src/NexusReader.Application/Abstractions/Services/IKnowledgeService.cs

@@ -5,10 +5,10 @@ namespace NexusReader.Application.Abstractions.Services;
 
 public interface IKnowledgeService
 {
-    Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, string tenantId, CancellationToken cancellationToken = default);
-    Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, string tenantId, CancellationToken cancellationToken = default);
-    Task<Result<KnowledgePacket>> GetKnowledgeMapAsync(string text, string tenantId, CancellationToken cancellationToken = default);
-    Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, string tenantId, CancellationToken cancellationToken = default);
+    Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default);
+    Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default);
+    Task<Result<KnowledgePacket>> GetKnowledgeMapAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default);
+    Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default);
     Task<Result<List<RelevantContext>>> GetRelevantContextAsync(string query, string tenantId, CancellationToken cancellationToken = default);
     Task<Result<GroundednessResult>> VerifyGroundednessAsync(string answer, string context, string tenantId, CancellationToken cancellationToken = default);
     Task<Result> ClearCacheAsync(CancellationToken cancellationToken = default);

src/NexusReader.Application/Queries/Graph/GetKnowledgeGraphQuery.cs

@@ -4,5 +4,6 @@ namespace NexusReader.Application.Queries.Graph;
 
 /// <param name="Text">Chapter or page content to extract the graph from.</param>
 /// <param name="TenantId">Tenant scope for knowledge extraction and caching.</param>
-public record GetKnowledgeGraphQuery(string Text, string TenantId) : IQuery<GraphDataDto>;
+/// <param name="EbookId">Optional Ebook ID to link the knowledge units to.</param>
+public record GetKnowledgeGraphQuery(string Text, string TenantId, Guid? EbookId = null) : IQuery<GraphDataDto>;
 

src/NexusReader.Application/Queries/Graph/GetKnowledgeGraphQueryHandler.cs

@@ -18,7 +18,11 @@ internal sealed class GetKnowledgeGraphQueryHandler : IQueryHandler<GetKnowledge
         if (string.IsNullOrWhiteSpace(request.Text))
             return Result.Ok(new GraphDataDto());
 
-        var result = await _knowledgeService.GetGraphDataAsync(request.Text, request.TenantId, cancellationToken);
+        var result = await _knowledgeService.GetGraphDataAsync(
+            request.Text, 
+            request.TenantId, 
+            ebookId: request.EbookId, 
+            cancellationToken: cancellationToken);
 
         if (result.IsFailed)
             return Result.Fail<GraphDataDto>(result.Errors);

src/NexusReader.Data/Migrations/AppDbContextModelSnapshot.cs

@@ -247,14 +247,12 @@ namespace NexusReader.Data.Migrations
                     b.Property<DateTime>("CreatedAt")
                         .HasColumnType("timestamp with time zone");
 
+                    b.Property<Guid?>("EbookId")
+                        .HasColumnType("uuid");
+
                     b.Property<string>("MetadataJson")
                         .HasColumnType("text");
 
-                    b.Property<string>("SourceId")
-                        .IsRequired()
-                        .HasMaxLength(128)
-                        .HasColumnType("character varying(128)");
-
                     b.Property<string>("TenantId")
                         .IsRequired()
                         .HasMaxLength(128)
@@ -273,7 +271,7 @@ namespace NexusReader.Data.Migrations
 
                     b.HasKey("Id");
 
-                    b.HasIndex("SourceId");
+                    b.HasIndex("EbookId");
 
                     b.HasIndex("TenantId");
 
@@ -635,6 +633,16 @@ namespace NexusReader.Data.Migrations
                     b.Navigation("User");
                 });
 
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnit", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.Ebook", "Ebook")
+                        .WithMany()
+                        .HasForeignKey("EbookId")
+                        .OnDelete(DeleteBehavior.Cascade);
+
+                    b.Navigation("Ebook");
+                });
+
             modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnitLink", b =>
                 {
                     b.HasOne("NexusReader.Domain.Entities.KnowledgeUnit", "SourceUnit")

src/NexusReader.Data/Persistence/AppDbContext.cs

@@ -65,8 +65,13 @@ public class AppDbContext : IdentityDbContext<NexusUser>
         {
             entity.HasKey(e => e.Id);
             entity.HasIndex(e => e.TenantId);
-            entity.HasIndex(e => e.SourceId);
+            entity.HasIndex(e => e.EbookId);
             entity.Property(e => e.Vector).HasColumnType("vector(768)");
+
+            entity.HasOne(e => e.Ebook)
+                .WithMany()
+                .HasForeignKey(e => e.EbookId)
+                .OnDelete(DeleteBehavior.Cascade);
         });
 
         modelBuilder.Entity<KnowledgeUnitLink>(entity =>

src/NexusReader.Data/Persistence/Migrations/20260513183726_FixKnowledgeUnitEbookId.Designer.cs

