feat: append-only audit trail for all mutations (P0)

- Database: kanzlai.audit_log table with RLS, append-only policies
  (no UPDATE/DELETE), indexes for entity, user, and time queries
- Backend: AuditService.Log() with context-based tenant/user/IP/UA
  extraction, wired into all 7 services (case, deadline, appointment,
  document, note, party, tenant)
- API: GET /api/audit-log with entity_type, entity_id, user_id,
  from/to date, and pagination filters
- Frontend: Protokoll tab on case detail page with chronological
  audit entries, diff preview, and pagination

Required by § 50 BRAO and DSGVO Art. 5(2).

AUDIT.md

@@ -0,0 +1,482 @@
+# KanzlAI-mGMT MVP Audit
+
+**Date:** 2026-03-28
+**Auditor:** athena (consultant)
+**Scope:** Full-stack audit of KanzlAI-mGMT — Go backend, Next.js frontend, Supabase database, deployment, security, UX, competitive positioning.
+**Codebase:** ~16,500 lines across ~60 source files, built 2026-03-25 in a single session with parallel workers.
+
+---
+
+## Executive Summary
+
+KanzlAI-mGMT is an impressive MVP built in ~2 hours. It covers the core Kanzleimanagement primitives: cases, deadlines, appointments, parties, documents, notes, dashboard, CalDAV sync, and AI-powered deadline extraction. The architecture is sound — clean separation between Go API and Next.js frontend, proper multi-tenant design with Supabase Auth, parameterized SQL throughout.
+
+However, the speed of construction shows. There are **critical security gaps** that must be fixed before any external user touches this. The frontend has good bones but lacks the polish and completeness a lawyer would expect. And the feature gap vs. established competitors (RA-MICRO, ADVOWARE, AnNoText, Actaport) is enormous — particularly around beA integration, billing/RVG, and document generation, which are table-stakes for German law firms.
+
+**Bottom line:** Fix the security issues, add error recovery and multi-tenant auth verification, then decide whether to pursue the Kanzleimanagement market (massive feature gap) or pivot back to the UPC niche (where you had a genuine competitive advantage).
+
+---
+
+## 1. Critical Issues (Fix Immediately)
+
+### 1.1 Tenant Isolation Bypass in TenantResolver
+**File:** `backend/internal/auth/tenant_resolver.go:37-42`
+
+When the `X-Tenant-ID` header is provided, the TenantResolver parses it and sets it in context **without verifying the user has access to that tenant**. Any authenticated user can access any tenant's data by setting this header.
+
+```go
+if header := r.Header.Get("X-Tenant-ID"); header != "" {
+    parsed, err := uuid.Parse(header)
+    // ... sets tenantID = parsed — NO ACCESS CHECK
+}
+```
+
+Compare with `helpers.go:32-44` where `resolveTenant()` correctly verifies access via `user_tenants` — but this function is unused in the middleware path. The TenantResolver middleware is what actually runs for all scoped routes.
+
+**Impact:** Complete tenant data isolation breach. User A can read/modify/delete User B's cases, deadlines, appointments, documents.
+
+**Fix:** Add `user_tenants` lookup in TenantResolver when X-Tenant-ID is provided, same as `resolveTenant()` does.
+
+### 1.2 Duplicate Tenant Resolution Logic
+**Files:** `backend/internal/auth/tenant_resolver.go` and `backend/internal/handlers/helpers.go:25-57`
+
+Two independent implementations of tenant resolution exist. The middleware (`TenantResolver`) is used for the scoped routes. The handler-level `resolveTenant()` function exists in helpers.go. The auth middleware in `middleware.go:39-47` also resolves a tenant into context. This triple-resolution creates confusion and the security bug above.
+
+**Fix:** Consolidate to a single path. Remove the handler-level `resolveTenant()` and the auth middleware's tenant resolution. Let TenantResolver be the single source of truth, but make it verify access.
+
+### 1.3 CalDAV Credentials Stored in Plaintext
+**File:** `backend/internal/services/caldav_service.go:29-35`
+
+CalDAV username and password are stored as plain JSON in the `tenants.settings` column:
+```go
+type CalDAVConfig struct {
+    URL      string `json:"url"`
+    Username string `json:"username"`
+    Password string `json:"password"`
+    ...
+}
+```
+
+Combined with the tenant isolation bypass above, any authenticated user can read any tenant's CalDAV credentials.
+
+**Fix:** Encrypt CalDAV credentials at rest (e.g., using `pgcrypto` or application-level encryption). At minimum, never return the password in API responses.
+
+### 1.4 No CORS Configuration
+**File:** `backend/internal/router/router.go`, `backend/cmd/server/main.go`
+
+There is zero CORS handling anywhere in the backend. The frontend uses Next.js rewrites to proxy `/api/` to the backend, which works in production. But:
+- If anyone accesses the backend directly (different origin), there's no CORS protection.
+- No `X-Frame-Options`, `X-Content-Type-Options`, or other security headers are set.
+
+**Fix:** Add CORS middleware restricting to the frontend origin. Add standard security headers.
+
+### 1.5 Internal Error Messages Leaked to Clients
+**Files:** Multiple handlers (e.g., `cases.go:44`, `cases.go:73`, `appointments.go`)
+
+```go
+writeError(w, http.StatusInternalServerError, err.Error())
+```
+
+Internal error messages (including SQL errors, connection errors, etc.) are sent directly to the client. This leaks implementation details.
+
+**Fix:** Log the full error server-side, return a generic message to the client.
+
+### 1.6 Race Condition in HolidayService Cache
+**File:** `backend/internal/services/holidays.go`
+
+The `HolidayService` uses a `map[int][]Holiday` cache without any mutex protection. Concurrent requests (e.g., multiple deadline calculations) will cause a data race. The Go race detector would flag this.
+
+**Fix:** Add `sync.RWMutex` to HolidayService.
+
+### 1.7 Rate Limiter Trivially Bypassable
+**File:** `backend/internal/middleware/ratelimit.go:78-79`
+
+```go
+ip := r.Header.Get("X-Forwarded-For")
+if ip == "" { ip = r.RemoteAddr }
+```
+
+Rate limiting keys off `X-Forwarded-For`, which any client can spoof. An attacker can bypass AI endpoint rate limits by rotating this header.
+
+**Fix:** Only trust `X-Forwarded-For` from configured reverse proxy IPs, or use `r.RemoteAddr` exclusively behind a trusted proxy.
+
+---
+
+## 2. Important Gaps (Fix Before Showing to Anyone)
+
+### 2.1 No Input Validation Beyond "Required Fields"
+**Files:** All handlers
+
+Input validation is minimal — typically just checking if required fields are empty:
+```go
+if input.CaseNumber == "" || input.Title == "" {
+    writeError(w, http.StatusBadRequest, "case_number and title are required")
+}
+```
+
+Missing:
+- Length limits on text fields (could store megabytes in a title field)
+- Status value validation (accepts any string for status fields)
+- Date format validation
+- Case type validation against allowed values
+- SQL-safe string validation (although parameterized queries protect against injection)
+
+### 2.2 No Pagination Defaults on Most List Endpoints
+**File:** `backend/internal/services/case_service.go:57-63`
+
+`CaseService.List` has sane defaults (limit=20, max=100). But other list endpoints (`appointments`, `deadlines`, `notes`, `parties`, `case_events`) have no pagination at all — they return all records for a tenant/case. As data grows, these become performance problems.
+
+### 2.3 Dashboard Page is Entirely Client-Side
+**File:** `frontend/src/app/(app)/dashboard/page.tsx`
+
+The entire dashboard is a `"use client"` component that fetches data via API. This means:
+- No SSR benefit — the page is blank until JS loads and API responds
+- SEO doesn't matter for a SaaS app, but initial load time does
+- The skeleton is nice but adds 200-400ms of perceived latency
+
+For an internal tool this is acceptable, but for a commercial product it should use server components for the initial render.
+
+### 2.4 Frontend Auth Uses `getSession()` Instead of `getUser()`
+**File:** `frontend/src/lib/api.ts:10-12`
+
+```typescript
+const { data: { session } } = await supabase.auth.getSession();
+```
+
+`getSession()` reads from local storage without server verification. If a session is expired or revoked server-side, the frontend will still try to use it until the backend rejects it. The middleware correctly uses `getUser()` (which validates server-side), but the API client does not.
+
+### 2.5 Missing Error Recovery in Frontend
+Throughout the frontend, API errors are handled with basic error states, but there's no:
+- Retry logic for transient failures
+- Token refresh on 401 responses
+- Optimistic UI rollback on mutation failures
+- Offline detection
+
+### 2.6 Missing `Content-Disposition` Header Sanitization
+**File:** `backend/internal/handlers/documents.go:133`
+
+```go
+w.Header().Set("Content-Disposition", fmt.Sprintf(`attachment; filename="%s"`, title))
+```
+
+The `title` (which comes from user input) is inserted directly into the header. A filename containing `"` or newlines could be used for response header injection.
+
+**Fix:** Sanitize the filename — strip or encode special characters.
+
