feat(ai): add tenant-safe hierarchical expense learning

server/src/app/services/auth.py

@@ -53,6 +53,7 @@ class AuthenticatedUser:
     avatar: str
     is_admin: bool = False
     employee_id: str | None = None
+    department_id: str | None = None
     tenant_id: str = "default"
 
 
@@ -116,7 +117,7 @@ class AuthService:
             }
             if auth_session.username.strip().casefold() not in allowed_identifiers:
                 return None
-            return self._build_admin_user(record)
+            return self._restore_session_scope(self._build_admin_user(record), auth_session)
 
         if auth_session.principal_type != "employee":
             return None
@@ -133,7 +134,17 @@ class AuthService:
         employee = self.db.execute(stmt).scalars().first()
         if employee is None or employee.employment_status == "停用":
             return None
-        return self._build_employee_user(employee)
+        return self._restore_session_scope(self._build_employee_user(employee), auth_session)
+
+    @staticmethod
+    def _restore_session_scope(
+        user: AuthenticatedUser,
+        auth_session: AuthSession,
+    ) -> AuthenticatedUser:
+        """会话恢复时以签发并认证过的会话租户为准，禁止回落到默认租户。"""
+
+        user.tenant_id = str(auth_session.tenant_id or "default").strip() or "default"
+        return user
 
     def get_user_snapshot(self, identifier: str) -> AuthUserRead | None:
         normalized = identifier.strip()
@@ -249,6 +260,7 @@ class AuthService:
             avatar=(employee.name or "?")[:1].upper(),
             is_admin=False,
             employee_id=employee.id,
+            department_id=employee.organization_unit_id,
         )
 
     @staticmethod