docs: add git workflow and MCP integration guidelines to agent persona documentation

.agent/skills/blazor-hybrid-bridge/SKILL.md

@@ -24,6 +24,10 @@ description: Standards for cross-platform compatibility (Web & MAUI Hybrid)
   - Use `IPlatformService.GetDeviceContext()` to determine `DeviceType` (Phone, Tablet, Desktop).
   - Adapt UI layout dynamically based on the context (e.g., sidebars on Tablet/Desktop, bottom navigation on Phone).
 
+- **Real-time & Events (SignalR / UI):**
+  - **Debouncing**: Implement trailing-edge debouncing using `CancellationTokenSource` and `Task.Delay` for high-frequency UI events (like scrolling). Do not just drop events inside a time window, as the final state might be lost.
+  - **Dependency Isolation**: Blazor WebAssembly (`Web.Client`) cannot reference projects that require `Microsoft.AspNetCore.App` (like SignalR Hubs). Keep SignalR abstractions in `UI.Shared` and the Hub implementation strictly on the server (`Infrastructure` or `Web.New`).
+
 - **Dependency Injection:**
   - Register implementations in `MauiProgram.cs` for mobile and `Program.cs` for web.
   - Components in `NexusReader.UI.Shared` must only depend on the interfaces.

.agent/skills/km-rag-methodology/SKILL.md

@@ -0,0 +1,29 @@
+---
+name: km-rag-methodology
+description: Expertise in implementing Knowledge-Map RAG (KM-RAG), focusing on structured Knowledge Units, Graph relationships, and multi-stage retrieval in .NET.
+tags: [RAG, KnowledgeMap, GraphRAG, AI, .NET, CleanArchitecture]
+version: 1.0.0
+---
+
+# KM-RAG Methodology
+
+This skill provides a comprehensive framework for transitioning from basic chunk-based RAG to a structured **Knowledge-Map RAG (KM-RAG)** approach.
+
+## Core Concepts
+- **Knowledge Units (KU)**: Granular pieces of information with stable IDs and types (Section, Table, Definition, Rule).
+- **Knowledge Map (Graph)**: Explicit links between units (`Next`, `Defines`, `Contains`) enabling contextual expansion.
+- **Multi-Stage Retrieval**: A pipeline starting with semantic candidate generation followed by graph expansion and optional reranking.
+- **Provenance & Governance**: Full traceability of AI answers back to their source units.
+
+## Key Artifacts
+- [Core Concepts](artifacts/core_concepts.md): Deep dive into the methodology.
+- [Implementation Patterns (.NET)](artifacts/implementation_patterns.md): C# code for units, links, and retrieval.
+- [Quality Checklist](artifacts/evaluation_checklist.md): Metrics and safety procedures.
+- [Deep Research Report](artifacts/deep-research-report-rag.md): Original research on the KM-RAG approach.
+
+## Usage
+Use this skill when:
+- Designing or refactoring RAG systems for high precision.
+- Implementing multi-tenant knowledge bases.
+- Enhancing AI answers with structural context from a graph.
+- Building evaluation pipelines for hallucination detection.

.agent/skills/km-rag-methodology/artifacts/core_concepts.md

@@ -0,0 +1,28 @@
+# Core Concepts of KM-RAG (Knowledge-Map RAG)
+
+Knowledge-Map RAG (KM-RAG) shifts the paradigm from "mechanical chunking" to "structured knowledge engineering".
+
+## 1. From Chunks to Knowledge Units (KU)
+Instead of random character-based splits, knowledge is partitioned into **Knowledge Units** that preserve structural meaning:
+- **Unit Types**: `Section`, `Table`, `Definition`, `ProcedureStep`, `PolicyRule`.
+- **Properties**: Stable ID, Version, Canonical Text, Rendered Context, Provenance (source, page, path).
+
+## 2. The Knowledge Map (Graph)
+Relationships between Knowledge Units are explicitly modeled to enhance retrieval and context assembly:
+- `HAS_UNIT`: Document contains Unit.
+- `NEXT` / `PREVIOUS`: Sequential flow between units.
+- `DEFINES`: Unit defines a specific entity or term.
+- `REFERENCES`: Unit refers to another unit.
+- `EXCEPTION_OF`: Unit describes an exception to a rule in another unit.
+
+## 3. Retrieval Strategy: "Plan over Similarity"
+Retrieval is not just `top-k` similarity but a multi-stage process:
+1. **Candidate Generation**: Hybrid search (Vector + Keyword) to find potential matches.
+2. **Graph Expansion**: Pulling related units (e.g., "Get the section this table belongs to" or "Get the definition of term X used here").
+3. **Reranking**: Using a Cross-Encoder to precisely score the expanded candidates.
+4. **Context Assembly**: Building a grounded context with explicit citations.
+
+## 4. Governance and Provenance
+- **Audit Trail**: Every answer must be traceable back to specific Knowledge Units with valid provenance.
+- **Permission-Aware**: Retrieval filters must enforce ACLs at the unit/graph level before the LLM sees the data.
+- **Continuous Evaluation**: Monitoring "Faithfulness" (groundedness) and "Answer Relevance" using tools like RAGAS or TruLens.