+### 2.7 No Graceful Shutdown
+**File:** `backend/cmd/server/main.go:42`
+
+```go
+http.ListenAndServe(":"+cfg.Port, handler)
+```
+
+No signal handling or graceful shutdown. When the process receives SIGTERM (e.g., during deployment), in-flight requests are dropped, CalDAV sync operations may be interrupted mid-write, and database connections are not cleanly closed.
+
+### 2.8 Database Connection Pool — search_path is Session-Level
+**File:** `backend/internal/db/connection.go:17`
+
+```go
+db.Exec("SET search_path TO kanzlai, public")
+```
+
+`SET search_path` is session-level in PostgreSQL. With connection pooling (`MaxOpenConns: 25`), this SET runs once on the initial connection. If a connection is recycled or a new one opened from the pool, it may not have the kanzlai search_path. This could cause queries to silently hit the wrong schema.
+
+**Fix:** Use `SET LOCAL search_path` in a transaction, or set it at the database/role level, or qualify all table references with the schema name.
+
+### 2.9 go.sum Missing from Dockerfile
+**File:** `backend/Dockerfile:4`
+
+```dockerfile
+COPY go.mod ./
+RUN go mod download
+```
+
+Only `go.mod` is copied, not `go.sum`. This means the build isn't reproducible and doesn't verify checksums. Should be `COPY go.mod go.sum ./`.
+
+### 2.10 German Umlaut Typos Throughout Frontend
+**Files:** Multiple frontend components
+
+German strings use ASCII approximations instead of proper characters:
+- `login/page.tsx`: "Zurueck" instead of "Zurück"
+- `cases/[id]/layout.tsx`: "Anhaengig" instead of "Anhängig"
+- `cases/[id]/fristen/page.tsx`: "Ueberfaellig" instead of "Überfällig"
+- `termine/page.tsx`: "Uberblick" instead of "Überblick"
+
+A German lawyer would notice this immediately. It signals "this was built by a machine, not tested by a human."
+
+### 2.11 Silent Error Swallowing in Event Creation
+**File:** `backend/internal/services/case_service.go:260-266`
+
+```go
+func createEvent(ctx context.Context, db *sqlx.DB, ...) {
+    db.ExecContext(ctx, /* ... */)  // Error completely ignored
+}
+```
+
+Case events (audit trail) silently fail to create. The calling functions don't check the return. This means you could have cases with no events and no way to know why.
+
+### 2.12 Missing Error Boundaries in Frontend
+No React error boundaries are implemented. If any component throws, the entire page crashes with a white screen. For a law firm tool where data integrity matters, this is unacceptable.
+
+### 2.13 No RLS Policies Defined at Database Level
+Multi-tenant isolation relies entirely on `WHERE tenant_id = $X` clauses in Go code. If any query forgets this clause, data leaks across tenants. There are no PostgreSQL RLS policies as a safety net.
+
+**Fix:** Enable RLS on all tenant-scoped tables and create policies tied to `auth.uid()` via `user_tenants`.
+
+---
+
+## 3. Architecture Assessment
+
+### 3.1 What's Good
+
+- **Clean monorepo structure** — `backend/` and `frontend/` are clearly separated. Each has its own Dockerfile. The Makefile provides unified commands.
+- **Go backend is well-organized** — `cmd/server/`, `internal/{auth,config,db,handlers,middleware,models,router,services}` follows Go best practices.
+- **Handler/Service separation** — handlers do HTTP concerns (parse request, write response), services do business logic. This is correct.
+- **Parameterized SQL everywhere** — no string concatenation in queries. All user input goes through `$N` placeholders.
+- **Multi-tenant design** — `tenant_id` on every row, context-based tenant resolution, RLS at the database level.
+- **Smart use of Go 1.22+ routing** — method+path patterns like `GET /api/cases/{id}` eliminate the need for a third-party router.
+- **CalDAV sync is genuinely impressive** — bidirectional sync with conflict resolution, etag tracking, background polling per-tenant. This is a differentiator.
+- **Deadline calculator** — ported from youpc.org with holiday awareness. Legally important and hard to build.
+- **Frontend routing structure** — German URL paths (`/fristen`, `/termine`, `/einstellungen`), nested case detail routes with layout.tsx for shared chrome. Proper use of App Router patterns.
+
+### 3.2 Structural Concerns
+
+- **No database migrations** — the schema was apparently created via SQL scripts run manually. There's a `seed/demo_data.sql` but no migration system. For a production system, this is unsustainable.
+- **No CI/CD pipeline** — no `.github/workflows/`, `.gitea/`, or any CI configuration. Tests run locally but not automatically.
+- **No API versioning** — all routes are at `/api/`. Adding breaking changes will break clients.
+- **Services take raw `*sqlx.DB`** — no transaction support across service boundaries. Creating a case + event is not atomic (if the event insert fails, the case still exists).
+- **Models are just struct definitions** — no validation methods, no constructor functions. Validation is scattered across handlers.
+
+### 3.3 Data Model
+
+Based on the seed data and model files, the schema is reasonable:
+- `tenants`, `user_tenants` (multi-tenancy)
+- `cases`, `parties` (case management)
+- `deadlines`, `appointments` (time management)
+- `documents`, `case_events`, `notes` (supporting data)
+- `proceeding_types`, `deadline_rules`, `holidays` (reference data)
+
+**Missing indexes likely needed:**
+- `deadlines(tenant_id, status, due_date)` — for dashboard queries
+- `appointments(tenant_id, start_at)` — for calendar queries
+- `case_events(case_id, created_at)` — for event feeds
+- `cases(tenant_id, status)` — for filtered lists
+
+**Missing constraints:**
+- No CHECK constraint on status values (cases, deadlines, appointments)
+- No UNIQUE constraint on `case_number` per tenant
+- No foreign key from `notes` to the parent entity (if polymorphic)
+
+---
+
+## 4. Security Assessment
+
+### 4.1 Authentication
+- **JWT validation is correct** — algorithm check (HMAC only), expiry check, sub claim extraction. Using `golang-jwt/v5`.
+- **Supabase Auth on frontend** — proper cookie-based session with server-side verification in middleware.
+- **No refresh token rotation** — the API client uses `getSession()` which may serve stale tokens.
+
+### 4.2 Authorization
+- **Critical: Tenant isolation bypass** (see 1.1)
+- **No role-based access control** — `user_tenants` has a `role` column but it's never checked. Any member can do anything.
+- **No resource-level permissions** — any user in a tenant can delete any case, document, etc.
+
+### 4.3 Input Validation
+- **SQL injection: Protected** — all queries use parameterized placeholders.
+- **XSS: Partially protected** — React auto-escapes, but the API returns raw strings that could contain HTML. The `Content-Disposition` header is vulnerable (see 2.6).
+- **File upload: Partially protected** — `MaxBytesReader` limits to 50MB, but no file type validation (could upload .exe, .html with scripts, etc.).
+- **Rate limiting: AI endpoints only** — the rest of the API has no rate limiting. Login/register go through Supabase (which has its own limits), but all CRUD endpoints are unlimited.
+
+### 4.4 Secrets
+- **No hardcoded secrets** — all via environment variables. Good.
+- **CalDAV credentials in plaintext** — see 1.3.
+- **Supabase service key in backend** — necessary for storage, but this key has full DB access. Should be scoped.
+
+---
+
+## 5. Testing Assessment
+
+### 5.1 Backend Tests (15 files)
+- **Integration test** — sets up real DB connection, creates JWT, tests full HTTP flow. Excellent pattern but requires DATABASE_URL (skips otherwise).
+- **Handler tests** — mock-based unit tests for most handlers. Test JSON parsing, error responses, basic happy paths.
+- **Service tests** — deadline calculator has solid date arithmetic tests. Holiday service tested. CalDAV service tested with mocks. AI service tested with mocked HTTP.
+- **Middleware tests** — rate limiter tested.
+- **Auth tests** — tenant resolver tested.
+
+### 5.2 Frontend Tests (4 files)
+- `api.test.ts` — tests the API client
+- `DeadlineTrafficLights.test.tsx` — component test
+- `CaseOverviewGrid.test.tsx` — component test
+- `LoginPage.test.tsx` — auth page test
+
+### 5.3 What's Missing
+- **No E2E tests** — no Playwright/Cypress. Critical for a law firm app where correctness matters.
+- **No contract tests** — frontend and backend are tested independently. A schema change could break the frontend without any test catching it.
+- **Deadline calculation edge cases** — needs tests for year boundaries, leap years, holidays falling on weekends, multiple consecutive holidays.
+- **Multi-tenant security tests** — no test verifying that User A can't access Tenant B's data. This is the most important test to add.
+- **Frontend test coverage is thin** — 4 tests for ~30 components. The dashboard, all forms, navigation, error states are untested.
+- **No load testing** — unknown how the system behaves under concurrent users.
+
+---
+
+## 6. UX Assessment
+
+### 6.1 What Works
+- **Dashboard is strong** — traffic light deadline indicators, upcoming timeline, case overview, quick actions. A lawyer can see what matters at a glance.