@@ -0,0 +1,712 @@
+// <auto-generated />
+using System;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
+using NexusReader.Data.Persistence;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+using Pgvector;
+
+#nullable disable
+
+namespace NexusReader.Data.Persistence.Migrations
+{
+    [DbContext(typeof(AppDbContext))]
+    [Migration("20260513183726_FixKnowledgeUnitEbookId")]
+    partial class FixKnowledgeUnitEbookId
+    {
+        /// <inheritdoc />
+        protected override void BuildTargetModel(ModelBuilder modelBuilder)
+        {
+#pragma warning disable 612, 618
+            modelBuilder
+                .HasAnnotation("ProductVersion", "10.0.7")
+                .HasAnnotation("Relational:MaxIdentifierLength", 63);
+
+            NpgsqlModelBuilderExtensions.HasPostgresExtension(modelBuilder, "vector");
+            NpgsqlModelBuilderExtensions.UseIdentityByDefaultColumns(modelBuilder);
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRole", b =>
+                {
+                    b.Property<string>("Id")
+                        .HasColumnType("text");
+
+                    b.Property<string>("ConcurrencyStamp")
+                        .IsConcurrencyToken()
+                        .HasColumnType("text");
+
+                    b.Property<string>("Name")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.Property<string>("NormalizedName")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("NormalizedName")
+                        .IsUnique()
+                        .HasDatabaseName("RoleNameIndex");
+
+                    b.ToTable("AspNetRoles", (string)null);
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRoleClaim<string>", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("ClaimType")
+                        .HasColumnType("text");
+
+                    b.Property<string>("ClaimValue")
+                        .HasColumnType("text");
+
+                    b.Property<string>("RoleId")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("RoleId");
+
+                    b.ToTable("AspNetRoleClaims", (string)null);
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserClaim<string>", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("ClaimType")
+                        .HasColumnType("text");
+
+                    b.Property<string>("ClaimValue")
+                        .HasColumnType("text");
+
+                    b.Property<string>("UserId")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("UserId");
+
+                    b.ToTable("AspNetUserClaims", (string)null);
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserLogin<string>", b =>
+                {
+                    b.Property<string>("LoginProvider")
+                        .HasColumnType("text");
+
+                    b.Property<string>("ProviderKey")
+                        .HasColumnType("text");
+
+                    b.Property<string>("ProviderDisplayName")
+                        .HasColumnType("text");
+
+                    b.Property<string>("UserId")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.HasKey("LoginProvider", "ProviderKey");
+
+                    b.HasIndex("UserId");
+
+                    b.ToTable("AspNetUserLogins", (string)null);
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserRole<string>", b =>
+                {
+                    b.Property<string>("UserId")
+                        .HasColumnType("text");
+
+                    b.Property<string>("RoleId")
+                        .HasColumnType("text");
+
+                    b.HasKey("UserId", "RoleId");
+
+                    b.HasIndex("RoleId");
+
+                    b.ToTable("AspNetUserRoles", (string)null);
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserToken<string>", b =>
+                {
+                    b.Property<string>("UserId")
+                        .HasColumnType("text");
+
+                    b.Property<string>("LoginProvider")
+                        .HasColumnType("text");
+
+                    b.Property<string>("Name")
+                        .HasColumnType("text");
+
+                    b.Property<string>("Value")
+                        .HasColumnType("text");
+
+                    b.HasKey("UserId", "LoginProvider", "Name");
+
+                    b.ToTable("AspNetUserTokens", (string)null);
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.Author", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("Name")
+                        .IsRequired()
+                        .HasMaxLength(255)
+                        .HasColumnType("character varying(255)");
+
+                    b.HasKey("Id");
+
+                    b.ToTable("Authors");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.Ebook", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("uuid");
+
+                    b.Property<DateTime>("AddedDate")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<int>("AuthorId")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("CoverUrl")
+                        .HasColumnType("text");
+
+                    b.Property<string>("FilePath")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<bool>("IsReadyForReading")
+                        .HasColumnType("boolean");
+
+                    b.Property<string>("LastChapter")
+                        .HasMaxLength(255)
+                        .HasColumnType("character varying(255)");
+
+                    b.Property<int>("LastChapterIndex")
+                        .HasColumnType("integer");
+
+                    b.Property<DateTime?>("LastReadDate")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<double>("Progress")
+                        .HasColumnType("double precision");
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<string>("Title")
+                        .IsRequired()
+                        .HasMaxLength(255)
+                        .HasColumnType("character varying(255)");
+
+                    b.Property<string>("UserId")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("AuthorId");
+
+                    b.HasIndex("TenantId");
+
+                    b.HasIndex("UserId");
+
+                    b.ToTable("Ebooks");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnit", b =>
+                {
+                    b.Property<string>("Id")
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<string>("Content")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<Guid>("EbookId")
+                        .HasColumnType("uuid");
+
+                    b.Property<string>("MetadataJson")
+                        .HasColumnType("text");
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<int>("Type")
+                        .HasColumnType("integer");
+
+                    b.Property<Vector>("Vector")
+                        .HasColumnType("vector(768)");
+
+                    b.Property<string>("Version")
+                        .IsRequired()
+                        .HasMaxLength(50)
+                        .HasColumnType("character varying(50)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("EbookId");
+
+                    b.HasIndex("TenantId");
+
+                    b.ToTable("KnowledgeUnits");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnitLink", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("RelationType")
+                        .IsRequired()
+                        .HasMaxLength(50)
+                        .HasColumnType("character varying(50)");
+
+                    b.Property<string>("SourceUnitId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<string>("TargetUnitId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("SourceUnitId");
+
+                    b.HasIndex("TargetUnitId");
+
+                    b.ToTable("KnowledgeUnitLinks");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.NexusUser", b =>
+                {
+                    b.Property<string>("Id")
+                        .HasColumnType("text");
+
+                    b.Property<int>("AITokenLimit")
+                        .HasColumnType("integer");
+
+                    b.Property<int>("AITokensUsed")
+                        .HasColumnType("integer");
+
+                    b.Property<int>("AccessFailedCount")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("ConcurrencyStamp")
+                        .IsConcurrencyToken()
+                        .HasColumnType("text");
+
+                    b.Property<string>("DisplayName")
+                        .HasMaxLength(100)
+                        .HasColumnType("character varying(100)");
+
+                    b.Property<string>("Email")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.Property<bool>("EmailConfirmed")
+                        .HasColumnType("boolean");
+
+                    b.Property<DateTime?>("LastAiActionDate")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<DateTime?>("LastReadAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("LastReadPageId")
+                        .HasMaxLength(255)
+                        .HasColumnType("character varying(255)");
+
+                    b.Property<bool>("LockoutEnabled")
+                        .HasColumnType("boolean");
+
