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

@@ -0,0 +1,21 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace NexusReader.Application.Abstractions.Persistence;
+
+/// <summary>
+/// Decoupled database store to retrieve active user reading states and chapter content.
+/// </summary>
+public interface IUserReadingStateStore
+{
+    /// <summary>
+    /// Retrieves the user's active reading state: last read ebook ID, last opened chapter/page ID, and tenant ID.
+    /// </summary>
+    Task<(Guid? EbookId, string? ChapterId, string? TenantId)> GetActiveReadingStateAsync(string userId, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Retrieves the text content of a specific chapter/page by its ID.
+    /// </summary>
+    Task<string?> GetChapterContentAsync(string chapterId, CancellationToken cancellationToken = default);
+}

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

@@ -8,7 +8,7 @@ namespace NexusReader.Application.Abstractions.Persistence;
 /// <summary>
 /// Represents a chunk of text retrieved from the semantic vector database.
 /// </summary>
-public record VectorChunk(string Content, string EbookId, double Score, string MetadataJson = "");
+public record VectorChunk(string Content, string EbookId, double Score, string MetadataJson = "", string BookTitle = "", string ChapterTitle = "");
 
 /// <summary>
 /// Abstraction for performing semantic vector searches, isolating Qdrant gRPC dependencies from the Application layer.
@@ -24,4 +24,9 @@ public interface IVectorSearchStore
     /// Searches within a whitelist of owned book IDs for the best semantic matches.
     /// </summary>
     Task<List<VectorChunk>> SearchLocalAsync(string queryText, string tenantId, List<Guid> whitelistedBookIds, int limit, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Searches the entire global catalog (filtered by tenant) for the best semantic matches, excluding a specific book ID.
+    /// </summary>
+    Task<List<VectorChunk>> SearchGlobalExcludeAsync(string queryText, string tenantId, Guid excludeBookId, int limit, CancellationToken cancellationToken = default);
 }

src/NexusReader.Application/Common/AppJsonContext.cs

@@ -13,6 +13,9 @@ namespace NexusReader.Application.Common;
 [JsonSerializable(typeof(List<GraphLinkDto>))]
 [JsonSerializable(typeof(GetGlobalIntelligenceRequest))]
 [JsonSerializable(typeof(IntelligenceResponse))]
+[JsonSerializable(typeof(NexusReader.Application.Queries.Recommendations.ContextualRecommendationResponse))]
+[JsonSerializable(typeof(NexusReader.Application.Queries.Recommendations.RecommendationDto))]
+[JsonSerializable(typeof(List<NexusReader.Application.Queries.Recommendations.RecommendationDto>))]
 public partial class AppJsonContext : JsonSerializerContext
 {
 }

src/NexusReader.Application/Queries/Recommendations/GetContextualRecommendationsQuery.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+using FluentResults;
+using MediatR;
+
+namespace NexusReader.Application.Queries.Recommendations;
+
+/// <summary>
+/// MediatR query to fetch contextual recommendations based on the user's active reading state.
+/// </summary>
+public record GetContextualRecommendationsQuery(string UserId) 
+    : IRequest<Result<ContextualRecommendationResponse>>;
+
+/// <summary>
+/// Response DTO containing contextual recommendations.
+/// </summary>
+public record ContextualRecommendationResponse(List<RecommendationDto> Recommendations);
+
+/// <summary>
+/// Individual contextual recommendation details.
+/// </summary>
+public record RecommendationDto(
+    string BookTitle,
+    string ChapterTitle,
+    int MatchPercentage,
+    bool IsPremiumUpsell,
+    Guid TargetBookId
+);

src/NexusReader.Infrastructure/DependencyInjection.cs

@@ -130,6 +130,7 @@ public static class DependencyInjection
         services.AddScoped<IQuizResultRepository, QuizResultRepository>();
         services.AddScoped<IConceptsMapReadRepository, ConceptsMapReadRepository>();
         services.AddScoped<IUserLibraryStore, UserLibraryStore>();
+        services.AddScoped<IUserReadingStateStore, UserReadingStateStore>();
         services.AddScoped<IVectorSearchStore, VectorSearchStore>();
 