+- **German localization** — UI is in German with proper legal terminology (Akten, Fristen, Termine, Parteien).
+- **Mobile responsive** — sidebar collapses to hamburger menu, layout uses responsive grids.
+- **Loading states** — skeleton screens on dashboard, not just spinners.
+- **Breadcrumbs** — navigation trail on all pages.
+- **Deadline calculator** — unique feature that provides real value for UPC litigation.
+
+### 6.2 What a Lawyer Would Stumble On
+1. **No onboarding flow** — after registration, user has no tenant, no cases. The app shows empty states but doesn't guide the user to create a tenant or import data.
+2. **No search** — there's no global search. A lawyer with 100+ cases needs to find things fast.
+3. **No keyboard shortcuts** — power users (lawyers are keyboard-heavy) have no shortcuts.
+4. **Sidebar mixes languages** — "Akten" (German) vs "AI Analyse" (English). Should be consistent.
+5. **No notifications** — overdue deadlines don't trigger any alert beyond the dashboard color. No email alerts, no push notifications.
+6. **No print view** — lawyers need to print deadline lists, case summaries. No print stylesheet.
+7. **No bulk operations** — can't mark multiple deadlines as complete, can't bulk-assign parties.
+8. **Document upload has no preview** — uploaded PDFs can't be viewed inline.
+9. **AI features require manual trigger** — AI summary and deadline extraction are manual. Should auto-trigger on document upload.
+10. **No activity log per user** — no audit trail of who changed what. Critical for law firm compliance.
+
+---
+
+## 7. Deployment Assessment
+
+### 7.1 Docker Setup
+- **Multi-stage builds** — both Dockerfiles use builder pattern. Good.
+- **Backend is minimal** — Alpine + static binary + ca-certificates. ~15MB image.
+- **Frontend** — Bun for deps/build, Node for runtime (standalone output). Reasonable.
+- **Missing:** go.sum not copied in backend Dockerfile (see 2.9).
+- **Missing:** No docker-compose.yml for local development.
+- **Missing:** No health check in Dockerfile (`HEALTHCHECK` instruction).
+
+### 7.2 Environment Handling
+- **Config validates required vars** — `DATABASE_URL` and `SUPABASE_JWT_SECRET` are checked at startup.
+- **Supabase URL/keys not validated** — if missing, features silently fail or crash at runtime.
+- **No .env.example** — new developers don't know what env vars are needed.
+
+### 7.3 Reliability
+- **No graceful shutdown** (see 2.7)
+- **No readiness/liveness probes** — `/health` exists but only checks DB connectivity. No readiness distinction.
+- **CalDAV sync runs in-process** — if the sync goroutine panics, it takes down the API server.
+- **No structured error recovery** — panics in handlers will crash the process (no recovery middleware).
+
+---
+
+## 8. Competitive Analysis
+
+### 8.1 The Market
+
+German Kanzleisoftware is a mature, crowded market:
+
+| Tool | Type | Price | Key Strength |
+|------|------|-------|-------------|
+| **RA-MICRO** | Desktop + Cloud | ~100-200 EUR/user/mo | Market leader, 30+ years, full beA integration |
+| **ADVOWARE** | Desktop + Cloud | from 20 EUR/mo | Budget-friendly, strong for small firms |
+| **AnNoText** (Wolters Kluwer) | Desktop + Cloud | Custom pricing | Enterprise, AI document analysis, DictNow |
+| **Actaport** | Cloud-native | from 79.80 EUR/mo | Modern UI, Mandantenportal, integrated Office |
+| **Haufe Advolux** | Cloud | Custom | User-friendly, full-featured |
+| **Renostar Legal Cloud** | Cloud | Custom | Browser-based, no installation |
+
+### 8.2 Table-Stakes Features KanzlAI is Missing
+
+These are **mandatory** for any German Kanzleisoftware to be taken seriously:
+
+1. **beA Integration** — since 2022, German lawyers must use the electronic court mailbox (besonderes elektronisches Anwaltspostfach). No Kanzleisoftware sells without it. This is a **massive** implementation effort (KSW-Schnittstelle from BRAK).
+
+2. **RVG Billing (Gebührenrechner)** — automated fee calculation per RVG (Rechtsanwaltsvergütungsgesetz). Every competitor has this built-in. Without it, lawyers can't bill clients.
+
+3. **Document Generation** — templates for Schriftsätze, Klageschriften, Mahnbescheide with auto-populated case data. Usually integrated with Word.
+
+4. **Accounting (FiBu)** — client trust accounts (Fremdgeld), DATEV export, tax-relevant bookkeeping. Legal requirement.
+
+5. **Conflict Check (Kollisionsprüfung)** — check if the firm has a conflict of interest before taking a case. Legally required (§ 43a BRAO).
+
+6. **Dictation System** — voice-to-text for lawyers. RA-MICRO has DictaNet, AnNoText has DictNow.
+
+### 8.3 Where KanzlAI Could Differentiate
+
+Despite the feature gap, KanzlAI has some advantages:
+
+1. **AI-native** — competitors are bolting AI onto 20-year-old software. KanzlAI has Claude API integration from day one. The deadline extraction from PDFs is genuinely useful.
+2. **UPC specialization** — the deadline calculator with UPC Rules of Procedure knowledge is unique. No competitor has deep UPC litigation support.
+3. **CalDAV sync** — bidirectional sync with external calendars is not common in German Kanzleisoftware.
+4. **Modern tech stack** — React + Go + Supabase vs. the .NET/Java/Desktop world of RA-MICRO et al.
+5. **Multi-tenant from day 1** — designed for SaaS, not converted from desktop software.
+
+### 8.4 Strategic Recommendation
+
+**Don't compete head-on with RA-MICRO.** The feature gap is 10+ person-years of work. Instead:
+
+**Option A: UPC Niche Tool** — Pivot back to UPC patent litigation. Build the best deadline calculator, case tracker, and AI-powered brief analysis tool for UPC practitioners. There are ~1000 UPC practitioners in Europe who need specialized tooling that RA-MICRO doesn't provide. Charge 200-500 EUR/mo.
+
+**Option B: AI-First Legal Assistant** — Don't call it "Kanzleimanagement." Position as an AI assistant that reads court documents, extracts deadlines, and syncs to the lawyer's existing Kanzleisoftware via CalDAV/iCal. This sidesteps the feature gap entirely.
+
+**Option C: Full Kanzleisoftware** — If you pursue this, beA integration is the first priority, then RVG billing. Without these two, no German lawyer will switch.
+
+---
+
+## 9. Strengths (What's Good, Keep Doing It)
+
+1. **Architecture is solid** — the Go + Next.js + Supabase stack is well-chosen. Clean separation of concerns.
+2. **SQL is safe** — parameterized queries throughout. No injection vectors.
+3. **Multi-tenant design** — tenant_id scoping with RLS is the right approach.
+4. **CalDAV implementation** — genuinely impressive for an MVP. Bidirectional sync with conflict resolution.
+5. **Deadline calculator** — ported from youpc.org with holiday awareness. Real domain value.
+6. **AI integration** — Claude API with tool use for structured extraction. Clean implementation.
+7. **Dashboard UX** — traffic lights, timeline, quick actions. Lawyers will get this immediately.
+8. **German-first** — proper legal terminology, German date formats, localized UI.
+9. **Test foundation** — 15 backend test files with integration tests. Good starting point.
+10. **Docker builds are lean** — multi-stage, Alpine-based, standalone Next.js output.
+
+---
+
+## 10. Priority Roadmap
+
+### P0 — This Week
+- [ ] Fix tenant isolation bypass in TenantResolver (1.1)
+- [ ] Consolidate tenant resolution logic (1.2)
+- [ ] Encrypt CalDAV credentials at rest (1.3)
+- [ ] Add CORS middleware + security headers (1.4)
+- [ ] Stop leaking internal errors to clients (1.5)
+- [ ] Add mutex to HolidayService cache (1.6)
+- [ ] Fix rate limiter X-Forwarded-For bypass (1.7)
+- [ ] Fix Dockerfile go.sum copy (2.9)
+
+### P1 — Before Demo/Beta
+- [ ] Add input validation (length limits, allowed values) (2.1)
+- [ ] Add pagination to all list endpoints (2.2)
+- [ ] Fix `search_path` connection pool issue (2.8)
+- [ ] Add graceful shutdown with signal handling (2.7)
+- [ ] Sanitize Content-Disposition filename (2.6)
+- [ ] Fix German umlaut typos throughout frontend (2.10)
+- [ ] Handle createEvent errors instead of swallowing (2.11)
+- [ ] Add React error boundaries (2.12)
+- [ ] Implement RLS policies on all tenant-scoped tables (2.13)
+- [ ] Add multi-tenant security tests
+- [ ] Add database migrations system
+- [ ] Add `.env.example` file
+- [ ] Add onboarding flow for new users
+
+### P2 — Next Iteration
+- [ ] Role-based access control (admin/member/readonly)
+- [ ] Global search
+- [ ] Email notifications for overdue deadlines
+- [ ] Audit trail / activity log per user
+- [ ] Auto-trigger AI extraction on document upload
+- [ ] Print-friendly views
+- [ ] E2E tests with Playwright
+- [ ] CI/CD pipeline
+
+### P3 — Strategic
+- [ ] Decide market positioning (UPC niche vs. AI assistant vs. full Kanzleisoftware)
+- [ ] If Kanzleisoftware: begin beA integration research
+- [ ] If Kanzleisoftware: RVG Gebührenrechner
+- [ ] If UPC niche: integrate lex-research case law database
+
+---
+
+*This audit was conducted by reading every source file in the repository, running all tests, analyzing the database schema via seed data, and comparing against established German Kanzleisoftware competitors.*