.agent/skills/km-rag-methodology/artifacts/deep-research-report-rag.md

@@ -0,0 +1,588 @@
+# Mapa Wiedzy i kontrola w RAG: jak wdrożyć „nowe podejście” w sposób inżynieryjny
+
+## Executive summary
+
+Autor posta (entity["people","Vladimir Alekseichenko","dataworkshop ceo"], entity["organization","DataWorkshop","ml/ai training poland"]) kontrastuje „klasyczny” RAG oparty o mechaniczne chunkowanie i wektoryzację z podejściem, w którym buduje się **Mapę Wiedzy**: „graf z metadanymi, powiązaniami i odniesieniami do źródeł” (w kontekście praktyki na danych z entity["organization","Giełda Papierów Wartościowych w Warszawie","warsaw stock exchange"]). citeturn2view0turn2view1
+
+W tym raporcie formalizuję tę ideę jako **Knowledge‑Map RAG (KM‑RAG)**: RAG, w którym warstwa „R” nie jest tylko wyszukiwaniem semantycznym po losowych fragmentach, ale **kontrolowanym wyborem jednostek wiedzy** (sekcja, tabela, rekord, definicja, reguła) powiązanych grafowo, z pełną **proweniencją (skąd to jest), politykami dostępu, wersjonowaniem i testowalnością**. To jest spójne z tezą autora, że „R w RAG” to przede wszystkim **ryzyko**: jeśli retrieval jest błędny, model będzie „pewnie” odpowiadał na podstawie złego kontekstu. citeturn2view0turn6view0
+
+Ponieważ nie podałeś ograniczeń (skala, budżet, SLA/latencja), przyjmuję **brak specyficznych constraintów** i podaję warianty: od małych wdrożeń (Postgres/pgvector) po architektury wielotenancy (Qdrant/Pinecone/Weaviate) oraz hybrydy graf + wektory. citeturn12search2turn14search1turn14search16turn14search0turn14search2
+
+Najważniejsze rekomendacje wdrożeniowe:
+
+Po pierwsze, zastąp „losowe chunki” **jednostkami sensu**: segmentacją strukturalną (nagłówki/sekcje/tabele) i/lub semantyczną, z metadanymi i relacjami (poprzedni/następny, należy do sekcji, cytuje, definiuje). citeturn6view0turn11search1turn11search29
+
+Po drugie, zbuduj **Mapę Wiedzy jako graf** (property graph) + indeksy (wektorowy i leksykalny/hybrydowy). Praktycznie: graf przechowuje relacje i proweniencję, a wektory dają tani „candidate generation”; dopiero potem używasz grafu do „dociągnięcia” brakujących kontekstów i do audytu. To jest zgodne z rodziną podejść GraphRAG (np. publikacja entity["company","Microsoft","tech company"] o GraphRAG: graf encji + „community summaries” dla lepszych odpowiedzi na pytania globalne). citeturn0search1turn3search4turn3search20
+
+Po trzecie, „kontrola zamiast nadziei” oznacza: (a) **mierniki retrieval i generation**, (b) automatyczne testy regresji i audyt ścieżki źródeł, (c) monitoring i alerty driftu oraz incydentów bezpieczeństwa (prompt injection, data leakage). W praktyce: RAGAS/TruLens + OWASP LLM Top 10 jako checklisty, plus logowanie „trace” (kontekst → odpowiedź → cytowania). citeturn4search1turn4search2turn4search6turn4search13turn4search7
+
+## Definicja podejścia „Mapa Wiedzy zamiast losowych chunków”
+
+W poście autor opisuje Mapę Wiedzy jako artefakt, który budujesz **w 3 dni**: „graf z metadanymi, powiązaniami i odniesieniami do źródeł” (wspomina też kontekst narzędziowy: repozytorium na entity["company","GitHub","code hosting platform"] i notatki w entity["company","Obsidian","note-taking app company"]). citeturn2view1
+
+Jednocześnie w dłuższym materiale autor rozwija intuicję, dlaczego „chunking + vector DB” bywa drogą donikąd: mechaniczne cięcie rozrywa jednostki sensu (akapit, tabela), a model językowy zwykle **nie weryfikuje kontekstu** – odpowiada w oparciu o to, co mu dostarczysz, nawet jeśli kontekst jest sprzeczny (stąd losowość i halucynacje). citeturn6view0turn7view1
+
+### Precyzyjna definicja operacyjna (KM‑RAG)
+
+**Knowledge‑Map RAG (KM‑RAG)** to architektura RAG, w której warstwa „R” jest realizowana przez:
+
+**Reprezentację wiedzy**: dokumenty są przekształcane do zbioru **jednostek wiedzy** (Knowledge Units) o stabilnej proweniencji (ID, wersja, lokalizacja w źródle) i spójnej semantyce (sekcja definicji, tabela, rozdział, procedura), a nie losowych wycinków znaków. citeturn6view0turn11search9turn16search0
+
+**Mapę (graf) zależności**: jednostki są węzłami grafu (np. DOCUMENT → SECTION → UNIT; ENTITY ↔ UNIT; UNIT ↔ UNIT przez „refers_to/next/derives_from”), a krawędzie niosą informację ułatwiającą retrieval i audyt (np. „to jest definicja terminu X”, „to jest wyjątek od reguły”). citeturn2view1turn10search3turn3search4
+
+**Polityki retrieval**: zapytanie jest mapowane na intencję i encje, a retrieval wykonuje plan: generuje kandydatów (wektory/keyword/hybrid), następnie rozszerza kontekst grafowo (np. sekcja nadrzędna, definicje encji, powiązane tabele), na końcu dokonuje selekcji (rerank/pruning) i buduje kontekst z cytowaniami. citeturn12search3turn12search11turn10search6turn10search31
+
+**Kontrolę i audytowalność**: system jest projektowany tak, aby można było odpowiedzieć na pytania: „Dlaczego ten fragment?”, „Czy użytkownik miał uprawnienia?”, „Jaka wersja źródła?”, „Czy odpowiedź jest ugruntowana (grounded) w kontekście?”. Autor wprost wiąże „mapę wiedzy” z uszczelnianiem rozwiązań, wymaganiami prawnymi/bezpieczeństwa oraz audytowalnością. citeturn7view1turn14search2
+
+### Dlaczego „losowe chunki” są słabą abstrakcją inżynieryjną
+
+Mechaniczne chunkowanie jest często liczone w znakach/tokenach; nawet z overlapem rozrywa strukturę i wymusza „magiczne” heurystyki (większy chunk_size, więcej chunków w kontekście), które łatwo psują wcześniej działające przypadki i utrudniają stabilną ewaluację. citeturn6view0
+
+Z perspektywy governance kluczowy problem jest też bezpieczeństwo: w jednym dokumencie mogą być fragmenty o różnych poziomach dostępu, więc „wrzucanie wszystkiego do jednego kontekstu” łamie zasady separacji i komplikuje zgodność (ten motyw pojawia się u autora wprost). citeturn7view1turn14search2
+
+## Architektura referencyjna i komponenty
+
+Poniżej przedstawiam architekturę komponentową KM‑RAG, obejmującą: ingestion, mapę wiedzy, strategie segmentacji, embeddingi i wektory, retrievery i rerankery, prompt engineering i grounding, oraz kontrolę halucynacji i ewaluację.
+
+### Diagram architektury
+
+```mermaid
+flowchart LR
+  subgraph Ingestion
+    A[Źródła: PDF/HTML/DOCX/DB] --> B[Parsing + normalizacja]
+    B --> C[Jednostki wiedzy: sekcje, tabele, rekordy]
+    C --> D[Metadane: źródło, wersja, ACL, lokalizacja]
+    C --> E[Ekstrakcja encji/relacji]
+    E --> G[(Graf / Mapa Wiedzy)]
+    C --> F[Embedding + indeks]
+    F --> V[(Vector DB)]
+  end
+
+  subgraph QueryTime
+    Q[Zapytanie użytkownika] --> R[Routing/intencja/encje]
+    R --> V1[Candidate gen: vector/keyword/hybrid]
+    V1 --> V
+    V --> K[Top-K kandydatów]
+    K --> G1[Graph expansion\n(definicje, zależności, sekcje)]
+    G1 --> G
+    G --> S[Context assembly + dedup + cytowania]
+    S --> L[LLM generacja\n(z zasadą "answer from sources")]
+    L --> O[Odpowiedź + cytowania + confidence]
+  end
+
+  subgraph Control
+    O --> M[Logi/trace]
+    M --> EV[Ewaluacja offline/online]
+    M --> MON[Monitoring KPI + alerty]
+  end
+```
+
+Model ten jest kompatybilny zarówno z „klasycznym RAG” w sensie pracy na wektorach (RAG w ujęciu Lewis et al. zakłada połączenie pamięci parametrycznej i nieparametrycznej poprzez retrieval z indeksu wektorowego), jak i z odmianami grafowymi (GraphRAG: budowa grafu encji i „community summaries” jako warstwa indeksu). citeturn0search2turn0search5turn0search1turn3search4
+
+image_group{"layout":"carousel","aspect_ratio":"16:9","query":["GraphRAG architecture diagram","knowledge graph retrieval augmented generation diagram","vector database similarity search diagram","Neo4j graph visualization example"],"num_per_query":1}
+
+### Ingestion: parsowanie, normalizacja i jednostki wiedzy
+
+W KM‑RAG ingestion nie kończy się na „wyciągnij tekst z PDF”. Kluczowe jest zachowanie/rekonstrukcja struktury: tytuły, listy, tabele, numer stron, sekcje. Biblioteka entity["company","Unstructured","document processing company"] wprost opisuje „partitioning” jako ekstrakcję ustrukturyzowanych elementów (Title/NarrativeText/ListItem itd.), aby móc decydować, co zachować. citeturn16search0turn16search8turn16search4
+
+Jeśli pracujesz na bardzo różnych formatach lub potrzebujesz także metadanych i obsługi np. zaszyfrowanych PDF, narzędzia z ekosystemu entity["organization","Apache Software Foundation","open source foundation"] (Apache Tika) podkreślają możliwość parsowania PDF, w tym obsługi dokumentów szyfrowanych przy podaniu hasła. citeturn16search1turn16search30
+
+Wniosek projektowy: „Jednostka wiedzy” w KM‑RAG to obiekt typu np.:
+
+- `unit_type`: `section`, `definition`, `table`, `row`, `procedure_step`, `policy_rule`
+- `canonical_text` (tekst do embeddingu i rerankingu)
+- `rendered_context` (tekst/fragment do wklejenia do prompta)
+- `provenance`: `source_id`, `page`, `section_path`, `span_offsets`
+- `governance`: `acl_tags`, `pii_class`, `retention_class`
+- `links`: `prev/next`, `references`, `same_topic`
+
+Taki model danych bezpośrednio adresuje problem autora: model nie „weźmie odpowiedzialności” za konfliktujący kontekst, więc to system ma pilnować jakości kontekstu i jego zaufania. citeturn6view0turn7view1
+
+### Strategie segmentacji: od „chunków” do „węzłów” (Nodes)
+
+Jeżeli musisz działać na tekście, i tak będziesz coś „dzielił” – różnica polega na tym, czy są to losowe fragmenty znaków, czy **węzły semantyczne**.
+
+- W ekosystemie entity["company","LangChain","llm app framework company"] często proponuje się `RecursiveCharacterTextSplitter` jako „solidny default” dla wielu przypadków, ale to nadal jest heurystyka bazująca na znakach i separatorach. citeturn11search8turn11search0  
+- entity["company","LlamaIndex","llm data framework company"] oferuje semantyczne parsowanie węzłów: `SemanticSplitterNodeParser` dzieli tekst na grupy zdań powiązane semantycznie (z użyciem embeddingów), a dokumentacja podkreśla, że to alternatywa dla stałego rozmiaru chunków. citeturn11search1turn11search9turn11search29
+
+KM‑RAG traktuje segmentację jako element modelowania danych: węzły mają typ, hierarchię i relacje.
+
+### Embeddingi i Vector DB: candidate generation + filtrowanie po metadanych
+
+Embeddingi są nadal bardzo użyteczne, ale w KM‑RAG pełnią rolę „szybkiego generatora kandydatów”, a nie „wyroczni”.
+
+Otwartoźródłowo, entity["company","Hugging Face","ml model hub company"] utrzymuje Sentence Transformers, które dostarcza zarówno modele embeddingowe (bi-encoders), jak i rerankery (cross-encoders). citeturn12search38turn12search3
+
+Warstwa metadanych jest w KM‑RAG krytyczna: np. do ograniczania domeny, wersji dokumentu, języka, daty wejścia w życie, uprawnień.
+
+- entity["company","Qdrant","vector database company"] opisuje payload/metadata i filtrowanie oraz zaleca indeksowanie pól payload dla efektywności filtrowania. citeturn11search2turn11search6turn11search37  
+- entity["company","Pinecone","vector database company"] opisuje filtrowanie po metadanych oraz pokazuje wzorzec multitenancy przez namespaces. citeturn11search7turn14search16turn14search12  
+- entity["company","Weaviate","vector database company"] opisuje hybrydę BM25F + wektory (fuzja wyników i wagi są konfigurowalne) oraz posiada natywną wielodzierżawność (tenant per request). citeturn12search0turn14search0  
+- entity["company","Milvus","vector database project"] dokumentuje hybrydę sparse+dense i wskazuje scenariusze, w których połączenie poprawia wyniki (semantyka + dopasowanie słów kluczowych). citeturn12search1turn12search5
+
+W KM‑RAG niemal zawsze warto rozważyć hybrid retrieval (dense + sparse), bo ogranicza „semantic drift” i poprawia precyzję przy terminach domenowych (np. numery, nazwy własne). Jest to wspólny wątek w dokumentacji Weaviate i Pinecone, opisującej fuzję wyników i podejścia do hybrydy. citeturn12search0turn11search3turn11search19
+
+### Retrievery, rerankery i kontrola halucynacji
+
+KM‑RAG rozdziela retrieval na etapy:
+
+**Candidate generation (tani):** dense retriever (np. dual-encoder) i/lub sparse (BM25). Klasyczna praca o dense retrieval (DPR) pokazuje dual-encoder jako praktyczny mechanizm retrieval i porównuje go do BM25 w QA. citeturn8search0turn8search4
+
+**Reranking (droższy):** cross-encoder reranker znacząco poprawia ranking, ale jest kosztowny, bo ocenia pary (query, doc) wspólnie w modelu. Sentence Transformers opisuje retrieve‑&‑rerank pipeline oraz rolę CrossEncodera. citeturn12search11turn12search19
+
+**Graph expansion (precyzja i kompletność):** graf dostarcza „brakujących mostów” (definicje, zależności, wyjątki, kontekst sekcji) oraz daje audyt – to jest sedno „Mapy Wiedzy”. W wariantach GraphRAG (Microsoft) graf jest budowany z encji i relacji, a następnie grupowany w społeczności i streszczany, co poprawia odpowiedzi na pytania „globalne” (np. „jakie są główne tematy w korpusie?”), gdzie naiwny RAG zawodzi. citeturn0search1turn0search13turn3search4turn3search20
+
+**Halucynacje i „kontrola”:** literatura proponuje pętle weryfikacji (np. Chain‑of‑Verification: draft → pytania weryfikacyjne → niezależne odpowiedzi → final) i mechanizmy samorefleksji (Self‑RAG) oraz korekty retrieval (CRAG). Są to techniki „kontroli” na poziomie architektury, a nie tylko promptu. citeturn8search3turn9search1turn9search2
+
+## Opcje projektowe i trade‑offy
+
+### Porównanie: klasyczny RAG vs KM‑RAG
+
+| Wymiar | Klasyczny „chunk + vector DB” | KM‑RAG (Mapa Wiedzy) | Konsekwencja praktyczna |
+|---|---|---|---|
+| Jednostka indeksowania | fragment znaków/tokenów | jednostka sensu: sekcja/tabela/rekord + typ | mniej „urwanych” kontekstów, mniej przypadkowości |
+| Reprezentacja | embedding + (czasem) metadata | embedding + metadata + graf relacji + proweniencja | lepsza ścieżka audytu i „dlaczego to” |
+| Retrieval | top‑k similarity | plan retrieval: hybrid + graf expansion + rerank | wyższa precyzja i odporność na trudne pytania |
+| Zmiany w danych | częsty re‑index, ryzyko regresji | wersjonowanie, testy regresji per typ jednostki | stabilniejsze wdrożenia i migracje |
+| Bezpieczeństwo/ACL | łatwo mieszać fragmenty o różnych uprawnieniach | ACL na poziomie jednostki i ścieżki grafu | mniejsze ryzyko wycieku kontekstu |
+| Debuggowanie | „dlaczego takie chunki?” | „jaki węzeł, z jakiego źródła, jaka relacja?” | szybsze RCA i audyt |
+
+Uzasadnienie co do problemów chunkingu i „model ufa kontekstowi” pochodzi z materiału autora; definicja Mapy Wiedzy jako grafu z metadanymi i odniesieniami jest wprost w poście. citeturn6view0turn2view1turn7view1
+
+### Wybory technologiczne: wektory, graf, hybryda
+
+Poniżej pokazuję typowe opcje i kompromisy (bez narzuconych constraintów – dobór zależy od QPS, wolumenu i wymagań bezpieczeństwa).
+
+**Vector store**
+
+- Qdrant: mocne filtrowanie payload + mechanizmy multitenancy (w tym „tiered multitenancy”). citeturn11search6turn14search1turn14search18  
+- Pinecone: proste multitenancy przez namespaces; dobrze opisane podejścia do hybrid search (single hybrid index vs osobne indeksy, z plusami i minusami). citeturn14search16turn11search3  
+- Weaviate: wbudowany hybrid BM25F + wektor, oraz multi‑tenancy z tenantem w operacjach. citeturn12search0turn14search0  
+- Milvus: rozbudowane podejścia do sparse+dense i multi‑vector, z dokumentacją dla hybrydy. citeturn12search1turn12search5turn12search33  
+- pgvector: dobre, gdy chcesz „mniej systemów” i akceptujesz kompromisy wydajności; repo dokumentuje różnice IVFFlat vs HNSW (build time/memory vs speed‑recall). citeturn12search2turn12search14  
+- Elasticsearch: istotny, gdy potrzebujesz „enterprise security” (RBAC, field/document‑level security) i hybrydowego wyszukiwania w jednej platformie. citeturn14search2turn14search15
+
+**Graph / Knowledge Map store**
+
+- Neo4j: bogate wzorce GraphRAG (graph traversal, full‑text, vector, text2cypher). Neo4j publikuje GraphRAG field guide i pakiet GraphRAG dla Pythona. citeturn10search18turn10search14turn10search31turn10search2  
+- Microsoft GraphRAG: gotowy pipeline budowy grafowego indeksu (encje → społeczności → streszczenia), open‑source na GitHubie + dokumentacja „Getting started”. citeturn3search0turn3search31turn3search20turn0search1  
+- LlamaIndex KnowledgeGraphIndex: praktyczna automatyzacja budowy grafu z tekstu i query po encjach. citeturn10search3turn10search11
+
+**Kompromisy**
+
+- Skalowalność: graf może zmniejszać liczbę „strzałów” w LLM (np. przez pre‑streszczenia społeczności w GraphRAG) kosztem cięższego ingestion i większej złożoności danych. citeturn0search1turn3search4  
+- Latencja: rerankery cross‑encoder podnoszą jakość, ale zwiększają czas (N par do oceny); dlatego standardem jest retrieval → rerank top‑N, nie rerank całego korpusu. citeturn12search11turn12search19  
+- Koszt: hybryda i graf często zwiększają koszt ingest (LLM do ekstrakcji encji/relacji), ale zmniejszają koszt „ratowania” jakości w runtime przez kolejne heurystyki. To jest w duchu argumentu autora o „dokładaniu mini‑klocków” versus poprawa fundamentu. citeturn6view0turn7view1  
+- Maintainability: mniej „magicznych” parametrów chunk_size; więcej jawnych typów jednostek i testów per typ. citeturn7view1turn13search3  
+- Security/data governance: najlepiej wspierać **permission‑aware retrieval** już w retrieverze (prefilter), bo wtedy model nie ma czego „wyciec”. Dokumentacja Elastic i wektor DB pokazuje mechanizmy RBAC/DLS, namespaces/tenants i filtrowanie po metadanych. citeturn14search2turn14search16turn14search0turn11search6
+
+## Migracja z klasycznego RAG do KM‑RAG
+
+Migracja jest łatwiejsza, jeśli potraktujesz ją jak refactoring warstwy danych i retrieval, a nie „przepisanie wszystkiego od zera”.
+
+### Ścieżka migracji krok po kroku
+
+**Krok pierwszy: ustal bazową prawdę (baseline) i testy.**  
+Bez ewaluacji będziesz „liczyć na cud” – wprost przeciwieństwo postulatu „kontrola zamiast nadziei”. Zacznij od małego zestawu pytań i oczekiwań (golden set) oraz logowania kontekstu i odpowiedzi. W praktyce możesz użyć RAGAS (metryki retrieval i faithfulness bez konieczności pełnych anotacji) oraz TruLens (RAG triad: context relevance, groundedness, answer relevance). citeturn4search1turn4search2turn4search6
+
+**Krok drugi: dołóż metadane i proweniencję zanim dołożysz graf.**  
+W klasycznym RAG często brakuje stabilnych ID i lokalizacji w źródle; tymczasem autor wiąże mapę wiedzy z odniesieniami do źródeł. Minimalny zestaw to: `source_id`, `version`, `page/section`, `timestamp`, `acl_tags`. Mechanizmy filtrowania po metadanych są standardem m.in. w Pinecone i Qdrant. citeturn2view1turn11search7turn11search6
+
+**Krok trzeci: zamień chunki na węzły o typach i relacjach.**  
+Zamiast „1000 znaków”, twórz: `SectionNode`, `TableNode`, `DefinitionNode`, `PolicyNode`. Jeśli nie możesz od razu, przejdź etapowo przez semantyczne node parsers (LlamaIndex) lub segmentację po strukturze dokumentu (partitioning). citeturn11search9turn16search0turn11search1
+
+**Krok czwarty: zbuduj Mapę Wiedzy (graf) i zacznij od najtańszego użycia w runtime.**  
+Nie musisz od razu robić pełnego „GraphRAG global”. Najpierw używaj grafu do: (a) definicji i wyjątków, (b) dołączania kontekstu „nadrzędna sekcja” / „poprzedni‑następny”, (c) audytu ścieżki cytowań. Dopiero potem dokładaj stricte grafowe retrievery. citeturn10search6turn10search31turn3search4
+
+**Krok piąty: wprowadź gating i rollout.**  
+Zgodnie z najlepszymi praktykami ewaluacji: iteruj, porównuj wersje, ustaw continuous evaluation i progi akceptacji. citeturn13search3turn13search35
+
+### Proponowana sekwencja wdrożenia
+
+| Faza | Co dostarczasz | Typowy czas (brak constraintów) | Kryterium „done” |
+|---|---|---:|---|
+| Audit RAG | logi + golden set + baseline metryk | 1–2 tyg. | masz mierzalne recall/faithfulness + top failure modes |
+| Metadata-first | proweniencja + filtry + ACL | 1–2 tyg. | brak „orphan” chunków bez źródła; prefiltrowanie działa |
+| Nodes & map | węzły typowane + relacje | 2–4 tyg. | stable IDs, relacje prev/next/contains/refers_to |
+| Hybrid + rerank | dense+sparse + rerank top‑N | 1–3 tyg. | poprawa metryk retrieval bez wzrostu halucynacji |
+| Graph expansion | dołączanie kontekstu grafem | 2–4 tyg. | poprawa trudnych pytań „łączących fakty” |
+| Produkcja | monitoring KPI + procedury incydentów | ciągłe | CE + alerty + playbook audytu |
+
+Metryki i praktykę continuous evaluation wspiera dokumentacja OpenAI (zalecenia dot. progów context recall/precision i pipeline’u ewaluacji), co jest spójne z „kontrolą” jako procesem, nie jednorazową konfiguracją. citeturn13search3turn13search27
+
+## Implementacje przykładowe
+
+Poniższe implementacje są „szkieletami” (reference implementations). W obu wariantach zakładam brak narzuconych wymagań co do skali, więc pokazuję rozwiązania, które da się skalować horyzontalnie (wektor DB) i/lub uprościć (pgvector zamiast osobnej bazy).
+
+### Stack A: open‑source embeddings + open‑source Vector DB (Sentence Transformers + Qdrant) + graf w Neo4j
+
+**Kiedy wybrać:** gdy chcesz uniezależnić embeddingi od dostawcy, mieć pełną kontrolę nad danymi i implementować multitenancy/filtry wprost w wektor DB. Payload/filtry i multitenancy są natywnie wspierane w Qdrant. citeturn11search6turn14search1turn14search7
+
+**Zależności (przykład):** `sentence-transformers`, `qdrant-client`, `neo4j`, parser dokumentów (`unstructured` lub Tika).
+
+```python
+# --- Ingestion: parse -> units -> embeddings -> Qdrant + graph ---
+from dataclasses import dataclass
+from typing import Iterable, Optional
+import hashlib
+import time
+
+from sentence_transformers import SentenceTransformer, CrossEncoder
+from qdrant_client import QdrantClient, models as qmodels
+from neo4j import GraphDatabase
+
+@dataclass
+class KnowledgeUnit:
+    unit_id: str
+    source_id: str
+    version: str
+    unit_type: str              # e.g. "section", "definition", "table"
+    text: str                   # canonical text for embedding
+    page: Optional[int] = None
+    section_path: Optional[str] = None
+    acl: str = "public"         # e.g. role/tenant tag
+
+def stable_id(source_id: str, version: str, unit_type: str, page: str, text: str) -> str:
+    raw = f"{source_id}|{version}|{unit_type}|{page}|{text}".encode("utf-8")
+    return hashlib.sha256(raw).hexdigest()[:24]
+
+# 1) Embeddings (bi-encoder) + reranker (cross-encoder)
+embed_model = SentenceTransformer("sentence-transformers/all-MiniLM-L6-v2")  # example
+reranker = CrossEncoder("cross-encoder/ms-marco-MiniLM-L-6-v2")              # example
+
+# 2) Vector DB: Qdrant
+qdrant = QdrantClient(url="http://localhost:6333", timeout=30)
+COLLECTION = "kmrag_units"
+
+DIM = embed_model.get_sentence_embedding_dimension()
+qdrant.recreate_collection(
+    collection_name=COLLECTION,
+    vectors_config=qmodels.VectorParams(size=DIM, distance=qmodels.Distance.COSINE),
+)
+
+# Index payload fields frequently used in filters (performance)
+qdrant.create_payload_index(
+    collection_name=COLLECTION,
+    field_name="acl",
+    field_schema=qmodels.PayloadSchemaType.KEYWORD,
+)
+qdrant.create_payload_index(
+    collection_name=COLLECTION,
+    field_name="source_id",
+    field_schema=qmodels.PayloadSchemaType.KEYWORD,
+)
+
+# 3) Graph DB: Neo4j (property graph)
+neo4j_driver = GraphDatabase.driver(
+    "neo4j://localhost:7687", auth=("neo4j", "password")
+)
+
+def upsert_units(units: Iterable[KnowledgeUnit]) -> None:
+    batch = list(units)
+    # embeddings
+    vectors = embed_model.encode([u.text for u in batch], normalize_embeddings=True)
+
+    # upsert into Qdrant with payload metadata (provenance + ACL)
+    qdrant.upsert(
+        collection_name=COLLECTION,
+        points=[
+            qmodels.PointStruct(
+                id=u.unit_id,
+                vector=vectors[i].tolist(),
+                payload={
+                    "source_id": u.source_id,
+                    "version": u.version,
+                    "unit_type": u.unit_type,
+                    "page": u.page,
+                    "section_path": u.section_path,
+                    "acl": u.acl,
+                    "ingested_at": int(time.time()),
+                },
+            )
+            for i, u in enumerate(batch)
+        ],
+    )
+
+    # build/update graph nodes + relationships
+    cypher = """
+    UNWIND $rows AS r
+    MERGE (d:Document {source_id: r.source_id, version: r.version})
+    MERGE (u:Unit {unit_id: r.unit_id})
+      SET u.unit_type = r.unit_type,
+          u.page = r.page,
+          u.section_path = r.section_path
+    MERGE (d)-[:HAS_UNIT]->(u)
+    """
+    with neo4j_driver.session() as s:
+        s.run(cypher, rows=[u.__dict__ for u in batch])
+
+# --- Query-time retrieval: vector -> graph expansion -> rerank -> context ---
+def retrieve(query: str, acl: str, top_k: int = 30, rerank_k: int = 8):
+    qvec = embed_model.encode([query], normalize_embeddings=True)[0].tolist()
+
+    # 1) Candidate generation with metadata filter (permission-aware)
+    hits = qdrant.search(
+        collection_name=COLLECTION,
+        query_vector=qvec,
+        limit=top_k,
+        query_filter=qmodels.Filter(
+            must=[qmodels.FieldCondition(key="acl", match=qmodels.MatchValue(value=acl))]
+        ),
+    )
+    candidate_ids = [h.id for h in hits]
+
+    # 2) Graph expansion: pull neighbor units from same document/section (simple example)
+    expand_cypher = """
+    MATCH (u:Unit) WHERE u.unit_id IN $ids
+    OPTIONAL MATCH (d:Document)-[:HAS_UNIT]->(u)
+    OPTIONAL MATCH (d)-[:HAS_UNIT]->(u2:Unit)
+    WHERE u2.section_path = u.section_path
+    RETURN DISTINCT u2.unit_id AS unit_id
+    LIMIT 200
+    """
+    with neo4j_driver.session() as s:
+        rows = s.run(expand_cypher, ids=candidate_ids).data()
+    expanded_ids = list({r["unit_id"] for r in rows}) or candidate_ids
+
+    # 3) Fetch texts for reranking (here: from Qdrant payload 'text' not stored; you'd load from your storage)
+    # In production: keep canonical text in your doc store; Qdrant payload keeps provenance only.
+    # For demo: assume we can map id->text elsewhere:
+    id_to_text = load_texts(expanded_ids)  # implement in your system
+
+    pairs = [(query, id_to_text[i]) for i in expanded_ids]
+    scores = reranker.predict(pairs)
+    ranked = sorted(zip(expanded_ids, scores), key=lambda x: x[1], reverse=True)[:rerank_k]
+
+    return ranked  # list of (unit_id, score) + you can also return provenance from payload
+
+def load_texts(unit_ids):
+    # Placeholder: pull canonical text from your document store / data lake
+    raise NotImplementedError
+```
+
+Co w tym szkielecie jest „Mapą Wiedzy”: Neo4j przechowuje relacje (Document→Unit, a dalej możesz dodać Entity↔Unit, REFERENCES, NEXT), a Qdrant przechowuje wektory + payload do filtrowania; filtrowanie i indeksowanie payload jest sformalizowane w dokumentacji Qdrant. citeturn11search6turn11search2turn14search7
+
+Rerank to klasyczny krok „retrieve‑then‑rerank” opisywany przez Sentence Transformers, gdzie CrossEncoder podnosi jakość finalnych wyników kosztem obliczeń. citeturn12search11turn12search19
+
+### Stack B: managed LLM + Vector DB (OpenAI + Pinecone) + graf (Neo4j GraphRAG / Text2Cypher)
+
+**Kiedy wybrać:** gdy zależy Ci na szybkości iteracji, jakości modeli oraz gotowych mechanizmach „structured output”, a retrieval chcesz oprzeć o managed vector DB z namespaces i hybrid search. citeturn13search1turn14search16turn11search3
+
+W wariancie managed sensownie jest też wykorzystać Structured Outputs do wymuszenia formatu odpowiedzi (np. `answer` + `citations[]`), co jest elementem „kontroli” i audytu. OpenAI opisuje Structured Outputs jako mechanizm gwarantujący zgodność odpowiedzi z JSON Schema. citeturn13search1turn13search8
+
+```python
+# --- Managed stack: OpenAI embeddings + Pinecone + structured outputs + graph retrieval ---
+from openai import OpenAI
+from pinecone import Pinecone
+from neo4j_graphrag import GraphRAG  # example usage; adjust to actual package API
+
+OPENAI_MODEL_EMB = "text-embedding-3-large"
+OPENAI_MODEL_GEN = "gpt-5.4-mini"   # example; choose by latency/cost needs
+
+client = OpenAI()
+pc = Pinecone(api_key="PINECONE_API_KEY")
+index = pc.Index("kmrag")
+
+def embed(texts):
+    resp = client.embeddings.create(model=OPENAI_MODEL_EMB, input=texts)
+    return [d.embedding for d in resp.data]
+
+def upsert_to_pinecone(units, namespace):
+    vecs = embed([u["text"] for u in units])
+    index.upsert(
+        vectors=[
+            (u["unit_id"], vecs[i], {
+                "source_id": u["source_id"],
+                "version": u["version"],
+                "unit_type": u["unit_type"],
+                "page": u.get("page"),
+                "section_path": u.get("section_path"),
+                "acl": u.get("acl"),
+            })
+            for i, u in enumerate(units)
+        ],
+        namespace=namespace,   # multitenancy / workspace isolation
+    )
+
+def retrieve_candidates(query, namespace, acl, top_k=30):
+    qvec = embed([query])[0]
+    res = index.query(
+        vector=qvec,
+        top_k=top_k,
+        include_metadata=True,
+        namespace=namespace,
+        filter={"acl": {"$eq": acl}},
+    )
+    return res["matches"]
+
+# Optional: graph retrieval pattern via Text2Cypher (Neo4j GraphRAG package)
+# The idea: use graph schema + question -> generated Cypher -> execute -> return records as extra grounded context.
+gr = GraphRAG(neo4j_uri="neo4j+s://...", user="neo4j", password="...")
+
+ANSWER_SCHEMA = {
+  "name": "kmrag_answer",
+  "schema": {
+    "type": "object",
+    "properties": {
+      "answer": {"type": "string"},
+      "citations": {
+        "type": "array",
+        "items": {
+          "type": "object",
+          "properties": {
+            "unit_id": {"type": "string"},
+            "source_id": {"type": "string"},
+            "quote": {"type": "string"}
+          },
+          "required": ["unit_id", "source_id"]
+        }
+      },
+      "confidence": {"type": "number", "minimum": 0, "maximum": 1}
+    },
+    "required": ["answer", "citations", "confidence"]
+  }
+}
+
+def answer(query, namespace, acl):
+    hits = retrieve_candidates(query, namespace, acl)
+    text_context = "\n\n".join(
+        f"[{m['id']}] ({m['metadata'].get('source_id')}) {load_unit_text(m['id'])}"
+        for m in hits[:8]
+    )
+
+    graph_context = gr.text2cypher_retrieve(query)  # e.g. definitions, relationships
+
+    system = (
+        "Odpowiadasz wyłącznie na podstawie kontekstu i grafu.\n"
+        "Jeśli brakuje danych, powiedz wprost, czego nie wiesz.\n"
+        "Zwróć cytowania do unit_id/source_id."
+    )
+
+    resp = client.responses.create(
+        model=OPENAI_MODEL_GEN,
+        input=[
+            {"role": "system", "content": system},
+            {"role": "user", "content": f"Pytanie: {query}\n\nKontekst:\n{text_context}\n\nGraf:\n{graph_context}"}
+        ],
+        text={
+            "format": {
+                "type": "json_schema",
+                "json_schema": {**ANSWER_SCHEMA, "strict": True}
+            }
+        }
+    )
+    return resp.output_text
+
+def load_unit_text(unit_id):
+    # fetch canonical unit text from your storage
+    raise NotImplementedError
+```
+
+Źródła dla tego stosu: OpenAI opisuje nowe modele embeddingowe (`text-embedding-3-small/large`) i guide embeddings, a także Structured Outputs i evaluation best practices. citeturn13search2turn13search1turn13search3turn13search9  
+Pinecone opisuje hybrydę oraz filtrowanie po metadanych i multitenancy przez namespaces. citeturn11search3turn11search7turn14search16  
+Wzorzec Text2Cypher – tłumaczenie pytania + schematu grafu na Cypher i wykonanie query – jest opisany w materiałach Neo4j. citeturn10search2turn10search6turn10search10
+
+## Kontrola jakości, audyt i monitoring
+
+„Kontrola zamiast nadziei” warto potraktować jako trzy warstwy: (A) kontrola danych i retrieval, (B) kontrola generacji, (C) kontrola procesu (ewaluacja i monitoring).
+
+### Metryki i ewaluacja
+
+**Ewaluacja retrieval** (czyt. „czy przynosimy właściwy kontekst”)
+
+- Recall@K / Precision@K / MRR / NDCG: standardowe metryki IR; w pracach o retrieval z grafami i/lub KG są one explicite używane do oceny retrieval (np. praca o RAG+KG dla customer service raportuje MRR/Recall@K/NDCG@K). citeturn10search1turn10search5  
+- Offline test set buduj iteracyjnie na podstawie prawdziwych porażek (failure traces) – to jest zgodne z podejściem „evaluation flywheel” i continuous evaluation. citeturn13search35turn13search3
+
+**Ewaluacja generation** (czyt. „czy odpowiedź jest ugruntowana w źródłach”)
+
+- RAGAS: framework do „reference‑free evaluation” RAG, mierzący różne wymiary retrieval i generation. citeturn4search1turn4search5  
+- TruLens: RAG triad – context relevance, groundedness, answer relevance – jako praktyczny zestaw ocen dla halucynacji. citeturn4search2turn4search6
+
+**Progi jakości (przykład)**  
+OpenAI w evaluation best practices podaje przykładowe targety (np. context recall ≥ 0.85, context precision > 0.7) jako część praktyk ewaluacji i porównywania wersji. Traktuj to jako punkt startowy, nie prawo natury. citeturn13search3
+
+### Checklist audytu KM‑RAG
+
+**Dane i ingestion**
+
+- Czy parser zachowuje strukturę (sekcje/tabele/numery stron) i czy masz testy parsera na „trudnych dokumentach” (tabele, wielokolumnowe layouty)? citeturn16search0turn16search10turn6view0  
+- Czy każda jednostka wiedzy ma stabilne `source_id`, `version`, lokalizację i politykę retencji/PII? citeturn7view1turn14search2
+
+**Mapa Wiedzy**
+
+- Czy graf ma jasno zdefiniowane typy węzłów i relacje (HAS_UNIT, DEFINES, EXCEPTION_OF, REFERENCES, NEXT), oraz czy masz reguły walidacji (np. brak cykli w „NEXT”, spójność sekcji)? citeturn2view1turn10search31  
+- Czy ekstrakcja encji/relacji jest mierzalna (precision/recall) i odporna na duplikaty/rozbieżności nazw? (w praktyce: canonicalization + entity resolution). Koncepcja grafu encji jako indeksu jest centralna w GraphRAG. citeturn0search1turn0search13
+
+**Retrieval**
+
+- Czy stosujesz prefilter po ACL/tenant (permission-aware retrieval), zanim cokolwiek trafi do prompta? (mechanizmy namespaces/tenants i DLS/RBAC istnieją w narzędziach retrieval). citeturn14search16turn14search0turn14search2  
+- Czy masz hybrydę dense+sparse tam, gdzie słowa kluczowe są krytyczne (regulacje, numery, tickery)? Pinecone i Weaviate opisują hybrydę jako fuzję wyników. citeturn11search3turn12search0  
+- Czy reranking działa na top‑N, a nie na setkach wyników (koszt/latencja), i czy jest mierzony? citeturn12search11turn12search19
+
+**Generacja i grounding**
+
+- Czy model ma jasną instrukcję „answer from sources” oraz czy odpowiedź wymusza strukturę (JSON schema) i cytowania? Structured Outputs jest mechanizmem wspierającym niezawodność formatu. citeturn13search1turn13search8  
+- Czy masz mechanizm „I don’t know / insufficient evidence” zamiast konfabulacji (np. minimalny próg evidence coverage)? Podejścia typu CoVe/Self‑RAG/CRAG pokazują, że pętle weryfikacji i korekty podnoszą factuality. citeturn8search3turn9search1turn9search2
+
+**Bezpieczeństwo**
+
+- Czy testujesz prompt injection na poziomie aplikacji, nie tylko promptu? OWASP opisuje prompt injection jako manipulację zachowaniem modelu przez wejście, a cheat sheet sugeruje praktyki obrony. citeturn4search3turn4search7turn4search13  
+- Czy masz kontrolę kosztu (rate limits, timeouts, budżety tokenów) – to też „kontrola”, bo DoS na LLM to realny wektor ryzyka (OWASP LLM Top 10 zawiera kategorie dot. DoS i supply chain). citeturn4search13turn13search12
+
+### KPI i monitoring w produkcji
+
+Rekomendowany zestaw KPI (z podziałem na warstwy):
+
+**Retrieval KPI**
+
+- Context Recall@K / Context Precision@K (offline i online na próbie logów). citeturn13search3turn4search1  
+- % zapytań, w których retrieval zwraca „pustkę” lub tylko niskie score (sugeruje routing lub brak danych).
+
+**Generation KPI**
+
+- Faithfulness/groundedness (TruLens/RAGAS). citeturn4search1turn4search6  
+- Citation coverage: % zdań mających przypisane źródło, oraz „citation accuracy” (czy cytat faktycznie zawiera wspierający fragment). Self‑RAG raportuje poprawę citation accuracy w długich generacjach jako jeden z efektów frameworku. citeturn9search1turn9search9
+
+**Ops KPI**
+
+- Latencja p95/p99 per etap (retrieval, rerank, LLM).  
+- Koszt per zapytanie (tokeny, liczba wywołań modeli) + alerty „unbounded consumption”. OpenAI publikuje production best practices i evaluation tooling jako część przejścia prototyp → produkcja. citeturn13search12turn13search3
+
+**Narzędzia do obserwowalności**
+
+- RAGAS opisuje łączenie ewaluacji z tracingiem/analizą (np. Phoenix). citeturn4search34  
+- TruLens ma integracje i dokumentację quickstart dla trace + feedback. citeturn4search2turn4search27  
+- Jeśli używasz OpenAI, masz też guidance dot. ewaluacji i ciągłego monitorowania regresji. citeturn13search3turn13search6
+
+### Typowe failure modes KM‑RAG i mitigacje
+
+**„Graf rośnie w chaos” (sprawl, duplikaty encji, zła kanonikalizacja).**  
+Mitigacja: wprowadź entity resolution, reguły normalizacji nazw, walidację schematu grafu i testy na podzbiorze; zacznij od grafu dokument‑sekcja‑unit, dopiero potem dodawaj encje/relacje automatyczne. GraphRAG wprost zaczyna od grafu encji jako indeksu, ale też pipeline’u budowy i transformacji danych, co sugeruje konieczność procesu, nie jednorazowego prompta. citeturn3search0turn0search1
+
+**„Retrieval jest poprawny semantycznie, ale zły merytorycznie” (conflicts).**  
+Mitigacja: hybryda dense+sparse + rerank + kontrola jakości źródeł + mechanizmy korekty (CRAG: evaluator jakości retrieval i akcje naprawcze). citeturn9search2turn11search3turn12search0
+
+**„Źródła przenoszą instrukcje (prompt injection z dokumentów)”**  
+Mitigacja: separacja „instructions vs data”, sanitation, polityki „nie wykonuj instrukcji z kontekstu”, oraz przede wszystkim permission-aware retrieval (prefilter). OWASP opisuje prompt injection i praktyki obrony. citeturn4search3turn4search7turn14search2
+
+**„Latency/cost eksploduje przez reranking i graf”**  
+Mitigacja: ogranicz N rerankowanych kandydatów; cache embeddingów; cache wyników graf expansion; pre‑streszczenia (GraphRAG community summaries) dla klas pytań globalnych. citeturn12search11turn0search1turn3search4
+
+**„Zgodność i audyt”**  
+Mitigacja: loguj trace: query → (filtry ACL) → dokumenty → fragmenty → odpowiedź; uzupełnij o standardy zarządzania ryzykiem i bezpieczeństwem (entity["organization","NIST","us standards institute"] AI RMF; entity["organization","ISO","international standards body"]/IEC 27001; entity["organization","OWASP","security foundation"] LLM Top 10). Zapewnia to język kontroli dla audytu, nawet jeśli implementacje są różne. citeturn15search1turn15search2turn4search13turn15search3
+
+### Źródła priorytetowe do dalszej pracy
+
+Najbardziej „nośne” (load‑bearing) źródła do wdrożenia KM‑RAG, w kolejności praktycznej użyteczności:
+
+Źródła autora: definicja Mapy Wiedzy (graf + metadane + odniesienia) oraz argument o „R jako ryzyku” i potrzebie kontroli retrieval. citeturn2view1turn7view1
+
+Podstawy RAG: praca Lewis et al. (RAG jako retrieval + generacja z nieparametrycznej pamięci) – jako fundament terminologiczny. citeturn0search2turn0search5
+
+GraphRAG: publikacja i repozytorium Microsoft (graf encji, społeczności, streszczenia) – jako referencyjny wariant Mapy Wiedzy w postaci pipeline’u. citeturn0search1turn3search0turn3search4turn3search20
+
+KG‑RAG / hybrydy: prace o łączeniu KG i RAG (np. HybridRAG; RAG+KG w customer service) – pokazują, że graf zmniejsza skutki segmentacji i poprawia retrieval. citeturn10search0turn10search1
+
+Ewaluacja i kontrola jakości: RAGAS + TruLens + best practices ewaluacji – jako praktyczny „system kontroli”. citeturn4search1turn4search2turn13search3
+
+Bezpieczeństwo: OWASP prompt injection i LLM Top 10 – jako checklisty dla warstwy „R” i integracji z danymi. citeturn4search3turn4search13turn4search7

.agent/skills/km-rag-methodology/artifacts/evaluation_checklist.md

@@ -0,0 +1,23 @@
+# Quality and Evaluation Checklist
+
+To move from "hope-based RAG" to "controlled RAG", implement these checks.
+
+## 1. Retrieval Metrics (Search Quality)
+- [ ] **Context Recall**: Are the units necessary to answer the question actually in the retrieved set?
+- [ ] **Context Precision**: Is the retrieved set clean of irrelevant noise?
+- [ ] **MRR (Mean Reciprocal Rank)**: Is the most relevant unit appearing at the top?
+
+## 2. Generation Metrics (Answer Quality)
+- [ ] **Faithfulness (Groundedness)**: Can every claim in the answer be traced to a retrieved Knowledge Unit?
+- [ ] **Answer Relevance**: Does the answer actually address the user's intent?
+- [ ] **Citation Accuracy**: Do the citations correctly point to the unit that supports the claim?
+
+## 3. Governance & Safety
+- [ ] **ACL Pre-Filtering**: Is there a hard check ensuring units from different tenants/roles are NEVER mixed?
+- [ ] **PII Scanning**: Are units scanned for sensitive data during ingestion?
+- [ ] **Hallucination Gating**: Is there a "Confidence Score" or "Low Evidence" flag to warn users?
+
+## 4. Operational Health
+- [ ] **Latency Monitoring**: Break down time spent in: Embedding -> Vector Search -> Graph Expansion -> Reranking -> LLM.
+- [ ] **Token Efficiency**: Are we sending unnecessary fluff to the LLM, or is the context tightly packed with relevant units?
+- [ ] **Index Drift**: Are we re-evaluating the "Golden Set" of questions when we update embedding models or chunking strategies?

.agent/skills/km-rag-methodology/artifacts/implementation_patterns.md

@@ -0,0 +1,89 @@
+# Implementation Patterns for KM-RAG in .NET
+
+This guide outlines how to implement KM-RAG patterns using C# and .NET, building on existing infrastructures like EF Core and `Microsoft.Extensions.AI`.
+
+## 1. Defining Knowledge Units
+Represent units as strongly-typed entities to capture metadata and relationships.
+
+```csharp
+public enum KnowledgeUnitType { Section, Table, Definition, Step, Rule }
+
+public class KnowledgeUnit
+{
+    public string Id { get; set; } // Stable Hash(Source, Content, Version)
+    public string SourceId { get; set; }
+    public string Version { get; set; }
+    public KnowledgeUnitType Type { get; set; }
+    public string Content { get; set; }
+    public string MetadataJson { get; set; } // page, section_path, etc.
+    public Vector? Embedding { get; set; }
+    
+    // Graph Relationships
+    public List<KnowledgeUnitLink> OutgoingLinks { get; set; } = new();
+}
+
+public class KnowledgeUnitLink
+{
+    public string TargetUnitId { get; set; }
+    public string RelationType { get; set; } // "Next", "Defines", "References"
+}
+```
+
+## 2. Multi-Stage Retrieval
+Transition from simple `Take(Limit)` to a pipeline.
+
+### Step A: Hybrid Candidate Generation
+Combine `pgvector` cosine similarity with full-text search if available.
+
+```csharp
+var queryVector = await _embeddingGenerator.GenerateAsync(queryText);
+
+var candidates = await _dbContext.KnowledgeUnits
+    .Where(u => u.TenantId == tenantId)
+    .OrderBy(u => u.Embedding.CosineDistance(queryVector))
+    .Take(20) // Get more candidates for reranking
+    .Select(u => new { u.Id, u.Content, u.Type })
+    .ToListAsync();
+```
+
+### Step B: Graph Expansion
+Retrieve related units to provide full context.
+
+```csharp
+// Example: Get "Contextual Neighbors"
+var expandedIds = await _dbContext.KnowledgeUnitLinks
+    .Where(l => candidateIds.Contains(l.SourceUnitId) && l.RelationType == "ParentSection")
+    .Select(l => l.TargetUnitId)
+    .Distinct()
+    .ToListAsync();
+
+var contextUnits = await _dbContext.KnowledgeUnits
+    .Where(u => expandedIds.Contains(u.Id))
+    .ToListAsync();
+```
+
+## 3. Reranking and Citations
+Use a model to score the relevance of the expanded context and ensure the LLM cites sources.
+
+```csharp
+// System Prompt for Grounded Generation
+var systemPrompt = @"
+You are a precision assistant. Answer ONLY using the provided Knowledge Units.
+If the information is missing, state 'Information not found in knowledge map'.
+Each answer segment MUST include a citation in format [UnitId].
+";
+
+// Response Structure (using System.Text.Json or Structured Outputs)
+public class RagResponse
+{
+    public string Answer { get; set; }
+    public List<Citation> Citations { get; set; }
+}
+```
+
+## 4. Ingestion Workflow
+Instead of `string.Split`, use structural parsers:
+1. **Parse**: Extract sections/tables (e.g., using `Unstructured` or custom Logic).
+2. **Normalize**: Assign stable IDs based on content hash + source metadata.
+3. **Embed**: Generate vectors for the canonical text of each unit.
+4. **Relate**: Build links (e.g., `prev` -> `curr` -> `next`).

