Python: Release the AgentChat activity signal when a message is rejected

python/semantic_kernel/agents/group_chat/agent_chat.py

@@ -108,15 +108,15 @@ async def add_chat_messages(self, messages: list[ChatMessageContent]) -> None:
         """Add chat messages."""
         self.set_activity_or_throw()
 
-        for message in messages:
-            if message.role == AuthorRole.SYSTEM:
-                error_message = "System messages cannot be added to the chat history."
-                logger.error(error_message)
-                raise AgentChatException(error_message)
+        try:
+            for message in messages:
+                if message.role == AuthorRole.SYSTEM:
+                    error_message = "System messages cannot be added to the chat history."
+                    logger.error(error_message)
+                    raise AgentChatException(error_message)
 
-        logger.info(f"Adding `{len(messages)}` agent chat messages")
+            logger.info(f"Adding `{len(messages)}` agent chat messages")
 
-        try:
             self.history.messages.extend(messages)
 
             # Broadcast message to other channels (in parallel)

python/tests/unit/agents/test_group_chat/test_agent_chat.py

@@ -200,6 +200,25 @@ async def test_add_chat_messages_throws_exception_for_system_role(agent_chat):
         await agent_chat.add_chat_messages([system_message])
 
 
+async def test_add_chat_messages_releases_activity_signal_when_a_message_is_rejected(agent_chat):
+    system_message = MagicMock(spec=ChatMessageContent)
+    system_message.role = AuthorRole.SYSTEM
+
+    with pytest.raises(AgentChatException, match="System messages cannot be added to the chat history."):
+        await agent_chat.add_chat_messages([system_message])
+
+    # The rejected message must not leave the chat active, otherwise every
+    # following operation fails with "Unable to proceed while another agent is active."
+    assert not agent_chat.is_active
+
+    # The chat is usable again and the rejected message was not added to the history.
+    user_message = MagicMock(spec=ChatMessageContent)
+    user_message.role = AuthorRole.USER
+    await agent_chat.add_chat_messages([user_message])
+
+    assert agent_chat.history.messages == [user_message]
+
+
 async def test_get_or_create_channel_creates_new_channel(agent_chat, agent):
     agent_chat.history.messages = [MagicMock(spec=ChatMessageContent)]
     channel_key = "test_channel_key"