backend/internal/auth/context.go

@@ -9,8 +9,10 @@ import (
 type contextKey string
 
 const (
-	userIDKey   contextKey = "user_id"
+	userIDKey    contextKey = "user_id"
-	tenantIDKey contextKey = "tenant_id"
+	tenantIDKey  contextKey = "tenant_id"
+	ipKey        contextKey = "ip_address"
+	userAgentKey contextKey = "user_agent"
 )
 
 func ContextWithUserID(ctx context.Context, userID uuid.UUID) context.Context {
@@ -30,3 +32,23 @@ func TenantFromContext(ctx context.Context) (uuid.UUID, bool) {
 	id, ok := ctx.Value(tenantIDKey).(uuid.UUID)
 	return id, ok
 }
+
+func ContextWithRequestInfo(ctx context.Context, ip, userAgent string) context.Context {
+	ctx = context.WithValue(ctx, ipKey, ip)
+	ctx = context.WithValue(ctx, userAgentKey, userAgent)
+	return ctx
+}
+
+func IPFromContext(ctx context.Context) *string {
+	if v, ok := ctx.Value(ipKey).(string); ok && v != "" {
+		return &v
+	}
+	return nil
+}
+
+func UserAgentFromContext(ctx context.Context) *string {
+	if v, ok := ctx.Value(userAgentKey).(string); ok && v != "" {
+		return &v
+	}
+	return nil
+}

backend/internal/auth/middleware.go

@@ -46,6 +46,13 @@ func (m *Middleware) RequireAuth(next http.Handler) http.Handler {
 		}
 		ctx = ContextWithTenantID(ctx, tenantID)
 
+		// Capture IP and user-agent for audit logging
+		ip := r.Header.Get("X-Forwarded-For")
+		if ip == "" {
+			ip = r.RemoteAddr
+		}
+		ctx = ContextWithRequestInfo(ctx, ip, r.UserAgent())
+
 		next.ServeHTTP(w, r.WithContext(ctx))
 	})
 }

backend/internal/handlers/audit_log.go

@@ -0,0 +1,63 @@
+package handlers
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/google/uuid"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
+)
+
+type AuditLogHandler struct {
+	svc *services.AuditService
+}
+
+func NewAuditLogHandler(svc *services.AuditService) *AuditLogHandler {
+	return &AuditLogHandler{svc: svc}
+}
+
+func (h *AuditLogHandler) List(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+
+	q := r.URL.Query()
+	page, _ := strconv.Atoi(q.Get("page"))
+	limit, _ := strconv.Atoi(q.Get("limit"))
+
+	filter := services.AuditFilter{
+		EntityType: q.Get("entity_type"),
+		From:       q.Get("from"),
+		To:         q.Get("to"),
+		Page:       page,
+		Limit:      limit,
+	}
+
+	if idStr := q.Get("entity_id"); idStr != "" {
+		if id, err := uuid.Parse(idStr); err == nil {
+			filter.EntityID = &id
+		}
+	}
+	if idStr := q.Get("user_id"); idStr != "" {
+		if id, err := uuid.Parse(idStr); err == nil {
+			filter.UserID = &id
+		}
+	}
+
+	entries, total, err := h.svc.List(r.Context(), tenantID, filter)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to fetch audit log")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]any{
+		"entries": entries,
+		"total":   total,
+		"page":    filter.Page,
+		"limit":   filter.Limit,
+	})
+}

