diff --git a/backend/app/core/tenant.py b/backend/app/core/tenant.py
new file mode 100644
index 0000000..036d953
--- /dev/null
+++ b/backend/app/core/tenant.py
@@ -0,0 +1,29 @@
+"""Tenant context: ensures all queries are tenant-scoped."""
+from typing import Optional
+from fastapi import Request
+
+
+class TenantContext:
+    """Thread-local-ish tenant context (stored on request state)."""
+
+    @staticmethod
+    def get_tenant_id(request: Request) -> Optional[int]:
+        """Extract tenant_id from request state (set by middleware)."""
+        return getattr(request.state, "tenant_id", None)
+
+    @staticmethod
+    def get_user_id(request: Request) -> Optional[int]:
+        """Extract user_id from request state."""
+        return getattr(request.state, "user_id", None)
+
+    @staticmethod
+    def get_user_role(request: Request) -> Optional[str]:
+        """Extract user role from request state."""
+        return getattr(request.state, "user_role", None)
+
+
+def apply_tenant_filter(query, model, tenant_id: int):
+    """Apply tenant_id filter to a SQLAlchemy query if the model has tenant_id."""
+    if hasattr(model, "tenant_id"):
+        return query.filter(model.tenant_id == tenant_id)
+    return query