         // Fix #2: SignalR broadcaster (scoped, wraps IHubContext which is itself a singleton wrapper)

src/NexusReader.Infrastructure/Persistence/UserReadingStateStore.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.EntityFrameworkCore;
+using NexusReader.Application.Abstractions.Persistence;
+using NexusReader.Data.Persistence;
+
+namespace NexusReader.Infrastructure.Persistence;
+
+/// <summary>
+/// EF Core implementation of <see cref="IUserReadingStateStore"/>.
+/// </summary>
+internal sealed class UserReadingStateStore : IUserReadingStateStore
+{
+    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;
+
+    public UserReadingStateStore(IDbContextFactory<AppDbContext> dbContextFactory)
+    {
+        _dbContextFactory = dbContextFactory;
+    }
+
+    /// <inheritdoc />
+    public async Task<(Guid? EbookId, string? ChapterId, string? TenantId)> GetActiveReadingStateAsync(string userId, CancellationToken cancellationToken = default)
+    {
+        await using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
+
+        var userState = await dbContext.Users
+            .Where(u => u.Id == userId)
+            .Select(u => new
+            {
+                u.TenantId,
+                u.LastReadPageId,
+                LastReadBookId = u.Ebooks.OrderByDescending(e => e.LastReadDate).Select(e => (Guid?)e.Id).FirstOrDefault()
+            })
+            .FirstOrDefaultAsync(cancellationToken);
+
+        if (userState == null)
+        {
+            return (null, null, null);
+        }
+
+        return (userState.LastReadBookId, userState.LastReadPageId, userState.TenantId);
+    }
+
+    /// <inheritdoc />
+    public async Task<string?> GetChapterContentAsync(string chapterId, CancellationToken cancellationToken = default)
+    {
+        await using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
+
+        return await dbContext.KnowledgeUnits
+            .Where(ku => ku.Id == chapterId)
+            .Select(ku => ku.Content)
+            .FirstOrDefaultAsync(cancellationToken);
+    }
+}

src/NexusReader.Infrastructure/Persistence/VectorSearchStore.cs

@@ -73,6 +73,25 @@ internal sealed class VectorSearchStore : IVectorSearchStore
         return await ExecuteSearchAsync(queryVector, filter, limit, cancellationToken);
     }
 
+    /// <inheritdoc />
+    public async Task<List<VectorChunk>> SearchGlobalExcludeAsync(string queryText, string tenantId, Guid excludeBookId, int limit, CancellationToken cancellationToken = default)
+    {
+        var queryVector = await GenerateEmbeddingAsync(queryText, cancellationToken);
+        var filter = BuildTenantFilter(tenantId);
+
+        // Exclude current book
+        filter.MustNot.Add(new Qdrant.Client.Grpc.Condition
+        {
+            Field = new Qdrant.Client.Grpc.FieldCondition
+            {
+                Key = "ebookId",
+                Match = new Qdrant.Client.Grpc.Match { Text = excludeBookId.ToString() }
+            }
+        });
+
+        return await ExecuteSearchAsync(queryVector, filter, limit, cancellationToken);
+    }
+
     private async Task<float[]> GenerateEmbeddingAsync(string text, CancellationToken cancellationToken)
     {
         var response = await _retryPipeline.ExecuteAsync(async ct => 
@@ -130,8 +149,10 @@ internal sealed class VectorSearchStore : IVectorSearchStore
                 var content = point.Payload.TryGetValue("content", out var cv) ? cv.StringValue : string.Empty;
                 var ebookId = point.Payload.TryGetValue("ebookId", out var ev) ? ev.StringValue : string.Empty;
                 var metadataJson = point.Payload.TryGetValue("metadataJson", out var mv) ? mv.StringValue : string.Empty;
+                var bookTitle = point.Payload.TryGetValue("bookTitle", out var btv) ? btv.StringValue : string.Empty;
+                var chapterTitle = point.Payload.TryGetValue("chapterTitle", out var ctv) ? ctv.StringValue : string.Empty;
 
-                return new VectorChunk(content, ebookId, point.Score, metadataJson);
+                return new VectorChunk(content, ebookId, point.Score, metadataJson, bookTitle, chapterTitle);
             }).ToList();
         }
         catch (Exception ex)

src/NexusReader.Infrastructure/Queries/GetContextualRecommendationsQueryHandler.cs

