Fix-swarm-handoff (#4198)

* fix select speaker for swarm

* Fix max-turn = 1 for swarm

python/packages/autogen-agentchat/src/autogen_agentchat/teams/_group_chat/_swarm_group_chat.py

@@ -40,14 +40,22 @@ class SwarmGroupChatManager(BaseGroupChatManager):
         self._current_speaker = self._participant_topic_types[0]
 
     async def select_speaker(self, thread: List[AgentMessage]) -> str:
-        """Select a speaker from the participants based on handoff message."""
-        if len(thread) > 0 and isinstance(thread[-1], HandoffMessage):
-            self._current_speaker = thread[-1].target
-            if self._current_speaker not in self._participant_topic_types:
-                raise ValueError("The selected speaker in the handoff message is not a participant.")
-            return self._current_speaker
-        else:
+        """Select a speaker from the participants based on handoff message.
+        Looks for the last handoff message in the thread to determine the next speaker."""
+        if len(thread) == 0:
             return self._current_speaker
+        for message in reversed(thread):
+            if isinstance(message, HandoffMessage):
+                self._current_speaker = message.target
+                if self._current_speaker not in self._participant_topic_types:
+                    raise ValueError(
+                        f"The target {self._current_speaker} in the handoff message "
+                        f"is not one of the participants {self._participant_topic_types}. "
+                        "If you are resuming the Swarm with a new task make sure to include in your task "
+                        "a handoff message with a valid participant as the target."
+                    )
+                return self._current_speaker
+        return self._current_speaker
 
 
 class Swarm(BaseGroupChat):

python/packages/autogen-agentchat/tests/test_group_chat.py

@@ -791,3 +791,27 @@ async def test_swarm_handoff_using_tool_calls(monkeypatch: pytest.MonkeyPatch) -
         else:
             assert message == result.messages[index]
         index += 1
+
+
+@pytest.mark.asyncio
+async def test_swarm_pause_and_resume() -> None:
+    first_agent = _HandOffAgent("first_agent", description="first agent", next_agent="second_agent")
+    second_agent = _HandOffAgent("second_agent", description="second agent", next_agent="third_agent")
+    third_agent = _HandOffAgent("third_agent", description="third agent", next_agent="first_agent")
+
+    team = Swarm([second_agent, first_agent, third_agent], max_turns=1)
+    result = await team.run(task="task")
+    assert len(result.messages) == 2
+    assert result.messages[0].content == "task"
+    assert result.messages[1].content == "Transferred to third_agent."
+
+    # Resume with a new task.
+    result = await team.run(task="new task")
+    assert len(result.messages) == 2
+    assert result.messages[0].content == "new task"
+    assert result.messages[1].content == "Transferred to first_agent."
+
+    # Resume with the same task.
+    result = await team.run()
+    assert len(result.messages) == 1
+    assert result.messages[0].content == "Transferred to second_agent."

python/packages/autogen-core/docs/src/user-guide/agentchat-user-guide/tutorial/selector-group-chat.ipynb

@@ -281,7 +281,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.11.5"
+   "version": "3.12.6"
   }
  },
  "nbformat": 4,

python/packages/autogen-core/docs/src/user-guide/agentchat-user-guide/tutorial/teams.ipynb

@@ -764,6 +764,16 @@
     "# Use `asyncio.run(Console(lazy_agent_team.run_stream(task=\"It is raining in New York.\")))` when running in a script.\n",
     "await Console(lazy_agent_team.run_stream(task=\"It is raining in New York.\"))"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "```{note}\n",
+    "Currently the handoff termination approach does not work with {py:class}`~autogen_agentchat.teams.Swarm`.\n",
+    "Please stay tuned for the updates.\n",
+    "```"
+   ]
   }
  ],
  "metadata": {