fix: avoid Telegram group reply thread session splits

gateway/platforms/telegram.py

@@ -4795,25 +4795,28 @@ class TelegramAdapter(BasePlatformAdapter):
         elif chat.type == ChatType.CHANNEL:
             chat_type = "channel"
 
-        # Resolve DM topic name and skill binding.
-        # In private chats, only preserve thread ids for real topic messages
-        # (is_topic_message=True).  Telegram puts message_thread_id on every
-        # DM that is a reply, even when the user is just replying to a
-        # previous message in the same DM — that bogus id then routes to a
-        # nonexistent thread and Telegram returns 'Message thread not found'
-        # on send (#3206).
+        # Resolve Telegram topic name and skill binding.
+        # Only preserve message_thread_id when Telegram marks the message as
+        # a real topic/forum message. Telegram can also populate
+        # message_thread_id for ordinary reply UI anchors; treating those as
+        # durable session threads fragments workflows such as CAPTCHA/login
+        # handoffs where the user later replies "done" in the same group.
+        # Private chats have the same pitfall: only real DM topic messages
+        # (is_topic_message=True) should keep the thread id, otherwise sends
+        # can hit Telegram's 'Message thread not found' error (#3206).
         thread_id_raw = message.message_thread_id
         is_topic_message = bool(getattr(message, "is_topic_message", False))
+        is_forum_group = getattr(chat, "is_forum", False) is True
         thread_id_str = None
         if thread_id_raw is not None:
-            if chat_type == "group":
+            if chat_type == "group" and (is_topic_message or is_forum_group):
                 thread_id_str = str(thread_id_raw)
             elif chat_type == "dm" and is_topic_message:
                 thread_id_str = str(thread_id_raw)
         # For forum groups without an explicit topic, default to the
         # General-topic id so the gateway routes back to the General topic
         # rather than dropping into the bot's main channel (#22423).
-        if chat_type == "group" and thread_id_str is None and getattr(chat, "is_forum", False):
+        if chat_type == "group" and thread_id_str is None and is_forum_group:
             thread_id_str = self._GENERAL_TOPIC_THREAD_ID
         chat_topic = None
         topic_skill = None

tests/gateway/test_dm_topics.py

@@ -449,13 +449,15 @@ def test_cache_dm_topic_from_message_no_overwrite():
 
 def _make_mock_message(chat_id=111, chat_type="private", text="hello", thread_id=None,
                        user_id=42, user_name="Test User", forum_topic_created=None,
-                       is_topic_message=None):
+                       is_topic_message=None, is_forum=None):
     """Create a mock Telegram Message for _build_message_event tests."""
     chat = SimpleNamespace(
         id=chat_id,
         type=chat_type,
         title=None,
     )
+    if is_forum is not None:
+        chat.is_forum = is_forum
     # Add full_name attribute for DM chats
     if not hasattr(chat, "full_name"):
         chat.full_name = user_name
@@ -594,7 +596,12 @@ def test_group_topic_skill_binding():
     ])
 
     msg = _make_mock_message(
-        chat_id=-1001234567890, chat_type=_ChatType.SUPERGROUP, thread_id=5, text="hello"
+        chat_id=-1001234567890,
+        chat_type=_ChatType.SUPERGROUP,
+        thread_id=5,
+        text="hello",
+        is_topic_message=True,
+        is_forum=True,
     )
     event = adapter._build_message_event(msg, MessageType.TEXT)
 
@@ -617,7 +624,12 @@ def test_group_topic_skill_binding_second_topic():
     ])
 
     msg = _make_mock_message(
-        chat_id=-1001234567890, chat_type=_ChatType.SUPERGROUP, thread_id=12, text="deal update"
+        chat_id=-1001234567890,
+        chat_type=_ChatType.SUPERGROUP,
+        thread_id=12,
+        text="deal update",
+        is_topic_message=True,
+        is_forum=True,
     )
     event = adapter._build_message_event(msg, MessageType.TEXT)
 
@@ -639,7 +651,12 @@ def test_group_topic_no_skill_binding():
     ])
 
     msg = _make_mock_message(
-        chat_id=-1001234567890, chat_type=_ChatType.SUPERGROUP, thread_id=1, text="hey"
+        chat_id=-1001234567890,
+        chat_type=_ChatType.SUPERGROUP,
+        thread_id=1,
+        text="hey",
+        is_topic_message=True,
+        is_forum=True,
     )
     event = adapter._build_message_event(msg, MessageType.TEXT)
 