+                    b.Property<DateTimeOffset?>("LockoutEnd")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("NormalizedEmail")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.Property<string>("NormalizedUserName")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.Property<string>("PasswordHash")
+                        .HasColumnType("text");
+
+                    b.Property<string>("PhoneNumber")
+                        .HasColumnType("text");
+
+                    b.Property<bool>("PhoneNumberConfirmed")
+                        .HasColumnType("boolean");
+
+                    b.Property<string>("SecurityStamp")
+                        .HasColumnType("text");
+
+                    b.Property<int>("SubscriptionPlanId")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer")
+                        .HasDefaultValue(1);
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<bool>("TwoFactorEnabled")
+                        .HasColumnType("boolean");
+
+                    b.Property<string>("UserName")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("NormalizedEmail")
+                        .HasDatabaseName("EmailIndex");
+
+                    b.HasIndex("NormalizedUserName")
+                        .IsUnique()
+                        .HasDatabaseName("UserNameIndex");
+
+                    b.HasIndex("SubscriptionPlanId");
+
+                    b.HasIndex("TenantId");
+
+                    b.ToTable("AspNetUsers", (string)null);
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.QuizResult", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("uuid");
+
+                    b.Property<DateTime>("CompletedDate")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<int>("Score")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<string>("Topic")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<int>("TotalQuestions")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("UserId")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("TenantId");
+
+                    b.HasIndex("UserId");
+
+                    b.ToTable("QuizResults");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.SemanticKnowledgeCache", b =>
+                {
+                    b.Property<string>("ContentHash")
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("JsonData")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<string>("ModelId")
+                        .IsRequired()
+                        .HasMaxLength(50)
+                        .HasColumnType("character varying(50)");
+
+                    b.Property<string>("OriginalText")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<string>("PromptVersion")
+                        .IsRequired()
+                        .HasMaxLength(10)
+                        .HasColumnType("character varying(10)");
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<Vector>("Vector")
+                        .HasColumnType("vector(1536)");
+
+                    b.HasKey("ContentHash");
+
+                    b.HasIndex("ContentHash")
+                        .IsUnique();
+
+                    b.HasIndex("TenantId");
+
+                    b.ToTable("SemanticKnowledgeCache");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.SubscriptionPlan", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<int>("AITokenLimit")
+                        .HasColumnType("integer");
+
+                    b.Property<bool>("IsUnlimitedTokens")
+                        .HasColumnType("boolean");
+
+                    b.Property<decimal>("MonthlyPrice")
+                        .HasColumnType("numeric");
+
+                    b.Property<string>("PlanName")
+                        .IsRequired()
+                        .HasMaxLength(50)
+                        .HasColumnType("character varying(50)");
+
+                    b.Property<string>("StripeProductId")
+                        .IsRequired()
+                        .HasMaxLength(50)
+                        .HasColumnType("character varying(50)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("PlanName")
+                        .IsUnique();
+
+                    b.ToTable("SubscriptionPlans");
+
+                    b.HasData(
+                        new
+                        {
+                            Id = 1,
+                            AITokenLimit = 5000,
+                            IsUnlimitedTokens = false,
+                            MonthlyPrice = 0m,
+                            PlanName = "Free",
+                            StripeProductId = "prod_Free789"
+                        },
+                        new
+                        {
+                            Id = 2,
+                            AITokenLimit = 10000,
+                            IsUnlimitedTokens = false,
+                            MonthlyPrice = 9.99m,
+                            PlanName = "Basic",
+                            StripeProductId = "prod_basic_placeholder"
+                        },
+                        new
+                        {
+                            Id = 3,
+                            AITokenLimit = 50000,
+                            IsUnlimitedTokens = false,
+                            MonthlyPrice = 19.99m,
+                            PlanName = "Pro",
+                            StripeProductId = "prod_pro_placeholder"
+                        },
+                        new
+                        {
+                            Id = 4,
+                            AITokenLimit = 1000000000,
+                            IsUnlimitedTokens = true,
+                            MonthlyPrice = 99.99m,
+                            PlanName = "Enterprise",
+                            StripeProductId = "prod_enterprise_placeholder"
+                        });
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRoleClaim<string>", b =>
+                {
+                    b.HasOne("Microsoft.AspNetCore.Identity.IdentityRole", null)
+                        .WithMany()
+                        .HasForeignKey("RoleId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserClaim<string>", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", null)
+                        .WithMany()
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserLogin<string>", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", null)
+                        .WithMany()
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserRole<string>", b =>
+                {
+                    b.HasOne("Microsoft.AspNetCore.Identity.IdentityRole", null)
+                        .WithMany()
+                        .HasForeignKey("RoleId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", null)
+                        .WithMany()
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserToken<string>", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", null)
+                        .WithMany()
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.Ebook", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.Author", "Author")
+                        .WithMany("Ebooks")
+                        .HasForeignKey("AuthorId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", "User")
+                        .WithMany("Ebooks")
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("Author");
+
+                    b.Navigation("User");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnit", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.Ebook", "Ebook")
+                        .WithMany()
+                        .HasForeignKey("EbookId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("Ebook");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnitLink", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.KnowledgeUnit", "SourceUnit")
+                        .WithMany("OutgoingLinks")
+                        .HasForeignKey("SourceUnitId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.HasOne("NexusReader.Domain.Entities.KnowledgeUnit", "TargetUnit")
+                        .WithMany("IncomingLinks")
+                        .HasForeignKey("TargetUnitId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("SourceUnit");
+
+                    b.Navigation("TargetUnit");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.NexusUser", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.SubscriptionPlan", "SubscriptionPlan")
+                        .WithMany()
+                        .HasForeignKey("SubscriptionPlanId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("SubscriptionPlan");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.QuizResult", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", "User")
+                        .WithMany("QuizResults")
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("User");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.Author", b =>
+                {
+                    b.Navigation("Ebooks");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnit", b =>
+                {
+                    b.Navigation("IncomingLinks");
+
+                    b.Navigation("OutgoingLinks");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.NexusUser", b =>
+                {
+                    b.Navigation("Ebooks");
+
+                    b.Navigation("QuizResults");
+                });
+#pragma warning restore 612, 618
+        }
+    }
+}

