fix(graph): propagate structured_output in graph node transitions

src/strands/agent/agent_result.py

@@ -56,6 +56,36 @@ def __str__(self) -> str:
 
         return result
 
+    def to_node_output(self) -> str:
+        """Get a complete representation for graph node transitions.
+
+        This method generates output suitable for passing between graph nodes,
+        including both text content and structured output when present. Unlike
+        __str__, this method always includes structured output alongside text
+        to ensure no data is lost during graph transitions.
+
+        Returns:
+            A string representation containing both text and structured output.
+        """
+        parts = []
+
+        # Extract text content from message
+        content_array = self.message.get("content", [])
+        text_content = ""
+        for item in content_array:
+            if isinstance(item, dict) and "text" in item:
+                text_content += item.get("text", "") + "\n"
+
+        if text_content:
+            parts.append(text_content.rstrip("\n"))
+
+        # Include structured output when present
+        if self.structured_output:
+            structured_json = self.structured_output.model_dump_json()
+            parts.append(f"[Structured Output]: {structured_json}")
+
+        return "\n".join(parts) if parts else ""
+
     @classmethod
     def from_dict(cls, data: dict[str, Any]) -> "AgentResult":
         """Rehydrate an AgentResult from persisted JSON.

src/strands/multiagent/graph.py

@@ -1001,7 +1001,7 @@ def _build_node_input(self, node: GraphNode) -> list[ContentBlock]:
             agent_results = node_result.get_agent_results()
             for result in agent_results:
                 agent_name = getattr(result, "agent_name", "Agent")
-                result_text = str(result)
+                result_text = result.to_node_output() if hasattr(result, "to_node_output") else str(result)
                 node_input.append(ContentBlock(text=f"  - {agent_name}: {result_text}"))
 
         return node_input

tests/strands/agent/test_agent_result.py

@@ -225,3 +225,86 @@ def test__str__empty_message_with_structured_output(mock_metrics, empty_message:
     assert "example" in message_string
     assert "123" in message_string
     assert "optional" in message_string
+
+
+# Tests for to_node_output() method - graph node transitions
+def test_to_node_output_text_only(mock_metrics, simple_message: Message):
+    """Test to_node_output() with text-only message returns just the text."""
+    result = AgentResult(stop_reason="end_turn", message=simple_message, metrics=mock_metrics, state={})
+
+    node_output = result.to_node_output()
+    assert node_output == "Hello world!"
+    assert "[Structured Output]" not in node_output
+
+
+def test_to_node_output_structured_output_only(mock_metrics, empty_message: Message):
+    """Test to_node_output() with only structured_output."""
+    structured_output = StructuredOutputModel(name="test", value=42)
+
+    result = AgentResult(
+        stop_reason="end_turn",
+        message=empty_message,
+        metrics=mock_metrics,
+        state={},
+        structured_output=structured_output,
+    )
+
+    node_output = result.to_node_output()
+    assert "[Structured Output]:" in node_output
+    assert '"name":"test"' in node_output
+    assert '"value":42' in node_output
+
+
+def test_to_node_output_text_and_structured_output(mock_metrics, simple_message: Message):
+    """Test to_node_output() includes BOTH text AND structured_output when present."""
+    structured_output = StructuredOutputModel(name="test", value=42)
+
+    result = AgentResult(
+        stop_reason="end_turn",
+        message=simple_message,
+        metrics=mock_metrics,
+        state={},
+        structured_output=structured_output,
+    )
+
+    node_output = result.to_node_output()
+
+    # Should contain both text and structured output
+    assert "Hello world!" in node_output
+    assert "[Structured Output]:" in node_output
+    assert '"name":"test"' in node_output
+    assert '"value":42' in node_output
+
+
+def test_to_node_output_empty_message_no_structured_output(mock_metrics, empty_message: Message):
+    """Test to_node_output() with empty message and no structured_output returns empty string."""
+    result = AgentResult(stop_reason="end_turn", message=empty_message, metrics=mock_metrics, state={})
+
+    node_output = result.to_node_output()
+    assert node_output == ""
+
+
+def test_to_node_output_complex_message(mock_metrics, complex_message: Message):
+    """Test to_node_output() with complex message containing multiple text blocks."""
+    structured_output = StructuredOutputModel(name="complex", value=999, optional_field="extra")
+
+    result = AgentResult(
+        stop_reason="end_turn",
+        message=complex_message,
+        metrics=mock_metrics,
+        state={},
+        structured_output=structured_output,
+    )
+
+    node_output = result.to_node_output()
+
+    # Should contain all text blocks
+    assert "First paragraph" in node_output
+    assert "Second paragraph" in node_output
+    assert "Third paragraph" in node_output
+
+    # Should contain structured output
+    assert "[Structured Output]:" in node_output
+    assert '"name":"complex"' in node_output
+    assert '"value":999' in node_output
+    assert '"optional_field":"extra"' in node_output