@@ -0,0 +1,129 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text.Json;
+using System.Threading;
+using System.Threading.Tasks;
+using FluentResults;
+using MediatR;
+using NexusReader.Application.Abstractions.Persistence;
+using NexusReader.Application.Queries.Recommendations;
+
+namespace NexusReader.Infrastructure.Queries;
+
+/// <summary>
+/// Handles <see cref="GetContextualRecommendationsQuery"/> by discovering the active reading state,
+/// performing semantic search using IVectorSearchStore with book exclusion, and mapping upsells.
+/// </summary>
+public class GetContextualRecommendationsQueryHandler : IRequestHandler<GetContextualRecommendationsQuery, Result<ContextualRecommendationResponse>>
+{
+    private readonly IUserReadingStateStore _readingStateStore;
+    private readonly IUserLibraryStore _libraryStore;
+    private readonly IVectorSearchStore _vectorSearchStore;
+
+    public GetContextualRecommendationsQueryHandler(
+        IUserReadingStateStore readingStateStore,
+        IUserLibraryStore libraryStore,
+        IVectorSearchStore vectorSearchStore)
+    {
+        _readingStateStore = readingStateStore;
+        _libraryStore = libraryStore;
+        _vectorSearchStore = vectorSearchStore;
+    }
+
+    public async Task<Result<ContextualRecommendationResponse>> Handle(GetContextualRecommendationsQuery request, CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrEmpty(request.UserId))
+        {
+            return Result.Fail("UserId cannot be empty.");
+        }
+
+        try
+        {
+            // Step 1: Discover active reading state
+            var (ebookId, chapterId, tenantId) = await _readingStateStore.GetActiveReadingStateAsync(request.UserId, cancellationToken);
+            if (ebookId == null)
+            {
+                // Fallback: brand-new user with no reading history, return empty recommendations list safely
+                return Result.Ok(new ContextualRecommendationResponse(new List<RecommendationDto>()));
+            }
+
+            // Step 2: Fetch specific content associated with active ChapterId
+            string? chapterContent = null;
+            if (!string.IsNullOrEmpty(chapterId))
+            {
+                chapterContent = await _readingStateStore.GetChapterContentAsync(chapterId, cancellationToken);
+            }
+
+            // Fallback: if no active chapter or content, try retrieving any chapter content from this book
+            if (string.IsNullOrEmpty(chapterContent))
+            {
+                return Result.Ok(new ContextualRecommendationResponse(new List<RecommendationDto>()));
+            }
+
+            // Step 3: Perform similarity search using IVectorSearchStore
+            var resolvedTenantId = tenantId ?? "global";
+            var searchResults = await _vectorSearchStore.SearchGlobalExcludeAsync(
+                chapterContent,
+                resolvedTenantId,
+                ebookId.Value,
+                limit: 2,
+                cancellationToken: cancellationToken
+            );
+
+            // Step 4: Process recommendations and cross-reference owned books
+            var ownedBookIds = await _libraryStore.GetOwnedBookIdsAsync(request.UserId, cancellationToken);
+            var recommendations = new List<RecommendationDto>();
+
+            foreach (var point in searchResults)
+            {
+                var targetEbookIdStr = point.EbookId;
+                if (!Guid.TryParse(targetEbookIdStr, out var targetEbookId))
+                    continue;
+
+                // Load bookTitle from point
+                var bookTitle = point.BookTitle;
+                if (string.IsNullOrEmpty(bookTitle))
+                {
+                    bookTitle = "Nieznana książka";
+                }
+
+                // Load chapterTitle from point or metadataJson
+                var chapterTitle = point.ChapterTitle;
+                if (string.IsNullOrEmpty(chapterTitle))
+                {
+                    chapterTitle = "Wiedza z rozdziału";
+                    if (!string.IsNullOrEmpty(point.MetadataJson))
+                    {
+                        try
+                        {
+                            using var doc = JsonDocument.Parse(point.MetadataJson);
+                            if (doc.RootElement.TryGetProperty("label", out var labelProp))
+                            {
+                                chapterTitle = labelProp.GetString() ?? chapterTitle;
+                            }
+                        }
+                        catch { }
+                    }
+                }
+
+                var isPremiumUpsell = !ownedBookIds.Contains(targetEbookId);
+                var matchPercentage = (int)Math.Round(point.Score * 100);
+
+                recommendations.Add(new RecommendationDto(
+                    BookTitle: bookTitle,
+                    ChapterTitle: chapterTitle,
+                    MatchPercentage: matchPercentage,
+                    IsPremiumUpsell: isPremiumUpsell,
+                    TargetBookId: targetEbookId
+                ));
+            }
+
+            return Result.Ok(new ContextualRecommendationResponse(recommendations));
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error("Downstream vector database or state query failed.").CausedBy(ex));
+        }
+    }
+}