src/NexusReader.Data/Persistence/Migrations/20260513183726_FixKnowledgeUnitEbookId.cs

@@ -0,0 +1,72 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace NexusReader.Data.Persistence.Migrations
+{
+    /// <inheritdoc />
+    public partial class FixKnowledgeUnitEbookId : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropIndex(
+                name: "IX_KnowledgeUnits_SourceId",
+                table: "KnowledgeUnits");
+
+            migrationBuilder.DropColumn(
+                name: "SourceId",
+                table: "KnowledgeUnits");
+
+            migrationBuilder.AddColumn<Guid>(
+                name: "EbookId",
+                table: "KnowledgeUnits",
+                type: "uuid",
+                nullable: false,
+                defaultValue: new Guid("00000000-0000-0000-0000-000000000000"));
+
+            migrationBuilder.CreateIndex(
+                name: "IX_KnowledgeUnits_EbookId",
+                table: "KnowledgeUnits",
+                column: "EbookId");
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_KnowledgeUnits_Ebooks_EbookId",
+                table: "KnowledgeUnits",
+                column: "EbookId",
+                principalTable: "Ebooks",
+                principalColumn: "Id",
+                onDelete: ReferentialAction.Cascade);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropForeignKey(
+                name: "FK_KnowledgeUnits_Ebooks_EbookId",
+                table: "KnowledgeUnits");
+
+            migrationBuilder.DropIndex(
+                name: "IX_KnowledgeUnits_EbookId",
+                table: "KnowledgeUnits");
+
+            migrationBuilder.DropColumn(
+                name: "EbookId",
+                table: "KnowledgeUnits");
+
+            migrationBuilder.AddColumn<string>(
+                name: "SourceId",
+                table: "KnowledgeUnits",
+                type: "character varying(128)",
+                maxLength: 128,
+                nullable: false,
+                defaultValue: "");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_KnowledgeUnits_SourceId",
+                table: "KnowledgeUnits",
+                column: "SourceId");
+        }
+    }
+}

src/NexusReader.Data/Persistence/Migrations/20260513185108_MakeKnowledgeUnitEbookIdNullable.Designer.cs

