fix: skip AgentState reset for MultiAgentBase executors in GraphNode

src/strands/multiagent/graph.py

@@ -184,11 +184,15 @@ def reset_executor_state(self) -> None:
 
         This is useful when nodes are executed multiple times and need to start
         fresh on each execution, providing stateless behavior.
+
+        For MultiAgentBase executors (e.g. nested Graph or Swarm), the state is a
+        GraphState/SwarmState dataclass — not an AgentState dict — so we skip the
+        state reset to avoid corrupting it with an incompatible type.
         """
         if hasattr(self.executor, "messages"):
             self.executor.messages = copy.deepcopy(self._initial_messages)
 
-        if hasattr(self.executor, "state"):
+        if hasattr(self.executor, "state") and not isinstance(self.executor, MultiAgentBase):
             self.executor.state = AgentState(self._initial_state.get())
 
         # Reset execution status

tests/strands/multiagent/test_graph.py

@@ -738,8 +738,14 @@ async def test_node_reset_executor_state():
 
     # Also modify execution status and result
     node.execution_status = Status.COMPLETED
+    agent_result = AgentResult(
+        message={"role": "assistant", "content": [{"text": "test"}]},
+        stop_reason="end_turn",
+        state={},
+        metrics=None,
+    )
     node.result = NodeResult(
-        result="test result",
+        result=agent_result,
         execution_time=100,
         status=Status.COMPLETED,
         accumulated_usage={"inputTokens": 10, "outputTokens": 20, "totalTokens": 30},
@@ -793,6 +799,49 @@ async def test_node_reset_executor_state():
     assert multi_agent_node.result is None
 
 
+def test_reset_executor_state_preserves_multiagent_state_type():
+    """Test that reset_executor_state does not overwrite MultiAgentBase.state with AgentState.
+
+    Regression test for https://github.com/strands-agents/sdk-python/issues/1775.
+    GraphNode.reset_executor_state() was unconditionally assigning AgentState(...) to
+    executor.state, corrupting the GraphState dataclass on nested Graph/Swarm executors.
+    """
+    multi_agent = create_mock_multi_agent("nested_graph")
+    # Simulate a MultiAgentBase that has a GraphState (like a nested Graph)
+    original_state = GraphState(task="original task")
+    multi_agent.state = original_state
+
+    node = GraphNode("nested_node", multi_agent)
+
+    # Modify execution status as if the node had run
+    node.execution_status = Status.COMPLETED
+    agent_result = AgentResult(
+        message={"role": "assistant", "content": [{"text": "test"}]},
+        stop_reason="end_turn",
+        state={},
+        metrics=None,
+    )
+    node.result = NodeResult(
+        result=agent_result,
+        execution_time=100,
+        status=Status.COMPLETED,
+        accumulated_usage={},
+        accumulated_metrics={},
+        execution_count=1,
+    )
+
+    # Reset should NOT corrupt the state type
+    node.reset_executor_state()
+
+    # The state must still be a GraphState, not an AgentState dict
+    assert isinstance(multi_agent.state, GraphState), (
+        f"Expected GraphState but got {type(multi_agent.state).__name__}; "
+        "reset_executor_state must not overwrite MultiAgentBase state with AgentState"
+    )
+    assert node.execution_status == Status.PENDING
+    assert node.result is None
+
+
 def test_graph_dataclasses_and_enums():
     """Test dataclass initialization, properties, and enum behavior."""
     # Test Status enum