.agent/skills/nexus-architecture-standards/SKILL.md

@@ -0,0 +1,40 @@
+---
+name: nexus-architecture-standards
+description: Guidelines and automated checks for maintaining Clean Architecture and SaaS standards in the NexusReader project.
+tags: [Architecture, CleanArchitecture, .NET, MediatR, SaaS, MultiTenancy]
+version: 1.0.0
+---
+
+# NexusReader Architecture Standards
+
+This skill defines the architectural guardrails for the NexusReader project to ensure consistency, scalability, and security.
+
+## Core Rules
+
+### 1. Clean Architecture Layers
+- **Domain**: Pure business logic, entities, and enums. Zero dependencies on other layers.
+- **Application**: Use cases, MediatR handlers, and interfaces. Depends ONLY on Domain.
+- **Infrastructure**: Implementation details (DB context, AI services, Auth). Depends on Application and Domain.
+- **Web/Mobile**: Presentation layer. Depends on Application (and Infrastructure for DI setup).
+
+> [!CAUTION]
+> **Application MUST NOT depend on Infrastructure.** This is a common failure mode. Always use abstractions (interfaces) in Application and implement them in Infrastructure.
+
+### 2. Multi-Tenancy (Tenant Isolation)
+- Every entity related to user data MUST have a `TenantId` property.
+- Every query MUST filter by `TenantId` to prevent data leakage.
+- Default `TenantId` is "global" for shared resources.
+
+### 3. Error Handling
+- Use `FluentResults` (`Result<T>`) for all Application services and handlers.
+- Avoid throwing exceptions for expected business failures; use `Result.Fail()`.
+
+### 4. MediatR Patterns
+- **Queries**: Read-only operations. Should return `Result<T>`. Use `AsNoTracking()` in EF Core.
+- **Commands**: State-changing operations. Should return `Result` or `Result<T>`.
+
+## Audit Scripts
+- [ArchCheck.sh](scripts/arch_check.sh): A shell script to scan for illegal cross-layer imports.
+
+## Reference Materials
+- [Layer Dependency Matrix](artifacts/layer_matrix.md)

.agent/skills/nexus-architecture-standards/scripts/arch_check.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+# Simple script to check for Clean Architecture violations in NexusReader
+
+APP_DIR="src/NexusReader.Application"
+VIOLATIONS=$(grep -r "using NexusReader.Infrastructure" "$APP_DIR")
+
+if [ -n "$VIOLATIONS" ]; then
+    echo "ERROR: Clean Architecture violations found in $APP_DIR:"
+    echo "$VIOLATIONS"
+    exit 1
+else
+    echo "SUCCESS: No illegal Infrastructure dependencies found in Application layer."
+    exit 0
+fi

.agent/skills/nexus-clean-architecture/SKILL.md

@@ -8,6 +8,7 @@ description: Clean Architecture & CQRS implementation for .NET 10 with Blazor Hy
   - `NexusReader.Domain`: Enterprise business rules (Entities, Value Objects, Domain Events).
   - `NexusReader.Application`: Application business rules (Commands, Queries, DTOs, Mappings, Interfaces).
   - `NexusReader.Infrastructure`: Data access, external services, and platform-specific implementations.
+    - **Persistence**: Use `IDbContextFactory<AppDbContext>` for long-running operations or when multiple units of work are needed in a single scope (especially in Blazor).
   - `NexusReader.UI.Shared`: UI logic and Blazor components.
   - `NexusReader.Maui` / `NexusReader.Web`: Platform host projects.
 
@@ -16,6 +17,7 @@ description: Clean Architecture & CQRS implementation for .NET 10 with Blazor Hy
   - **Queries**: Read-only operations, return `Task<Result<T>>`.
   - **Commands**: State-changing operations, return `Task<Result>` or `Task<Result<T>>`.
   - **Handlers**: Located in `Application` layer, grouped by feature (e.g., `Queries/Reader/...`).
+  - **Client-Server Boundaries**: DO NOT execute MediatR handlers directly from WASM/MAUI clients if the handler relies on server-only infrastructure (e.g., `AppDbContext`, `IHubContext`). Instead, the client must trigger an API or SignalR endpoint, and the server dispatches the MediatR command.
 
 - **Functional Error Handling:**
   - Mandatory use of `FluentResults`.
@@ -35,4 +37,7 @@ description: Clean Architecture & CQRS implementation for .NET 10 with Blazor Hy
 
 - **Cross-Platform Strategy:**
   - Maximize code sharing in `NexusReader.UI.Shared`.
-  - Use `IPlatformService` (or similar abstractions) for native features, implemented in `Infrastructure.Mobile` or Maui projects.
+  - Use `IPlatformService` (or similar abstractions) for native features, implemented in `Infrastructure.Mobile` or Maui projects.
+
+- **Code Validation (CRITICAL):**
+  - **Mandatory Build Verification**: After any code change, the agent MUST run `dotnet build` on the solution. The agent must verify that the build completes with `Exit code: 0` and without errors before concluding the task or requesting user feedback.

.agent/skills/nexus-code-review/SKILL.md

@@ -0,0 +1,30 @@
+---
+name: nexus-code-review
+description: Code Review Checklist and Standards for NexusReader SaaS
+---
+# NexusReader Code Review Standards
+
+When conducting or receiving a code review for NexusReader, ensure the implementation adheres to the following critical architectural and performance standards:
+
+## 1. Architectural Boundaries (CQRS & Blazor Hybrid)
+- [ ] **Client vs. Server Execution**: MediatR handlers that depend on server-side infrastructure (`AppDbContext`, `IHubContext`, secrets) MUST NOT be executed directly from client environments (WASM/MAUI).
+- [ ] **Dependency Leakage**: Ensure `NexusReader.Web.Client` (WASM) does not reference `NexusReader.Infrastructure` if the infrastructure requires `Microsoft.AspNetCore.App` framework references.
+- [ ] **SignalR Bridges**: Client-initiated state changes should be sent via SignalR `SendAsync` to a server Hub, which then dispatches the internal `MediatR` command.
+
+## 2. Event Handling & Debouncing
+- [ ] **High-Frequency UI Events**: UI actions like scrolling, resizing, or typing must be debounced.
+- [ ] **Trailing-Edge Debounce**: Use a `CancellationTokenSource` and `Task.Delay` to ensure the *last* event in a rapid sequence is executed. Do not use simple time-window drops, as they result in lost final states.
+- [ ] **Async Void**: Ensure UI event handlers do not use `async void` unless they are top-level framework event bindings, and even then, they must catch all exceptions.
+
+## 3. SignalR & Real-Time Contexts
+- [ ] **Authentication Context**: Do not rely on `IHttpContextAccessor` inside MediatR handlers triggered by SignalR Hubs. Use `Context.UserIdentifier` directly from the Hub and pass it as a command parameter.
+- [ ] **Connection State**: Always check `HubConnection.State == HubConnectionState.Connected` before attempting to send messages from the client.
+- [ ] **Targeted Broadcasting**: Use SignalR `Groups` (e.g., `$"User_{userId}"`) to broadcast updates only to the devices owned by the relevant user.
+
+## 4. Performance & Scalability
+- [ ] **Database Write Contention**: High-frequency telemetry (like reading progress) should ideally be batched or cached in-memory before writing to SQL, unless real-time persistence is strictly required.
+- [ ] **Memory Leaks**: Ensure all components and services that subscribe to events (e.g., `OnProgressReceived`, JS Observers) implement `IDisposable` or `IAsyncDisposable` and properly unsubscribe.
+
+## 5. Standard Nexus Guidelines
+- [ ] **Result Pattern**: Ensure all application logic returns `Result` or `Result<T>` via FluentResults. No exceptions for control flow.
+- [ ] **AI Prompts**: Ensure changes to AI logic do not bypass the `PromptRegistry` or token estimation limits defined in `AiSettings`.

.agents/DOD.md

@@ -1,11 +0,0 @@
-# Definition of Done (DoD)
-
-1. **Architecture Compliance:** Feature follows CQRS flow. Logic is in Handlers. Result is wrapped in `Result<T>` from FluentResult.
-2. **Modularization:** Code is in `/src`, tests in `/tests`. Module-specific logic is isolated.
-3. **UI/UX Integrity:** - "Vertical Flow Check" passed (Assistant is part of the document stream, not an absolute pop-up).
-    - No "Layout Shift" during AI content streaming.
-    - Safe-area-insets respected for iOS/Android notches.
-4. **Code Quality:** C# 14 syntax used (Primary Constructors, etc.). Scoped CSS (.razor.css) implemented.
-5. **D3.js Performance:** JS Modules correctly disposed using `IAsyncDisposable`.
-6. **Persistence:** State survives manual page refresh (Local/Session Storage integration).
-7. **Mapping:** All entity-to-DTO conversions must use Mapster.

.agents/agents.md

@@ -1,16 +0,0 @@
-# Agent Personas
-
-## NexusArchitect
-- **Role:** Lead Architect & Creative Technologist (.NET 10 & Blazor)
-- **Persona:** Professional, precise, Senior Full-Stack Engineer focused on performance and "invisible UI".
-- **Architecture Role:** Lead Clean Architecture Specialist.
-- **Skills:** [nexus-clean-architecture, nexus-ui-engine, nexus-graph-d3, blazor-state-performance, blazor-hybrid-bridge, semantic-kernel-orchestrator, nexus-identity-saas, dotnet-async-void]
-- **Technical Constraints:**
-    - **Directory Structure:** Strict separation: `/src` (app code) and `/tests` (testing code) at solution root level.
-    - **Patterns:** Mandatory CQRS via `MediatR` (LuckyPennySoftware implementation). No business logic in UI components.
-    - **Async:** Strict zero-tolerance for `async void`. All async operations must return `Task` or `ValueTask`. Event handlers must use `Func<Task>` or async-compatible patterns.
-    - **Error Handling:** All handlers must return `Result<T>` via `FluentResult`.
-    - **Mapping:** Use `Mapster` exclusively. Zero-tolerance for AutoMapper.
-    - **Platform:** Target .NET 10 with Native AOT compatibility in mind for mobile performance.
-    - **Verification:** Follow "Verification-led development" — the agent must plan the test before writing the feature code.
-    - **UI Framework:** Use Blazor Component Model. NEVER generate raw HTML/CSS; always use isolated Razor Components (.razor + .razor.css).

GEMINI.md

@@ -0,0 +1,49 @@
+---
+type: agent-definitions
+version: 1.0
+---
+
+# Agent Personas
+
+## 👤 NexusArchitect
+
+**Role:** Lead Architect & Creative Technologist (.NET 10 & Blazor)  
+**Persona:** Professional, precise, Senior Full-Stack Engineer focused on performance and "invisible UI".
+
+---
+
+## 🏗️ Architecture Philosophy
+
+- **Clean Architecture:** Strict separation of concerns. `Domain` -> `Application` <- `Infrastructure`.
+- **CQRS Pattern:** Mandatory use of `MediatR`. Logic belongs in handlers, not UI components.
+- **Result Pattern:** Zero exceptions for flow control. All handlers return `Result<T>` via `FluentResult`.
+- **Mapping:** Exclusive use of `Mapster`. (Zero tolerance for AutoMapper).
+
+---
+
+## 🛠️ Technical Constraints
+>
+> [!IMPORTANT]
+> **Zero Tolerance for `async void`**  
+> All async operations must return `Task` or `ValueTask`. Event handlers must use `Func<Task>` or async-compatible patterns.
+
+- **Platform:** Target .NET 10 with **Native AOT** compatibility. Optimize for mobile performance.
+- **UI Framework:** Blazor Component Model. No raw HTML/CSS; use isolated Razor Components (.razor + .razor.css).
+- **Directory Structure:** `/src` for app code and `/tests` for testing code at solution root level.
+
+---
+
+## 🧪 Development Workflow
+
+1. **Verification-Led:** Plan and define tests/verification steps *before* writing feature code.
+2. **Step-by-Step Execution:** Break complex tasks into manageable, verifiable chunks.
+3. **Layer Integrity:** Always check for illegal cross-layer dependencies (e.g., Application depending on Infrastructure).
+4. **Mandatory Build Gate:** After **every** code change, run `dotnet build` on the full solution. The agent MUST NOT proceed or report completion if there are any `error CS*` compiler errors. All build errors must be resolved before moving to the next step.
+
+> [!IMPORTANT]
+> **Build command:** `dotnet build NexusReader.slnx --no-restore`  
+> Run from the solution root `/home/mjasin/Projekty/ejajBook`. Build warnings are acceptable; errors are not.
+
+> [!IMPORTANT]
+> **Git Workflow & Integration**
+> All tasks originating from the repository must be performed on a separate branch. To connect to the Git repository, use the `gitea-ovh` MCP server.

backlog-code-review.md

@@ -0,0 +1,127 @@
+# 🔍 NexusReader Code Review Backlog
+
+## 🔴 CRITICAL — Fix Before Next Release
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Removed `AddMediatR` from `AddApplication()` and `AddInfrastructure()`. Unified registration in Host (`Program.cs`, `MauiProgram.cs`). Added `IInfrastructureMarker` and a startup validation check in `Web.New` that throws `InvalidOperationException` if `AddInfrastructure` is missing.
+- **DoD:** Application fails fast with a clear error if `AddInfrastructure()` is omitted.
+
+---
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Added `VerifyGroundednessAsync` to `IKnowledgeService` and implemented it in `KnowledgeService` (Infrastructure). Updated `VerifyGroundednessCommandHandler` in Application to inject `IKnowledgeService` instead of `IChatClient`.
+- **DoD:** No `IChatClient` or `IEmbeddingGenerator` references remain in `NexusReader.Application`.
+
+---
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Threaded `tenantId` through all `IKnowledgeService` methods and `ProcessKnowledgeUnitsAsync`. Scoped `SemanticKnowledgeCache` and `KnowledgeUnit` lookups/writes to the provided `tenantId`. Updated API endpoints in `Program.cs` and `WasmKnowledgeService` to pass the authenticated user's `TenantId`.
+- **DoD:** No hardcoded `"global"` TenantId in write paths. Extracted units are always scoped to the caller's tenant.
+
+---
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Changed `NexusUser.TenantId` from `Guid` to `string`. All entities now use `string` for `TenantId`, allowing the use of `"global"` as a sentinel value.
+- **DoD:** All entities use the same `TenantId` type. All query filters are consistent.
+
+---
+
+## 🟠 MAJOR — High Priority Fixes
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Added `File.Exists` check and granular `try-catch` around `EpubReader.ReadBookAsync` to prevent unhandled exceptions and provide descriptive error messages.
+- **DoD:** Corrupted or missing files return `Result.Fail` instead of crashing.
+
+---
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Verified `IDbContextFactory<AppDbContext>` is correctly registered via `AddDbContextFactory` in `Infrastructure/DependencyInjection.cs`.
+- **DoD:** Webhook and profile endpoints successfully resolve the factory.
+
+---
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Implemented `Coordinator.Clear()` (which calls `KnowledgeGraphService.Clear()`) in `ReaderCanvas.razor`'s `OnInitialized`.
+- **DoD:** Stale graph data is cleared upon component initialization.
+
+---
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Created `UserProfileDto` to exclude sensitive internal IDs like `TenantId` and DB GUIDs. Updated `/identity/profile` endpoint to project into this DTO using `.Select()`.
+- **DoD:** Internal IDs are no longer exposed in the profile API.
+
+---
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Added `HasIndex(x => x.TenantId)` to `NexusUser`, `Ebook`, and `QuizResult` in `AppDbContext`. `KnowledgeUnit` and `SemanticKnowledgeCache` already had them.
+- **DoD:** Tenant-scoped queries are optimized via DB indexes.
+
+---
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Refactored `KnowledgeService.ProcessKnowledgeUnitsAsync` to pre-fetch all existing unit IDs in a single batch query, eliminating the N+1 `FindAsync` and `AnyAsync` calls.
+- **DoD:** Batch processing performance is significantly improved.
+
+---
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Added `TenantId` property to `Ebook` entity with mandatory validation and index. Updated `AppDbContext` configuration.
+- **DoD:** Ebooks are now isolated at the database level.
+
+---
+
+- **Status:** ✅ Resolved (2026-05-03)
+- **Implementation:** Added `TenantId` property to `QuizResult` entity with mandatory validation and index.
+- **DoD:** Quiz results are now isolated at the database level.
+
+---
+
+## 🟡 MINOR — Technical Debt & UX
+
+### [MN-01] Missing Logging in `KnowledgeCoordinator`
+- **Action:** Add `ILogger<KnowledgeCoordinator>` and log successful/failed extraction steps.
+
+### [MN-02] Hardcoded "Gemini-1.5-Flash" in Domain
+- **File:** `Domain/Entities/SemanticKnowledgeCache.cs:20`
+- **Action:** Move the default model ID to a constant in `AiSettings`.
+
+### [MN-03] UI: Shimmer Effect Lack Animation
+- **File:** `UI.Shared/Components/Molecules/GroundednessBadge.razor`
+- **Action:** Add `@keyframes` for the shimmer effect in CSS.
+
+### [MN-04] Identity: Google Callback Lack Error Handling
+- **File:** `Web.New/Program.cs:340`
+- **Action:** Better UI feedback when `ExternalLoginInfo` is null.
+
+### [MN-05] Tokenizer Initialization is Expensive
+- **File:** `Infrastructure/Services/KnowledgeService.cs:43`
+- **Action:** Make `_tokenizer` static or Singleton to avoid recreating it per request.
+
+### [MN-06] Mapster: Global Configuration Check
+- **Action:** Ensure `TypeAdapterConfig.GlobalSettings.Scan(...)` is only called once.
+
+### [MN-07] SignalR: Missing Reconnection Logic
+- **Action:** Implement `hubConnection.OnReconnected` in `SyncService.cs`.
+
+### [MN-10] Performance: Large EPUB Parsing
+- **Action:** Implement streaming extraction for EPUBs over 10MB.
+
+---
+
+## 🧪 TESTING — Coverage Gaps
+
+### [TEST-01] Integration Tests for KM-RAG Retrieval
+- **Action:** Create `tests/NexusReader.IntegrationTests`.
+- **Scenario:** Ingest a document, then verify that `GetRelevantContext` returns the correct snippets with tenant isolation active.
+
+---
+
+## 📊 Summary Table
+
+| Severity | Count | Status |
+|---|---|---|
+| 🔴 Critical | 4 | 4 resolved |
+| 🟠 Major | 8 | 8 resolved |
+| 🟡 Minor | 8 | Unresolved |
+| 🧪 Tests | 1 | Unresolved |
+| **Total** | **21** | **12 resolved** |

docker-compose.yml

@@ -1,6 +1,6 @@
 services:
   db:
-    image: postgres:17-alpine
+    image: pgvector/pgvector:pg17
     container_name: nexus-db
     environment:
       POSTGRES_USER: nexus_user

scratch/check_db.cs

@@ -0,0 +1,44 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.EntityFrameworkCore;
+using NexusReader.Infrastructure.Persistence;
+using Microsoft.Extensions.Configuration;
+using NexusReader.Domain.Entities;
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+
+var configuration = new ConfigurationBuilder()
+    .AddJsonFile("src/NexusReader.Web.New/appsettings.json")
+    .Build();
+
+var services = new ServiceCollection();
+var pgConnectionString = configuration.GetConnectionString("PostgresConnection");
+if (!string.IsNullOrEmpty(pgConnectionString))
+{
+    services.AddDbContext<AppDbContext>(options => options.UseNpgsql(pgConnectionString));
+}
+else
+{
+    services.AddDbContext<AppDbContext>(options => options.UseSqlite(configuration.GetConnectionString("SqliteConnection")));
+}
+
+var serviceProvider = services.BuildServiceProvider();
+using var scope = serviceProvider.CreateScope();
+var dbContext = scope.ServiceProvider.GetRequiredService<AppDbContext>();
+
+try 
+{
+    var user = await dbContext.Users.FirstOrDefaultAsync(u => u.Email == "admin@nexus.com");
+    if (user == null)
+    {
+        Console.WriteLine("User admin@nexus.com NOT FOUND in database.");
+    }
+    else
+    {
+        Console.WriteLine($"User found: {user.Email}, Id: {user.Id}, EmailConfirmed: {user.EmailConfirmed}");
+    }
+}
+catch (Exception ex)
+{
+    Console.WriteLine($"Error accessing database: {ex.Message}");
+}

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

@@ -0,0 +1,15 @@
+using Microsoft.EntityFrameworkCore;
+using NexusReader.Domain.Entities;
+
+namespace NexusReader.Application.Abstractions.Persistence;
+
+public interface IApplicationDbContext
+{
+    DbSet<SemanticKnowledgeCache> SemanticKnowledgeCache { get; }
+    DbSet<KnowledgeUnit> KnowledgeUnits { get; }
+    DbSet<KnowledgeUnitLink> KnowledgeUnitLinks { get; }
+    DbSet<Ebook> Ebooks { get; }
+    DbSet<QuizResult> QuizResults { get; }
+    
+    Task<int> SaveChangesAsync(CancellationToken cancellationToken = default);
+}

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

@@ -1,9 +0,0 @@
-using FluentResults;
-using NexusReader.Application.Queries.Quiz;
-
-namespace NexusReader.Application.Abstractions.Services;
-
-public interface IAiGenerateQuizService
-{
-    Task<Result<QuizDto>> GenerateQuizAsync(string contextBlockId, CancellationToken cancellationToken = default);
-}

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

@@ -5,8 +5,13 @@ namespace NexusReader.Application.Abstractions.Services;
 
 public interface IKnowledgeService
 {
-    Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, CancellationToken cancellationToken = default);
-    Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, CancellationToken cancellationToken = default);
-    Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, CancellationToken cancellationToken = default);
+    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<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);
 }
+
+public record GroundednessResult(float Score, string Rationale, bool IsGrounded);

src/NexusReader.Application/Commands/AI/VerifyGroundednessCommand.cs

@@ -0,0 +1,22 @@
+using FluentResults;
+using MediatR;
+using NexusReader.Application.Abstractions.Services;
+
+namespace NexusReader.Application.Commands.AI;
+
+public record VerifyGroundednessCommand(string Answer, string Context, string TenantId) : IRequest<Result<GroundednessResult>>;
+
+public class VerifyGroundednessCommandHandler : IRequestHandler<VerifyGroundednessCommand, Result<GroundednessResult>>
+{
+    private readonly IKnowledgeService _knowledgeService;
+
+    public VerifyGroundednessCommandHandler(IKnowledgeService knowledgeService)
+    {
+        _knowledgeService = knowledgeService;
+    }
+
+    public async Task<Result<GroundednessResult>> Handle(VerifyGroundednessCommand request, CancellationToken cancellationToken)
+    {
+        return await _knowledgeService.VerifyGroundednessAsync(request.Answer, request.Context, request.TenantId, cancellationToken);
+    }
+}

src/NexusReader.Application/Commands/Sync/UpdateReadingProgressCommand.cs

@@ -0,0 +1,6 @@
+using FluentResults;
+using MediatR;
+
+namespace NexusReader.Application.Commands.Sync;
+
+public record UpdateReadingProgressCommand(string PageId, string UserId) : IRequest<Result>;

src/NexusReader.Application/DTOs/AI/KnowledgePacket.cs

@@ -13,10 +13,15 @@ public record QuizQuestion(
     [property: JsonPropertyName("correct_index")] int CorrectIndex
 );
 
+public record KnowledgeUnitDto(string Id, string Type, string Content, Dictionary<string, object>? Metadata = null);
+public record KnowledgeLinkDto(string Source, string Target, string Relation);
+
 public record KnowledgePacket
 {
     [JsonPropertyName("concepts")] public List<KeyConcept> Concepts { get; init; } = new();
     [JsonPropertyName("quizzes")] public List<QuizQuestion> Quizzes { get; init; } = new();
+    [JsonPropertyName("units")] public List<KnowledgeUnitDto> Units { get; init; } = new();
+    [JsonPropertyName("links")] public List<KnowledgeLinkDto> Links { get; init; } = new();
     [JsonPropertyName("graph")] public NexusReader.Application.Queries.Graph.GraphDataDto? Graph { get; init; }
     [JsonPropertyName("summary")] public string? Summary { get; init; }
 }

src/NexusReader.Application/DTOs/AI/RelevantContext.cs

@@ -0,0 +1,8 @@
+namespace NexusReader.Application.DTOs.AI;
+
+public class RelevantContext
+{
+    public string Text { get; set; } = string.Empty;
+    public string SourceId { get; set; } = string.Empty; // ContentHash or EbookTitle
+    public double Confidence { get; set; }
+}

src/NexusReader.Application/DTOs/AI/SemanticSearchResultDto.cs

@@ -0,0 +1,11 @@
+namespace NexusReader.Application.DTOs.AI;
+
+public class SemanticSearchResultDto
+{
+    public string ContentHash { get; set; } = string.Empty;
+    public string Snippet { get; set; } = string.Empty;
+    public string? UnitType { get; set; }
+    public float RelevanceScore { get; set; }
+    public string? SourceBookTitle { get; set; }
+    public Dictionary<string, object>? Metadata { get; set; } // Bonus context
+}

src/NexusReader.Application/DTOs/User/SubscriptionPlanDto.cs

@@ -0,0 +1,9 @@
+namespace NexusReader.Application.DTOs.User;
+
+public record SubscriptionPlanDto
+{
+    public int Id { get; init; }
+    public string Name { get; init; } = string.Empty;
+    public int AITokenLimit { get; init; }
+    public decimal MonthlyPrice { get; init; }
+}

src/NexusReader.Application/DTOs/User/UserProfileDto.cs

@@ -0,0 +1,25 @@
+namespace NexusReader.Application.DTOs.User;
+
+public record UserProfileDto
+{
+    public string Email { get; init; } = string.Empty;
+    public int AITokensUsed { get; init; }
+    
+    /// <summary>
+    /// Relational data for the current subscription plan.
+    /// </summary>
+    public SubscriptionPlanDto Plan { get; init; } = new();
+
+    public int AverageQuizScore { get; init; }
+    
+    /// <summary>
+    /// Summary of the last read book.
+    /// </summary>
+    public LastReadBookDto? LastReadBook { get; init; }
+}
+
+public record LastReadBookDto
+{
+    public Guid Id { get; init; }
+    public string Title { get; init; } = string.Empty;
+}

src/NexusReader.Application/DependencyInjection.cs

@@ -9,11 +9,8 @@ public static class DependencyInjection
     {
         services.AddMapsterConfiguration();
 