@@ -0,0 +1,711 @@
+// <auto-generated />
+using System;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
+using NexusReader.Data.Persistence;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+using Pgvector;
+
+#nullable disable
+
+namespace NexusReader.Data.Persistence.Migrations
+{
+    [DbContext(typeof(AppDbContext))]
+    [Migration("20260513185108_MakeKnowledgeUnitEbookIdNullable")]
+    partial class MakeKnowledgeUnitEbookIdNullable
+    {
+        /// <inheritdoc />
+        protected override void BuildTargetModel(ModelBuilder modelBuilder)
+        {
+#pragma warning disable 612, 618
+            modelBuilder
+                .HasAnnotation("ProductVersion", "10.0.7")
+                .HasAnnotation("Relational:MaxIdentifierLength", 63);
+
+            NpgsqlModelBuilderExtensions.HasPostgresExtension(modelBuilder, "vector");
+            NpgsqlModelBuilderExtensions.UseIdentityByDefaultColumns(modelBuilder);
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRole", b =>
+                {
+                    b.Property<string>("Id")
+                        .HasColumnType("text");
+
+                    b.Property<string>("ConcurrencyStamp")
+                        .IsConcurrencyToken()
+                        .HasColumnType("text");
+
+                    b.Property<string>("Name")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.Property<string>("NormalizedName")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("NormalizedName")
+                        .IsUnique()
+                        .HasDatabaseName("RoleNameIndex");
+
+                    b.ToTable("AspNetRoles", (string)null);
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRoleClaim<string>", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("ClaimType")
+                        .HasColumnType("text");
+
+                    b.Property<string>("ClaimValue")
+                        .HasColumnType("text");
+
+                    b.Property<string>("RoleId")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("RoleId");
+
+                    b.ToTable("AspNetRoleClaims", (string)null);
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserClaim<string>", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("ClaimType")
+                        .HasColumnType("text");
+
+                    b.Property<string>("ClaimValue")
+                        .HasColumnType("text");
+
+                    b.Property<string>("UserId")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("UserId");
+
+                    b.ToTable("AspNetUserClaims", (string)null);
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserLogin<string>", b =>
+                {
+                    b.Property<string>("LoginProvider")
+                        .HasColumnType("text");
+
+                    b.Property<string>("ProviderKey")
+                        .HasColumnType("text");
+
+                    b.Property<string>("ProviderDisplayName")
+                        .HasColumnType("text");
+
+                    b.Property<string>("UserId")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.HasKey("LoginProvider", "ProviderKey");
+
+                    b.HasIndex("UserId");
+
+                    b.ToTable("AspNetUserLogins", (string)null);
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserRole<string>", b =>
+                {
+                    b.Property<string>("UserId")
+                        .HasColumnType("text");
+
+                    b.Property<string>("RoleId")
+                        .HasColumnType("text");
+
+                    b.HasKey("UserId", "RoleId");
+
+                    b.HasIndex("RoleId");
+
+                    b.ToTable("AspNetUserRoles", (string)null);
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserToken<string>", b =>
+                {
+                    b.Property<string>("UserId")
+                        .HasColumnType("text");
+
+                    b.Property<string>("LoginProvider")
+                        .HasColumnType("text");
+
+                    b.Property<string>("Name")
+                        .HasColumnType("text");
+
+                    b.Property<string>("Value")
+                        .HasColumnType("text");
+
+                    b.HasKey("UserId", "LoginProvider", "Name");
+
+                    b.ToTable("AspNetUserTokens", (string)null);
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.Author", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("Name")
+                        .IsRequired()
+                        .HasMaxLength(255)
+                        .HasColumnType("character varying(255)");
+
+                    b.HasKey("Id");
+
+                    b.ToTable("Authors");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.Ebook", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("uuid");
+
+                    b.Property<DateTime>("AddedDate")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<int>("AuthorId")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("CoverUrl")
+                        .HasColumnType("text");
+
+                    b.Property<string>("FilePath")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<bool>("IsReadyForReading")
+                        .HasColumnType("boolean");
+
+                    b.Property<string>("LastChapter")
+                        .HasMaxLength(255)
+                        .HasColumnType("character varying(255)");
+
+                    b.Property<int>("LastChapterIndex")
+                        .HasColumnType("integer");
+
+                    b.Property<DateTime?>("LastReadDate")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<double>("Progress")
+                        .HasColumnType("double precision");
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<string>("Title")
+                        .IsRequired()
+                        .HasMaxLength(255)
+                        .HasColumnType("character varying(255)");
+
+                    b.Property<string>("UserId")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("AuthorId");
+
+                    b.HasIndex("TenantId");
+
+                    b.HasIndex("UserId");
+
+                    b.ToTable("Ebooks");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnit", b =>
+                {
+                    b.Property<string>("Id")
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<string>("Content")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<Guid?>("EbookId")
+                        .HasColumnType("uuid");
+
+                    b.Property<string>("MetadataJson")
+                        .HasColumnType("text");
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<int>("Type")
+                        .HasColumnType("integer");
+
+                    b.Property<Vector>("Vector")
+                        .HasColumnType("vector(768)");
+
+                    b.Property<string>("Version")
+                        .IsRequired()
+                        .HasMaxLength(50)
+                        .HasColumnType("character varying(50)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("EbookId");
+
+                    b.HasIndex("TenantId");
+
+                    b.ToTable("KnowledgeUnits");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnitLink", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("RelationType")
+                        .IsRequired()
+                        .HasMaxLength(50)
+                        .HasColumnType("character varying(50)");
+
+                    b.Property<string>("SourceUnitId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<string>("TargetUnitId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("SourceUnitId");
+
+                    b.HasIndex("TargetUnitId");
+
+                    b.ToTable("KnowledgeUnitLinks");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.NexusUser", b =>
+                {
+                    b.Property<string>("Id")
+                        .HasColumnType("text");
+
+                    b.Property<int>("AITokenLimit")
+                        .HasColumnType("integer");
+
+                    b.Property<int>("AITokensUsed")
+                        .HasColumnType("integer");
+
+                    b.Property<int>("AccessFailedCount")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("ConcurrencyStamp")
+                        .IsConcurrencyToken()
+                        .HasColumnType("text");
+
+                    b.Property<string>("DisplayName")
+                        .HasMaxLength(100)
+                        .HasColumnType("character varying(100)");
+
+                    b.Property<string>("Email")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.Property<bool>("EmailConfirmed")
+                        .HasColumnType("boolean");
+
+                    b.Property<DateTime?>("LastAiActionDate")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<DateTime?>("LastReadAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("LastReadPageId")
+                        .HasMaxLength(255)
+                        .HasColumnType("character varying(255)");
+
+                    b.Property<bool>("LockoutEnabled")
+                        .HasColumnType("boolean");
+
+                    b.Property<DateTimeOffset?>("LockoutEnd")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("NormalizedEmail")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.Property<string>("NormalizedUserName")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.Property<string>("PasswordHash")