backend/internal/handlers/deadlines.go

@@ -113,7 +113,7 @@ func (h *DeadlineHandlers) Create(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	deadline, err := h.deadlines.Create(tenantID, input)
+	deadline, err := h.deadlines.Create(r.Context(), tenantID, input)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "failed to create deadline")
 		return
@@ -142,7 +142,7 @@ func (h *DeadlineHandlers) Update(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	deadline, err := h.deadlines.Update(tenantID, deadlineID, input)
+	deadline, err := h.deadlines.Update(r.Context(), tenantID, deadlineID, input)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "failed to update deadline")
 		return
@@ -169,7 +169,7 @@ func (h *DeadlineHandlers) Complete(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	deadline, err := h.deadlines.Complete(tenantID, deadlineID)
+	deadline, err := h.deadlines.Complete(r.Context(), tenantID, deadlineID)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "failed to complete deadline")
 		return
@@ -196,7 +196,7 @@ func (h *DeadlineHandlers) Delete(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	err = h.deadlines.Delete(tenantID, deadlineID)
+	err = h.deadlines.Delete(r.Context(), tenantID, deadlineID)
 	if err != nil {
 		writeError(w, http.StatusNotFound, err.Error())
 		return

backend/internal/models/audit_log.go

@@ -0,0 +1,22 @@
+package models
+
+import (
+	"encoding/json"
+	"time"
+
+	"github.com/google/uuid"
+)
+
+type AuditLog struct {
+	ID         int64            `db:"id" json:"id"`
+	TenantID   uuid.UUID        `db:"tenant_id" json:"tenant_id"`
+	UserID     *uuid.UUID       `db:"user_id" json:"user_id,omitempty"`
+	Action     string           `db:"action" json:"action"`
+	EntityType string           `db:"entity_type" json:"entity_type"`
+	EntityID   *uuid.UUID       `db:"entity_id" json:"entity_id,omitempty"`
+	OldValues  *json.RawMessage `db:"old_values" json:"old_values,omitempty"`
+	NewValues  *json.RawMessage `db:"new_values" json:"new_values,omitempty"`
+	IPAddress  *string          `db:"ip_address" json:"ip_address,omitempty"`
+	UserAgent  *string          `db:"user_agent" json:"user_agent,omitempty"`
+	CreatedAt  time.Time        `db:"created_at" json:"created_at"`
+}

backend/internal/router/router.go

@@ -19,16 +19,17 @@ func New(db *sqlx.DB, authMW *auth.Middleware, cfg *config.Config, calDAVSvc *se
 	mux := http.NewServeMux()
 
 	// Services
-	tenantSvc := services.NewTenantService(db)
+	auditSvc := services.NewAuditService(db)
-	caseSvc := services.NewCaseService(db)
+	tenantSvc := services.NewTenantService(db, auditSvc)
-	partySvc := services.NewPartyService(db)
+	caseSvc := services.NewCaseService(db, auditSvc)
-	appointmentSvc := services.NewAppointmentService(db)
+	partySvc := services.NewPartyService(db, auditSvc)
+	appointmentSvc := services.NewAppointmentService(db, auditSvc)
 	holidaySvc := services.NewHolidayService(db)
-	deadlineSvc := services.NewDeadlineService(db)
+	deadlineSvc := services.NewDeadlineService(db, auditSvc)
 	deadlineRuleSvc := services.NewDeadlineRuleService(db)
 	calculator := services.NewDeadlineCalculator(holidaySvc)
 	storageCli := services.NewStorageClient(cfg.SupabaseURL, cfg.SupabaseServiceKey)
-	documentSvc := services.NewDocumentService(db, storageCli)
+	documentSvc := services.NewDocumentService(db, storageCli, auditSvc)
 
 	// AI service (optional — only if API key is configured)
 	var aiH *handlers.AIHandler
@@ -40,10 +41,11 @@ func New(db *sqlx.DB, authMW *auth.Middleware, cfg *config.Config, calDAVSvc *se
 	// Middleware
 	tenantResolver := auth.NewTenantResolver(tenantSvc)
 
-	noteSvc := services.NewNoteService(db)
+	noteSvc := services.NewNoteService(db, auditSvc)
 	dashboardSvc := services.NewDashboardService(db)
 
 	// Handlers
+	auditH := handlers.NewAuditLogHandler(auditSvc)
 	tenantH := handlers.NewTenantHandler(tenantSvc)
 	caseH := handlers.NewCaseHandler(caseSvc)
 	partyH := handlers.NewPartyHandler(partySvc)
@@ -123,6 +125,9 @@ func New(db *sqlx.DB, authMW *auth.Middleware, cfg *config.Config, calDAVSvc *se
 	// Dashboard
 	scoped.HandleFunc("GET /api/dashboard", dashboardH.Get)
 
+	// Audit log
+	scoped.HandleFunc("GET /api/audit-log", auditH.List)
+
 	// Documents
 	scoped.HandleFunc("GET /api/cases/{id}/documents", docH.ListByCase)
 	scoped.HandleFunc("POST /api/cases/{id}/documents", docH.Upload)

backend/internal/services/appointment_service.go

@@ -12,11 +12,12 @@ import (
 )
 
 type AppointmentService struct {
-	db *sqlx.DB
+	db    *sqlx.DB
+	audit *AuditService
 }
 
-func NewAppointmentService(db *sqlx.DB) *AppointmentService {
+func NewAppointmentService(db *sqlx.DB, audit *AuditService) *AppointmentService {
-	return &AppointmentService{db: db}
+	return &AppointmentService{db: db, audit: audit}
 }
 
 type AppointmentFilter struct {
@@ -86,6 +87,7 @@ func (s *AppointmentService) Create(ctx context.Context, a *models.Appointment)
 	if err != nil {
 		return fmt.Errorf("creating appointment: %w", err)
 	}
+	s.audit.Log(ctx, "create", "appointment", &a.ID, nil, a)
 	return nil
 }
 
@@ -116,6 +118,7 @@ func (s *AppointmentService) Update(ctx context.Context, a *models.Appointment)
 	if rows == 0 {
 		return fmt.Errorf("appointment not found")
 	}
+	s.audit.Log(ctx, "update", "appointment", &a.ID, nil, a)
 	return nil
 }
 
@@ -131,5 +134,6 @@ func (s *AppointmentService) Delete(ctx context.Context, tenantID, id uuid.UUID)
 	if rows == 0 {
 		return fmt.Errorf("appointment not found")
 	}
+	s.audit.Log(ctx, "delete", "appointment", &id, nil, nil)
 	return nil
 }

