);
 
         // Act
         var result = await handler.Handle(command, CancellationToken.None);
@@ -98,10 +92,8 @@ public class SubmitQuizResultCommandHandlerTests : IDisposable
         // Assert
         result.IsFailed.Should().BeTrue();
         result.Errors.Should().ContainSingle(e => e.Message == "User not found.");
-    }
 
-    public void Dispose()
-    {
-        _connection.Dispose();
+        _repositoryMock.Verify(r => r.AddQuizResult(It.IsAny<QuizResult>()), Times.Never);
+        _repositoryMock.Verify(r => r.SaveChangesAsync(It.IsAny<CancellationToken>()), Times.Never);
     }
 }