+                        .HasColumnType("text");
+
+                    b.Property<string>("PhoneNumber")
+                        .HasColumnType("text");
+
+                    b.Property<bool>("PhoneNumberConfirmed")
+                        .HasColumnType("boolean");
+
+                    b.Property<string>("SecurityStamp")
+                        .HasColumnType("text");
+
+                    b.Property<int>("SubscriptionPlanId")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer")
+                        .HasDefaultValue(1);
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<bool>("TwoFactorEnabled")
+                        .HasColumnType("boolean");
+
+                    b.Property<string>("UserName")
+                        .HasMaxLength(256)
+                        .HasColumnType("character varying(256)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("NormalizedEmail")
+                        .HasDatabaseName("EmailIndex");
+
+                    b.HasIndex("NormalizedUserName")
+                        .IsUnique()
+                        .HasDatabaseName("UserNameIndex");
+
+                    b.HasIndex("SubscriptionPlanId");
+
+                    b.HasIndex("TenantId");
+
+                    b.ToTable("AspNetUsers", (string)null);
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.QuizResult", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("uuid");
+
+                    b.Property<DateTime>("CompletedDate")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<int>("Score")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<string>("Topic")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<int>("TotalQuestions")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("UserId")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("TenantId");
+
+                    b.HasIndex("UserId");
+
+                    b.ToTable("QuizResults");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.SemanticKnowledgeCache", b =>
+                {
+                    b.Property<string>("ContentHash")
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("JsonData")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<string>("ModelId")
+                        .IsRequired()
+                        .HasMaxLength(50)
+                        .HasColumnType("character varying(50)");
+
+                    b.Property<string>("OriginalText")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<string>("PromptVersion")
+                        .IsRequired()
+                        .HasMaxLength(10)
+                        .HasColumnType("character varying(10)");
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    b.Property<Vector>("Vector")
+                        .HasColumnType("vector(1536)");
+
+                    b.HasKey("ContentHash");
+
+                    b.HasIndex("ContentHash")
+                        .IsUnique();
+
+                    b.HasIndex("TenantId");
+
+                    b.ToTable("SemanticKnowledgeCache");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.SubscriptionPlan", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<int>("AITokenLimit")
+                        .HasColumnType("integer");
+
+                    b.Property<bool>("IsUnlimitedTokens")
+                        .HasColumnType("boolean");
+
+                    b.Property<decimal>("MonthlyPrice")
+                        .HasColumnType("numeric");
+
+                    b.Property<string>("PlanName")
+                        .IsRequired()
+                        .HasMaxLength(50)
+                        .HasColumnType("character varying(50)");
+
+                    b.Property<string>("StripeProductId")
+                        .IsRequired()
+                        .HasMaxLength(50)
+                        .HasColumnType("character varying(50)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("PlanName")
+                        .IsUnique();
+
+                    b.ToTable("SubscriptionPlans");
+
+                    b.HasData(
+                        new
+                        {
+                            Id = 1,
+                            AITokenLimit = 5000,
+                            IsUnlimitedTokens = false,
+                            MonthlyPrice = 0m,
+                            PlanName = "Free",
+                            StripeProductId = "prod_Free789"
+                        },
+                        new
+                        {
+                            Id = 2,
+                            AITokenLimit = 10000,
+                            IsUnlimitedTokens = false,
+                            MonthlyPrice = 9.99m,
+                            PlanName = "Basic",
+                            StripeProductId = "prod_basic_placeholder"
+                        },
+                        new
+                        {
+                            Id = 3,
+                            AITokenLimit = 50000,
+                            IsUnlimitedTokens = false,
+                            MonthlyPrice = 19.99m,
+                            PlanName = "Pro",
+                            StripeProductId = "prod_pro_placeholder"
+                        },
+                        new
+                        {
+                            Id = 4,
+                            AITokenLimit = 1000000000,
+                            IsUnlimitedTokens = true,
+                            MonthlyPrice = 99.99m,
+                            PlanName = "Enterprise",
+                            StripeProductId = "prod_enterprise_placeholder"
+                        });
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRoleClaim<string>", b =>
+                {
+                    b.HasOne("Microsoft.AspNetCore.Identity.IdentityRole", null)
+                        .WithMany()
+                        .HasForeignKey("RoleId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserClaim<string>", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", null)
+                        .WithMany()
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserLogin<string>", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", null)
+                        .WithMany()
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserRole<string>", b =>
+                {
+                    b.HasOne("Microsoft.AspNetCore.Identity.IdentityRole", null)
+                        .WithMany()
+                        .HasForeignKey("RoleId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", null)
+                        .WithMany()
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
+            modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserToken<string>", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", null)
+                        .WithMany()
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.Ebook", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.Author", "Author")
+                        .WithMany("Ebooks")
+                        .HasForeignKey("AuthorId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", "User")
+                        .WithMany("Ebooks")
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("Author");
+
+                    b.Navigation("User");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnit", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.Ebook", "Ebook")
+                        .WithMany()
+                        .HasForeignKey("EbookId")
+                        .OnDelete(DeleteBehavior.Cascade);
+
+                    b.Navigation("Ebook");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnitLink", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.KnowledgeUnit", "SourceUnit")
+                        .WithMany("OutgoingLinks")
+                        .HasForeignKey("SourceUnitId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.HasOne("NexusReader.Domain.Entities.KnowledgeUnit", "TargetUnit")
+                        .WithMany("IncomingLinks")
+                        .HasForeignKey("TargetUnitId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("SourceUnit");
+
+                    b.Navigation("TargetUnit");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.NexusUser", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.SubscriptionPlan", "SubscriptionPlan")
+                        .WithMany()
+                        .HasForeignKey("SubscriptionPlanId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("SubscriptionPlan");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.QuizResult", b =>
+                {
+                    b.HasOne("NexusReader.Domain.Entities.NexusUser", "User")
+                        .WithMany("QuizResults")
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("User");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.Author", b =>
+                {
+                    b.Navigation("Ebooks");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnit", b =>
+                {
+                    b.Navigation("IncomingLinks");
+
+                    b.Navigation("OutgoingLinks");
+                });
+
+            modelBuilder.Entity("NexusReader.Domain.Entities.NexusUser", b =>
+                {
+                    b.Navigation("Ebooks");
+
+                    b.Navigation("QuizResults");
+                });
+#pragma warning restore 612, 618
+        }
+    }
+}