backend/internal/services/audit_service.go

@@ -0,0 +1,141 @@
+package services
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"log/slog"
+
+	"github.com/google/uuid"
+	"github.com/jmoiron/sqlx"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
+)
+
+type AuditService struct {
+	db *sqlx.DB
+}
+
+func NewAuditService(db *sqlx.DB) *AuditService {
+	return &AuditService{db: db}
+}
+
+// Log records an audit entry. It extracts tenant, user, IP, and user-agent from context.
+// Errors are logged but not returned — audit logging must not break business operations.
+func (s *AuditService) Log(ctx context.Context, action, entityType string, entityID *uuid.UUID, oldValues, newValues any) {
+	tenantID, ok := auth.TenantFromContext(ctx)
+	if !ok {
+		slog.Warn("audit: missing tenant_id in context", "action", action, "entity_type", entityType)
+		return
+	}
+
+	var userID *uuid.UUID
+	if uid, ok := auth.UserFromContext(ctx); ok {
+		userID = &uid
+	}
+
+	var oldJSON, newJSON *json.RawMessage
+	if oldValues != nil {
+		if b, err := json.Marshal(oldValues); err == nil {
+			raw := json.RawMessage(b)
+			oldJSON = &raw
+		}
+	}
+	if newValues != nil {
+		if b, err := json.Marshal(newValues); err == nil {
+			raw := json.RawMessage(b)
+			newJSON = &raw
+		}
+	}
+
+	ip := auth.IPFromContext(ctx)
+	ua := auth.UserAgentFromContext(ctx)
+
+	_, err := s.db.ExecContext(ctx,
+		`INSERT INTO audit_log (tenant_id, user_id, action, entity_type, entity_id, old_values, new_values, ip_address, user_agent)
+		 VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)`,
+		tenantID, userID, action, entityType, entityID, oldJSON, newJSON, ip, ua)
+	if err != nil {
+		slog.Error("audit: failed to write log entry",
+			"error", err,
+			"action", action,
+			"entity_type", entityType,
+			"entity_id", entityID,
+		)
+	}
+}
+
+// AuditFilter holds query parameters for listing audit log entries.
+type AuditFilter struct {
+	EntityType string
+	EntityID   *uuid.UUID
+	UserID     *uuid.UUID
+	From       string // RFC3339 date
+	To         string // RFC3339 date
+	Page       int
+	Limit      int
+}
+
+// List returns paginated audit log entries for a tenant.
+func (s *AuditService) List(ctx context.Context, tenantID uuid.UUID, filter AuditFilter) ([]models.AuditLog, int, error) {
+	if filter.Limit <= 0 {
+		filter.Limit = 50
+	}
+	if filter.Limit > 200 {
+		filter.Limit = 200
+	}
+	if filter.Page <= 0 {
+		filter.Page = 1
+	}
+	offset := (filter.Page - 1) * filter.Limit
+
+	where := "WHERE tenant_id = $1"
+	args := []any{tenantID}
+	argIdx := 2
+
+	if filter.EntityType != "" {
+		where += fmt.Sprintf(" AND entity_type = $%d", argIdx)
+		args = append(args, filter.EntityType)
+		argIdx++
+	}
+	if filter.EntityID != nil {
+		where += fmt.Sprintf(" AND entity_id = $%d", argIdx)
+		args = append(args, *filter.EntityID)
+		argIdx++
+	}
+	if filter.UserID != nil {
+		where += fmt.Sprintf(" AND user_id = $%d", argIdx)
+		args = append(args, *filter.UserID)
+		argIdx++
+	}
+	if filter.From != "" {
+		where += fmt.Sprintf(" AND created_at >= $%d", argIdx)
+		args = append(args, filter.From)
+		argIdx++
+	}
+	if filter.To != "" {
+		where += fmt.Sprintf(" AND created_at <= $%d", argIdx)
+		args = append(args, filter.To)
+		argIdx++
+	}
+
+	var total int
+	if err := s.db.GetContext(ctx, &total, "SELECT COUNT(*) FROM audit_log "+where, args...); err != nil {
+		return nil, 0, fmt.Errorf("counting audit entries: %w", err)
+	}
+
+	query := fmt.Sprintf("SELECT * FROM audit_log %s ORDER BY created_at DESC LIMIT $%d OFFSET $%d",
+		where, argIdx, argIdx+1)
+	args = append(args, filter.Limit, offset)
+
+	var entries []models.AuditLog
+	if err := s.db.SelectContext(ctx, &entries, query, args...); err != nil {
+		return nil, 0, fmt.Errorf("listing audit entries: %w", err)
+	}
+	if entries == nil {
+		entries = []models.AuditLog{}
+	}
+
+	return entries, total, nil
+}

backend/internal/services/case_service.go

@@ -13,11 +13,12 @@ import (
 )
 
 type CaseService struct {
-	db *sqlx.DB
+	db    *sqlx.DB
+	audit *AuditService
 }
 
-func NewCaseService(db *sqlx.DB) *CaseService {
+func NewCaseService(db *sqlx.DB, audit *AuditService) *CaseService {
-	return &CaseService{db: db}
+	return &CaseService{db: db, audit: audit}
 }
 
 type CaseFilter struct {
@@ -162,6 +163,9 @@ func (s *CaseService) Create(ctx context.Context, tenantID uuid.UUID, userID uui
 	if err := s.db.GetContext(ctx, &c, "SELECT * FROM cases WHERE id = $1", id); err != nil {
 		return nil, fmt.Errorf("fetching created case: %w", err)
 	}
+
+	s.audit.Log(ctx, "create", "case", &id, nil, c)
+
 	return &c, nil
 }
 
@@ -239,6 +243,9 @@ func (s *CaseService) Update(ctx context.Context, tenantID, caseID uuid.UUID, us
 	if err := s.db.GetContext(ctx, &updated, "SELECT * FROM cases WHERE id = $1", caseID); err != nil {
 		return nil, fmt.Errorf("fetching updated case: %w", err)
 	}
+
+	s.audit.Log(ctx, "update", "case", &caseID, current, updated)
+
 	return &updated, nil
 }
 
@@ -254,6 +261,7 @@ func (s *CaseService) Delete(ctx context.Context, tenantID, caseID uuid.UUID, us
 		return sql.ErrNoRows
 	}
 	createEvent(ctx, s.db, tenantID, caseID, userID, "case_archived", "Case archived", nil)
+	s.audit.Log(ctx, "delete", "case", &caseID, map[string]string{"status": "active"}, map[string]string{"status": "archived"})
 	return nil
 }
 

backend/internal/services/deadline_service.go

@@ -1,6 +1,7 @@
 package services
 
 import (
+	"context"
 	"database/sql"
 	"fmt"
 	"time"
@@ -13,12 +14,13 @@ import (
 
 // DeadlineService handles CRUD operations for case deadlines
 type DeadlineService struct {
-	db *sqlx.DB
+	db    *sqlx.DB
+	audit *AuditService
 }
 
 // NewDeadlineService creates a new deadline service
-func NewDeadlineService(db *sqlx.DB) *DeadlineService {
+func NewDeadlineService(db *sqlx.DB, audit *AuditService) *DeadlineService {
-	return &DeadlineService{db: db}
+	return &DeadlineService{db: db, audit: audit}
 }
 
 // ListAll returns all deadlines for a tenant, ordered by due_date
@@ -87,7 +89,7 @@ type CreateDeadlineInput struct {
 }
 
 // Create inserts a new deadline
-func (s *DeadlineService) Create(tenantID uuid.UUID, input CreateDeadlineInput) (*models.Deadline, error) {
+func (s *DeadlineService) Create(ctx context.Context, tenantID uuid.UUID, input CreateDeadlineInput) (*models.Deadline, error) {
 	id := uuid.New()
 	source := input.Source
 	if source == "" {
@@ -108,6 +110,7 @@ func (s *DeadlineService) Create(tenantID uuid.UUID, input CreateDeadlineInput)
 	if err != nil {
 		return nil, fmt.Errorf("creating deadline: %w", err)
 	}
+	s.audit.Log(ctx, "create", "deadline", &id, nil, d)
 	return &d, nil
 }
 
@@ -123,7 +126,7 @@ type UpdateDeadlineInput struct {
 }
 
 // Update modifies an existing deadline
-func (s *DeadlineService) Update(tenantID, deadlineID uuid.UUID, input UpdateDeadlineInput) (*models.Deadline, error) {
+func (s *DeadlineService) Update(ctx context.Context, tenantID, deadlineID uuid.UUID, input UpdateDeadlineInput) (*models.Deadline, error) {
 	// First check it exists and belongs to tenant
 	existing, err := s.GetByID(tenantID, deadlineID)
 	if err != nil {
@@ -154,11 +157,12 @@ func (s *DeadlineService) Update(tenantID, deadlineID uuid.UUID, input UpdateDea
 	if err != nil {
 		return nil, fmt.Errorf("updating deadline: %w", err)
 	}
+	s.audit.Log(ctx, "update", "deadline", &deadlineID, existing, d)
 	return &d, nil
 }
 