src/NexusReader.Infrastructure/Services/KnowledgeService.cs

@@ -339,6 +339,17 @@ public class KnowledgeService : IKnowledgeService
         {
             try
             {
+                // Retrieve the book's title from the database using EF Core
+                string bookTitle = "Nieznana książka";
+                if (ebookId.HasValue)
+                {
+                    var ebook = await dbContext.Ebooks.FindAsync(new object[] { ebookId.Value }, cancellationToken);
+                    if (ebook != null)
+                    {
+                        bookTitle = ebook.Title;
+                    }
+                }
+
                 var contents = unitsToEmbed.Select(u => u.Content).ToList();
                 
                 var embeddingResponse = await _retryPipeline.ExecuteAsync(async ct => 
@@ -355,6 +366,12 @@ public class KnowledgeService : IKnowledgeService
                     var unitDto = unitsToEmbed[i];
                     var vector = embeddings[i].Vector.ToArray();
 
+                    string chapterTitle = "Wiedza z rozdziału";
+                    if (unitDto.Metadata != null && unitDto.Metadata.TryGetValue("label", out var labelVal) && labelVal is string labelStr)
+                    {
+                        chapterTitle = labelStr;
+                    }
+
                     var point = new PointStruct
                     {
                         Id = GetDeterministicGuid(unitDto.Id),
@@ -365,6 +382,8 @@ public class KnowledgeService : IKnowledgeService
                             ["type"] = unitDto.Type ?? string.Empty,
                             ["tenantId"] = tenantId,
                             ["ebookId"] = ebookId?.ToString() ?? string.Empty,
+                            ["bookTitle"] = bookTitle,
+                            ["chapterTitle"] = chapterTitle,
                             ["metadataJson"] = JsonSerializer.Serialize(unitDto.Metadata)
                         }
                     };

src/NexusReader.Web/Program.cs

@@ -437,6 +437,20 @@ app.MapPost("/api/intelligence", async (
     return Results.BadRequest(errorMsg);
 }).RequireAuthorization();
 
+app.MapGet("/api/recommendations", async (
+    ClaimsPrincipal user,
+    IMediator mediator) =>
+{
+    var userId = user.FindFirstValue(ClaimTypes.NameIdentifier);
+    if (string.IsNullOrEmpty(userId)) return Results.Unauthorized();
+
+    var result = await mediator.Send(new NexusReader.Application.Queries.Recommendations.GetContextualRecommendationsQuery(userId));
+    if (result.IsSuccess) return Results.Ok(result.Value);
+
+    var errorMsg = result.Errors.Count > 0 ? result.Errors[0].Message : "Failed to fetch contextual recommendations";
+    return Results.BadRequest(errorMsg);
+}).RequireAuthorization();
+
 app.MapPost("/api/library/ingest", async ([FromBody] IngestEbookRequest request, ClaimsPrincipal user, IMediator mediator) =>
 {
     var userId = user.FindFirstValue(ClaimTypes.NameIdentifier);

tests/NexusReader.Application.Tests/Queries/GetContextualRecommendationsQueryTests.cs