src/NexusReader.Data/Persistence/Migrations/20260513185108_MakeKnowledgeUnitEbookIdNullable.cs

@@ -0,0 +1,37 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace NexusReader.Data.Persistence.Migrations
+{
+    /// <inheritdoc />
+    public partial class MakeKnowledgeUnitEbookIdNullable : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AlterColumn<Guid>(
+                name: "EbookId",
+                table: "KnowledgeUnits",
+                type: "uuid",
+                nullable: true,
+                oldClrType: typeof(Guid),
+                oldType: "uuid");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AlterColumn<Guid>(
+                name: "EbookId",
+                table: "KnowledgeUnits",
+                type: "uuid",
+                nullable: false,
+                defaultValue: new Guid("00000000-0000-0000-0000-000000000000"),
+                oldClrType: typeof(Guid),
+                oldType: "uuid",
+                oldNullable: true);
+        }
+    }
+}

src/NexusReader.Domain/Entities/KnowledgeUnit.cs

@@ -11,9 +11,10 @@ public class KnowledgeUnit
     [MaxLength(128)]
     public string Id { get; set; } = string.Empty; // Hash(Source + Content + Version)
 
-    [Required]
-    [MaxLength(128)]
-    public string SourceId { get; set; } = string.Empty;
+    public Guid? EbookId { get; set; }
+ 
+     [ForeignKey(nameof(EbookId))]
+    public virtual Ebook? Ebook { get; set; }
 
     [Required]
     [MaxLength(50)]

src/NexusReader.Infrastructure/Services/KnowledgeService.cs

@@ -50,27 +50,27 @@ public class KnowledgeService : IKnowledgeService
         _tokenizer = TiktokenTokenizer.CreateForModel("gpt-4");
     }
 
-    public async Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, string tenantId, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default)
     {
-        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.KnowledgeExtractionSystemPrompt, "full", cancellationToken);
+        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.KnowledgeExtractionSystemPrompt, "full", ebookId, cancellationToken);
     }
 
-    public async Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, string tenantId, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default)
     {
-        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.GraphExtractionPrompt, "graph", cancellationToken);
+        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.GraphExtractionPrompt, "graph", ebookId, cancellationToken);
     }
 
-    public async Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, string tenantId, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default)
     {
-        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.SummaryAndQuizPrompt, "summary_quiz", cancellationToken);
+        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.SummaryAndQuizPrompt, "summary_quiz", ebookId, cancellationToken);
     }
 
-    public async Task<Result<KnowledgePacket>> GetKnowledgeMapAsync(string text, string tenantId, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetKnowledgeMapAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default)
     {
-        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.KM_ExtractionPrompt, "km_map", cancellationToken);
+        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.KM_ExtractionPrompt, "km_map", ebookId, cancellationToken);
     }
 
-    private async Task<Result<KnowledgePacket>> GetKnowledgeInternalAsync(string text, string tenantId, string systemPrompt, string traceType, CancellationToken cancellationToken)
+    private async Task<Result<KnowledgePacket>> GetKnowledgeInternalAsync(string text, string tenantId, string systemPrompt, string traceType, Guid? ebookId, CancellationToken cancellationToken)
     {
         if (string.IsNullOrWhiteSpace(text)) return Result.Fail("Input text is empty.");
 
@@ -161,7 +161,7 @@ public class KnowledgeService : IKnowledgeService
                 }
 
                 // 5. Process structured KnowledgeUnits (Graph Expansion)
-                await ProcessKnowledgeUnitsAsync(knowledgePacket, tenantId, dbContext, cancellationToken);
+                await ProcessKnowledgeUnitsAsync(knowledgePacket, tenantId, ebookId, dbContext, cancellationToken);
 
                 await dbContext.SaveChangesAsync(cancellationToken);
                 return Result.Ok(knowledgePacket);
@@ -178,7 +178,7 @@ public class KnowledgeService : IKnowledgeService
         }
     }
 
-    private async Task ProcessKnowledgeUnitsAsync(KnowledgePacket packet, string tenantId, AppDbContext dbContext, CancellationToken cancellationToken)
+    private async Task ProcessKnowledgeUnitsAsync(KnowledgePacket packet, string tenantId, Guid? ebookId, AppDbContext dbContext, CancellationToken cancellationToken)
     {
         var unitIds = packet.Units.Select(u => u.Id).ToList();
         var linkSourceIds = packet.Links.Select(l => l.Source).ToList();
@@ -207,7 +207,11 @@ public class KnowledgeService : IKnowledgeService
 
             unit.Type = Enum.TryParse<NexusReader.Domain.Enums.KnowledgeUnitType>(unitDto.Type, true, out var type) ? type : NexusReader.Domain.Enums.KnowledgeUnitType.Snippet;
             unit.Content = unitDto.Content;
-            unit.SourceId = "extracted";
+            
+            // Link to the specific ebook if provided. 
+            // Link to ebook if provided
+            unit.EbookId = ebookId; 
+            
             unit.MetadataJson = JsonSerializer.Serialize(unitDto.Metadata);
 
             try

src/NexusReader.Web.Client/Services/WasmKnowledgeService.cs

@@ -14,24 +14,24 @@ public class WasmKnowledgeService : IKnowledgeService
         _httpClient = httpClient;
     }
 