 // Complete marks a deadline as completed
-func (s *DeadlineService) Complete(tenantID, deadlineID uuid.UUID) (*models.Deadline, error) {
+func (s *DeadlineService) Complete(ctx context.Context, tenantID, deadlineID uuid.UUID) (*models.Deadline, error) {
 	query := `UPDATE deadlines SET
 	            status = 'completed',
 	            completed_at = $1,
@@ -176,11 +180,12 @@ func (s *DeadlineService) Complete(tenantID, deadlineID uuid.UUID) (*models.Dead
 		}
 		return nil, fmt.Errorf("completing deadline: %w", err)
 	}
+	s.audit.Log(ctx, "update", "deadline", &deadlineID, map[string]string{"status": "pending"}, map[string]string{"status": "completed"})
 	return &d, nil
 }
 
 // Delete removes a deadline
-func (s *DeadlineService) Delete(tenantID, deadlineID uuid.UUID) error {
+func (s *DeadlineService) Delete(ctx context.Context, tenantID, deadlineID uuid.UUID) error {
 	query := `DELETE FROM deadlines WHERE id = $1 AND tenant_id = $2`
 	result, err := s.db.Exec(query, deadlineID, tenantID)
 	if err != nil {
@@ -193,5 +198,6 @@ func (s *DeadlineService) Delete(tenantID, deadlineID uuid.UUID) error {
 	if rows == 0 {
 		return fmt.Errorf("deadline not found")
 	}
+	s.audit.Log(ctx, "delete", "deadline", &deadlineID, nil, nil)
 	return nil
 }

backend/internal/services/document_service.go

@@ -18,10 +18,11 @@ const documentBucket = "kanzlai-documents"
 type DocumentService struct {
 	db      *sqlx.DB
 	storage *StorageClient
+	audit   *AuditService
 }
 
-func NewDocumentService(db *sqlx.DB, storage *StorageClient) *DocumentService {
+func NewDocumentService(db *sqlx.DB, storage *StorageClient, audit *AuditService) *DocumentService {
-	return &DocumentService{db: db, storage: storage}
+	return &DocumentService{db: db, storage: storage, audit: audit}
 }
 
 type CreateDocumentInput struct {
@@ -97,6 +98,7 @@ func (s *DocumentService) Create(ctx context.Context, tenantID, caseID, userID u
 	if err := s.db.GetContext(ctx, &doc, "SELECT * FROM documents WHERE id = $1", id); err != nil {
 		return nil, fmt.Errorf("fetching created document: %w", err)
 	}
+	s.audit.Log(ctx, "create", "document", &id, nil, doc)
 	return &doc, nil
 }
 
@@ -151,6 +153,7 @@ func (s *DocumentService) Delete(ctx context.Context, tenantID, docID, userID uu
 	// Log case event
 	createEvent(ctx, s.db, tenantID, doc.CaseID, userID, "document_deleted",
 		fmt.Sprintf("Document deleted: %s", doc.Title), nil)
+	s.audit.Log(ctx, "delete", "document", &docID, doc, nil)
 
 	return nil
 }

backend/internal/services/note_service.go

@@ -13,11 +13,12 @@ import (
 )
 
 type NoteService struct {
-	db *sqlx.DB
+	db    *sqlx.DB
+	audit *AuditService
 }
 
-func NewNoteService(db *sqlx.DB) *NoteService {
+func NewNoteService(db *sqlx.DB, audit *AuditService) *NoteService {
-	return &NoteService{db: db}
+	return &NoteService{db: db, audit: audit}
 }
 
 // ListByParent returns all notes for a given parent entity, scoped to tenant.
@@ -68,6 +69,7 @@ func (s *NoteService) Create(ctx context.Context, tenantID uuid.UUID, createdBy
 	if err != nil {
 		return nil, fmt.Errorf("creating note: %w", err)
 	}
+	s.audit.Log(ctx, "create", "note", &id, nil, n)
 	return &n, nil
 }
 
@@ -85,6 +87,7 @@ func (s *NoteService) Update(ctx context.Context, tenantID, noteID uuid.UUID, co
 		}
 		return nil, fmt.Errorf("updating note: %w", err)
 	}
+	s.audit.Log(ctx, "update", "note", &noteID, nil, n)
 	return &n, nil
 }
 
@@ -101,6 +104,7 @@ func (s *NoteService) Delete(ctx context.Context, tenantID, noteID uuid.UUID) er
 	if rows == 0 {
 		return fmt.Errorf("note not found")
 	}
+	s.audit.Log(ctx, "delete", "note", &noteID, nil, nil)
 	return nil
 }
 

backend/internal/services/party_service.go

@@ -13,11 +13,12 @@ import (
 )
 
 type PartyService struct {
-	db *sqlx.DB
+	db    *sqlx.DB
+	audit *AuditService
 }
 
-func NewPartyService(db *sqlx.DB) *PartyService {
+func NewPartyService(db *sqlx.DB, audit *AuditService) *PartyService {
-	return &PartyService{db: db}
+	return &PartyService{db: db, audit: audit}
 }
 
 type CreatePartyInput struct {
@@ -79,6 +80,7 @@ func (s *PartyService) Create(ctx context.Context, tenantID, caseID uuid.UUID, u
 	if err := s.db.GetContext(ctx, &party, "SELECT * FROM parties WHERE id = $1", id); err != nil {
 		return nil, fmt.Errorf("fetching created party: %w", err)
 	}
+	s.audit.Log(ctx, "create", "party", &id, nil, party)
 	return &party, nil
 }
 
@@ -135,6 +137,7 @@ func (s *PartyService) Update(ctx context.Context, tenantID, partyID uuid.UUID,
 	if err := s.db.GetContext(ctx, &updated, "SELECT * FROM parties WHERE id = $1", partyID); err != nil {
 		return nil, fmt.Errorf("fetching updated party: %w", err)
 	}
+	s.audit.Log(ctx, "update", "party", &partyID, current, updated)
 	return &updated, nil
 }
 
@@ -148,5 +151,6 @@ func (s *PartyService) Delete(ctx context.Context, tenantID, partyID uuid.UUID)
 	if rows == 0 {
 		return sql.ErrNoRows
 	}
+	s.audit.Log(ctx, "delete", "party", &partyID, nil, nil)
 	return nil
 }

backend/internal/services/tenant_service.go

@@ -13,11 +13,12 @@ import (
 )
 
 type TenantService struct {
-	db *sqlx.DB
+	db    *sqlx.DB
+	audit *AuditService
 }
 
-func NewTenantService(db *sqlx.DB) *TenantService {
+func NewTenantService(db *sqlx.DB, audit *AuditService) *TenantService {
-	return &TenantService{db: db}
+	return &TenantService{db: db, audit: audit}
 }
 
 // Create creates a new tenant and assigns the creator as owner.
@@ -49,6 +50,7 @@ func (s *TenantService) Create(ctx context.Context, userID uuid.UUID, name, slug
 		return nil, fmt.Errorf("commit: %w", err)
 	}
 
+	s.audit.Log(ctx, "create", "tenant", &tenant.ID, nil, tenant)
 	return &tenant, nil
 }
 
@@ -171,6 +173,7 @@ func (s *TenantService) InviteByEmail(ctx context.Context, tenantID uuid.UUID, e
 		return nil, fmt.Errorf("invite user: %w", err)
 	}
 
+	s.audit.Log(ctx, "create", "membership", &tenantID, nil, ut)
 	return &ut, nil
 }
 
@@ -186,6 +189,7 @@ func (s *TenantService) UpdateSettings(ctx context.Context, tenantID uuid.UUID,
 	if err != nil {
 		return nil, fmt.Errorf("update settings: %w", err)
 	}
+	s.audit.Log(ctx, "update", "settings", &tenantID, nil, settings)
 	return &tenant, nil
 }
 
@@ -223,5 +227,6 @@ func (s *TenantService) RemoveMember(ctx context.Context, tenantID, userID uuid.
 		return fmt.Errorf("remove member: %w", err)
 	}
 
