diff --git a/.brain/adr-log.md b/.brain/adr-log.md
index e69de29..4e77ef1 100644
--- a/.brain/adr-log.md
+++ b/.brain/adr-log.md
@@ -0,0 +1,17 @@
+# ADR 001: PostgreSQL 16 Hybrid Multi-Tenant Architektur
+
+## Status
+Akzeptiert
+
+## Kontext
+Gastro-SaaS Tischreservierung benötigt strenge Mandantentrennung bei hoher Performance.
+
+## Entscheidung
+- Nutzung von PostgreSQL 16 Schema-basierter Multi-Tenancy.
+- Master-Schema (`public` / `tenants` Tabelle) für Mandantenverwaltung.
+- Eigene Schemas pro Tenant (`tenant_<id>`) für operative Daten (`reservations`, `restaurant_tables`, `guests`).
+- Spring Boot 3 `SchemaBasedMultiTenantConnectionProvider` & `CurrentTenantIdentifierResolver`.
+
+## Konsequenzen
+- Hohe Datenisolation & einfache Backups pro Tenant.
+- Migrationen laufen schemaweise über Flyway.
diff --git a/.brain/index.md b/.brain/index.md
index ba1c8d5..5dfb12d 100644
--- a/.brain/index.md
+++ b/.brain/index.md
@@ -1,5 +1,7 @@
 # Second Brain Wiki
 
-- [Supabase Schema](file:///c:/source/webshop/.brain/supabase-schema.md)
-- [ADR Log](file:///c:/source/webshop/.brain/adr-log.md)
-- [LicServer API Spezifikation](file:///c:/source/webshop/.brain/licserver-api.md)
+- [PostgreSQL Hybrid Multi-Tenant Setup](file:///c:/source/SmartSeat/SmartSeat/.brain/postgres-multi-tenant.md)
+- [ADR Log](file:///c:/source/SmartSeat/SmartSeat/.brain/adr-log.md)
+- [Supabase Schema](file:///c:/source/SmartSeat/SmartSeat/.brain/supabase-schema.md)
+- [LicServer API Spezifikation](file:///c:/source/SmartSeat/SmartSeat/.brain/licserver-api.md)
+
diff --git a/.brain/postgres-multi-tenant.md b/.brain/postgres-multi-tenant.md
new file mode 100644
index 0000000..2e3793f
--- /dev/null
+++ b/.brain/postgres-multi-tenant.md
@@ -0,0 +1,12 @@
+# PostgreSQL 16 Hybrid Multi-Tenant Setup
+
+## Architektur Overview
+- **Docker Setup**: PostgreSQL 16 Alpine via Docker Compose.
+- **Rollen-Isolation**: `app_user` (DML) & `migration_user` (DDL).
+- **Master Schema**: `tenants` Tabelle in `V1__init_master_schema.sql`.
+- **Tenant Schemas**: `dining_areas`, `restaurant_tables`, `guests`, `reservations`, `reservation_table_assignments`, `staff_users` in `V1__init_tenant_schema.sql`.
+
+## Backend Integration
+- `TenantContext` (ThreadLocal Schema Resolver)
+- `SchemaBasedMultiTenantConnectionProvider` (Hibernate Connection Handling)
+- HikariCP Connection Pool optimiert für Postgres in `application.yml`.