-    public async Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, string tenantId, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default)
     {
-        return await CallKnowledgeApiAsync("/api/knowledge", text, cancellationToken);
+        return await CallKnowledgeApiAsync("/api/knowledge", text, ebookId, cancellationToken);
     }
 
-    public async Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, string tenantId, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default)
     {
-        return await CallKnowledgeApiAsync("/api/knowledge/graph", text, cancellationToken);
+        return await CallKnowledgeApiAsync("/api/knowledge/graph", text, ebookId, cancellationToken);
     }
 
-    public async Task<Result<KnowledgePacket>> GetKnowledgeMapAsync(string text, string tenantId, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetKnowledgeMapAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default)
     {
-        return await CallKnowledgeApiAsync("/api/knowledge/map", text, cancellationToken);
+        return await CallKnowledgeApiAsync("/api/knowledge/map", text, ebookId, cancellationToken);
     }
 
-    public async Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, string tenantId, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, string tenantId, Guid? ebookId = null, CancellationToken cancellationToken = default)
     {
-        return await CallKnowledgeApiAsync("/api/knowledge/summary", text, cancellationToken);
+        return await CallKnowledgeApiAsync("/api/knowledge/summary", text, ebookId, cancellationToken);
     }
 
     public async Task<Result<List<RelevantContext>>> GetRelevantContextAsync(string query, string tenantId, CancellationToken cancellationToken = default)
@@ -73,11 +73,11 @@ public class WasmKnowledgeService : IKnowledgeService
         }
     }
 
-    private async Task<Result<KnowledgePacket>> CallKnowledgeApiAsync(string endpoint, string text, CancellationToken cancellationToken)
+    private async Task<Result<KnowledgePacket>> CallKnowledgeApiAsync(string endpoint, string text, Guid? ebookId, CancellationToken cancellationToken)
     {
         try
         {
-            var response = await _httpClient.PostAsJsonAsync(endpoint, new { text }, cancellationToken);
+            var response = await _httpClient.PostAsJsonAsync(endpoint, new { text, ebookId }, cancellationToken);
             if (response.IsSuccessStatusCode)
             {
                 var packet = await response.Content.ReadFromJsonAsync<KnowledgePacket>(cancellationToken: cancellationToken);

src/NexusReader.Web/Program.cs

@@ -258,7 +258,7 @@ var knowledgeApi = app.MapGroup("/api/knowledge").RequireAuthorization("HasAvail
 knowledgeApi.MapPost("/", async (KnowledgeRequest request, ClaimsPrincipal user, IKnowledgeService knowledgeService) =>
 {
     var tenantId = user.FindFirstValue("TenantId") ?? "global";
-    var result = await knowledgeService.GetKnowledgeAsync(request.Text, tenantId);
+    var result = await knowledgeService.GetKnowledgeAsync(request.Text, tenantId, request.EbookId);
     if (result.IsSuccess) return Results.Ok(result.Value);
     return Results.BadRequest(result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error");
 });
@@ -266,7 +266,7 @@ knowledgeApi.MapPost("/", async (KnowledgeRequest request, ClaimsPrincipal user,
 knowledgeApi.MapPost("/graph", async (KnowledgeRequest request, ClaimsPrincipal user, IKnowledgeService knowledgeService) =>
 {
     var tenantId = user.FindFirstValue("TenantId") ?? "global";
-    var result = await knowledgeService.GetGraphDataAsync(request.Text, tenantId);
+    var result = await knowledgeService.GetGraphDataAsync(request.Text, tenantId, request.EbookId);
     if (result.IsSuccess) return Results.Ok(result.Value);
     return Results.BadRequest(result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error");
 });
@@ -274,7 +274,15 @@ knowledgeApi.MapPost("/graph", async (KnowledgeRequest request, ClaimsPrincipal
 knowledgeApi.MapPost("/summary", async (KnowledgeRequest request, ClaimsPrincipal user, IKnowledgeService knowledgeService) =>
 {
     var tenantId = user.FindFirstValue("TenantId") ?? "global";
-    var result = await knowledgeService.GetSummaryAndQuizAsync(request.Text, tenantId);
+    var result = await knowledgeService.GetSummaryAndQuizAsync(request.Text, tenantId, request.EbookId);
+    if (result.IsSuccess) return Results.Ok(result.Value);
+    return Results.BadRequest(result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error");
+});
+
+knowledgeApi.MapPost("/map", async (KnowledgeRequest request, ClaimsPrincipal user, IKnowledgeService knowledgeService) =>
+{
+    var tenantId = user.FindFirstValue("TenantId") ?? "global";
+    var result = await knowledgeService.GetKnowledgeMapAsync(request.Text, tenantId, request.EbookId);
     if (result.IsSuccess) return Results.Ok(result.Value);
     return Results.BadRequest(result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error");
 });
@@ -519,5 +527,5 @@ app.MapRazorComponents<App>()
 
 app.Run();
 
-public record KnowledgeRequest(string Text);
+public record KnowledgeRequest(string Text, Guid? EbookId = null);
 public record GroundednessRequest(string Answer, string Context);