@@ -661,7 +678,12 @@ def test_group_topic_unmapped_thread_id():
     ])
 
     msg = _make_mock_message(
-        chat_id=-1001234567890, chat_type=_ChatType.SUPERGROUP, thread_id=999, text="random"
+        chat_id=-1001234567890,
+        chat_type=_ChatType.SUPERGROUP,
+        thread_id=999,
+        text="random",
+        is_topic_message=True,
+        is_forum=True,
     )
     event = adapter._build_message_event(msg, MessageType.TEXT)
 
@@ -683,7 +705,12 @@ def test_group_topic_unmapped_chat_id():
     ])
 
     msg = _make_mock_message(
-        chat_id=-1009999999999, chat_type=_ChatType.SUPERGROUP, thread_id=5, text="wrong group"
+        chat_id=-1009999999999,
+        chat_type=_ChatType.SUPERGROUP,
+        thread_id=5,
+        text="wrong group",
+        is_topic_message=True,
+        is_forum=True,
     )
     event = adapter._build_message_event(msg, MessageType.TEXT)
 
@@ -720,7 +747,12 @@ def test_group_topic_chat_id_int_string_coercion():
     ])
 
     msg = _make_mock_message(
-        chat_id=-1001234567890, chat_type=_ChatType.SUPERGROUP, thread_id=7, text="test"
+        chat_id=-1001234567890,
+        chat_type=_ChatType.SUPERGROUP,
+        thread_id=7,
+        text="test",
+        is_topic_message=True,
+        is_forum=True,
     )
     event = adapter._build_message_event(msg, MessageType.TEXT)
 

tests/gateway/test_telegram_thread_fallback.py

@@ -134,6 +134,70 @@ def _make_adapter():
     return adapter
 
 
+def test_non_forum_group_reply_thread_id_does_not_fork_session_key():
+    """Reply-derived thread ids in ordinary groups must not create topic lanes."""
+    from gateway.platforms import telegram as telegram_mod
+
+    adapter = _make_adapter()
+    message = SimpleNamespace(
+        text="Done",
+        caption=None,
+        chat=SimpleNamespace(
+            id=-100123,
+            type=telegram_mod.ChatType.SUPERGROUP,
+            is_forum=False,
+            title="Regular group",
+        ),
+        from_user=SimpleNamespace(id=456, full_name="Alice"),
+        message_thread_id=461,
+        is_topic_message=False,
+        reply_to_message=SimpleNamespace(
+            message_id=460,
+            text="Please complete the CAPTCHA/login, then reply done.",
+            caption=None,
+        ),
+        message_id=462,
+        date=None,
+    )
+
+    event = adapter._build_message_event(message, msg_type=MessageType.TEXT)
+
+    assert event.source.chat_id == "-100123"
+    assert event.source.chat_type == "group"
+    assert event.source.thread_id is None
+    assert build_session_key(event.source) == "agent:main:telegram:group:-100123:456"
+
+
+def test_forum_group_topic_message_preserves_thread_session_key():
+    """Real Telegram forum-topic messages should still route by topic id."""
+    from gateway.platforms import telegram as telegram_mod
+
+    adapter = _make_adapter()
+    message = SimpleNamespace(
+        text="hello from topic",
+        caption=None,
+        chat=SimpleNamespace(
+            id=-100123,
+            type=telegram_mod.ChatType.SUPERGROUP,
+            is_forum=True,
+            title="Forum group",
+        ),
+        from_user=SimpleNamespace(id=456, full_name="Alice"),
+        message_thread_id=17585,
+        is_topic_message=True,
+        reply_to_message=None,
+        message_id=10,
+        date=None,
+    )
+
+    event = adapter._build_message_event(message, msg_type=MessageType.TEXT)
+
+    assert event.source.chat_id == "-100123"
+    assert event.source.chat_type == "group"
+    assert event.source.thread_id == "17585"
+    assert build_session_key(event.source) == "agent:main:telegram:group:-100123:17585"
+
+
 def test_forum_general_topic_without_message_thread_id_keeps_thread_context():
     """Forum General-topic messages should keep synthetic thread context."""
     from gateway.platforms import telegram as telegram_mod