-        services.AddMediatR(config => 
-        {
-            config.RegisterServicesFromAssembly(typeof(DependencyInjection).Assembly);
-        });
-
         return services;
     }
+
+    public static System.Reflection.Assembly Assembly => typeof(DependencyInjection).Assembly;
 }

src/NexusReader.Application/NexusReader.Application.csproj

@@ -10,7 +10,10 @@
     <PackageReference Include="Mapster.DependencyInjection" Version="10.0.7" />
     <PackageReference Include="MediatR" Version="12.1.1" />
     <PackageReference Include="Microsoft.AspNetCore.Authorization" Version="10.0.7" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="10.0.7" />
+    <PackageReference Include="Microsoft.Extensions.AI" Version="10.5.0" />
     <PackageReference Include="Microsoft.Extensions.Identity.Core" Version="10.0.7" />
+    <PackageReference Include="Pgvector.EntityFrameworkCore" Version="0.2.1" />
   </ItemGroup>
 
   <PropertyGroup>

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

@@ -2,4 +2,7 @@ using NexusReader.Application.Abstractions.Messaging;
 
 namespace NexusReader.Application.Queries.Graph;
 
-public record GetKnowledgeGraphQuery : IQuery<GraphDataDto>;
+/// <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>;
+

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

@@ -1,15 +1,30 @@
 using FluentResults;
 using NexusReader.Application.Abstractions.Messaging;
+using NexusReader.Application.Abstractions.Services;
 
 namespace NexusReader.Application.Queries.Graph;
 
 internal sealed class GetKnowledgeGraphQueryHandler : IQueryHandler<GetKnowledgeGraphQuery, GraphDataDto>
 {
-    public Task<Result<GraphDataDto>> Handle(GetKnowledgeGraphQuery request, CancellationToken cancellationToken)
-    {
-        var nodes = new List<GraphNodeDto>();
-        var links = new List<GraphLinkDto>();
+    private readonly IKnowledgeService _knowledgeService;
 
-        return Task.FromResult(Result.Ok(new GraphDataDto { Nodes = nodes, Links = links }));
+    public GetKnowledgeGraphQueryHandler(IKnowledgeService knowledgeService)
+    {
+        _knowledgeService = knowledgeService;
+    }
+
+    public async Task<Result<GraphDataDto>> Handle(GetKnowledgeGraphQuery request, CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrWhiteSpace(request.Text))
+            return Result.Ok(new GraphDataDto());
+
+        var result = await _knowledgeService.GetGraphDataAsync(request.Text, request.TenantId, cancellationToken);
+
+        if (result.IsFailed)
+            return Result.Fail<GraphDataDto>(result.Errors);
+
+        var graph = result.Value.Graph;
+
+        return graph is null ? Result.Ok(new GraphDataDto()) : Result.Ok(graph);
     }
 }

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

@@ -1,7 +1,7 @@
 namespace NexusReader.Application.Queries.Graph;
 
-public record GraphNodeDto(string Id, string Label, string Group);
-public record GraphLinkDto(string Source, string Target, int Value);
+public record GraphNodeDto(string Id, string Label, string Group, string? Type = null);
+public record GraphLinkDto(string Source, string Target, string RelationType, int Value = 1);
 public record GraphDataDto
 {
     public List<GraphNodeDto> Nodes { get; init; } = new();

src/NexusReader.Application/Queries/Library/SearchLibrarySemanticallyQuery.cs

@@ -0,0 +1,116 @@
+using FluentResults;
+using Mapster;
+using MediatR;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.AI;
+using NexusReader.Application.DTOs.AI;
+using NexusReader.Application.Abstractions.Persistence;
+using Pgvector;
+using Pgvector.EntityFrameworkCore;
+using System.Text.Json;
+
+namespace NexusReader.Application.Queries.Library;
+
+public record SearchLibrarySemanticallyQuery(string QueryText, string TenantId, int Limit = 5) 
+    : IRequest<Result<List<SemanticSearchResultDto>>>;
+
+public class SearchLibrarySemanticallyQueryHandler : IRequestHandler<SearchLibrarySemanticallyQuery, Result<List<SemanticSearchResultDto>>>
+{
+    private readonly IApplicationDbContext _dbContext;
+    private readonly IEmbeddingGenerator<string, Embedding<float>> _embeddingGenerator;
+
+    public SearchLibrarySemanticallyQueryHandler(
+        IApplicationDbContext dbContext,
+        IEmbeddingGenerator<string, Embedding<float>> embeddingGenerator)
+    {
+        _dbContext = dbContext;
+        _embeddingGenerator = embeddingGenerator;
+    }
+
+    public async Task<Result<List<SemanticSearchResultDto>>> Handle(SearchLibrarySemanticallyQuery request, CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrWhiteSpace(request.QueryText))
+        {
+            return Result.Fail("Query text cannot be empty.");
+        }
+
+        try
+        {
+            // 1. Generate embedding for user query
+            var embeddingResponse = await _embeddingGenerator.GenerateAsync(new[] { request.QueryText }, cancellationToken: cancellationToken);
+            var queryVector = new Vector(embeddingResponse.First().Vector.ToArray());
+
+            // 2. Perform Cosine Similarity Search on Knowledge Units
+            var candidates = await _dbContext.KnowledgeUnits
+                .AsNoTracking()
+                .Where(x => (x.TenantId == request.TenantId || x.TenantId == "global") && x.Vector != null)
+                .OrderBy(x => x.Vector!.CosineDistance(queryVector))
+                .Take(request.Limit)
+                .ToListAsync(cancellationToken);
+
+            if (!candidates.Any())
+            {
+                // Fallback to legacy cache if no granular units found
+                var legacyResults = await _dbContext.SemanticKnowledgeCache
+                    .AsNoTracking()
+                    .Where(x => x.TenantId == request.TenantId && x.Vector != null)
+                    .OrderBy(x => x.Vector!.CosineDistance(queryVector))
+                    .Take(request.Limit)
+                    .ToListAsync(cancellationToken);
+
+                return Result.Ok(legacyResults.Select(r => new SemanticSearchResultDto
+                {
+                    ContentHash = r.ContentHash,
+                    Snippet = r.OriginalText,
+                    RelevanceScore = (float)(1 - r.Vector!.CosineDistance(queryVector))
+                }).ToList());
+            }
+
+            // 3. Graph Expansion: Pull related units (e.g. Definitions, Next steps)
+            var candidateIds = candidates.Select(c => c.Id).ToList();
+            var links = await _dbContext.KnowledgeUnitLinks
+                .AsNoTracking()
+                .Where(l => candidateIds.Contains(l.SourceUnitId) && (l.RelationType == "Defines" || l.RelationType == "Next"))
+                .ToListAsync(cancellationToken);
+
+            var relatedIds = links.Select(l => l.TargetUnitId).Distinct().ToList();
+            var relatedUnits = await _dbContext.KnowledgeUnits
+                .AsNoTracking()
+                .Where(u => relatedIds.Contains(u.Id))
+                .ToDictionaryAsync(u => u.Id, cancellationToken);
+
+            // 4. Mapping with Context Enrichment
+            var dtos = candidates.Select(c => 
+            {
+                var dto = new SemanticSearchResultDto
+                {
+                    ContentHash = c.Id,
+                    Snippet = c.Content,
+                    UnitType = c.Type.ToString(),
+                    RelevanceScore = (float)(1 - c.Vector!.CosineDistance(queryVector)),
+                    Metadata = string.IsNullOrEmpty(c.MetadataJson) 
+                        ? null 
+                        : JsonSerializer.Deserialize<Dictionary<string, object>>(c.MetadataJson)
+                };
+
+                // Enrich snippet with definitions if present
+                var unitLinks = links.Where(l => l.SourceUnitId == c.Id && l.RelationType == "Defines").ToList();
+                if (unitLinks.Any())
+                {
+                    var definitions = unitLinks
+                        .Where(l => relatedUnits.ContainsKey(l.TargetUnitId))
+                        .Select(l => relatedUnits[l.TargetUnitId].Content);
+                    dto.Snippet = $"[Context: {string.Join("; ", definitions)}]\n{dto.Snippet}";
+                }
+
+                return dto;
+            }).ToList();
+
+            return Result.Ok(dtos);
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error("Failed to perform semantic search").CausedBy(ex));
+        }
+    }
+}

src/NexusReader.Application/Queries/Quiz/GetQuizQuestionsQuery.cs

@@ -1,5 +0,0 @@
-using NexusReader.Application.Abstractions.Messaging;
-
-namespace NexusReader.Application.Queries.Quiz;
-
-public record GetQuizQuestionsQuery(string ContextBlockId) : IQuery<QuizDto>;

src/NexusReader.Application/Queries/Quiz/GetQuizQuestionsQueryHandler.cs

@@ -1,20 +0,0 @@
-using FluentResults;
-using NexusReader.Application.Abstractions.Messaging;
-using NexusReader.Application.Abstractions.Services;
-
-namespace NexusReader.Application.Queries.Quiz;
-
-internal sealed class GetQuizQuestionsQueryHandler : IQueryHandler<GetQuizQuestionsQuery, QuizDto>
-{
-    private readonly IAiGenerateQuizService _aiService;
-
-    public GetQuizQuestionsQueryHandler(IAiGenerateQuizService aiService)
-    {
-        _aiService = aiService;
-    }
-
-    public async Task<Result<QuizDto>> Handle(GetQuizQuestionsQuery request, CancellationToken cancellationToken)
-    {
-        return await _aiService.GenerateQuizAsync(request.ContextBlockId, cancellationToken);
-    }
-}

src/NexusReader.Application/Security/Authorization/ProUserHandler.cs

@@ -31,7 +31,7 @@ public class ProUserHandler : AuthorizationHandler<ProUserRequirement>
         }
 
         // Rule 1: Explicit Pro plan
-        if (user.CurrentPlan == "Pro")
+        if (user.SubscriptionPlanId == SubscriptionPlan.ProId)
         {
             context.Succeed(requirement);
             return;

src/NexusReader.Domain/Entities/Ebook.cs

@@ -23,6 +23,10 @@ public class Ebook
 
     public string? CoverUrl { get; set; }
 
+    [Required]
+    [MaxLength(128)]
+    public string TenantId { get; set; } = "global";
+
     public DateTime AddedDate { get; set; } = DateTime.UtcNow;
 
     public DateTime? LastReadDate { get; set; }

src/NexusReader.Domain/Entities/KnowledgeUnit.cs

@@ -0,0 +1,41 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using NexusReader.Domain.Enums;
+using Pgvector;
+
+namespace NexusReader.Domain.Entities;
+
+public class KnowledgeUnit
+{
+    [Key]
+    [MaxLength(128)]
+    public string Id { get; set; } = string.Empty; // Hash(Source + Content + Version)
+
+    [Required]
+    [MaxLength(128)]
+    public string SourceId { get; set; } = string.Empty;
+
+    [Required]
+    [MaxLength(50)]
+    public string Version { get; set; } = "1.0";
+
+    [Required]
+    public KnowledgeUnitType Type { get; set; }
+
+    [Required]
+    public string Content { get; set; } = string.Empty;
+
+    public string? MetadataJson { get; set; } // e.g. { "page": 1, "path": "Chapter 1 > Intro" }
+
+    [Required]
+    [MaxLength(128)]
+    public string TenantId { get; set; } = string.Empty;
+
+    public Vector? Vector { get; set; }
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    // Relationships
+    public ICollection<KnowledgeUnitLink> OutgoingLinks { get; set; } = new List<KnowledgeUnitLink>();
+    public ICollection<KnowledgeUnitLink> IncomingLinks { get; set; } = new List<KnowledgeUnitLink>();
+}

src/NexusReader.Domain/Entities/KnowledgeUnitLink.cs

@@ -0,0 +1,28 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace NexusReader.Domain.Entities;
+
+public class KnowledgeUnitLink
+{
+    [Key]
+    public int Id { get; set; }
+
+    [Required]
+    [MaxLength(128)]
+    public string SourceUnitId { get; set; } = string.Empty;
+
+    [Required]
+    [MaxLength(128)]
+    public string TargetUnitId { get; set; } = string.Empty;
+
+    [Required]
+    [MaxLength(50)]
+    public string RelationType { get; set; } = "References"; // e.g., "Next", "Defines", "Contains"
+
+    [ForeignKey(nameof(SourceUnitId))]
+    public KnowledgeUnit SourceUnit { get; set; } = null!;
+
+    [ForeignKey(nameof(TargetUnitId))]
+    public KnowledgeUnit TargetUnit { get; set; } = null!;
+}

src/NexusReader.Domain/Entities/NexusUser.cs

@@ -1,31 +1,49 @@
 using Microsoft.AspNetCore.Identity;
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
 
 namespace NexusReader.Domain.Entities;
 
-/// <summary>
-/// Extended Identity user for the Nexus AI E-Reader SaaS platform.
-/// </summary>
 public class NexusUser : IdentityUser
 {
     /// <summary>
-    /// Total number of AI tokens allowed for the current billing period.
+    /// User's display name or full name.
+    /// </summary>
+    [MaxLength(100)]
+    public string? DisplayName { get; set; }
+
+    /// <summary>
+    /// Total AI tokens available for the user (depends on subscription).
     /// </summary>
     public int AITokenLimit { get; set; }
 
     /// <summary>
-    /// Number of AI tokens consumed in the current billing period.
+    /// AI tokens consumed by the user in the current billing period.
     /// </summary>
     public int AITokensUsed { get; set; }
 
     /// <summary>
-    /// Unique identifier for the tenant (SaaS multi-tenancy support).
+    /// Date when the user last performed an AI-related action.
     /// </summary>
-    public Guid TenantId { get; set; }
+    public DateTime? LastAiActionDate { get; set; }
 
     /// <summary>
-    /// Current subscription plan (e.g., "Free", "Pro", "Enterprise").
+    /// Multi-tenant identifier.
     /// </summary>
-    public string CurrentPlan { get; set; } = "Free";
+    [Required]
+    [MaxLength(128)]
+    public string TenantId { get; set; } = "global";
+
+    /// <summary>
+    /// Foreign key for the current subscription plan.
+    /// </summary>
+    [Required]
+    public int SubscriptionPlanId { get; set; }
+
+    /// <summary>
+    /// Navigation property for the current subscription plan.
+    /// </summary>
+    public SubscriptionPlan? SubscriptionPlan { get; set; }
 
     /// <summary>
     /// Collection of e-books owned by the user.
@@ -36,4 +54,15 @@ public class NexusUser : IdentityUser
     /// Collection of quiz results completed by the user.
     /// </summary>
     public ICollection<QuizResult> QuizResults { get; set; } = new List<QuizResult>();
+
+    /// <summary>
+    /// ID of the last page read by the user.
+    /// </summary>
+    [MaxLength(255)]
+    public string? LastReadPageId { get; set; }
+
+    /// <summary>
+    /// Last read timestamp.
+    /// </summary>
+    public DateTime? LastReadAt { get; set; }
 }

src/NexusReader.Domain/Entities/QuizResult.cs

@@ -17,6 +17,10 @@ public class QuizResult
     [ForeignKey(nameof(UserId))]
     public NexusUser? User { get; set; }
 
+    [Required]
+    [MaxLength(128)]
+    public string TenantId { get; set; } = "global";
+
     [Required]
     public string Topic { get; set; } = string.Empty;
 

src/NexusReader.Domain/Entities/SemanticKnowledgeCache.cs

@@ -1,4 +1,6 @@
 using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Pgvector;
 
 namespace NexusReader.Domain.Entities;
 
@@ -11,6 +13,9 @@ public class SemanticKnowledgeCache
     [Required]
     public string JsonData { get; set; } = string.Empty;
 
+    [Required]
+    public string OriginalText { get; set; } = string.Empty;
+
     [Required]
     [MaxLength(50)]
     public string ModelId { get; set; } = "gemini-1.5-flash";
@@ -19,5 +24,11 @@ public class SemanticKnowledgeCache
     [MaxLength(10)]
     public string PromptVersion { get; set; } = "1.0";
 
+    [Required]
+    [MaxLength(128)]
+    public string TenantId { get; set; } = string.Empty;
+
+    public Vector? Vector { get; set; }
+
     public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
 }

src/NexusReader.Domain/Entities/SubscriptionPlan.cs

@@ -0,0 +1,30 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace NexusReader.Domain.Entities;
+
+public class SubscriptionPlan
+{
+    public const string FreeName = "Free";
+    public const string BasicName = "Basic";
+    public const string ProName = "Pro";
+    public const string EnterpriseName = "Enterprise";
+
+    public const int FreeId = 1;
+    public const int BasicId = 2;
+    public const int ProId = 3;
+    public const int EnterpriseId = 4;
+
+    [Key]
+    public int Id { get; set; }
+
+    [Required]
+    [MaxLength(50)]
+    public string PlanName { get; set; } = string.Empty;
+
+    public int AITokenLimit { get; set; }
+
+    public decimal MonthlyPrice { get; set; }
+
+    [MaxLength(50)]
+    public string StripeProductId { get; set; } = string.Empty;
+}

src/NexusReader.Domain/Enums/KnowledgeUnitType.cs

@@ -0,0 +1,12 @@
+namespace NexusReader.Domain.Enums;
+
+public enum KnowledgeUnitType
+{
+    Section,
+    Table,
+    Definition,
+    ProcedureStep,
+    PolicyRule,
+    KeyConcept,
+    Snippet
+}

src/NexusReader.Domain/NexusReader.Domain.csproj

@@ -9,6 +9,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.Identity.Stores" Version="10.0.7" />
+    <PackageReference Include="Pgvector" Version="0.3.2" />
   </ItemGroup>
 
 </Project>

src/NexusReader.Infrastructure/Configuration/AiSettings.cs

@@ -6,7 +6,13 @@ public class AiSettings
 
     public string ApiKey { get; set; } = string.Empty;
     public string Model { get; set; } = "gemini-1.5-flash";
-    public int MaxInputLength { get; set; } = 15000;
+    public string EmbeddingModel { get; set; } = "text-embedding-004";
+    
+    /// <summary>
+    /// Maximum number of tokens allowed for input.
+    /// </summary>
+    public int MaxInputTokens { get; set; } = 15000;
+    
     public int MaxOutputTokens { get; set; } = 1000;
     public int RetryAttempts { get; set; } = 3;
     public double Temperature { get; set; } = 0.1;

src/NexusReader.Infrastructure/Configuration/StripeSettings.cs

@@ -0,0 +1,9 @@
+namespace NexusReader.Infrastructure.Configuration;
+
+public record StripeSettings
+{
+    public const string SectionName = "Stripe";
+    public string ProProductId { get; init; } = string.Empty;
+    public string BasicProductId { get; init; } = string.Empty;
+    public string FreeProductId { get; init; } = string.Empty;
+}

src/NexusReader.Infrastructure/DependencyInjection.cs

@@ -1,5 +1,6 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Configuration;
+using Pgvector.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.AI;
 using GeminiDotnet;
@@ -24,17 +25,18 @@ public static class DependencyInjection
         var pgConnectionString = configuration.GetConnectionString("PostgresConnection");
         if (!string.IsNullOrEmpty(pgConnectionString))
         {
-            services.AddDbContext<AppDbContext>(options =>
-                options.UseNpgsql(pgConnectionString));
+            services.AddDbContextFactory<AppDbContext>(options =>
+                options.UseNpgsql(pgConnectionString, x => x.UseVector()));
         }
         else
         {
             var sqliteConnectionString = configuration.GetConnectionString("SqliteConnection") ?? "Data Source=nexus.db";
-            services.AddDbContext<AppDbContext>(options =>
+            services.AddDbContextFactory<AppDbContext>(options =>
                 options.UseSqlite(sqliteConnectionString));
         }
 
         services.Configure<AiSettings>(configuration.GetSection(AiSettings.SectionName));
+        services.Configure<StripeSettings>(configuration.GetSection(StripeSettings.SectionName));
         var aiSettings = configuration.GetSection(AiSettings.SectionName).Get<AiSettings>() ?? new AiSettings();
 
         Console.WriteLine($"[Infrastructure] AI Configured: Model={aiSettings.Model}, KeyPresent={!string.IsNullOrWhiteSpace(aiSettings.ApiKey) && aiSettings.ApiKey != "PLACEHOLDER"}");
@@ -63,8 +65,13 @@ public static class DependencyInjection
             ModelId = aiSettings.Model 
         }));
 
+        services.AddEmbeddingGenerator(new GeminiEmbeddingGenerator(new GeminiClientOptions
+        {
+            ApiKey = aiSettings.ApiKey,
+            ModelId = aiSettings.EmbeddingModel ?? "text-embedding-004"
+        }));
+
         services.AddScoped<IKnowledgeService, KnowledgeService>();
-        services.AddTransient<IAiGenerateQuizService, FakeAiGenerateQuizService>();
         services.AddTransient<IEpubService, EpubService>();
 
         services.AddAuthorizationCore(options =>
@@ -74,6 +81,13 @@ public static class DependencyInjection
 
         services.AddScoped<IAuthorizationHandler, ProUserHandler>();
 
+        services.AddScoped<IInfrastructureMarker, InfrastructureMarker>();
+
         return services;
     }
+
+    public static System.Reflection.Assembly Assembly => typeof(DependencyInjection).Assembly;
 }
+
+public interface IInfrastructureMarker { }
+internal class InfrastructureMarker : IInfrastructureMarker { }

src/NexusReader.Infrastructure/Handlers/UpdateReadingProgressCommandHandler.cs

@@ -0,0 +1,46 @@
+using FluentResults;
+using MediatR;
+using Microsoft.AspNetCore.SignalR;
+using Microsoft.EntityFrameworkCore;
+using NexusReader.Application.Commands.Sync;
+using NexusReader.Domain.Entities;
+using NexusReader.Infrastructure.Persistence;
+using NexusReader.Infrastructure.RealTime;
+
+namespace NexusReader.Infrastructure.Handlers;
+
+public class UpdateReadingProgressCommandHandler : IRequestHandler<UpdateReadingProgressCommand, Result>
+{
+    private readonly AppDbContext _context;
+    private readonly IHubContext<SyncHub> _hubContext;
+
+    public UpdateReadingProgressCommandHandler(
+        AppDbContext context, 
+        IHubContext<SyncHub> hubContext)
+    {
+        _context = context;
+        _hubContext = hubContext;
+    }
+
+    public async Task<Result> Handle(UpdateReadingProgressCommand request, CancellationToken cancellationToken)
+    {
+        var user = await _context.Users.FirstOrDefaultAsync(u => u.Id == request.UserId, cancellationToken);
+        if (user == null)
+        {
+            return Result.Fail("User not found.");
+        }
+
+        var now = DateTime.UtcNow;
+        user.LastReadPageId = request.PageId;
+        user.LastReadAt = now;
+
+        await _context.SaveChangesAsync(cancellationToken);
+
+        // Broadcast to other devices
+        await _hubContext.Clients
+            .Group($"User_{request.UserId}")
+            .SendAsync("ProgressUpdated", request.PageId, now, cancellationToken);
+
+        return Result.Ok();
+    }
+}

src/NexusReader.Infrastructure/Migrations/20260503175906_FinalNormalizedSubscriptionArchitecture.Designer.cs

@@ -0,0 +1,652 @@
+// <auto-generated />
+using System;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
+using NexusReader.Infrastructure.Persistence;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+using Pgvector;
+
+#nullable disable
+
+namespace NexusReader.Infrastructure.Migrations
+{
+    [DbContext(typeof(AppDbContext))]
+    [Migration("20260503175906_FinalNormalizedSubscriptionArchitecture")]
+    partial class FinalNormalizedSubscriptionArchitecture
+    {
+        /// <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.Ebook", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("uuid");
+
+                    b.Property<DateTime>("AddedDate")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("Author")
+                        .IsRequired()
+                        .HasMaxLength(255)
+                        .HasColumnType("character varying(255)");
+
+                    b.Property<string>("CoverUrl")
+                        .HasColumnType("text");
+
+                    b.Property<string>("FilePath")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<DateTime?>("LastReadDate")
+                        .HasColumnType("timestamp with time zone");
+
+                    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("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<string>("MetadataJson")
+                        .HasColumnType("text");
+
+                    b.Property<string>("SourceId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    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("SourceId");
+
+                    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<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 = 1000,
+                            MonthlyPrice = 0m,
+                            PlanName = "Free",
+                            StripeProductId = ""
+                        },
+                        new
+                        {
+                            Id = 2,
+                            AITokenLimit = 10000,
+                            MonthlyPrice = 9.99m,
+                            PlanName = "Basic",
+                            StripeProductId = "prod_basic_placeholder"
+                        },
+                        new
+                        {
+                            Id = 3,
+                            AITokenLimit = 50000,
+                            MonthlyPrice = 19.99m,
+                            PlanName = "Pro",
+                            StripeProductId = "prod_pro_placeholder"
+                        },
+                        new
+                        {
+                            Id = 4,
+                            AITokenLimit = 500000,
+                            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.NexusUser", "User")
+                        .WithMany("Ebooks")
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("User");
+                });
+
+            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.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.Infrastructure/Migrations/20260503175906_FinalNormalizedSubscriptionArchitecture.cs

