fix(gateway): route forum supergroup General topic messages by including 'supergroup' chat type (#13607)

Forum supergroups always have chat.type == SUPERGROUP in the Telegram API,
but the General topic fallback in _build_message_event() only checked for
chat_type == "group". While the current mapping happens to map SUPERGROUP
to "group", this is fragile — other methods (e.g. _is_group_chat) already
distinguish the two types, and any refactor to the mapping would silently
break General topic routing.

Extend the check to accept both "group" and "supergroup", and add a debug
log when the fallback fires to aid future diagnosis.

gateway/platforms/telegram.py

@@ -2989,8 +2989,12 @@ class TelegramAdapter(BasePlatformAdapter):
         # Resolve DM topic name and skill binding
         thread_id_raw = message.message_thread_id
         thread_id_str = str(thread_id_raw) if thread_id_raw is not None else None
-        if chat_type == "group" and thread_id_str is None and getattr(chat, "is_forum", False):
+        if chat_type in ("group", "supergroup") and thread_id_str is None and getattr(chat, "is_forum", False):
             thread_id_str = self._GENERAL_TOPIC_THREAD_ID
+            logger.debug(
+                "Forum %s message without thread_id — routing to General topic (thread=%s)",
+                chat_type, thread_id_str,
+            )
         chat_topic = None
         topic_skill = None
 

tests/gateway/test_telegram_thread_fallback.py

@@ -132,6 +132,86 @@ def test_forum_general_topic_without_message_thread_id_keeps_thread_context():
     assert event.source.thread_id == "1"
 
 
+def test_forum_group_general_topic_fallback():
+    """Forum GROUP chat without thread_id should also fall back to General topic."""
+    from gateway.platforms import telegram as telegram_mod
+
+    adapter = _make_adapter()
+    message = SimpleNamespace(
+        text="hello from group forum General",
+        caption=None,
+        chat=SimpleNamespace(
+            id=-100999,
+            type=telegram_mod.ChatType.GROUP,
+            is_forum=True,
+            title="Group forum",
+        ),
+        from_user=SimpleNamespace(id=789, full_name="Bob"),
+        message_thread_id=None,
+        reply_to_message=None,
+        message_id=20,
+        date=None,
+    )
+
+    event = adapter._build_message_event(message, msg_type=SimpleNamespace(value="text"))
+
+    assert event.source.chat_id == "-100999"
+    assert event.source.chat_type == "group"
+    assert event.source.thread_id == "1"
+
+
+def test_forum_supergroup_with_thread_id_preserves_it():
+    """Forum supergroup messages WITH a thread_id should keep the original value."""
+    from gateway.platforms import telegram as telegram_mod
+
+    adapter = _make_adapter()
+    message = SimpleNamespace(
+        text="hello from a named 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=42,
+        reply_to_message=None,
+        message_id=30,
+        date=None,
+    )
+
+    event = adapter._build_message_event(message, msg_type=SimpleNamespace(value="text"))
+
+    assert event.source.thread_id == "42"
+
+
+def test_non_forum_supergroup_without_thread_id_stays_none():
+    """Non-forum supergroup messages without thread_id should NOT get General topic."""
+    from gateway.platforms import telegram as telegram_mod
+
+    adapter = _make_adapter()
+    message = SimpleNamespace(
+        text="hello from a regular supergroup",
+        caption=None,
+        chat=SimpleNamespace(
+            id=-100555,
+            type=telegram_mod.ChatType.SUPERGROUP,
+            is_forum=False,
+            title="Regular supergroup",
+        ),
+        from_user=SimpleNamespace(id=456, full_name="Alice"),
+        message_thread_id=None,
+        reply_to_message=None,
+        message_id=40,
+        date=None,
+    )
+
+    event = adapter._build_message_event(message, msg_type=SimpleNamespace(value="text"))
+
+    assert event.source.thread_id is None
+
+
 @pytest.mark.asyncio
 async def test_send_omits_general_topic_thread_id():
     """Telegram sends to forum General should omit message_thread_id=1."""