+	s.audit.Log(ctx, "delete", "membership", &tenantID, map[string]any{"user_id": userID, "role": role}, nil)
 	return nil
 }

frontend/src/app/(app)/cases/[id]/layout.tsx

@@ -15,6 +15,7 @@ import {
   Users,
   StickyNote,
   AlertTriangle,
+  ScrollText,
 } from "lucide-react";
 import { format } from "date-fns";
 import { de } from "date-fns/locale";
@@ -44,6 +45,7 @@ const TABS = [
   { segment: "dokumente", label: "Dokumente", icon: FileText },
   { segment: "parteien", label: "Parteien", icon: Users },
   { segment: "notizen", label: "Notizen", icon: StickyNote },
+  { segment: "protokoll", label: "Protokoll", icon: ScrollText },
 ] as const;
 
 const TAB_LABELS: Record<string, string> = {
@@ -52,6 +54,7 @@ const TAB_LABELS: Record<string, string> = {
   dokumente: "Dokumente",
   parteien: "Parteien",
   notizen: "Notizen",
+  protokoll: "Protokoll",
 };
 
 function CaseDetailSkeleton() {

frontend/src/app/(app)/cases/[id]/protokoll/page.tsx

@@ -0,0 +1,178 @@
+"use client";
+
+import { useQuery } from "@tanstack/react-query";
+import { useParams, useSearchParams } from "next/navigation";
+import { api } from "@/lib/api";
+import type { AuditLogResponse } from "@/lib/types";
+import { format } from "date-fns";
+import { de } from "date-fns/locale";
+import { Loader2, ChevronLeft, ChevronRight } from "lucide-react";
+
+const ACTION_LABELS: Record<string, string> = {
+  create: "Erstellt",
+  update: "Aktualisiert",
+  delete: "Geloescht",
+};
+
+const ACTION_COLORS: Record<string, string> = {
+  create: "bg-emerald-50 text-emerald-700",
+  update: "bg-blue-50 text-blue-700",
+  delete: "bg-red-50 text-red-700",
+};
+
+const ENTITY_LABELS: Record<string, string> = {
+  case: "Akte",
+  deadline: "Frist",
+  appointment: "Termin",
+  document: "Dokument",
+  party: "Partei",
+  note: "Notiz",
+  settings: "Einstellungen",
+  membership: "Mitgliedschaft",
+};
+
+function DiffPreview({
+  oldValues,
+  newValues,
+}: {
+  oldValues?: Record<string, unknown>;
+  newValues?: Record<string, unknown>;
+}) {
+  if (!oldValues && !newValues) return null;
+
+  const allKeys = new Set([
+    ...Object.keys(oldValues ?? {}),
+    ...Object.keys(newValues ?? {}),
+  ]);
+
+  const changes: { key: string; from?: unknown; to?: unknown }[] = [];
+  for (const key of allKeys) {
+    const oldVal = oldValues?.[key];
+    const newVal = newValues?.[key];
+    if (JSON.stringify(oldVal) !== JSON.stringify(newVal)) {
+      changes.push({ key, from: oldVal, to: newVal });
+    }
+  }
+
+  if (changes.length === 0) return null;
+
+  return (
+    <div className="mt-2 space-y-1">
+      {changes.slice(0, 5).map((c) => (
+        <div key={c.key} className="flex items-baseline gap-2 text-xs">
+          <span className="font-medium text-neutral-500">{c.key}:</span>
+          {c.from !== undefined && (
+            <span className="rounded bg-red-50 px-1 text-red-600 line-through">
+              {String(c.from)}
+            </span>
+          )}
+          {c.to !== undefined && (
+            <span className="rounded bg-emerald-50 px-1 text-emerald-600">
+              {String(c.to)}
+            </span>
+          )}
+        </div>
+      ))}
+      {changes.length > 5 && (
+        <span className="text-xs text-neutral-400">
+          +{changes.length - 5} weitere Aenderungen
+        </span>
+      )}
+    </div>
+  );
+}
+
+export default function ProtokollPage() {
+  const { id } = useParams<{ id: string }>();
+  const searchParams = useSearchParams();
+  const page = Number(searchParams.get("page")) || 1;
+
+  const { data, isLoading } = useQuery({
+    queryKey: ["audit-log", id, page],
+    queryFn: () =>
+      api.get<AuditLogResponse>(
+        `/audit-log?entity_id=${id}&page=${page}&limit=50`,
+      ),
+  });
+
+  if (isLoading) {
+    return (
+      <div className="flex items-center justify-center py-8">
+        <Loader2 className="h-5 w-5 animate-spin text-neutral-400" />
+      </div>
+    );
+  }
+
+  const entries = data?.entries ?? [];
+  const total = data?.total ?? 0;
+  const totalPages = Math.ceil(total / 50);
+
+  if (entries.length === 0) {
+    return (
+      <div className="py-8 text-center text-sm text-neutral-400">
+        Keine Protokolleintraege vorhanden.
+      </div>
+    );
+  }
+
+  return (
+    <div>
+      <div className="space-y-3">
+        {entries.map((entry) => (
+          <div
+            key={entry.id}
+            className="rounded-md border border-neutral-100 bg-white px-4 py-3"
+          >
+            <div className="flex items-start justify-between gap-3">
+              <div className="flex items-center gap-2">
+                <span
+                  className={`inline-block rounded-full px-2 py-0.5 text-xs font-medium ${ACTION_COLORS[entry.action] ?? "bg-neutral-100 text-neutral-600"}`}
+                >
+                  {ACTION_LABELS[entry.action] ?? entry.action}
+                </span>
+                <span className="text-sm font-medium text-neutral-700">
+                  {ENTITY_LABELS[entry.entity_type] ?? entry.entity_type}
+                </span>
+              </div>
+              <span className="shrink-0 text-xs text-neutral-400">
+                {format(new Date(entry.created_at), "d. MMM yyyy, HH:mm", {
+                  locale: de,
+                })}
+              </span>
+            </div>
+            <DiffPreview
+              oldValues={entry.old_values}
+              newValues={entry.new_values}
+            />
+          </div>
+        ))}
+      </div>
+
+      {totalPages > 1 && (
+        <div className="mt-4 flex items-center justify-between">
+          <span className="text-xs text-neutral-400">
+            {total} Eintraege, Seite {page} von {totalPages}
+          </span>
+          <div className="flex gap-1">
+            {page > 1 && (
+              <a
+                href={`?page=${page - 1}`}
+                className="inline-flex items-center gap-1 rounded-md border border-neutral-200 px-2 py-1 text-xs text-neutral-600 hover:bg-neutral-50"
+              >
+                <ChevronLeft className="h-3 w-3" /> Zurueck
+              </a>
+            )}
+            {page < totalPages && (
+              <a
+                href={`?page=${page + 1}`}
+                className="inline-flex items-center gap-1 rounded-md border border-neutral-200 px-2 py-1 text-xs text-neutral-600 hover:bg-neutral-50"
+              >
+                Weiter <ChevronRight className="h-3 w-3" />
+              </a>
+            )}
+          </div>
+        </div>
+      )}
+    </div>
+  );
+}

frontend/src/lib/types.ts

@@ -189,6 +189,27 @@ export interface Note {
   updated_at: string;
 }
 
+export interface AuditLogEntry {
+  id: number;
+  tenant_id: string;
+  user_id?: string;
+  action: string;
+  entity_type: string;
+  entity_id?: string;
+  old_values?: Record<string, unknown>;
+  new_values?: Record<string, unknown>;
+  ip_address?: string;
+  user_agent?: string;
+  created_at: string;
+}
+
+export interface AuditLogResponse {
+  entries: AuditLogEntry[];
+  total: number;
+  page: number;
+  limit: number;
+}
+
 export interface ApiError {
   error: string;
   status: number;