@@ -0,0 +1,399 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+using Pgvector;
+
+#nullable disable
+
+#pragma warning disable CA1814 // Prefer jagged arrays over multidimensional
+
+namespace NexusReader.Infrastructure.Migrations
+{
+    /// <inheritdoc />
+    public partial class FinalNormalizedSubscriptionArchitecture : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "CurrentPlan",
+                table: "AspNetUsers");
+
+            migrationBuilder.AlterDatabase()
+                .Annotation("Npgsql:PostgresExtension:vector", ",,");
+
+            migrationBuilder.AlterColumn<DateTime>(
+                name: "CreatedAt",
+                table: "SemanticKnowledgeCache",
+                type: "timestamp with time zone",
+                nullable: false,
+                oldClrType: typeof(DateTime),
+                oldType: "timestamp without time zone");
+
+            migrationBuilder.AddColumn<string>(
+                name: "OriginalText",
+                table: "SemanticKnowledgeCache",
+                type: "text",
+                nullable: false,
+                defaultValue: "");
+
+            migrationBuilder.AddColumn<string>(
+                name: "TenantId",
+                table: "SemanticKnowledgeCache",
+                type: "character varying(128)",
+                maxLength: 128,
+                nullable: false,
+                defaultValue: "");
+
+            migrationBuilder.AddColumn<Vector>(
+                name: "Vector",
+                table: "SemanticKnowledgeCache",
+                type: "vector(1536)",
+                nullable: true);
+
+            migrationBuilder.AlterColumn<DateTime>(
+                name: "CompletedDate",
+                table: "QuizResults",
+                type: "timestamp with time zone",
+                nullable: false,
+                oldClrType: typeof(DateTime),
+                oldType: "timestamp without time zone");
+
+            migrationBuilder.AddColumn<string>(
+                name: "TenantId",
+                table: "QuizResults",
+                type: "character varying(128)",
+                maxLength: 128,
+                nullable: false,
+                defaultValue: "");
+
+            migrationBuilder.AlterColumn<DateTime>(
+                name: "LastReadDate",
+                table: "Ebooks",
+                type: "timestamp with time zone",
+                nullable: true,
+                oldClrType: typeof(DateTime),
+                oldType: "timestamp without time zone",
+                oldNullable: true);
+
+            migrationBuilder.AlterColumn<DateTime>(
+                name: "AddedDate",
+                table: "Ebooks",
+                type: "timestamp with time zone",
+                nullable: false,
+                oldClrType: typeof(DateTime),
+                oldType: "timestamp without time zone");
+
+            migrationBuilder.AddColumn<string>(
+                name: "TenantId",
+                table: "Ebooks",
+                type: "character varying(128)",
+                maxLength: 128,
+                nullable: false,
+                defaultValue: "");
+
+            migrationBuilder.AlterColumn<string>(
+                name: "TenantId",
+                table: "AspNetUsers",
+                type: "character varying(128)",
+                maxLength: 128,
+                nullable: false,
+                oldClrType: typeof(Guid),
+                oldType: "uuid");
+
+            migrationBuilder.AddColumn<string>(
+                name: "DisplayName",
+                table: "AspNetUsers",
+                type: "character varying(100)",
+                maxLength: 100,
+                nullable: true);
+
+            migrationBuilder.AddColumn<DateTime>(
+                name: "LastAiActionDate",
+                table: "AspNetUsers",
+                type: "timestamp with time zone",
+                nullable: true);
+
+            migrationBuilder.AddColumn<DateTime>(
+                name: "LastReadAt",
+                table: "AspNetUsers",
+                type: "timestamp with time zone",
+                nullable: true);
+
+            migrationBuilder.AddColumn<string>(
+                name: "LastReadPageId",
+                table: "AspNetUsers",
+                type: "character varying(255)",
+                maxLength: 255,
+                nullable: true);
+
+            migrationBuilder.AddColumn<int>(
+                name: "SubscriptionPlanId",
+                table: "AspNetUsers",
+                type: "integer",
+                nullable: false,
+                defaultValue: 1);
+
+            migrationBuilder.CreateTable(
+                name: "KnowledgeUnits",
+                columns: table => new
+                {
+                    Id = table.Column<string>(type: "character varying(128)", maxLength: 128, nullable: false),
+                    SourceId = table.Column<string>(type: "character varying(128)", maxLength: 128, nullable: false),
+                    Version = table.Column<string>(type: "character varying(50)", maxLength: 50, nullable: false),
+                    Type = table.Column<int>(type: "integer", nullable: false),
+                    Content = table.Column<string>(type: "text", nullable: false),
+                    MetadataJson = table.Column<string>(type: "text", nullable: true),
+                    TenantId = table.Column<string>(type: "character varying(128)", maxLength: 128, nullable: false),
+                    Vector = table.Column<Vector>(type: "vector(768)", nullable: true),
+                    CreatedAt = table.Column<DateTime>(type: "timestamp with time zone", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_KnowledgeUnits", x => x.Id);
+                });
+
+            migrationBuilder.CreateTable(
+                name: "SubscriptionPlans",
+                columns: table => new
+                {
+                    Id = table.Column<int>(type: "integer", nullable: false)
+                        .Annotation("Npgsql:ValueGenerationStrategy", NpgsqlValueGenerationStrategy.IdentityByDefaultColumn),
+                    PlanName = table.Column<string>(type: "character varying(50)", maxLength: 50, nullable: false),
+                    AITokenLimit = table.Column<int>(type: "integer", nullable: false),
+                    MonthlyPrice = table.Column<decimal>(type: "numeric", nullable: false),
+                    StripeProductId = table.Column<string>(type: "character varying(50)", maxLength: 50, nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_SubscriptionPlans", x => x.Id);
+                });
+
+            migrationBuilder.CreateTable(
+                name: "KnowledgeUnitLinks",
+                columns: table => new
+                {
+                    Id = table.Column<int>(type: "integer", nullable: false)
+                        .Annotation("Npgsql:ValueGenerationStrategy", NpgsqlValueGenerationStrategy.IdentityByDefaultColumn),
+                    SourceUnitId = table.Column<string>(type: "character varying(128)", maxLength: 128, nullable: false),
+                    TargetUnitId = table.Column<string>(type: "character varying(128)", maxLength: 128, nullable: false),
+                    RelationType = table.Column<string>(type: "character varying(50)", maxLength: 50, nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_KnowledgeUnitLinks", x => x.Id);
+                    table.ForeignKey(
+                        name: "FK_KnowledgeUnitLinks_KnowledgeUnits_SourceUnitId",
+                        column: x => x.SourceUnitId,
+                        principalTable: "KnowledgeUnits",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Cascade);
+                    table.ForeignKey(
+                        name: "FK_KnowledgeUnitLinks_KnowledgeUnits_TargetUnitId",
+                        column: x => x.TargetUnitId,
+                        principalTable: "KnowledgeUnits",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Cascade);
+                });
+
+            migrationBuilder.InsertData(
+                table: "SubscriptionPlans",
+                columns: new[] { "Id", "AITokenLimit", "MonthlyPrice", "PlanName", "StripeProductId" },
+                values: new object[,]
+                {
+                    { 1, 1000, 0m, "Free", "" },
+                    { 2, 10000, 9.99m, "Basic", "prod_basic_placeholder" },
+                    { 3, 50000, 19.99m, "Pro", "prod_pro_placeholder" },
+                    { 4, 500000, 99.99m, "Enterprise", "prod_enterprise_placeholder" }
+                });
+
+            migrationBuilder.CreateIndex(
+                name: "IX_SemanticKnowledgeCache_TenantId",
+                table: "SemanticKnowledgeCache",
+                column: "TenantId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_QuizResults_TenantId",
+                table: "QuizResults",
+                column: "TenantId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_Ebooks_TenantId",
+                table: "Ebooks",
+                column: "TenantId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_AspNetUsers_SubscriptionPlanId",
+                table: "AspNetUsers",
+                column: "SubscriptionPlanId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_AspNetUsers_TenantId",
+                table: "AspNetUsers",
+                column: "TenantId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_KnowledgeUnitLinks_SourceUnitId",
+                table: "KnowledgeUnitLinks",
+                column: "SourceUnitId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_KnowledgeUnitLinks_TargetUnitId",
+                table: "KnowledgeUnitLinks",
+                column: "TargetUnitId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_KnowledgeUnits_SourceId",
+                table: "KnowledgeUnits",
+                column: "SourceId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_KnowledgeUnits_TenantId",
+                table: "KnowledgeUnits",
+                column: "TenantId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_SubscriptionPlans_PlanName",
+                table: "SubscriptionPlans",
+                column: "PlanName",
+                unique: true);
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_AspNetUsers_SubscriptionPlans_SubscriptionPlanId",
+                table: "AspNetUsers",
+                column: "SubscriptionPlanId",
+                principalTable: "SubscriptionPlans",
+                principalColumn: "Id",
+                onDelete: ReferentialAction.Restrict);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropForeignKey(
+                name: "FK_AspNetUsers_SubscriptionPlans_SubscriptionPlanId",
+                table: "AspNetUsers");
+
+            migrationBuilder.DropTable(
+                name: "KnowledgeUnitLinks");
+
+            migrationBuilder.DropTable(
+                name: "SubscriptionPlans");
+
+            migrationBuilder.DropTable(
+                name: "KnowledgeUnits");
+
+            migrationBuilder.DropIndex(
+                name: "IX_SemanticKnowledgeCache_TenantId",
+                table: "SemanticKnowledgeCache");
+
+            migrationBuilder.DropIndex(
+                name: "IX_QuizResults_TenantId",
+                table: "QuizResults");
+
+            migrationBuilder.DropIndex(
+                name: "IX_Ebooks_TenantId",
+                table: "Ebooks");
+
+            migrationBuilder.DropIndex(
+                name: "IX_AspNetUsers_SubscriptionPlanId",
+                table: "AspNetUsers");
+
+            migrationBuilder.DropIndex(
+                name: "IX_AspNetUsers_TenantId",
+                table: "AspNetUsers");
+
+            migrationBuilder.DropColumn(
+                name: "OriginalText",
+                table: "SemanticKnowledgeCache");
+
+            migrationBuilder.DropColumn(
+                name: "TenantId",
+                table: "SemanticKnowledgeCache");
+
+            migrationBuilder.DropColumn(
+                name: "Vector",
+                table: "SemanticKnowledgeCache");
+
+            migrationBuilder.DropColumn(
+                name: "TenantId",
+                table: "QuizResults");
+
+            migrationBuilder.DropColumn(
+                name: "TenantId",
+                table: "Ebooks");
+
+            migrationBuilder.DropColumn(
+                name: "DisplayName",
+                table: "AspNetUsers");
+
+            migrationBuilder.DropColumn(
+                name: "LastAiActionDate",
+                table: "AspNetUsers");
+
+            migrationBuilder.DropColumn(
+                name: "LastReadAt",
+                table: "AspNetUsers");
+
+            migrationBuilder.DropColumn(
+                name: "LastReadPageId",
+                table: "AspNetUsers");
+
+            migrationBuilder.DropColumn(
+                name: "SubscriptionPlanId",
+                table: "AspNetUsers");
+
+            migrationBuilder.AlterDatabase()
+                .OldAnnotation("Npgsql:PostgresExtension:vector", ",,");
+
+            migrationBuilder.AlterColumn<DateTime>(
+                name: "CreatedAt",
+                table: "SemanticKnowledgeCache",
+                type: "timestamp without time zone",
+                nullable: false,
+                oldClrType: typeof(DateTime),
+                oldType: "timestamp with time zone");
+
+            migrationBuilder.AlterColumn<DateTime>(
+                name: "CompletedDate",
+                table: "QuizResults",
+                type: "timestamp without time zone",
+                nullable: false,
+                oldClrType: typeof(DateTime),
+                oldType: "timestamp with time zone");
+
+            migrationBuilder.AlterColumn<DateTime>(
+                name: "LastReadDate",
+                table: "Ebooks",
+                type: "timestamp without time zone",
+                nullable: true,
+                oldClrType: typeof(DateTime),
+                oldType: "timestamp with time zone",
+                oldNullable: true);
+
+            migrationBuilder.AlterColumn<DateTime>(
+                name: "AddedDate",
+                table: "Ebooks",
+                type: "timestamp without time zone",
+                nullable: false,
+                oldClrType: typeof(DateTime),
+                oldType: "timestamp with time zone");
+
+            migrationBuilder.AlterColumn<Guid>(
+                name: "TenantId",
+                table: "AspNetUsers",
+                type: "uuid",
+                nullable: false,
+                oldClrType: typeof(string),
+                oldType: "character varying(128)",
+                oldMaxLength: 128);
+
+            migrationBuilder.AddColumn<string>(
+                name: "CurrentPlan",
+                table: "AspNetUsers",
+                type: "text",
+                nullable: false,
+                defaultValue: "");
+        }
+    }
+}

src/NexusReader.Infrastructure/Migrations/AppDbContextModelSnapshot.cs

@@ -5,6 +5,7 @@ using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
 using NexusReader.Infrastructure.Persistence;
 using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+using Pgvector;
 
 #nullable disable
 
@@ -20,6 +21,7 @@ namespace NexusReader.Infrastructure.Migrations
                 .HasAnnotation("ProductVersion", "10.0.7")
                 .HasAnnotation("Relational:MaxIdentifierLength", 63);
 
+            NpgsqlModelBuilderExtensions.HasPostgresExtension(modelBuilder, "vector");
             NpgsqlModelBuilderExtensions.UseIdentityByDefaultColumns(modelBuilder);
 
             modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRole", b =>
@@ -161,7 +163,7 @@ namespace NexusReader.Infrastructure.Migrations
                         .HasColumnType("uuid");
 
                     b.Property<DateTime>("AddedDate")
-                        .HasColumnType("timestamp without time zone");
+                        .HasColumnType("timestamp with time zone");
 
                     b.Property<string>("Author")
                         .IsRequired()
@@ -176,7 +178,12 @@ namespace NexusReader.Infrastructure.Migrations
                         .HasColumnType("text");
 
                     b.Property<DateTime?>("LastReadDate")
-                        .HasColumnType("timestamp without time zone");
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("TenantId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
 
                     b.Property<string>("Title")
                         .IsRequired()
@@ -189,11 +196,91 @@ namespace NexusReader.Infrastructure.Migrations
 
                     b.HasKey("Id");
 
+                    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<string>("MetadataJson")
+                        .HasColumnType("text");
+
+                    b.Property<string>("SourceId")
+                        .IsRequired()
+                        .HasMaxLength(128)
+                        .HasColumnType("character varying(128)");
+
+                    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("SourceId");
+
+                    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")
@@ -212,9 +299,9 @@ namespace NexusReader.Infrastructure.Migrations
                         .IsConcurrencyToken()
                         .HasColumnType("text");
 
-                    b.Property<string>("CurrentPlan")
-                        .IsRequired()
-                        .HasColumnType("text");
+                    b.Property<string>("DisplayName")
+                        .HasMaxLength(100)
+                        .HasColumnType("character varying(100)");
 
                     b.Property<string>("Email")
                         .HasMaxLength(256)
@@ -223,6 +310,16 @@ namespace NexusReader.Infrastructure.Migrations
                     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");
 
@@ -249,8 +346,15 @@ namespace NexusReader.Infrastructure.Migrations
                     b.Property<string>("SecurityStamp")
                         .HasColumnType("text");
 
-                    b.Property<Guid>("TenantId")
-                        .HasColumnType("uuid");
+                    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");
@@ -268,6 +372,10 @@ namespace NexusReader.Infrastructure.Migrations
                         .IsUnique()
                         .HasDatabaseName("UserNameIndex");
 
+                    b.HasIndex("SubscriptionPlanId");
+
+                    b.HasIndex("TenantId");
+
                     b.ToTable("AspNetUsers", (string)null);
                 });
 
@@ -278,11 +386,16 @@ namespace NexusReader.Infrastructure.Migrations
                         .HasColumnType("uuid");
 
                     b.Property<DateTime>("CompletedDate")
-                        .HasColumnType("timestamp without time zone");
+                        .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");
@@ -296,6 +409,8 @@ namespace NexusReader.Infrastructure.Migrations
 
                     b.HasKey("Id");
 
+                    b.HasIndex("TenantId");
+
                     b.HasIndex("UserId");
 
                     b.ToTable("QuizResults");
@@ -308,7 +423,7 @@ namespace NexusReader.Infrastructure.Migrations
                         .HasColumnType("character varying(128)");
 
                     b.Property<DateTime>("CreatedAt")
-                        .HasColumnType("timestamp without time zone");
+                        .HasColumnType("timestamp with time zone");
 
                     b.Property<string>("JsonData")
                         .IsRequired()
@@ -319,19 +434,99 @@ namespace NexusReader.Infrastructure.Migrations
                         .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<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 = 1000,
+                            MonthlyPrice = 0m,
+                            PlanName = "Free",
+                            StripeProductId = ""
+                        },
+                        new
+                        {
+                            Id = 2,
+                            AITokenLimit = 10000,
+                            MonthlyPrice = 9.99m,
+                            PlanName = "Basic",
+                            StripeProductId = "prod_basic_placeholder"
+                        },
+                        new
+                        {
+                            Id = 3,
+                            AITokenLimit = 50000,
+                            MonthlyPrice = 19.99m,
+                            PlanName = "Pro",
+                            StripeProductId = "prod_pro_placeholder"
+                        },
+                        new
+                        {
+                            Id = 4,
+                            AITokenLimit = 500000,
+                            MonthlyPrice = 99.99m,
+                            PlanName = "Enterprise",
+                            StripeProductId = "prod_enterprise_placeholder"
+                        });
+                });
+
             modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRoleClaim<string>", b =>
                 {
                     b.HasOne("Microsoft.AspNetCore.Identity.IdentityRole", null)
@@ -394,6 +589,36 @@ namespace NexusReader.Infrastructure.Migrations
                     b.Navigation("User");
                 });
 
+            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")
@@ -405,6 +630,13 @@ namespace NexusReader.Infrastructure.Migrations
                     b.Navigation("User");
                 });
 
+            modelBuilder.Entity("NexusReader.Domain.Entities.KnowledgeUnit", b =>
+                {
+                    b.Navigation("IncomingLinks");
+
+                    b.Navigation("OutgoingLinks");
+                });
+
             modelBuilder.Entity("NexusReader.Domain.Entities.NexusUser", b =>
                 {
                     b.Navigation("Ebooks");

src/NexusReader.Infrastructure/NexusReader.Infrastructure.csproj

@@ -1,9 +1,13 @@
-<Project Sdk="Microsoft.NET.Sdk">
-
-  <ItemGroup>
-    <ProjectReference Include="..\NexusReader.Application\NexusReader.Application.csproj" />
-  </ItemGroup>
-
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <ItemGroup>
+    <ProjectReference Include="..\NexusReader.Application\NexusReader.Application.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <FrameworkReference Include="Microsoft.AspNetCore.App" />
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="GeminiDotnet.Extensions.AI" Version="0.23.0" />
     <PackageReference Include="Microsoft.AspNetCore.Authorization" Version="10.0.7" />
@@ -15,7 +19,10 @@
     <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="10.0.7" />
     <PackageReference Include="Microsoft.Extensions.AI" Version="10.5.0" />
     <PackageReference Include="Microsoft.Extensions.Resilience" Version="10.5.0" />
+    <PackageReference Include="Microsoft.ML.Tokenizers" Version="2.0.0" />
+    <PackageReference Include="Microsoft.ML.Tokenizers.Data.Cl100kBase" Version="2.0.0" />
     <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="10.0.0" />
+    <PackageReference Include="Pgvector.EntityFrameworkCore" Version="0.3.0" />
     <PackageReference Include="Polly" Version="8.6.6" />
     <PackageReference Include="Polly.Extensions.Http" Version="3.0.0" />
     <PackageReference Include="Stripe.net" Version="51.1.0" />

src/NexusReader.Infrastructure/Persistence/AppDbContext.cs

@@ -1,27 +1,78 @@
 using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore;
 using NexusReader.Domain.Entities;
+using NexusReader.Application.Abstractions.Persistence;
 
 namespace NexusReader.Infrastructure.Persistence;
 
-public class AppDbContext : IdentityDbContext<NexusUser>
+public class AppDbContext : IdentityDbContext<NexusUser>, IApplicationDbContext
 {
     public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
     {
     }
 
     public DbSet<SemanticKnowledgeCache> SemanticKnowledgeCache => Set<SemanticKnowledgeCache>();
+    public DbSet<KnowledgeUnit> KnowledgeUnits => Set<KnowledgeUnit>();
+    public DbSet<KnowledgeUnitLink> KnowledgeUnitLinks => Set<KnowledgeUnitLink>();
     public DbSet<Ebook> Ebooks => Set<Ebook>();
     public DbSet<QuizResult> QuizResults => Set<QuizResult>();
+    public DbSet<SubscriptionPlan> SubscriptionPlans => Set<SubscriptionPlan>();
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
+        modelBuilder.HasPostgresExtension("vector");
+
+        modelBuilder.Entity<NexusUser>(entity =>
+        {
+            entity.Property(u => u.LastReadPageId).HasMaxLength(255);
+            entity.Property(u => u.LastReadAt).IsRequired(false);
+            entity.HasIndex(u => u.TenantId);
+
+            entity.HasOne(u => u.SubscriptionPlan)
+                .WithMany()
+                .HasForeignKey(u => u.SubscriptionPlanId)
+                .OnDelete(DeleteBehavior.Restrict);
+            
+            // Note: DefaultValue for int is 1 (which corresponds to 'Free' in our seed)
+            entity.Property(u => u.SubscriptionPlanId)
+                .HasDefaultValue(1);
+        });
+
         base.OnModelCreating(modelBuilder);
 
+        modelBuilder.Entity<SubscriptionPlan>(entity =>
+        {
+            entity.HasIndex(p => p.PlanName).IsUnique();
+        });
+
         modelBuilder.Entity<SemanticKnowledgeCache>(entity =>
         {
             entity.HasKey(e => e.ContentHash);
             entity.HasIndex(e => e.ContentHash).IsUnique();
+            entity.HasIndex(e => e.TenantId);
+            entity.Property(e => e.Vector).HasColumnType("vector(1536)");
+        });
+
+        modelBuilder.Entity<KnowledgeUnit>(entity =>
+        {
+            entity.HasKey(e => e.Id);
+            entity.HasIndex(e => e.TenantId);
+            entity.HasIndex(e => e.SourceId);
+            entity.Property(e => e.Vector).HasColumnType("vector(768)");
+        });
+
+        modelBuilder.Entity<KnowledgeUnitLink>(entity =>
+        {
+            entity.HasKey(e => e.Id);
+            entity.HasOne(e => e.SourceUnit)
+                .WithMany(u => u.OutgoingLinks)
+                .HasForeignKey(e => e.SourceUnitId)
+                .OnDelete(DeleteBehavior.Cascade);
+
+            entity.HasOne(e => e.TargetUnit)
+                .WithMany(u => u.IncomingLinks)
+                .HasForeignKey(e => e.TargetUnitId)
+                .OnDelete(DeleteBehavior.Cascade);
         });
 
         modelBuilder.Entity<Ebook>(entity =>
@@ -30,6 +81,8 @@ public class AppDbContext : IdentityDbContext<NexusUser>
                 .WithMany(u => u.Ebooks)
                 .HasForeignKey(e => e.UserId)
                 .OnDelete(DeleteBehavior.Cascade);
+            
+            entity.HasIndex(e => e.TenantId);
         });
 
         modelBuilder.Entity<QuizResult>(entity =>
@@ -38,6 +91,16 @@ public class AppDbContext : IdentityDbContext<NexusUser>
                 .WithMany(u => u.QuizResults)
                 .HasForeignKey(e => e.UserId)
                 .OnDelete(DeleteBehavior.Cascade);
+            
+            entity.HasIndex(e => e.TenantId);
         });
+
+        // Seed Subscription Plans with deterministic IDs
+        modelBuilder.Entity<SubscriptionPlan>().HasData(
+            new SubscriptionPlan { Id = 1, PlanName = SubscriptionPlan.FreeName, AITokenLimit = 1000, MonthlyPrice = 0m, StripeProductId = "" },
+            new SubscriptionPlan { Id = 2, PlanName = SubscriptionPlan.BasicName, AITokenLimit = 10000, MonthlyPrice = 9.99m, StripeProductId = "prod_basic_placeholder" },
+            new SubscriptionPlan { Id = 3, PlanName = SubscriptionPlan.ProName, AITokenLimit = 50000, MonthlyPrice = 19.99m, StripeProductId = "prod_pro_placeholder" },
+            new SubscriptionPlan { Id = 4, PlanName = SubscriptionPlan.EnterpriseName, AITokenLimit = 500000, MonthlyPrice = 99.99m, StripeProductId = "prod_enterprise_placeholder" }
+        );
     }
 }

src/NexusReader.Infrastructure/Persistence/AppDbContextFactory.cs

@@ -0,0 +1,45 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Design;
+using Microsoft.Extensions.Configuration;
+using Pgvector.EntityFrameworkCore;
+
+namespace NexusReader.Infrastructure.Persistence;
+
+public class AppDbContextFactory : IDesignTimeDbContextFactory<AppDbContext>
+{
+    public AppDbContext CreateDbContext(string[] args)
+    {
+        var environment = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Development";
+        
+        // Try to find the Web project directory by looking for the solution root
+        var currentDir = new DirectoryInfo(Directory.GetCurrentDirectory());
+        while (currentDir != null && !File.Exists(Path.Combine(currentDir.FullName, "NexusReader.slnx")))
+        {
+            currentDir = currentDir.Parent;
+        }
+
+        var basePath = currentDir != null 
+            ? Path.Combine(currentDir.FullName, "src", "NexusReader.Web.New")
+            : Directory.GetCurrentDirectory();
+
+        var configuration = new ConfigurationBuilder()
+            .SetBasePath(basePath)
+            .AddJsonFile("appsettings.json", optional: true)
+            .AddJsonFile($"appsettings.{environment}.json", optional: true)
+            .AddEnvironmentVariables()
+            .Build();
+
+        var optionsBuilder = new DbContextOptionsBuilder<AppDbContext>();
+        var connectionString = configuration.GetConnectionString("PostgresConnection");
+
+        if (string.IsNullOrEmpty(connectionString))
+        {
+             // For design time, if no PG connection is found, we might be using Sqlite or just testing
+             connectionString = "Host=localhost;Database=nexus_reader;Username=postgres;Password=postgres";
+        }
+
+        optionsBuilder.UseNpgsql(connectionString, x => x.UseVector());
+
+        return new AppDbContext(optionsBuilder.Options);
+    }
+}

src/NexusReader.Infrastructure/Persistence/DbInitializer.cs

@@ -0,0 +1,88 @@
+using Microsoft.AspNetCore.Identity;
+using Microsoft.Extensions.DependencyInjection;
+using NexusReader.Domain.Entities;
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using System.Collections.Generic;
+using Microsoft.EntityFrameworkCore;
+
+namespace NexusReader.Infrastructure.Persistence;
+
+public static class DbInitializer
+{
+    public static async Task SeedAsync(IServiceProvider serviceProvider)
+    {
+        using var scope = serviceProvider.CreateScope();
+        var userManager = scope.ServiceProvider.GetRequiredService<UserManager<NexusUser>>();
+        var roleManager = scope.ServiceProvider.GetRequiredService<RoleManager<IdentityRole>>();
+        var dbContext = scope.ServiceProvider.GetRequiredService<AppDbContext>();
+
+        try
+        {
+            Console.WriteLine("[Seeder] Starting database seeding...");
+
+            // Seed Subscription Plans
+            if (!dbContext.SubscriptionPlans.Any())
+            {
+                dbContext.SubscriptionPlans.AddRange(new List<SubscriptionPlan>
+                {
+                    new SubscriptionPlan { Id = SubscriptionPlan.FreeId, PlanName = SubscriptionPlan.FreeName, AITokenLimit = 5000, MonthlyPrice = 0, StripeProductId = "prod_Free789" },
+                    new SubscriptionPlan { Id = SubscriptionPlan.ProId, PlanName = SubscriptionPlan.ProName, AITokenLimit = 50000, MonthlyPrice = 19, StripeProductId = "prod_Pro123" },
+                    new SubscriptionPlan { Id = SubscriptionPlan.EnterpriseId, PlanName = SubscriptionPlan.EnterpriseName, AITokenLimit = 500000, MonthlyPrice = 99, StripeProductId = "prod_Enterprise456" }
+                });
+                await dbContext.SaveChangesAsync();
+                Console.WriteLine("[Seeder] Subscription plans seeded.");
+            }
+
+            // Seed Roles
+            string[] roleNames = { "Admin", "User" };
+            foreach (var roleName in roleNames)
+            {
+                var roleExist = await roleManager.RoleExistsAsync(roleName);
+                if (!roleExist)
+                {
+                    await roleManager.CreateAsync(new IdentityRole(roleName));
+                    Console.WriteLine($"[Seeder] Created role: {roleName}");
+                }
+            }
+
+            // Seed Admin User
+            var adminEmail = "admin@nexus.com";
+            var adminUser = await userManager.FindByEmailAsync(adminEmail);
+
+            if (adminUser == null)
+            {
+                adminUser = new NexusUser
+                {
+                    UserName = adminEmail,
+                    Email = adminEmail,
+                    EmailConfirmed = true,
+                    SubscriptionPlanId = SubscriptionPlan.EnterpriseId,
+                    AITokenLimit = 1000000,
+                    TenantId = Guid.NewGuid().ToString()
+                };
+
+                var createPowerUser = await userManager.CreateAsync(adminUser, "Admin123!");
+                if (createPowerUser.Succeeded)
+                {
+                    await userManager.AddToRoleAsync(adminUser, "Admin");
+                    Console.WriteLine($"[Seeder] Admin user created successfully: {adminEmail}");
+                }
+                else
+                {
+                    var errors = string.Join(", ", createPowerUser.Errors.Select(e => e.Description));
+                    Console.WriteLine($"[Seeder] Failed to create admin user: {errors}");
+                }
+            }
+            else
+            {
+                Console.WriteLine("[Seeder] Admin user already exists.");
+            }
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"[Seeder] Critical error during seeding: {ex.Message}");
+        }
+    }
+}

src/NexusReader.Infrastructure/RealTime/SyncHub.cs

@@ -0,0 +1,46 @@
+using MediatR;
+using Microsoft.AspNetCore.SignalR;
+using Microsoft.AspNetCore.Authorization;
+using NexusReader.Application.Commands.Sync;
+
+namespace NexusReader.Infrastructure.RealTime;
+
+[Authorize]
+public class SyncHub : Hub
+{
+    private readonly IMediator _mediator;
+
+    public SyncHub(IMediator mediator)
+    {
+        _mediator = mediator;
+    }
+
+    public async Task UpdateProgress(string pageId)
+    {
+        var userId = Context.UserIdentifier;
+        if (!string.IsNullOrEmpty(userId))
+        {
+            await _mediator.Send(new UpdateReadingProgressCommand(pageId, userId));
+        }
+    }
+
+    public override async Task OnConnectedAsync()
+    {
+        var userId = Context.UserIdentifier;
+        if (!string.IsNullOrEmpty(userId))
+        {
+            await Groups.AddToGroupAsync(Context.ConnectionId, $"User_{userId}");
+        }
+        await base.OnConnectedAsync();
+    }
+
+    public override async Task OnDisconnectedAsync(Exception? exception)
+    {
+        var userId = Context.UserIdentifier;
+        if (!string.IsNullOrEmpty(userId))
+        {
+            await Groups.RemoveFromGroupAsync(Context.ConnectionId, $"User_{userId}");
+        }
+        await base.OnDisconnectedAsync(exception);
+    }
+}

src/NexusReader.Infrastructure/Services/BillingService.cs

@@ -1,7 +1,10 @@
 using Microsoft.AspNetCore.Identity;
 using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
 using NexusReader.Application.Abstractions.Services;
 using NexusReader.Domain.Entities;
+using NexusReader.Infrastructure.Configuration;
 using NexusReader.Infrastructure.Persistence;
 
 namespace NexusReader.Infrastructure.Services;
@@ -10,44 +13,90 @@ public class BillingService : IBillingService
 {
     private readonly AppDbContext _dbContext;
     private readonly UserManager<NexusUser> _userManager;
+    private readonly StripeSettings _stripeSettings;
+    private readonly ILogger<BillingService> _logger;
 
