Fix #1743: scene handling for channel updates (#1763)

* Fix scene handling for channel updates with missing FSM state (#1743)

* Add changelog entry for scene handling fix

* Refine scene context error handling

tests/test_fsm/test_middleware.py

@@ -0,0 +1,90 @@
+from aiogram.fsm.middleware import FSMContextMiddleware
+from aiogram.fsm.storage.memory import DisabledEventIsolation, MemoryStorage
+from aiogram.fsm.strategy import FSMStrategy
+from tests.mocked_bot import MockedBot
+
+CHANNEL_ID = -1001234567890
+THREAD_ID = 42
+
+
+def create_middleware(strategy: FSMStrategy) -> FSMContextMiddleware:
+    return FSMContextMiddleware(
+        storage=MemoryStorage(),
+        events_isolation=DisabledEventIsolation(),
+        strategy=strategy,
+    )
+
+
+class TestFSMContextMiddleware:
+    def test_resolve_context_for_channel_in_chat_strategy(self):
+        bot = MockedBot()
+        middleware = create_middleware(FSMStrategy.CHAT)
+
+        context = middleware.resolve_context(
+            bot=bot,
+            chat_id=CHANNEL_ID,
+            user_id=None,
+        )
+
+        assert context is not None
+        assert context.key.chat_id == CHANNEL_ID
+        assert context.key.user_id == CHANNEL_ID
+
+    def test_resolve_context_with_missing_user_in_chat_topic_strategy_uses_chat_id_for_user_id(
+        self,
+    ):
+        """
+        When user_id is absent (e.g., channel-like updates), chat-scoped strategies
+        should still build a stable FSM key by mirroring chat_id into user_id.
+        """
+        bot = MockedBot()
+        middleware = create_middleware(FSMStrategy.CHAT_TOPIC)
+
+        context = middleware.resolve_context(
+            bot=bot,
+            chat_id=CHANNEL_ID,
+            user_id=None,
+            thread_id=THREAD_ID,
+        )
+
+        assert context is not None
+        assert context.key.chat_id == CHANNEL_ID
+        assert context.key.user_id == CHANNEL_ID
+        assert context.key.thread_id == THREAD_ID
+
+    def test_resolve_context_for_channel_in_user_in_chat_strategy(self):
+        bot = MockedBot()
+        middleware = create_middleware(FSMStrategy.USER_IN_CHAT)
+
+        context = middleware.resolve_context(
+            bot=bot,
+            chat_id=CHANNEL_ID,
+            user_id=None,
+        )
+
+        assert context is None
+
+    def test_resolve_context_for_channel_in_global_user_strategy(self):
+        bot = MockedBot()
+        middleware = create_middleware(FSMStrategy.GLOBAL_USER)
+
+        context = middleware.resolve_context(
+            bot=bot,
+            chat_id=CHANNEL_ID,
+            user_id=None,
+        )
+
+        assert context is None
+
+    def test_resolve_context_for_channel_in_user_in_topic_strategy(self):
+        bot = MockedBot()
+        middleware = create_middleware(FSMStrategy.USER_IN_TOPIC)
+
+        context = middleware.resolve_context(
+            bot=bot,
+            chat_id=CHANNEL_ID,
+            user_id=None,
+            thread_id=THREAD_ID,
+        )
+
+        assert context is None