diff --git a/backend/app/api/auth.py b/backend/app/api/auth.py
index 0725e20..17af9ce 100644
--- a/backend/app/api/auth.py
+++ b/backend/app/api/auth.py
@@ -51,6 +51,8 @@ _INSTANCE = hashlib.sha256(
 ).hexdigest()
 _generations: dict[str, int] = {}
 _active_sockets: dict[str, weakref.WeakKeyDictionary] = {}
+# Logins already revoked because their users row disappeared.
+_vanished: set[str] = set()
 AUTH_GENERATION_SYNC_SECONDS = 1.0
 AUTH_GENERATION_MAX_AGE_SECONDS = 2.0
 _generations_synced_at: float | None = None
@@ -121,10 +123,13 @@ async def sync_generations() -> None:
     # The local-only dev-token principal is synthetic, never stored in users;
     # a DB watcher must not revoke its in-memory generation during test/demo
     # flows that deliberately exercise account invalidation.
+    # The revoked generation stays cached: dropping it would make the next
+    # lookup fall back to 0 and re-accept cookies issued before the revocation.
     synthetic = {"dev"} if get_settings().dev_auth_bypass else set()
-    for login in _generations.keys() - current.keys() - synthetic:
+    _vanished.intersection_update(_generations.keys() - current.keys())
+    for login in _generations.keys() - current.keys() - synthetic - _vanished:
         invalidate_login(login)
-        _generations.pop(login, None)
+        _vanished.add(login)
     global _generations_synced_at
     _generations_synced_at = time.monotonic()
 
diff --git a/backend/tests/test_auth_hardening.py b/backend/tests/test_auth_hardening.py
index 05f22cc..eec963a 100644
--- a/backend/tests/test_auth_hardening.py
+++ b/backend/tests/test_auth_hardening.py
@@ -272,6 +272,40 @@ def test_peer_node_generation_sync_closes_revoked_websocket(monkeypatch):
     asyncio.run(run())
 
 
+def test_generation_sync_keeps_revocation_of_login_missing_from_db(monkeypatch):
+    # Демо-логины синтетические, в users их нет. Сброс поколения к 0 после
+    # выхода вернул бы силу cookie, выданной до выхода.
+    login = "demo-instructor"
+
+    class FakeResult:
+        def all(self):
+            return []
+
+    class FakeDb:
+        async def execute(self, _query):
+            return FakeResult()
+
+    class FakeSession:
+        async def __aenter__(self):
+            return FakeDb()
+
+        async def __aexit__(self, *_args):
+            return None
+
+    monkeypatch.setattr(auth, "get_sessionmaker", lambda: lambda: FakeSession())
+    auth.prime_generations({})
+    who = auth._demo_principal(Role.INSTRUCTOR)
+    request = SimpleNamespace(session={})
+    auth._issue_session(request, who)
+    stale = dict(request.session)
+
+    auth.invalidate_login(login)
+    asyncio.run(auth.sync_generations())
+
+    assert auth._session_principal(stale) is None
+    auth._generations.pop(login, None)
+
+
 def test_revocation_does_not_log_error_if_socket_already_disconnected():
     class DisconnectedSocket:
         async def close(self, **_kwargs):