-    public BillingService(AppDbContext dbContext, UserManager<NexusUser> userManager)
+    public BillingService(
+        AppDbContext dbContext, 
+        UserManager<NexusUser> userManager,
+        IOptions<StripeSettings> stripeSettings,
+        ILogger<BillingService> logger)
     {
         _dbContext = dbContext;
         _userManager = userManager;
+        _stripeSettings = stripeSettings.Value;
+        _logger = logger;
     }
 
     public async Task<bool> HandleSubscriptionUpdatedAsync(string customerEmail, string stripeProductId)
     {
         var user = await _userManager.FindByEmailAsync(customerEmail);
-        if (user == null) return false;
-
-        // Map Stripe Product IDs to Nexus Plans
-        // These IDs would typically come from configuration
-        if (stripeProductId.Contains("pro")) 
+        if (user == null) 
         {
-            user.CurrentPlan = "Pro";
-            user.AITokenLimit = 50000;
-        }
-        else if (stripeProductId.Contains("basic"))
-        {
-            user.CurrentPlan = "Basic";
-            user.AITokenLimit = 10000;
+            _logger.LogWarning("Attempted to update subscription for non-existent user: {Email}", customerEmail);
+            return false;
+        }
+
+        string targetPlanName = SubscriptionPlan.FreeName;
+        int tokenLimit = 1000;
+
+        if (stripeProductId == _stripeSettings.ProProductId)
+        {
+            targetPlanName = SubscriptionPlan.ProName;
+            tokenLimit = 50000;
+        }
+        else if (stripeProductId == _stripeSettings.BasicProductId)
+        {
+            targetPlanName = SubscriptionPlan.BasicName;
+            tokenLimit = 10000;
+        }
+        else if (!string.IsNullOrEmpty(stripeProductId) && stripeProductId != _stripeSettings.FreeProductId)
+        {
+             _logger.LogWarning("Unrecognized Stripe Product ID: {ProductId} for user {Email}. Falling back to Free tier.", stripeProductId, customerEmail);
+        }
+
+        var plan = await _dbContext.SubscriptionPlans.FirstOrDefaultAsync(p => p.PlanName == targetPlanName);
+        if (plan != null)
+        {
+            user.SubscriptionPlanId = plan.Id;
+            user.AITokenLimit = tokenLimit;
+        }
+
+        var result = await _userManager.UpdateAsync(user);
+        if (!result.Succeeded)
+        {
+            _logger.LogError("Failed to update user {Email} after subscription change: {Errors}", 
+                customerEmail, string.Join(", ", result.Errors.Select(e => e.Description)));
+            return false;
         }
 
-        await _userManager.UpdateAsync(user);
         return true;
     }
 
     public async Task<bool> HandleSubscriptionDeletedAsync(string customerEmail)
     {
         var user = await _userManager.FindByEmailAsync(customerEmail);
-        if (user == null) return false;
+        if (user == null)
+        {
+            _logger.LogWarning("Attempted to delete subscription for non-existent user: {Email}", customerEmail);
+            return false;
+        }
 
-        user.CurrentPlan = "Free";
-        user.AITokenLimit = 1000; // Reset to free limit
+        var freePlan = await _dbContext.SubscriptionPlans.FirstOrDefaultAsync(p => p.PlanName == SubscriptionPlan.FreeName);
+        if (freePlan != null)
+        {
+            user.SubscriptionPlanId = freePlan.Id;
+            user.AITokenLimit = freePlan.AITokenLimit;
+        }
         
-        await _userManager.UpdateAsync(user);
+        var result = await _userManager.UpdateAsync(user);
+        if (!result.Succeeded)
+        {
+            _logger.LogError("Failed to reset user {Email} to Free tier after subscription deletion: {Errors}", 
+                customerEmail, string.Join(", ", result.Errors.Select(e => e.Description)));
+            return false;
+        }
+
         return true;
     }
 }

src/NexusReader.Infrastructure/Services/EpubService.cs

@@ -41,7 +41,20 @@ public class EpubService : IEpubService
                 return Result.Fail($"EPUB file not found. Checked {searchPaths.Count} locations, including: {string.Join(", ", searchPaths.Take(3))}");
             }
 
-            EpubBook book = await EpubReader.ReadBookAsync(fullPath);
+            if (!File.Exists(fullPath))
+            {
+                return Result.Fail($"EPUB file at '{fullPath}' is not accessible or does not exist.");
+            }
+
+            EpubBook book;
+            try 
+            {
+                book = await EpubReader.ReadBookAsync(fullPath);
+            }
+            catch (Exception ex)
+            {
+                return Result.Fail(new Error($"Failed to parse EPUB file. It might be corrupted or in use. Path: {fullPath}").CausedBy(ex));
+            }
             var blocks = new List<ContentBlock>();
             int totalWordCount = 0;
             int blockCounter = 0;

src/NexusReader.Infrastructure/Services/FakeAiGenerateQuizService.cs

@@ -1,23 +0,0 @@
-using FluentResults;
-using NexusReader.Application.Abstractions.Services;
-using NexusReader.Application.Queries.Quiz;
-
-namespace NexusReader.Infrastructure.Services;
-
-public sealed class FakeAiGenerateQuizService : IAiGenerateQuizService
-{
-    public async Task<Result<QuizDto>> GenerateQuizAsync(string contextBlockId, CancellationToken cancellationToken = default)
-    {
-        // 2000ms delay to highlight Skeleton loader visually
-        await Task.Delay(2000, cancellationToken);
-
-        var fakeQuiz = new List<QuizQuestionDto>
-        {
-            new("Co było głównym centrum włoskiego Renesansu?", new List<string> { "Wenecja", "Rzym", "Florencja", "Mediolan" }, 2),
-            new("Kto stanowił wpływowy ród mecenasów sztuki?", new List<string> { "Habsburgowie", "Medyceusze", "Borgiowie", "Sforzowie" }, 1),
-            new("Jaką koncepcją filozoficzną charakteryzował się renesans?", new List<string> { "Teocentryzmem", "Nihilizmem", "Humanizmem", "Egzystencjalizmem" }, 2)
-        };
-
-        return Result.Ok(new QuizDto(fakeQuiz));
-    }
-}

src/NexusReader.Infrastructure/Services/KnowledgeService.cs

@@ -2,6 +2,7 @@ using System.Text.Json;
 using FluentResults;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.AI;
+using Microsoft.ML.Tokenizers;
 using NexusReader.Application.Abstractions.Services;
 using NexusReader.Application.DTOs.AI;
 using NexusReader.Domain.Entities;
@@ -11,77 +12,82 @@ using Polly;
 using Polly.Registry;
 using Microsoft.Extensions.Options;
 using NexusReader.Infrastructure.Configuration;
+using Pgvector;
+using Pgvector.EntityFrameworkCore;
 
 namespace NexusReader.Infrastructure.Services;
 
 public class KnowledgeService : IKnowledgeService
 {
     private readonly IChatClient _chatClient;
-    private readonly AppDbContext _dbContext;
+    private readonly IEmbeddingGenerator<string, Embedding<float>> _embeddingGenerator;
+    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;
     private readonly ResiliencePipeline _retryPipeline;
     private readonly AiSettings _settings;
+    private readonly Tokenizer _tokenizer;
     private const string PromptVersion = "1.0";
 
     public KnowledgeService(
-        IChatClient chatClient, 
-        AppDbContext dbContext,
+        IChatClient chatClient,
+        IEmbeddingGenerator<string, Embedding<float>> embeddingGenerator,
+        IDbContextFactory<AppDbContext> dbContextFactory,
         ResiliencePipelineProvider<string> pipelineProvider,
         IOptions<AiSettings> settings)
     {
         _chatClient = chatClient;
-        _dbContext = dbContext;
+        _embeddingGenerator = embeddingGenerator;
+        _dbContextFactory = dbContextFactory;
         _retryPipeline = pipelineProvider.GetPipeline("ai-retry");
         _settings = settings.Value;
+        // Use Tiktoken (cl100k_base) which is a standard for modern LLMs and provides 
+        // a very reliable estimation for token usage in Gemini-based workloads.
+        _tokenizer = TiktokenTokenizer.CreateForModel("gpt-4");
     }
 
-    public async Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, string tenantId, CancellationToken cancellationToken = default)
     {
-        return await GetKnowledgeInternalAsync(text, PromptRegistry.KnowledgeExtractionSystemPrompt, "full", cancellationToken);
+        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.KnowledgeExtractionSystemPrompt, "full", cancellationToken);
     }
 
-    public async Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, string tenantId, CancellationToken cancellationToken = default)
     {
-        return await GetKnowledgeInternalAsync(text, PromptRegistry.GraphExtractionPrompt, "graph", cancellationToken);
+        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.GraphExtractionPrompt, "graph", cancellationToken);
     }
 
-    public async Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, string tenantId, CancellationToken cancellationToken = default)
     {
-        return await GetKnowledgeInternalAsync(text, PromptRegistry.SummaryAndQuizPrompt, "summary_quiz", cancellationToken);
+        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.SummaryAndQuizPrompt, "summary_quiz", cancellationToken);
     }
 
-    private async Task<Result<KnowledgePacket>> GetKnowledgeInternalAsync(string text, string systemPrompt, string cacheSuffix, CancellationToken cancellationToken)
+    public async Task<Result<KnowledgePacket>> GetKnowledgeMapAsync(string text, string tenantId, CancellationToken cancellationToken = default)
     {
-        if (string.IsNullOrWhiteSpace(text))
-        {
-            return Result.Fail("Input text is empty.");
-        }
+        return await GetKnowledgeInternalAsync(text, tenantId, PromptRegistry.KM_ExtractionPrompt, "km_map", cancellationToken);
+    }
 
-        Console.WriteLine($"[KnowledgeService] Starting extraction ({cacheSuffix}) for text sample: {text.Substring(0, Math.Min(text.Length, 50))}...");
+    private async Task<Result<KnowledgePacket>> GetKnowledgeInternalAsync(string text, string tenantId, string systemPrompt, string traceType, CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrWhiteSpace(text)) return Result.Fail("Input text is empty.");
 
-        var normalizedText = ContentHasher.Normalize(text);
-        if (normalizedText.Length > _settings.MaxInputLength)
-        {
-            normalizedText = normalizedText.Substring(0, _settings.MaxInputLength);
-            Console.WriteLine($"[KnowledgeService] WARNING: Input text truncated to {_settings.MaxInputLength} chars.");
-        }
-
-        var hash = ContentHasher.ComputeHash(normalizedText) + "_" + cacheSuffix;
+        using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
+        var normalizedText = text.Trim();
+        var hash = ContentHasher.ComputeHash(normalizedText);
 
         // 1. Check Cache
-        var cached = await _dbContext.SemanticKnowledgeCache
-            .FirstOrDefaultAsync(c => c.ContentHash == hash && c.PromptVersion == PromptVersion, cancellationToken);
-
-        if (cached != null)
+        var cached = await dbContext.SemanticKnowledgeCache
+            .FirstOrDefaultAsync(c => c.ContentHash == hash && c.TenantId == tenantId, cancellationToken);
+        
+        if (cached != null && cached.PromptVersion == PromptVersion)
         {
+            Console.WriteLine($"[KnowledgeService] Cache Hit for {traceType} ({hash})");
             try
             {
                 var packet = JsonSerializer.Deserialize<KnowledgePacket>(cached.JsonData, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });
                 if (packet != null) return Result.Ok(packet);
             }
-            catch { }
+            catch { /* fallback to regen */ }
         }
 
-        // 2. Call AI Client
+        Console.WriteLine($"[KnowledgeService] Cache Miss for {traceType} ({hash}). Requesting AI...");
         try
         {
             var options = new ChatOptions
@@ -109,20 +115,46 @@ public class KnowledgeService : IKnowledgeService
                 var knowledgePacket = JsonSerializer.Deserialize<KnowledgePacket>(jsonResponse, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });
                 if (knowledgePacket == null) return Result.Fail("Failed to deserialize AI response.");
                 
-                // 3. Save to Cache
+                // 3. Generate Embedding if not present
+                float[]? vector = null;
+                try
+                {
+                    var embeddingResponse = await _retryPipeline.ExecuteAsync(async ct => 
+                        await _embeddingGenerator.GenerateAsync(new[] { normalizedText }, cancellationToken: ct), cancellationToken);
+                    vector = embeddingResponse.First().Vector.ToArray();
+                }
+                catch (Exception ex)
+                {
+                    Console.WriteLine($"[KnowledgeService] Embedding Error: {ex.Message}");
+                    // We continue even if embedding fails, as the primary goal was knowledge extraction
+                }
+
+                // 4. Save to Cache
                 var cacheEntry = new SemanticKnowledgeCache
                 {
                     ContentHash = hash,
                     JsonData = jsonResponse,
+                    OriginalText = normalizedText,
                     ModelId = _settings.Model,
                     PromptVersion = PromptVersion,
+                    TenantId = tenantId,
+                    Vector = vector != null ? new Vector(vector) : null,
                     CreatedAt = DateTime.UtcNow
                 };
 
-                if (cached == null) _dbContext.SemanticKnowledgeCache.Add(cacheEntry);
-                else { cached.JsonData = jsonResponse; cached.CreatedAt = DateTime.UtcNow; }
+                if (cached == null) dbContext.SemanticKnowledgeCache.Add(cacheEntry);
+                else 
+                { 
+                    cached.JsonData = jsonResponse; 
+                    cached.OriginalText = normalizedText;
+                    cached.Vector = vector != null ? new Vector(vector) : null;
+                    cached.CreatedAt = DateTime.UtcNow; 
+                }
 
-                await _dbContext.SaveChangesAsync(cancellationToken);
+                // 5. Process structured KnowledgeUnits (Graph Expansion)
+                await ProcessKnowledgeUnitsAsync(knowledgePacket, tenantId, dbContext, cancellationToken);
+
+                await dbContext.SaveChangesAsync(cancellationToken);
                 return Result.Ok(knowledgePacket);
             }
             catch (JsonException ex)
@@ -137,18 +169,154 @@ public class KnowledgeService : IKnowledgeService
         }
     }
 
-    public async Task<Result> ClearCacheAsync(CancellationToken cancellationToken = default)
+    private async Task ProcessKnowledgeUnitsAsync(KnowledgePacket packet, string tenantId, AppDbContext dbContext, CancellationToken cancellationToken)
     {
+        var unitIds = packet.Units.Select(u => u.Id).ToList();
+        var linkSourceIds = packet.Links.Select(l => l.Source).ToList();
+        var linkTargetIds = packet.Links.Select(l => l.Target).ToList();
+        
+        var allCandidateIds = unitIds.Concat(linkSourceIds).Concat(linkTargetIds).Distinct().ToList();
+
+        // Single batch query to find existing units
+        var existingUnits = await dbContext.KnowledgeUnits
+            .Where(u => allCandidateIds.Contains(u.Id))
+            .ToDictionaryAsync(u => u.Id, cancellationToken);
+
+        var processedUnitIds = new HashSet<string>();
+
+        foreach (var unitDto in packet.Units)
+        {
+            var unitId = unitDto.Id;
+            existingUnits.TryGetValue(unitId, out var unit);
+
+            if (unit == null)
+            {
+                unit = new KnowledgeUnit { Id = unitId, TenantId = tenantId };
+                dbContext.KnowledgeUnits.Add(unit);
+                existingUnits[unitId] = unit;
+            }
+
+            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";
+            unit.MetadataJson = JsonSerializer.Serialize(unitDto.Metadata);
+
+            try
+            {
+                var emb = await _retryPipeline.ExecuteAsync(async ct => 
+                    await _embeddingGenerator.GenerateAsync(new[] { unit.Content }, cancellationToken: ct), cancellationToken);
+                unit.Vector = new Vector(emb.First().Vector.ToArray());
+            }
+            catch { /* Ignore embedding errors for now */ }
+
+            processedUnitIds.Add(unit.Id);
+        }
+
+        foreach (var linkDto in packet.Links)
+        {
+            var sourceExists = processedUnitIds.Contains(linkDto.Source) || existingUnits.ContainsKey(linkDto.Source);
+            var targetExists = processedUnitIds.Contains(linkDto.Target) || existingUnits.ContainsKey(linkDto.Target);
+
+            if (sourceExists && targetExists)
+            {
+                // Check if link already exists to avoid duplicates if necessary
+                // For now, assume we can add them or they are new in this session
+                var link = new KnowledgeUnitLink
+                {
+                    SourceUnitId = linkDto.Source,
+                    TargetUnitId = linkDto.Target,
+                    RelationType = linkDto.Relation
+                };
+                dbContext.KnowledgeUnitLinks.Add(link);
+            }
+            else
+            {
+                Console.WriteLine($"[KnowledgeService] WARNING: Skipping invalid link {linkDto.Source} -> {linkDto.Target} (Missing units).");
+            }
+        }
+    }
+
+    public async Task<Result<GroundednessResult>> VerifyGroundednessAsync(string answer, string context, string tenantId, CancellationToken cancellationToken = default)
+    {
+        var systemPrompt = @"
+        You are a Fact-Checking AI. Evaluate if the 'Answer' is supported by the 'Context'.
+        Rate the groundedness from 0.0 to 1.0.
+        Return ONLY a JSON object: { ""score"": 0.9, ""rationale"": ""string"", ""isGrounded"": true }
+        ";
+
+        var userPrompt = $"Context: {context}\n\nAnswer: {answer}";
+
         try
         {
-            Console.WriteLine("[KnowledgeService] Clearing SemanticKnowledgeCache...");
-            _dbContext.SemanticKnowledgeCache.RemoveRange(_dbContext.SemanticKnowledgeCache);
-            await _dbContext.SaveChangesAsync(cancellationToken);
+            var options = new ChatOptions
+            {
+                Temperature = 0.0f, // Low temperature for factual checks
+                MaxOutputTokens = 500
+            };
+
+            var response = await _retryPipeline.ExecuteAsync(async ct => 
+                await _chatClient.GetResponseAsync(new List<ChatMessage>
+                {
+                    new ChatMessage(ChatRole.System, systemPrompt),
+                    new ChatMessage(ChatRole.User, userPrompt)
+                }, options, cancellationToken: ct), cancellationToken);
+
+            var rawJson = response.Text?.Trim() ?? "{}";
+            rawJson = rawJson.Replace("```json", "").Replace("```", "").Trim();
+            
+            var result = JsonSerializer.Deserialize<GroundednessResult>(rawJson, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });
+            
+            return result != null ? Result.Ok(result) : Result.Fail("Failed to parse groundedness result");
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error("Failed to verify groundedness").CausedBy(ex));
+        }
+    }
+
+    public async Task<Result<List<RelevantContext>>> GetRelevantContextAsync(string query, string tenantId, CancellationToken cancellationToken = default)
+    {
+        using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
+        try
+        {
+            var queryEmbedding = await _retryPipeline.ExecuteAsync(async ct => 
+                await _embeddingGenerator.GenerateAsync(new[] { query }, cancellationToken: ct), cancellationToken);
+            var queryVector = new Vector(queryEmbedding.First().Vector.ToArray());
+
+            var relevantUnits = await dbContext.KnowledgeUnits
+                .Where(u => u.TenantId == tenantId)
+                .OrderBy(u => u.Vector!.L2Distance(queryVector))
+                .Take(5)
+                .Select(u => new RelevantContext { Text = u.Content, Confidence = 1.0 })
+                .ToListAsync(cancellationToken);
+
+            return Result.Ok(relevantUnits);
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error("Failed to retrieve relevant context").CausedBy(ex));
+        }
+    }
+
+    public async Task<Result> ClearCacheAsync(CancellationToken cancellationToken = default)
+    {
+        using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
+        try
+        {
+            await dbContext.SemanticKnowledgeCache.ExecuteDeleteAsync(cancellationToken);
+            await dbContext.KnowledgeUnits.ExecuteDeleteAsync(cancellationToken);
+            await dbContext.KnowledgeUnitLinks.ExecuteDeleteAsync(cancellationToken);
             return Result.Ok();
         }
         catch (Exception ex)
         {
-            return Result.Fail($"Failed to clear cache: {ex.Message}");
+            return Result.Fail(new Error("Failed to clear knowledge cache").CausedBy(ex));
         }
     }
+
+    private int EstimateTokenCount(string text)
+    {
+        if (string.IsNullOrEmpty(text)) return 0;
+        return _tokenizer.CountTokens(text);
+    }
 }

src/NexusReader.Infrastructure/Services/PromptRegistry.cs

@@ -21,4 +21,13 @@ public static class PromptRegistry
     public const string SummaryAndQuizPrompt = 
         "You are an expert educator. Provide a concise summary of the text and generate a challenging quiz (3-5 questions). " +
         "Return ONLY minified JSON. Schema: { \"summary\": \"string\", \"quizzes\": [ { \"question\": \"string\", \"options\": [ \"string\" ], \"correct_index\": 0 } ] }";
+
+    public const string KM_ExtractionPrompt = 
+        "You are an expert at Knowledge Engineering. Segment the provided text into discrete Knowledge Units. " +
+        "Identify 'units' (sections, tables, definitions, rules) and 'links' (how they relate). " +
+        "CRITICAL: Units must be granular. " +
+        "Schema: { " +
+        "\"units\": [ { \"id\": \"string\", \"type\": \"Section|Table|Definition|Rule\", \"content\": \"string\", \"metadata\": { \"page\": 0 } } ], " +
+        "\"links\": [ { \"source\": \"string\", \"target\": \"string\", \"relation\": \"Next|Defines|Contains|References\" } ] " +
+        "}.";
 }

src/NexusReader.Maui/Main.razor

@@ -3,7 +3,11 @@
 
 <Router AppAssembly="@typeof(NexusReader.UI.Shared._Imports).Assembly">
     <Found Context="routeData">
-        <RouteView RouteData="@routeData" DefaultLayout="@typeof(NexusReader.UI.Shared.Layout.MainLayout)" />
+        <AuthorizeRouteView RouteData="@routeData" DefaultLayout="@typeof(NexusReader.UI.Shared.Layout.MainLayout)">
+            <NotAuthorized>
+                <RedirectToLogin />
+            </NotAuthorized>
+        </AuthorizeRouteView>
         <FocusOnNavigate RouteData="@routeData" Selector="h1" />
     </Found>
     <NotFound>

src/NexusReader.Maui/MauiProgram.cs

@@ -2,6 +2,8 @@ using Microsoft.Extensions.Logging;
 using NexusReader.Application.Abstractions.Services;
 using NexusReader.Infrastructure.Mobile.Services;
 using NexusReader.UI.Shared.Services;
+using NexusReader.Application;
+using MediatR;
 
 namespace NexusReader.Maui;
 
@@ -39,6 +41,18 @@ public static class MauiProgram
 			builder.Services.AddScoped<IThemeService, ThemeService>();
 			builder.Services.AddScoped<IFocusModeService, FocusModeService>();
 			builder.Services.AddScoped<IQuizStateService, QuizStateService>();
+			builder.Services.AddScoped<IReaderNavigationService, ReaderNavigationService>();
+			builder.Services.AddScoped<IKnowledgeGraphService, KnowledgeGraphService>();
+			builder.Services.AddScoped<IReaderInteractionService, ReaderInteractionService>();
+			builder.Services.AddScoped<KnowledgeCoordinator>();
+			builder.Services.AddScoped<ISyncService, SyncService>();
+			builder.Services.AddScoped<IIdentityService, IdentityService>();
+			
+			builder.Services.AddApplication();
+			
+			builder.Services.AddMediatR(cfg => cfg.RegisterServicesFromAssemblies(
+				NexusReader.Application.DependencyInjection.Assembly
+			));
 
 			return builder.Build();
 		}

src/NexusReader.Maui/wwwroot/index.html

@@ -11,7 +11,12 @@
 
 <body>
 
-    <div id="app">Loading...</div>
+    <div id="app">
+        <div id="app-preloader">
+            <div class="preloader-spinner"></div>
+            <div class="preloader-text">Nexus Reader</div>
+        </div>
+    </div>
 
     <div id="blazor-error-ui">
         An unhandled error has occurred.

