FIX: GraphFlow serialize/deserialize and adding test (#6434)

## Why are these changes needed?
❗ Before

Previously, GraphFlow.__init__() modified the inner_chats and
termination_condition for internal execution logic (e.g., constructing
_StopAgent or composing OrTerminationCondition).
However, these modified values were also used during dump_component(),
meaning the serialized config no longer matched the original inputs.

As a result:
1. dump_component() → load_component() → dump_component() produced
non-idempotent configs.
2. Internal-only constructs like _StopAgent were mistakenly serialized,
even though they should only exist in runtime.

⸻

✅ After

This patch changes the behavior to:
• Store original inner_chats and termination_condition as-is at
initialization.
	•	During to_config(), serialize only the original unmodified versions.
	•	Avoid serializing _StopAgent or other dynamically built agents.
• Ensure deserialization (from_config) produces a logically equivalent
object without additional nesting or duplication.

This ensures that:
• GraphFlow.dump_component() → load_component() round-trip produces
consistent, minimal configs.
• Internal execution logic and serialized component structure are
properly separated.
<!-- Please give a short summary of the change and the problem this
solves. -->

## Related issue number

<!-- For example: "Closes #1234" -->
Closes #6431 

## Checks

- [ ] I've included any doc changes needed for
<https://microsoft.github.io/autogen/>. See
<https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md> to
build and test documentation locally.
- [x] I've added tests (if relevant) corresponding to the changes
introduced in this PR.
- [x] I've made sure all auto checks have passed.

Author: SongChiYoung

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

@@ -646,6 +646,9 @@ def __init__(
         runtime: AgentRuntime | None = None,
         custom_message_types: List[type[BaseAgentEvent | BaseChatMessage]] | None = None,
     ) -> None:
+        self._input_participants = participants
+        self._input_termination_condition = termination_condition
+
         stop_agent = _StopAgent()
         stop_agent_termination = StopMessageTermination()
         termination_condition = (
@@ -700,8 +703,10 @@ def _factory() -> GraphFlowManager:
 
     def _to_config(self) -> GraphFlowConfig:
         """Converts the instance into a configuration object."""
-        participants = [participant.dump_component() for participant in self._participants]
-        termination_condition = self._termination_condition.dump_component() if self._termination_condition else None
+        participants = [participant.dump_component() for participant in self._input_participants]
+        termination_condition = (
+            self._input_termination_condition.dump_component() if self._input_termination_condition else None
+        )
         return GraphFlowConfig(
             participants=participants,
             termination_condition=termination_condition,

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

@@ -13,7 +13,7 @@
 )
 from autogen_agentchat.base import Response, TaskResult
 from autogen_agentchat.conditions import MaxMessageTermination
-from autogen_agentchat.messages import BaseChatMessage, ChatMessage, MessageFactory, TextMessage
+from autogen_agentchat.messages import BaseChatMessage, ChatMessage, MessageFactory, StopMessage, TextMessage
 from autogen_agentchat.messages import BaseTextChatMessage as TextChatMessage
 from autogen_agentchat.teams import (
     DiGraphBuilder,
@@ -1399,3 +1399,51 @@ async def test_graph_builder_with_filter_agent(runtime: AgentRuntime | None) ->
     result = await team.run(task="Hello")
     assert any(m.source == "X" and m.content == "Hello" for m in result.messages)  # type: ignore[union-attr]
     assert result.stop_reason is not None
+
+
+@pytest.mark.asyncio
+async def test_graph_flow_serialize_deserialize() -> None:
+    client_a = ReplayChatCompletionClient(list(map(str, range(10))))
+    client_b = ReplayChatCompletionClient(list(map(str, range(10))))
+    a = AssistantAgent("A", model_client=client_a)
+    b = AssistantAgent("B", model_client=client_b)
+
+    builder = DiGraphBuilder()
+    builder.add_node(a).add_node(b)
+    builder.add_edge(a, b)
+    builder.set_entry_point(a)
+
+    team = GraphFlow(
+        participants=builder.get_participants(),
+        graph=builder.build(),
+        runtime=None,
+        termination_condition=MaxMessageTermination(5),
+    )
+
+    serialized = team.dump_component()
+    deserialized_team = GraphFlow.load_component(serialized)
+    serialized_deserialized = deserialized_team.dump_component()
+
+    results = await team.run(task="Start")
+    de_results = await deserialized_team.run(task="Start")
+
+    assert serialized == serialized_deserialized
+    assert results == de_results
+    assert results.stop_reason is not None
+    assert results.stop_reason == de_results.stop_reason
+    assert results.messages == de_results.messages
+    assert isinstance(results.messages[0], TextMessage)
+    assert results.messages[0].source == "user"
+    assert results.messages[0].content == "Start"
+    assert isinstance(results.messages[1], TextMessage)
+    assert results.messages[1].source == "A"
+    assert results.messages[1].content == "0"
+    assert isinstance(results.messages[2], TextMessage)
+    assert results.messages[2].source == "A"
+    assert results.messages[2].content == "1"
+    assert isinstance(results.messages[3], TextMessage)
+    assert results.messages[3].source == "B"
+    assert results.messages[3].content == "0"
+    assert isinstance(results.messages[-1], StopMessage)
+    assert results.messages[-1].source == _DIGRAPH_STOP_AGENT_NAME
+    assert results.messages[-1].content == "Digraph execution is complete"