@@ -0,0 +1,128 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using FluentAssertions;
+using Moq;
+using NexusReader.Application.Abstractions.Persistence;
+using NexusReader.Application.Queries.Recommendations;
+using NexusReader.Infrastructure.Queries;
+using Xunit;
+
+namespace NexusReader.Application.Tests.Queries;
+
+public class GetContextualRecommendationsQueryTests
+{
+    private readonly Mock<IUserReadingStateStore> _readingStateStoreMock;
+    private readonly Mock<IUserLibraryStore> _libraryStoreMock;
+    private readonly Mock<IVectorSearchStore> _vectorSearchStoreMock;
+    private readonly GetContextualRecommendationsQueryHandler _handler;
+
+    public GetContextualRecommendationsQueryTests()
+    {
+        _readingStateStoreMock = new Mock<IUserReadingStateStore>();
+        _libraryStoreMock = new Mock<IUserLibraryStore>();
+        _vectorSearchStoreMock = new Mock<IVectorSearchStore>();
+
+        _handler = new GetContextualRecommendationsQueryHandler(
+            _readingStateStoreMock.Object,
+            _libraryStoreMock.Object,
+            _vectorSearchStoreMock.Object
+        );
+    }
+
+    [Fact]
+    public async Task Handle_WithNoActiveReadingState_ReturnsEmptyRecommendations()
+    {
+        // Arrange
+        var userId = "user-123";
+        _readingStateStoreMock.Setup(s => s.GetActiveReadingStateAsync(userId, It.IsAny<CancellationToken>()))
+            .ReturnsAsync((null, null, null));
+
+        var query = new GetContextualRecommendationsQuery(userId);
+
+        // Act
+        var result = await _handler.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.IsSuccess.Should().BeTrue();
+        result.Value.Recommendations.Should().BeEmpty();
+    }
+
+    [Fact]
+    public async Task Handle_WithActiveReadingState_PerformsSimilaritySearchAndReturnsRecommendations()
+    {
+        // Arrange
+        var userId = "user-123";
+        var activeEbookId = Guid.NewGuid();
+        var activeChapterId = "chapter-1";
+        var tenantId = "tenant-abc";
+        var chapterContent = "Active chapter content description";
+
+        _readingStateStoreMock.Setup(s => s.GetActiveReadingStateAsync(userId, It.IsAny<CancellationToken>()))
+            .ReturnsAsync((activeEbookId, activeChapterId, tenantId));
+
+        _readingStateStoreMock.Setup(s => s.GetChapterContentAsync(activeChapterId, It.IsAny<CancellationToken>()))
+            .ReturnsAsync(chapterContent);
+
+        // Mock vector search results using clean VectorChunk list
+        var targetEbookId1 = Guid.NewGuid();
+        var targetEbookId2 = Guid.NewGuid();
+
+        var mockChunks = new List<VectorChunk>
+        {
+            new VectorChunk(
+                Content: "Result pattern details",
+                EbookId: targetEbookId1.ToString(),
+                Score: 0.88,
+                MetadataJson: "",
+                BookTitle: "Clean Architecture deep dive",
+                ChapterTitle: "Chapter 3: Result Pattern"
+            ),
+            new VectorChunk(
+                Content: "Performance optimizations",
+                EbookId: targetEbookId2.ToString(),
+                Score: 0.72,
+                MetadataJson: "",
+                BookTitle: "Advanced C# 14",
+                ChapterTitle: "Chapter 5: Span and Performance"
+            )
+        };
+
+        _vectorSearchStoreMock.Setup(v => v.SearchGlobalExcludeAsync(
+                chapterContent,
+                tenantId,
+                activeEbookId,
+                2,
+                It.IsAny<CancellationToken>()))
+            .ReturnsAsync(mockChunks);
+
+        // User owns the second book but not the first one
+        _libraryStoreMock.Setup(l => l.GetOwnedBookIdsAsync(userId, It.IsAny<CancellationToken>()))
+            .ReturnsAsync(new List<Guid> { targetEbookId2 });
+
+        var query = new GetContextualRecommendationsQuery(userId);
+
+        // Act
+        var result = await _handler.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.IsSuccess.Should().BeTrue();
+        result.Value.Recommendations.Should().HaveCount(2);
+
+        var firstRec = result.Value.Recommendations.First();
+        firstRec.BookTitle.Should().Be("Clean Architecture deep dive");
+        firstRec.ChapterTitle.Should().Be("Chapter 3: Result Pattern");
+        firstRec.MatchPercentage.Should().Be(88);
+        firstRec.IsPremiumUpsell.Should().BeTrue(); // User does not own book 1
+        firstRec.TargetBookId.Should().Be(targetEbookId1);
+
+        var secondRec = result.Value.Recommendations.Last();
+        secondRec.BookTitle.Should().Be("Advanced C# 14");
+        secondRec.ChapterTitle.Should().Be("Chapter 5: Span and Performance");
+        secondRec.MatchPercentage.Should().Be(72);
+        secondRec.IsPremiumUpsell.Should().BeFalse(); // User owns book 2
+        secondRec.TargetBookId.Should().Be(targetEbookId2);
+    }
+}