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

@@ -0,0 +1,39 @@
+@namespace NexusReader.UI.Shared.Components.Atoms
+
+<div class="nexus-search-container @(IsActive ? "active" : "")">
+    <div class="search-wrapper">
+        <i class="nexus-icon @IconClass"></i>
+        <input type="text" 
+               @bind="SearchValue" 
+               @bind:event="oninput"
+               @onkeypress="HandleKeyPress"
+               placeholder="@Placeholder" 
+               class="nexus-search-input" />
+        @if (!string.IsNullOrEmpty(SearchValue))
+        {
+            <button class="clear-btn" @onclick="ClearSearch">×</button>
+        }
+    </div>
+</div>
+
+@code {
+    [Parameter] public string Placeholder { get; set; } = "Search your library...";
+    [Parameter] public string IconClass { get; set; } = "bi bi-search";
+    [Parameter] public EventCallback<string> OnSearch { get; set; }
+    
+    private string SearchValue { get; set; } = string.Empty;
+    private bool IsActive => !string.IsNullOrEmpty(SearchValue);
+
+    private async Task HandleKeyPress(KeyboardEventArgs e)
+    {
+        if (e.Key == "Enter")
+        {
+            await OnSearch.InvokeAsync(SearchValue);
+        }
+    }
+
+    private void ClearSearch()
+    {
+        SearchValue = string.Empty;
+    }
+}

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

@@ -0,0 +1,57 @@
+.nexus-search-container {
+    width: 100%;
+    max-width: 500px;
+    margin: 1rem auto;
+    transition: all 0.3s ease;
+}
+
+.search-wrapper {
+    position: relative;
+    display: flex;
+    align-items: center;
+    background: var(--nexus-card, #141414);
+    border: 1px solid rgba(255, 255, 255, 0.1);
+    border-radius: 12px;
+    padding: 0.5rem 1rem;
+    transition: border-color 0.3s ease, box-shadow 0.3s ease;
+}
+
+.nexus-search-container.active .search-wrapper,
+.search-wrapper:focus-within {
+    border-color: var(--nexus-neon, #00ff99);
+    box-shadow: 0 0 15px rgba(0, 255, 153, 0.2);
+}
+
+.nexus-icon {
+    color: rgba(255, 255, 255, 0.5);
+    margin-right: 0.75rem;
+    font-size: 1.1rem;
+}
+
+.nexus-search-input {
+    flex: 1;
+    background: transparent;
+    border: none;
+    color: white;
+    font-family: 'Inter', sans-serif;
+    font-size: 0.95rem;
+    outline: none;
+}
+
+.nexus-search-input::placeholder {
+    color: rgba(255, 255, 255, 0.3);
+}
+
+.clear-btn {
+    background: transparent;
+    border: none;
+    color: rgba(255, 255, 255, 0.4);
+    font-size: 1.2rem;
+    cursor: pointer;
+    padding: 0 0.5rem;
+    transition: color 0.2s ease;
+}
+
+.clear-btn:hover {
+    color: var(--nexus-neon, #00ff99);
+}

src/NexusReader.UI.Shared/Components/Molecules/AiAssistantBubble.razor

@@ -1,36 +1,126 @@
 @using NexusReader.UI.Shared.Services
+@using NexusReader.Application.DTOs.AI
 @inject IQuizStateService QuizState
+@inject KnowledgeCoordinator Coordinator
+@implements IDisposable
 
 <div class="ai-bubble-container">
     <div class="ai-bubble">
         <div class="ai-avatar">
             <div class="avatar-ring"></div>
-            <NexusIcon Name="robot" Size="48" Class="neon-pulse" />
+            <NexusIcon Name="robot" Size="48" Class="@(_isStreaming ? "neon-pulse" : "neon-glow")" />
             <div class="avatar-label">
                 <span class="name">E-Czytnik</span>
                 <span class="role">Asystent AI</span>
             </div>
         </div>
         <div class="ai-content">
-            <NexusTypography Variant="NexusTypography.TypographyVariant.UI">@Dialogue</NexusTypography>
-            
+            @if (_isLoading)
+            {
+                <div class="loading-state">
+                    <div class="shimmer">Analizuję fragment...</div>
+                </div>
+            }
+            else
+            {
+                <NexusTypography Variant="NexusTypography.TypographyVariant.UI">
+                    @_displayedText@(_isStreaming ? "▍" : "")
+                </NexusTypography>
+            }
+
             <div class="ai-actions">
                 <button class="action-btn ghost" @onclick='() => HandleActionClick("more")'>Pokaż więcej informacji</button>
-                <button class="action-btn neon-border" @onclick='() => HandleActionClick("quiz")'>Rozwiąż quiz</button>
+                <button class="action-btn neon-border" @onclick='() => HandleActionClick("quiz")' disabled="@(_isLoading)">Rozwiąż quiz</button>
             </div>
-
         </div>
         <div class="bubble-pointer"></div>
     </div>
 </div>
 
-
 @code {
     [Parameter] public string ContextBlockId { get; set; } = string.Empty;
+    /// <summary>Fallback static dialogue shown when no live AI content is available.</summary>
     [Parameter] public string Dialogue { get; set; } = string.Empty;
     [Parameter] public List<string> Actions { get; set; } = new();
     [Parameter] public EventCallback<string> OnActionTriggered { get; set; }
 
+    private string _displayedText = string.Empty;
+    private bool _isLoading = false;
+    private bool _isStreaming = false;
+    private string _lastFetchedBlockId = string.Empty;
+    private KnowledgePacket? _packet;
+    private CancellationTokenSource? _streamCts;
+
+    protected override async Task OnParametersSetAsync()
+    {
+        // Only re-fetch when the block context actually changes
+        if (string.IsNullOrEmpty(ContextBlockId) || ContextBlockId == _lastFetchedBlockId)
+            return;
+
+        _lastFetchedBlockId = ContextBlockId;
+        await FetchAndStreamAsync();
+    }
+
+    private async Task FetchAndStreamAsync()
+    {
+        // Cancel any in-progress stream
+        _streamCts?.Cancel();
+        _streamCts = new CancellationTokenSource();
+        var token = _streamCts.Token;
+
+        _isLoading = true;
+        _isStreaming = false;
+        _displayedText = string.Empty;
+        _packet = null;
+        StateHasChanged();
+
+        try
+        {
+            _packet = await Coordinator.RequestSummaryAndQuizAsync(
+                $"[ID: {ContextBlockId}]\n{Dialogue}");
+
+            var summary = _packet?.Summary;
+
+            if (string.IsNullOrWhiteSpace(summary))
+            {
+                // Fall back to the static Dialogue parameter
+                _displayedText = string.IsNullOrEmpty(Dialogue)
+                    ? "Brak danych do analizy."
+                    : Dialogue;
+                _isLoading = false;
+                StateHasChanged();
+                return;
+            }
+
+            _isLoading = false;
+            _isStreaming = true;
+
+            // Word-by-word reveal (streaming simulation)
+            var words = summary.Split(' ');
+            foreach (var word in words)
+            {
+                if (token.IsCancellationRequested) break;
+                _displayedText += (string.IsNullOrEmpty(_displayedText) ? "" : " ") + word;
+                StateHasChanged();
+                await Task.Delay(40, token); // ~25 words/sec
+            }
+        }
+        catch (OperationCanceledException)
+        {
+            // Superseded by a newer block — silently drop
+        }
+        catch (Exception ex)
+        {
+            _displayedText = string.IsNullOrEmpty(Dialogue) ? "Błąd analizy." : Dialogue;
+            Console.WriteLine($"[AiAssistantBubble] Error fetching summary: {ex.Message}");
+        }
+        finally
+        {
+            _isStreaming = false;
+            StateHasChanged();
+        }
+    }
+
     private async Task HandleActionClick(string action)
     {
         if (action.Contains("quiz", StringComparison.OrdinalIgnoreCase))
@@ -43,4 +133,10 @@
             await OnActionTriggered.InvokeAsync(action);
         }
     }
+
+    public void Dispose()
+    {
+        _streamCts?.Cancel();
+        _streamCts?.Dispose();
+    }
 }

src/NexusReader.UI.Shared/Components/Molecules/GroundednessBadge.razor

@@ -0,0 +1,103 @@
+@using MediatR
+@using NexusReader.Application.Commands.AI
+@using NexusReader.Application.Abstractions.Services
+@using NexusReader.UI.Shared.Components.Atoms
+@using Microsoft.AspNetCore.Components.Authorization
+@inject IMediator Mediator
+@inject AuthenticationStateProvider AuthProvider
+
+<div class="groundedness-badge @GetStatusClass()" title="@_result?.Rationale">
+    @if (_isChecking)
+    {
+        <span class="shimmer">Weryfikacja...</span>
+    }
+    else if (_result != null)
+    {
+        <NexusIcon Name="@(GetIcon())" Size="14" />
+        <span>@((_result.Score * 100).ToString("0"))% Grounded</span>
+    }
+</div>
+
+<style>
+    .groundedness-badge {
+        display: inline-flex;
+        align-items: center;
+        gap: 6px;
+        padding: 4px 8px;
+        border-radius: 12px;
+        font-size: 0.75rem;
+        font-weight: 600;
+        background: rgba(255, 255, 255, 0.05);
+        border: 1px solid rgba(255, 255, 255, 0.1);
+        transition: all 0.3s ease;
+    }
+
+    .groundedness-badge.status-high {
+        color: var(--nexus-neon);
+        border-color: var(--nexus-neon);
+    }
+
+    .groundedness-badge.status-medium {
+        color: #ffaa00;
+        border-color: #ffaa00;
+    }
+
+    .groundedness-badge.status-low {
+        color: #ff4444;
+        border-color: #ff4444;
+    }
+
+    .shimmer {
+        opacity: 0.6;
+    }
+</style>
+
+@code {
+    [Parameter] public string Answer { get; set; } = string.Empty;
+    [Parameter] public string Context { get; set; } = string.Empty;
+
+    private GroundednessResult? _result;
+    private bool _isChecking;
+
+    protected override async Task OnParametersSetAsync()
+    {
+        if (!string.IsNullOrEmpty(Answer) && !string.IsNullOrEmpty(Context) && _result == null)
+        {
+            await RunCheck();
+        }
+    }
+
+    private async Task RunCheck()
+    {
+        _isChecking = true;
+        StateHasChanged();
+
+        var authState = await AuthProvider.GetAuthenticationStateAsync();
+        var tenantId = authState.User.FindFirst("TenantId")?.Value ?? "global";
+
+        var res = await Mediator.Send(new VerifyGroundednessCommand(Answer, Context, tenantId));
+        if (res.IsSuccess)
+        {
+            _result = res.Value;
+        }
+
+        _isChecking = false;
+        StateHasChanged();
+    }
+
+    private string GetStatusClass()
+    {
+        if (_result == null) return "";
+        if (_result.Score >= 0.8) return "status-high";
+        if (_result.Score >= 0.5) return "status-medium";
+        return "status-low";
+    }
+
+    private string GetIcon()
+    {
+        if (_result == null) return "help";
+        if (_result.Score >= 0.8) return "check-circle";
+        if (_result.Score >= 0.5) return "info-circle";
+        return "alert-triangle";
+    }
+}

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

@@ -0,0 +1,61 @@
+@using NexusReader.Application.DTOs.AI
+@using NexusReader.UI.Shared.Components.Atoms
+@namespace NexusReader.UI.Shared.Components.Organisms
+
+<div class="global-intelligence-panel">
+    <div class="panel-header">
+        <h3><i class="bi bi-cpu"></i> Global Intelligence</h3>
+        <p>Semantic search across your library</p>
+    </div>
+
+    <NexusSearchBox Placeholder="Ask a question about your books..." OnSearch="HandleSearch" />
+
+    <div class="results-container">
+        @if (IsLoading)
+        {
+            <div class="loading-state">
+                <div class="nexus-spinner"></div>
+                <span>Analyzing your library...</span>
+            </div>
+        }
+        else if (Results != null && Results.Any())
+        {
+            @foreach (var result in Results)
+            {
+                <div class="search-result-item">
+                    <div class="result-meta">
+                        <span class="relevance">@(Math.Round(result.RelevanceScore * 100))% Relevant</span>
+                        @if (!string.IsNullOrEmpty(result.SourceBookTitle))
+                        {
+                            <span class="source">in <strong>@result.SourceBookTitle</strong></span>
+                        }
+                    </div>
+                    <div class="result-snippet">
+                        @result.Snippet
+                    </div>
+                </div>
+            }
+        }
+        else if (HasSearched)
+        {
+            <div class="empty-state">
+                <i class="bi bi-search"></i>
+                <p>No semantic matches found.</p>
+            </div>
+        }
+    </div>
+</div>
+
+@code {
+    [Parameter] public List<SemanticSearchResultDto>? Results { get; set; }
+    [Parameter] public bool IsLoading { get; set; }
+    [Parameter] public EventCallback<string> OnPerformSearch { get; set; }
+
+    private bool HasSearched { get; set; }
+
+    private async Task HandleSearch(string query)
+    {
+        HasSearched = true;
+        await OnPerformSearch.InvokeAsync(query);
+    }
+}

src/NexusReader.UI.Shared/Components/Organisms/GlobalIntelligencePanel.razor.css

@@ -0,0 +1,94 @@
+.global-intelligence-panel {
+    background: var(--nexus-bg, #0a0a0a);
+    border-left: 1px solid rgba(255, 255, 255, 0.05);
+    height: 100%;
+    display: flex;
+    flex-direction: column;
+    padding: 1.5rem;
+}
+
+.panel-header h3 {
+    margin: 0;
+    color: var(--nexus-neon, #00ff99);
+    font-size: 1.25rem;
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+}
+
+.panel-header p {
+    color: rgba(255, 255, 255, 0.5);
+    font-size: 0.85rem;
+    margin: 0.25rem 0 1.5rem 0;
+}
+
+.results-container {
+    flex: 1;
+    overflow-y: auto;
+    margin-top: 1rem;
+    padding-right: 0.5rem;
+}
+
+.search-result-item {
+    background: var(--nexus-card, #141414);
+    border-radius: 8px;
+    padding: 1rem;
+    margin-bottom: 1rem;
+    border: 1px solid rgba(255, 255, 255, 0.05);
+    transition: transform 0.2s ease, border-color 0.2s ease;
+}
+
+.search-result-item:hover {
+    transform: translateX(4px);
+    border-color: rgba(0, 255, 153, 0.3);
+}
+
+.result-meta {
+    display: flex;
+    justify-content: space-between;
+    font-size: 0.75rem;
+    margin-bottom: 0.5rem;
+}
+
+.relevance {
+    color: var(--nexus-neon, #00ff99);
+    font-weight: 600;
+}
+
+.source {
+    color: rgba(255, 255, 255, 0.4);
+}
+
+.result-snippet {
+    color: rgba(255, 255, 255, 0.8);
+    font-size: 0.9rem;
+    line-height: 1.5;
+    display: -webkit-box;
+    -webkit-line-clamp: 4;
+    -webkit-box-orient: vertical;
+    overflow: hidden;
+}
+
+.loading-state, .empty-state {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    height: 200px;
+    color: rgba(255, 255, 255, 0.3);
+    text-align: center;
+}
+
+.nexus-spinner {
+    width: 30px;
+    height: 30px;
+    border: 2px solid rgba(0, 255, 153, 0.1);
+    border-top-color: var(--nexus-neon, #00ff99);
+    border-radius: 50%;
+    animation: spin 1s linear infinite;
+    margin-bottom: 1rem;
+}
+
+@keyframes spin {
+    to { transform: rotate(360deg); }
+}

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

@@ -10,6 +10,7 @@
 @inject IReaderNavigationService NavigationService
 @inject KnowledgeCoordinator Coordinator
 @inject IReaderInteractionService InteractionService
+@inject ISyncService SyncService
 
 <div class="reader-canvas @(ThemeService.IsLightMode ? "theme-light" : "theme-dark")">
     @if (ViewModel == null)
@@ -53,6 +54,7 @@
 
     protected override void OnInitialized()
     {
+        Coordinator.Clear();
         ThemeService.OnThemeChanged += StateHasChanged;
         NavigationService.OnNavigationChanged += OnNavigationChanged;
         
@@ -77,6 +79,11 @@
 
     protected override async Task OnAfterRenderAsync(bool firstRender)
     {
+        if (firstRender)
+        {
+            await SyncService.InitializeAsync();
+        }
+
         if (ViewModel != null && !_isJsInitialized)
         {
             _isJsInitialized = true;
@@ -109,6 +116,23 @@
     public void HandleBlockReached(string blockId, string content)
     {
         Coordinator.OnBlockReached(blockId, content);
+        
+        // Debounce sync update (simple version: every 5 seconds or on a timer)
+        _ = SyncService.UpdateProgressAsync(blockId);
+    }
+
+    private void HandleSyncProgressReceived(string blockId, DateTime timestamp)
+    {
+        // For now, let's just scroll to the node if it's in the current view, 
+        // or just log it. Usually, we should prompt the user.
+        Console.WriteLine($"[Sync] Received progress from another device: {blockId} at {timestamp}");
+        
+        // Simple auto-scroll if it's newer than what we have (we don't track our own timestamp yet, 
+        // but we can assume incoming syncs are from other active devices)
+        _ = InvokeAsync(async () => {
+             await ScrollToNodeAsync(blockId);
+             StateHasChanged();
+        });
     }
 
     [JSInvokable]
@@ -196,5 +220,6 @@
         InteractionService.OnScrollToBlockRequested -= HandleScrollRequested;
         InteractionService.OnHighlightBlockRequested -= HandleHighlightRequested;
         InteractionService.OnTextSelected -= HandleTextSelected;
+        SyncService.OnProgressReceived -= HandleSyncProgressReceived;
     }
 }

src/NexusReader.UI.Shared/Layout/MainLayout.razor

@@ -3,35 +3,38 @@
 @using NexusReader.UI.Shared.Services
 @using NexusReader.UI.Shared.Components.Molecules
 @using NexusReader.UI.Shared.Components.Organisms
+@using Microsoft.Extensions.Logging
 @inject IPlatformService PlatformService
 @inject IFocusModeService FocusMode
 @inject IQuizStateService QuizService
 @inject IJSRuntime JS
 @inject IIdentityService IdentityService
 @inject NavigationManager NavigationManager
+@inject Microsoft.Extensions.Logging.ILogger<MainLayout> Logger
 @implements IDisposable
 
-<div class="app-container @_platformClass @(FocusMode.IsFocusModeActive ? "focus-mode-active" : "")">
-    <div class="reader-pane">
-        <main>
-            @Body
-        </main>
-        <ReaderFooter />
-    </div>
+<AuthorizeView>
+    <Authorized>
+        <div class="app-container @_platformClass @(FocusMode.IsFocusModeActive ? "focus-mode-active" : "")">
+            <div class="reader-pane">
+                <main>
+                    @Body
+                </main>
+                <ReaderFooter />
+            </div>
 
-    <div class="resizer" id="sidebar-resizer"></div>
+            <div class="resizer" id="sidebar-resizer"></div>
 
-    <AuthorizeView>
-        <Authorized>
             <div class="intelligence-sidebar">
                 <IntelligenceToolbar />
                 <div class="intelligence-content">
                     <div class="intelligence-header">
                         <div class="ai-title">
-                            <NexusIcon Name="robot" Size="20" Class="@($"neon-glow {(QuizService.HasNewQuiz ? "quiz-available" : "")}")" />
+                            <NexusIcon Name="robot" Size="20"
+                                Class="@($"neon-glow {(QuizService.HasNewQuiz ? "quiz-available" : "")}")" />
                             <span>Asystent AI</span>
                         </div>
-                        
+
                         <div class="user-profile">
                             <span class="user-email">@context.User.Identity?.Name</span>
                             <button class="logout-btn" @onclick="HandleLogout">Logout</button>
@@ -39,16 +42,28 @@
 
                         <button class="close-btn">×</button>
                     </div>
-                    
+
                     <div class="intelligence-scroll-area">
-                        <KnowledgeGraph />
+                        @if (!_isMobile)
+                        {
+                            <KnowledgeGraph />
+                        }
                         <KnowledgeCheck />
                     </div>
                 </div>
             </div>
-        </Authorized>
-    </AuthorizeView>
-</div>
+        </div>
+    </Authorized>
+    <Authorizing>
+        <div class="app-preloader">
+            <div class="preloader-spinner"></div>
+            <div class="preloader-text">Weryfikacja...</div>
+        </div>
+    </Authorizing>
+    <NotAuthorized>
+        @Body
+    </NotAuthorized>
+</AuthorizeView>
 
 <div id="blazor-error-ui" data-nosnippet>
     An unhandled error has occurred.
@@ -58,20 +73,23 @@
 
 @code {
     private string _platformClass = "platform-desktop";
+    private bool _isMobile = false;
 
     protected override void OnInitialized()
     {
         FocusMode.OnFocusModeChanged += StateHasChanged;
         QuizService.OnQuizUpdated += StateHasChanged;
-        
+
         var context = PlatformService.GetDeviceContext();
         if (context.IsSuccess)
         {
-            _platformClass = context.Value.DeviceType switch
+            _isMobile = context.Value.DeviceType switch
             {
-                DeviceType.Phone or DeviceType.Tablet => "platform-mobile",
-                _ => "platform-desktop"
+                DeviceType.Phone or DeviceType.Tablet => true,
+                _ => false
             };
+            
+            _platformClass = _isMobile ? "platform-mobile" : "platform-desktop";
         }
     }
 
@@ -90,7 +108,10 @@
                 var module = await JS.InvokeAsync<IJSObjectReference>("import", "./_content/NexusReader.UI.Shared/js/layoutResizer.js");
                 await module.InvokeVoidAsync("initResizer", ".app-container", "#sidebar-resizer", "--sidebar-width");
             }
-            catch { }
+            catch (Exception ex)
+            {
+                Logger.LogError(ex, "Failed to initialize layout resizer JS module.");
+            }
         }
     }
 
@@ -100,4 +121,3 @@
         QuizService.OnQuizUpdated -= StateHasChanged;
     }
 }
-

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

@@ -12,6 +12,8 @@
     <PackageReference Include="Microsoft.AspNetCore.Components.Authorization" Version="10.0.7" />
     <PackageReference Include="Microsoft.AspNetCore.Components.Web" Version="10.0.7" />
     <PackageReference Include="MediatR" Version="12.1.1" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.7" />
+    <PackageReference Include="Microsoft.AspNetCore.SignalR.Client" Version="10.0.7" />
   </ItemGroup>
 
   <ItemGroup>

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

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

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

@@ -38,7 +38,7 @@ public sealed class KnowledgeCoordinator : IDisposable
         _interactionService.RequestHighlightBlock(nodeId);
     }
 
-    public async Task ProcessFullPageAsync(string fullContent)
+    public async Task ProcessFullPageAsync(string fullContent, string tenantId = "global")
     {
         if (string.IsNullOrWhiteSpace(fullContent)) return;
 
@@ -49,7 +49,7 @@ public sealed class KnowledgeCoordinator : IDisposable
         
         try
         {
-            var result = await _knowledgeService.GetGraphDataAsync(fullContent);
+            var result = await _knowledgeService.GetGraphDataAsync(fullContent, tenantId);
             if (result.IsSuccess)
             {
                 var packet = result.Value;
@@ -73,12 +73,12 @@ public sealed class KnowledgeCoordinator : IDisposable
         _graphService.SetActiveNode(blockId);
     }
 
-    public async Task<KnowledgePacket?> RequestSummaryAndQuizAsync(string content)
+    public async Task<KnowledgePacket?> RequestSummaryAndQuizAsync(string content, string tenantId = "global")
     {
         _quizService.SetHydrating(true);
         try
         {
-            var result = await _knowledgeService.GetSummaryAndQuizAsync(content);
+            var result = await _knowledgeService.GetSummaryAndQuizAsync(content, tenantId);
             if (result.IsSuccess)
             {
                 var packet = result.Value;
@@ -98,6 +98,12 @@ public sealed class KnowledgeCoordinator : IDisposable
         return null;
     }
 
+    public void Clear()
+    {
+        _graphService.Clear();
+        _quizService.SetQuiz(null, null);
+    }
+
     public void Dispose()
     {
         _interactionService.OnNodeSelected -= HandleNodeSelected;

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

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

src/NexusReader.UI.Shared/_Imports.razor

@@ -15,3 +15,4 @@
 @using NexusReader.UI.Shared.Components.Molecules
 @using NexusReader.UI.Shared.Components.Organisms
 @using NexusReader.UI.Shared.Services
+@using Microsoft.Extensions.Logging

src/NexusReader.UI.Shared/wwwroot/app.css

@@ -99,4 +99,57 @@ h1:focus {
     color: white;
     margin: 1rem;
     border-radius: 8px;
-}
+}
+
+/* Preloader Styles */
+#app-preloader, .app-preloader {
+    position: fixed;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    background: radial-gradient(circle at center, #1a1a1a 0%, var(--nexus-bg) 100%);
+    display: flex;
+    flex-direction: column;
+    justify-content: center;
+    align-items: center;
+    z-index: 9999;
+    transition: opacity 0.8s ease, visibility 0.8s;
+}
+
+#app-preloader.loaded {
+    opacity: 0;
+    visibility: hidden;
+}
+
+.preloader-spinner {
+    width: 80px;
+    height: 80px;
+    border: 3px solid rgba(0, 255, 153, 0.1);
+    border-top: 3px solid var(--nexus-neon);
+    border-radius: 50%;
+    animation: spin 1s cubic-bezier(0.4, 0, 0.2, 1) infinite;
+    filter: drop-shadow(0 0 10px var(--nexus-neon));
+    margin-bottom: 20px;
+}
+
+.preloader-text {
+    color: var(--nexus-neon);
+    font-family: var(--nexus-font-sans);
+    letter-spacing: 4px;
+    text-transform: uppercase;
+    font-size: 0.8rem;
+    font-weight: 500;
+    animation: pulse 2s infinite;
+}
+
+@keyframes spin {
+    0% { transform: rotate(0deg); }
+    100% { transform: rotate(360deg); }
+}
+
+@keyframes pulse {
+    0%, 100% { opacity: 1; transform: scale(1); }
+    50% { opacity: 0.5; transform: scale(0.95); }
+}
+

src/NexusReader.UI.Shared/wwwroot/js/knowledgeGraph.js

@@ -122,13 +122,19 @@ export function updateData(data) {
     // Update Links
     link = rootGroup.select(".links-layer")
         .selectAll("path")
-        .data(data.links, d => d.source + "-" + d.target)
+        .data(data.links, d => d.source + "-" + d.target + "-" + d.relationType)
         .join(
             enter => enter.append("path")
-                .attr("stroke", "rgba(255,255,255,0.05)")
+                .attr("stroke", d => {
+                    if (d.relationType === 'Defines') return 'var(--nexus-accent)';
+                    if (d.relationType === 'Next') return 'rgba(255,255,255,0.2)';
+                    if (d.relationType === 'Contains') return 'var(--nexus-neon)';
+                    return 'rgba(255,255,255,0.1)';
+                })
                 .attr("fill", "none")
-                .attr("stroke-width", 1.5)
-                .call(e => e.transition().duration(500).attr("stroke", "rgba(255,255,255,0.1)")),
+                .attr("stroke-width", d => d.relationType === 'Defines' ? 2 : 1)
+                .attr("stroke-dasharray", d => d.relationType === 'References' ? "5,5" : "0")
+                .call(e => e.transition().duration(500).attr("opacity", 1)),
             update => update,
             exit => exit.remove()
         );
@@ -150,7 +156,12 @@ export function updateData(data) {
 
                 g.append("circle")
                     .attr("r", 30)
-                    .attr("fill", "url(#nebulaGlow)")
+                    .attr("fill", d => {
+                        if (d.type === 'Definition') return 'var(--nexus-accent)';
+                        if (d.type === 'Table') return 'var(--nexus-neon)';
+                        if (d.type === 'Rule') return '#ff4444';
+                        return "url(#nebulaGlow)";
+                    })
                     .attr("opacity", 0)
                     .transition().duration(1000).attr("opacity", d => d.group === 'current' ? 0.6 : 0.2);
 
@@ -162,14 +173,18 @@ export function updateData(data) {
                     .attr("height", 24)
                     .attr("rx", 12)
                     .attr("fill", "rgba(20, 20, 20, 0.9)")
-                    .attr("stroke", "rgba(255, 255, 255, 0.1)")
+                    .attr("stroke", d => {
+                        if (d.type === 'Definition') return 'var(--nexus-accent)';
+                        if (d.type === 'Rule') return '#ff4444';
+                        return "rgba(255, 255, 255, 0.1)";
+                    })
                     .attr("stroke-width", 1);
 
                 g.append("text")
                     .text(d => d.label)
                     .attr("text-anchor", "middle")
                     .attr("y", 4)
-                    .attr("fill", "#ccc")
+                    .attr("fill", d => d.type === 'Definition' ? 'var(--nexus-accent)' : '#ccc')
                     .attr("font-size", "0.8rem");
                 
                 return g;

src/NexusReader.Web.Client/NexusReader.Web.Client.csproj

@@ -16,7 +16,6 @@
 
   <ItemGroup>
     <ProjectReference Include="..\NexusReader.Application\NexusReader.Application.csproj" />
-    <ProjectReference Include="..\NexusReader.Infrastructure\NexusReader.Infrastructure.csproj" />
     <ProjectReference Include="..\NexusReader.UI.Shared\NexusReader.UI.Shared.csproj" />
   </ItemGroup>
 

src/NexusReader.Web.Client/Program.cs

@@ -4,8 +4,7 @@ using NexusReader.Application.Abstractions.Services;
 using NexusReader.Web.Client.Services;
 using NexusReader.UI.Shared.Services;
 using NexusReader.Application;
-using NexusReader.Infrastructure;
-using NexusReader.Infrastructure.Services;
+
 
 var builder = WebAssemblyHostBuilder.CreateDefault(args);
 
@@ -19,6 +18,7 @@ builder.Services.AddScoped<IReaderNavigationService, ReaderNavigationService>();
 builder.Services.AddScoped<IKnowledgeGraphService, KnowledgeGraphService>();
 builder.Services.AddScoped<IReaderInteractionService, ReaderInteractionService>();
 builder.Services.AddScoped<KnowledgeCoordinator>();
+builder.Services.AddScoped<ISyncService, SyncService>();
 
 // Identity & Auth Services
 builder.Services.AddOptions();
@@ -34,6 +34,5 @@ builder.Services.AddScoped(sp => new HttpClient { BaseAddress = new Uri(builder.
 
 builder.Services.AddApplication();
 builder.Services.AddScoped<IEpubService, WasmEpubService>();
-builder.Services.AddTransient<IAiGenerateQuizService, FakeAiGenerateQuizService>();
 
 await builder.Build().RunAsync();

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

@@ -14,21 +14,65 @@ public class WasmKnowledgeService : IKnowledgeService
         _httpClient = httpClient;
     }
 
-    public async Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, string tenantId, CancellationToken cancellationToken = default)
     {
         return await CallKnowledgeApiAsync("/api/knowledge", text, cancellationToken);
     }
 
-    public async Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetGraphDataAsync(string text, string tenantId, CancellationToken cancellationToken = default)
     {
         return await CallKnowledgeApiAsync("/api/knowledge/graph", text, cancellationToken);
     }
 
-    public async Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, CancellationToken cancellationToken = default)
+    public async Task<Result<KnowledgePacket>> GetKnowledgeMapAsync(string text, string tenantId, CancellationToken cancellationToken = default)
+    {
+        return await CallKnowledgeApiAsync("/api/knowledge/map", text, cancellationToken);
+    }
+
+    public async Task<Result<KnowledgePacket>> GetSummaryAndQuizAsync(string text, string tenantId, CancellationToken cancellationToken = default)
     {
         return await CallKnowledgeApiAsync("/api/knowledge/summary", text, cancellationToken);
     }
 
+    public async Task<Result<List<RelevantContext>>> GetRelevantContextAsync(string query, string tenantId, CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            var response = await _httpClient.PostAsJsonAsync("/api/knowledge/relevant", new { query, tenantId }, cancellationToken);
+            if (response.IsSuccessStatusCode)
+            {
+                var context = await response.Content.ReadFromJsonAsync<List<RelevantContext>>(cancellationToken: cancellationToken);
+                return context != null ? Result.Ok(context) : Result.Fail("Failed to deserialize relevant context.");
+            }
+
+            var errorBody = await response.Content.ReadAsStringAsync(cancellationToken);
+            return Result.Fail($"Server error ({response.StatusCode}): {errorBody}");
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error($"Network error: {ex.Message}").CausedBy(ex));
+        }
+    }
+    public async Task<Result<GroundednessResult>> VerifyGroundednessAsync(string answer, string context, string tenantId, CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            var response = await _httpClient.PostAsJsonAsync("/api/knowledge/verify-groundedness", new { answer, context, tenantId }, cancellationToken);
+            if (response.IsSuccessStatusCode)
+            {
+                var result = await response.Content.ReadFromJsonAsync<GroundednessResult>(cancellationToken: cancellationToken);
+                return result != null ? Result.Ok(result) : Result.Fail("Failed to deserialize groundedness result.");
+            }
+
+            var errorBody = await response.Content.ReadAsStringAsync(cancellationToken);
+            return Result.Fail($"Server error ({response.StatusCode}): {errorBody}");
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error($"Network error: {ex.Message}").CausedBy(ex));
+        }
+    }
+
     private async Task<Result<KnowledgePacket>> CallKnowledgeApiAsync(string endpoint, string text, CancellationToken cancellationToken)
     {
         try

src/NexusReader.Web.New/Components/App.razor

@@ -5,7 +5,6 @@
     <meta charset="utf-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <base href="/" />
-    <ResourcePreloader />
     <link rel="stylesheet" href="_content/NexusReader.UI.Shared/app.css" />
     <link rel="stylesheet" href="NexusReader.Web.styles.css" />
     <ImportMap />
@@ -14,9 +13,35 @@
 </head>
 
 <body>
+    <div id="app-preloader">
+        <div class="preloader-spinner"></div>
+        <div class="preloader-text">Nexus Reader</div>
+    </div>
+
     <NexusReader.UI.Shared.Routes @rendermode="InteractiveAuto" />
     <ReconnectModal />
     <script src="_framework/blazor.web.js"></script>
+    <script>
+        (function() {
+            function hidePreloader() {
+                const preloader = document.getElementById('app-preloader');
+                if (preloader) {
+                    preloader.classList.add('loaded');
+                    // Completely remove from DOM after transition for better accessibility
+                    setTimeout(() => preloader.style.display = 'none', 1000);
+                }
+            }
+
+            if (document.readyState === 'complete') {
+                hidePreloader();
+            } else {
+                window.addEventListener('load', hidePreloader);
+            }
+            
+            // Fallback: If for some reason 'load' doesn't fire (e.g. big assets), hide after 3s anyway
+            setTimeout(hidePreloader, 3000);
+        })();
+    </script>
 </body>
 
 

src/NexusReader.Web.New/Controllers/StripeWebhookController.cs

@@ -1,97 +0,0 @@
-using Microsoft.AspNetCore.Identity;
-using Microsoft.AspNetCore.Mvc;
-using NexusReader.Domain.Entities;
-using Stripe;
-
-namespace NexusReader.Web.New.Controllers;
-
-[Route("api/[controller]")]
-[ApiController]
-public class StripeWebhookController : ControllerBase
-{
-    private readonly UserManager<NexusUser> _userManager;
-    private readonly IConfiguration _configuration;
-    private readonly string _webhookSecret;
-
-    public StripeWebhookController(UserManager<NexusUser> userManager, IConfiguration configuration)
-    {
-        _userManager = userManager;
-        _configuration = configuration;
-        _webhookSecret = _configuration["Stripe:WebhookSecret"] ?? "";
-    }
-
-    [HttpPost]
-    public async Task<IActionResult> Index()
-    {
-        var json = await new StreamReader(HttpContext.Request.Body).ReadToEndAsync();
-
-        try
-        {
-            var stripeEvent = EventUtility.ConstructEvent(
-                json,
-                Request.Headers["Stripe-Signature"],
-                _webhookSecret
-            );
-
-            switch (stripeEvent.Type)
-            {
-                case EventTypes.CheckoutSessionCompleted:
-                    var session = stripeEvent.Data.Object as Stripe.Checkout.Session;
-                    await HandleSubscriptionSuccess(session?.CustomerEmail, session?.Metadata);
-                    break;
-
-                case EventTypes.CustomerSubscriptionUpdated:
-                    var subscription = stripeEvent.Data.Object as Stripe.Subscription;
-                    // Subscription update might not have email directly, would need to fetch customer
-                    // For now, assuming email is in metadata if we set it during checkout
-                    await HandleSubscriptionSuccess(subscription?.Metadata["CustomerEmail"], subscription?.Metadata);
-                    break;
-
-                case EventTypes.CustomerSubscriptionDeleted:
-                    var deletedSubscription = stripeEvent.Data.Object as Stripe.Subscription;
-                    await HandleSubscriptionCancellation(deletedSubscription?.Metadata["CustomerEmail"]);
-                    break;
-            }
-
-            return Ok();
-        }
-        catch (StripeException e)
-        {
-            return BadRequest(e.Message);
-        }
-    }
-
-    private async Task HandleSubscriptionSuccess(string? email, Dictionary<string, string>? metadata)
-    {
-        if (string.IsNullOrEmpty(email)) return;
-
-        var user = await _userManager.FindByEmailAsync(email);
-        if (user != null)
-        {
-            var plan = metadata != null && metadata.ContainsKey("Plan") ? metadata["Plan"] : "Pro";
-            
-            user.CurrentPlan = plan;
-            user.AITokenLimit = plan.ToLower() switch
-            {
-                "pro" => 50000,
-                "enterprise" => 500000,
-                _ => 10000 // default for unknown or free
-            };
-            
-            await _userManager.UpdateAsync(user);
-        }
-    }
-
-    private async Task HandleSubscriptionCancellation(string? email)
-    {
-        if (string.IsNullOrEmpty(email)) return;
-
-        var user = await _userManager.FindByEmailAsync(email);
-        if (user != null)
-        {
-            user.CurrentPlan = "Free";
-            user.AITokenLimit = 5000; // Free tier limit
-            await _userManager.UpdateAsync(user);
-        }
-    }
-}

src/NexusReader.Web.New/Program.cs

@@ -2,6 +2,7 @@ using NexusReader.Web.Components;
 using NexusReader.Application;
 using NexusReader.Infrastructure;
 using NexusReader.Application.Abstractions.Services;
+using NexusReader.Application.DTOs.User;
 using NexusReader.Web.Client.Services;
 using NexusReader.UI.Shared.Services;
 using NexusReader.Domain.Entities;
@@ -14,6 +15,7 @@ using NexusReader.Infrastructure.Identity;
 using Microsoft.AspNetCore.Authentication;
 using System.Security.Claims;
 using NexusReader.Infrastructure.Services;
+using Stripe;
 
 AppContext.SetSwitch("Npgsql.EnableLegacyTimestampBehavior", true);
 
@@ -24,14 +26,14 @@ builder.Services.AddRazorComponents()
     .AddInteractiveServerComponents()
     .AddInteractiveWebAssemblyComponents();
 
-builder.Services.AddControllers();
-
 // Enable detailed circuit errors for Server‑Side Blazor components
 builder.Services.AddServerSideBlazor()
     .AddCircuitOptions(options =>
     {
         options.DetailedErrors = true;
     });
+builder.Services.AddSignalR();
+builder.Services.AddHttpContextAccessor();
 
 builder.Services.AddScoped<IPlatformService, WebPlatformService>();
 builder.Services.AddScoped<INativeStorageService, NexusReader.UI.Shared.Services.WebStorageService>();
@@ -42,6 +44,7 @@ builder.Services.AddScoped<IReaderNavigationService, ReaderNavigationService>();
 builder.Services.AddScoped<IKnowledgeGraphService, KnowledgeGraphService>();
 builder.Services.AddScoped<IReaderInteractionService, ReaderInteractionService>();
 builder.Services.AddScoped<KnowledgeCoordinator>();
+builder.Services.AddScoped<ISyncService, SyncService>();
 
 builder.Services.AddHttpClient("NexusAPI", client => 
 {
@@ -49,7 +52,7 @@ builder.Services.AddHttpClient("NexusAPI", client =>
 });
 builder.Services.AddScoped(sp => sp.GetRequiredService<IHttpClientFactory>().CreateClient("NexusAPI"));
 
-builder.Services.AddScoped<IIdentityService, IdentityService>();
+builder.Services.AddScoped<IIdentityService, NexusReader.UI.Shared.Services.IdentityService>();
 builder.Services.AddScoped<NexusAuthenticationStateProvider>();
 builder.Services.AddScoped<AuthenticationStateProvider>(sp => sp.GetRequiredService<NexusAuthenticationStateProvider>());
 builder.Services.AddCascadingAuthenticationState();
@@ -57,16 +60,19 @@ builder.Services.AddCascadingAuthenticationState();
 builder.Services.AddApplication();
 builder.Services.AddInfrastructure(builder.Configuration);
 
+builder.Services.AddMediatR(cfg => cfg.RegisterServicesFromAssemblies(
+    NexusReader.Application.DependencyInjection.Assembly,
+    NexusReader.Infrastructure.DependencyInjection.Assembly
+));
+
 // Authorization Policies
 builder.Services.AddScoped<IAuthorizationHandler, TokenLimitHandler>();
-builder.Services.AddAuthorization(options =>
-{
-    options.AddPolicy("ProUser", policy => policy.RequireClaim("Plan", "Pro", "Enterprise"));
-    options.AddPolicy("HasAvailableTokens", policy => policy.AddRequirements(new TokenLimitRequirement()));
-});
+builder.Services.AddAuthorizationBuilder()
+    .AddPolicy("ProUser", policy => policy.RequireClaim("Plan", SubscriptionPlan.ProName, SubscriptionPlan.EnterpriseName))
+    .AddPolicy("HasAvailableTokens", policy => policy.AddRequirements(new TokenLimitRequirement()));
 
 // Billing & Stripe
-builder.Services.AddScoped<IBillingService, BillingService>();
+builder.Services.AddScoped<IBillingService, NexusReader.Infrastructure.Services.BillingService>();
 
 // Authentication
 builder.Services.AddAuthentication(options =>
@@ -81,6 +87,7 @@ builder.Services.AddAuthentication(options =>
     });
 
 builder.Services.AddIdentityApiEndpoints<NexusUser>()
+    .AddRoles<IdentityRole>()
     .AddEntityFrameworkStores<AppDbContext>();
 
 builder.Services.ConfigureApplicationCookie(options =>
@@ -113,11 +120,63 @@ builder.Services.Configure<IdentityOptions>(options =>
 
 var app = builder.Build();
 
-// Ensure Database is initialized
+// Startup Validation
 using (var scope = app.Services.CreateScope())
 {
-    var dbContext = scope.ServiceProvider.GetRequiredService<NexusReader.Infrastructure.Persistence.AppDbContext>();
-    await dbContext.Database.MigrateAsync();
+    var marker = scope.ServiceProvider.GetService<IInfrastructureMarker>();
+    if (marker == null)
+    {
+        throw new InvalidOperationException("CRITICAL: Infrastructure layer was not registered. Ensure AddInfrastructure() is called in Program.cs.");
+    }
+}
+
+// Ensure Database is initialized and seeded
+using (var scope = app.Services.CreateScope())
+{
+    var services = scope.ServiceProvider;
+    var logger = services.GetRequiredService<ILogger<Program>>();
+    var dbContext = services.GetRequiredService<NexusReader.Infrastructure.Persistence.AppDbContext>();
+    
+    int maxRetries = 5;
+    int delayMs = 2000;
+    
+    for (int i = 0; i < maxRetries; i++)
+    {
+        try
+        {
+            if (logger.IsEnabled(LogLevel.Information))
+            {
+                logger.LogInformation("Próba połączenia z bazą danych (próba {Attempt}/{MaxRetries})...", i + 1, maxRetries);
+            }
+
+            await dbContext.Database.MigrateAsync();
+            await DbInitializer.SeedAsync(services);
+
+            if (logger.IsEnabled(LogLevel.Information))
+            {
+                logger.LogInformation("Baza danych zainicjowana pomyślnie.");
+            }
+            break;
+        }
+        catch (Npgsql.NpgsqlException ex) when (i < maxRetries - 1)
+        {
+            if (logger.IsEnabled(LogLevel.Warning))
+            {
+                logger.LogWarning(ex, "Błąd połączenia z bazą danych. Ponowna próba za {Delay}ms...", delayMs);
+            }
+
+            await Task.Delay(delayMs);
+            delayMs *= 2; // Exponential backoff
+        }
+        catch (Exception ex)
+        {
+            if (logger.IsEnabled(LogLevel.Critical))
+            {
+                logger.LogCritical(ex, "Krytyczny błąd podczas inicjalizacji bazy danych.");
+            }
+            throw;
+        }
+    }
 }
 
 // Configure the HTTP request pipeline.
@@ -141,7 +200,7 @@ app.UseAntiforgery();
 app.UseAuthentication();
 app.UseAuthorization();
 app.MapStaticAssets();
-app.MapControllers();
+app.MapHub<NexusReader.Infrastructure.RealTime.SyncHub>("/synchub");
 
 // API endpoint for WASM client to fetch EPUB content
 app.MapGet("/api/epub/{index}", async (int index, IEpubService epubService) =>
@@ -149,40 +208,137 @@ app.MapGet("/api/epub/{index}", async (int index, IEpubService epubService) =>
     var result = await epubService.GetEpubContentAsync(index);
     if (result.IsSuccess) return Results.Ok(result.Value);
     
-    var errorMsg = result.Errors.FirstOrDefault()?.Message ?? "Unknown server error";
+    var errorMsg = result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error";
     return Results.BadRequest(errorMsg);
-});
+}).RequireAuthorization();
 
-app.MapPost("/api/knowledge", async (KnowledgeRequest request, IKnowledgeService knowledgeService) =>
+var knowledgeApi = app.MapGroup("/api/knowledge").RequireAuthorization("HasAvailableTokens");
+
+knowledgeApi.MapPost("/", async (KnowledgeRequest request, ClaimsPrincipal user, IKnowledgeService knowledgeService) =>
 {
-    var result = await knowledgeService.GetKnowledgeAsync(request.Text);
+    var tenantId = user.FindFirstValue("TenantId") ?? "global";
+    var result = await knowledgeService.GetKnowledgeAsync(request.Text, tenantId);
     if (result.IsSuccess) return Results.Ok(result.Value);
-    return Results.BadRequest(result.Errors.FirstOrDefault()?.Message ?? "Unknown server error");
+    return Results.BadRequest(result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error");
 });
 
-app.MapPost("/api/knowledge/graph", async (KnowledgeRequest request, IKnowledgeService knowledgeService) =>
+knowledgeApi.MapPost("/graph", async (KnowledgeRequest request, ClaimsPrincipal user, IKnowledgeService knowledgeService) =>
 {
-    var result = await knowledgeService.GetGraphDataAsync(request.Text);
+    var tenantId = user.FindFirstValue("TenantId") ?? "global";
+    var result = await knowledgeService.GetGraphDataAsync(request.Text, tenantId);
     if (result.IsSuccess) return Results.Ok(result.Value);
-    return Results.BadRequest(result.Errors.FirstOrDefault()?.Message ?? "Unknown server error");
+    return Results.BadRequest(result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error");
 });
 
-app.MapPost("/api/knowledge/summary", async (KnowledgeRequest request, IKnowledgeService knowledgeService) =>
+knowledgeApi.MapPost("/summary", async (KnowledgeRequest request, ClaimsPrincipal user, IKnowledgeService knowledgeService) =>
 {
-    var result = await knowledgeService.GetSummaryAndQuizAsync(request.Text);
+    var tenantId = user.FindFirstValue("TenantId") ?? "global";
+    var result = await knowledgeService.GetSummaryAndQuizAsync(request.Text, tenantId);
     if (result.IsSuccess) return Results.Ok(result.Value);
-    return Results.BadRequest(result.Errors.FirstOrDefault()?.Message ?? "Unknown server error");
+    return Results.BadRequest(result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error");
 });
 
-app.MapDelete("/api/knowledge", async (IKnowledgeService knowledgeService) =>
+knowledgeApi.MapPost("/verify-groundedness", async (GroundednessRequest request, ClaimsPrincipal user, IKnowledgeService knowledgeService) =>
+{
+    var tenantId = user.FindFirstValue("TenantId") ?? "global";
+    var result = await knowledgeService.VerifyGroundednessAsync(request.Answer, request.Context, tenantId);
+    if (result.IsSuccess) return Results.Ok(result.Value);
+    return Results.BadRequest(result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error");
+});
+
+knowledgeApi.MapDelete("/", async (IKnowledgeService knowledgeService) =>
 {
     var result = await knowledgeService.ClearCacheAsync();
     if (result.IsSuccess) return Results.Ok();
     
-    var errorMsg = result.Errors.FirstOrDefault()?.Message ?? "Unknown server error";
+    var errorMsg = result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error";
     return Results.BadRequest(errorMsg);
 });
 
+app.MapPost("/api/StripeWebhook", async (
+    HttpContext context, 
+    UserManager<NexusUser> userManager, 
+    IConfiguration configuration,
+    IDbContextFactory<AppDbContext> dbContextFactory) =>
+{
+    using var dbContext = await dbContextFactory.CreateDbContextAsync();
+    var json = await new StreamReader(context.Request.Body).ReadToEndAsync();
+    var webhookSecret = configuration["Stripe:WebhookSecret"] ?? "";
+
+    try
+    {
+        var stripeEvent = EventUtility.ConstructEvent(
+            json,
+            context.Request.Headers["Stripe-Signature"],
+            webhookSecret
+        );
+
+        switch (stripeEvent.Type)
+        {
+            case EventTypes.CheckoutSessionCompleted:
+                var session = stripeEvent.Data.Object as Stripe.Checkout.Session;
+                await HandleSubscriptionSuccess(session?.CustomerEmail, session?.Metadata, userManager, dbContext);
+                break;
+
+            case EventTypes.CustomerSubscriptionUpdated:
+                var subscription = stripeEvent.Data.Object as Stripe.Subscription;
+                await HandleSubscriptionSuccess(subscription?.Metadata["CustomerEmail"], subscription?.Metadata, userManager, dbContext);
+                break;
+
+            case EventTypes.CustomerSubscriptionDeleted:
+                var deletedSubscription = stripeEvent.Data.Object as Stripe.Subscription;
+                await HandleSubscriptionCancellation(deletedSubscription?.Metadata["CustomerEmail"], userManager, dbContext);
+                break;
+        }
+        return Results.Ok();
+    }
+    catch (StripeException e)
+    {
+        return Results.BadRequest(e.Message);
+    }
+});
+
+async Task HandleSubscriptionSuccess(
+    string? email, 
+    Dictionary<string, string>? metadata, 
+    UserManager<NexusUser> userManager,
+    AppDbContext dbContext)
+{
+    if (string.IsNullOrEmpty(email)) return;
+
+    var user = await userManager.FindByEmailAsync(email);
+    if (user != null)
+    {
+        var planName = metadata?.GetValueOrDefault("Plan") ?? SubscriptionPlan.ProName;
+        var plan = await dbContext.SubscriptionPlans.FirstOrDefaultAsync(p => p.PlanName == planName);
+        
+        if (plan != null)
+        {
+            user.SubscriptionPlanId = plan.Id;
+            user.AITokenLimit = plan.AITokenLimit;
+        }
+        
+        await userManager.UpdateAsync(user);
+    }
+}
+
+async Task HandleSubscriptionCancellation(
+    string? email, 
+    UserManager<NexusUser> userManager,
+    AppDbContext dbContext)
+{
+    if (string.IsNullOrEmpty(email)) return;
+
+    var user = await userManager.FindByEmailAsync(email);
+    if (user != null)
+    {
+        var freePlan = await dbContext.SubscriptionPlans.FindAsync(SubscriptionPlan.FreeId);
+        user.SubscriptionPlanId = SubscriptionPlan.FreeId;
+        user.AITokenLimit = freePlan?.AITokenLimit ?? 5000;
+        await userManager.UpdateAsync(user);
+    }
+}
+
 app.MapGroup("/identity").MapIdentityApi<NexusUser>();
 
 app.MapGet("/identity/login/google", (string? returnUrl) =>
@@ -226,36 +382,38 @@ app.MapGet("/identity/callback/google", async (
     return Results.Redirect("/account/login?error=ProvisioningFailed");
 });
 
-app.MapGet("/identity/profile", async (ClaimsPrincipal user, UserManager<NexusUser> userManager, AppDbContext dbContext) =>
+app.MapGet("/identity/profile", async (ClaimsPrincipal user, UserManager<NexusUser> userManager, IDbContextFactory<AppDbContext> dbContextFactory) =>
 {
     var userId = user.FindFirstValue(ClaimTypes.NameIdentifier);
     if (userId == null) return Results.Unauthorized();
 
-    var nexusUser = await dbContext.Users
-        .Include(u => u.Ebooks)
-        .Include(u => u.QuizResults)
-        .FirstOrDefaultAsync(u => u.Id == userId);
+    using var dbContext = await dbContextFactory.CreateDbContextAsync();
 
-    if (nexusUser == null) return Results.NotFound();
+    var profile = await dbContext.Users
+        .Where(u => u.Id == userId)
+        .Select(u => new UserProfileDto
+        {
+            Email = u.Email ?? string.Empty,
+            AITokensUsed = u.AITokensUsed,
+            Plan = u.SubscriptionPlan != null ? new SubscriptionPlanDto
+            {
+                Id = u.SubscriptionPlan.Id,
+                Name = u.SubscriptionPlan.PlanName,
+                AITokenLimit = u.SubscriptionPlan.AITokenLimit,
+                MonthlyPrice = u.SubscriptionPlan.MonthlyPrice
+            } : new SubscriptionPlanDto(),
+            AverageQuizScore = u.QuizResults.Any() ? (int)u.QuizResults.Average(q => q.Percentage) : 0,
+            LastReadBook = u.Ebooks.OrderByDescending(e => e.LastReadDate).Select(e => new LastReadBookDto
+            {
+                Id = e.Id,
+                Title = e.Title
+            }).FirstOrDefault()
+        })
+        .FirstOrDefaultAsync();
 
-    var avgScore = nexusUser.QuizResults.Any() 
-        ? (int)nexusUser.QuizResults.Average(q => q.Percentage) 
-        : 0;
-    
-    var lastReadBook = nexusUser.Ebooks
-        .OrderByDescending(e => e.LastReadDate)
-        .FirstOrDefault()?.Title ?? "None";
+    if (profile == null) return Results.NotFound();
 
-    return Results.Ok(new
-    {
-        nexusUser.Email,
-        nexusUser.AITokenLimit,
-        nexusUser.AITokensUsed,
-        nexusUser.CurrentPlan,
-        nexusUser.TenantId,
-        AverageQuizScore = avgScore,
-        LastReadBookTitle = lastReadBook
-    });
+    return Results.Ok(profile);
 }).RequireAuthorization();
 
 app.MapRazorComponents<App>()
@@ -266,3 +424,4 @@ app.MapRazorComponents<App>()
 app.Run();
 
 public record KnowledgeRequest(string Text);
+public record GroundednessRequest(string Answer, string Context);

src/NexusReader.Web.New/appsettings.json

@@ -1,7 +1,10 @@
 {
   "Stripe": {
     "ApiKey": "sk_test_placeholder",
-    "WebhookSecret": "whsec_placeholder"
+    "WebhookSecret": "whsec_placeholder",
+    "ProProductId": "prod_Pro123",
+    "BasicProductId": "prod_Basic456",
+    "FreeProductId": "prod_Free789"
   },
   "Logging": {
     "LogLevel": {
@@ -24,7 +27,9 @@
     "Google": {
       "ApiKey": "PLACEHOLDER",
       "Model": "gemini-2.5-flash-lite",
+      "MaxInputTokens": 15000,
       "MaxOutputTokens": 8192
     }
-  }
-}
+  },
+  "ApiBaseUrl": "http://localhost:5000"
+}