fix(sdk-python): LangGraphAGUIAgent serializes Context objects to dicts (CopilotKit#3690) (CopilotKit#3787)

## Summary
- `LangGraphAGUIAgent.langgraph_default_merge_state` now calls
`model_dump()` on Pydantic Context objects before storing in copilotkit
state
- Previously stored raw Pydantic objects, causing JSON serialization
failures downstream
- Handles mixed types: Pydantic objects get `model_dump()`, plain dicts
pass through unchanged
- Matches the existing pattern already used in `CopilotKitMiddleware`

## Test plan
- [x] Red-green test: AG-UI Context objects stored as plain dicts, not
Pydantic
- [x] Red-green test: mixed Pydantic + dict context items all
serializable
- [x] Full test suite passes (15/15)

Closes CopilotKit#3690

Author: AlemTuzlak

sdk-python/copilotkit/langgraph_agui_agent.py

@@ -198,8 +198,8 @@ def langgraph_default_merge_state(self, state: State, messages: List[BaseMessage
         return {
             **merged_state,
             'copilotkit': {
-                'actions': agui_properties.get('tools', []),
-                'context': agui_properties.get('context', [])
+                'actions': [a.model_dump() if hasattr(a, 'model_dump') else a for a in agui_properties.get('tools', [])],
+                'context': [c.model_dump() if hasattr(c, 'model_dump') else c for c in agui_properties.get('context', [])]
             },
         }
 

sdk-python/tests/test_agui_context_serializable.py

@@ -0,0 +1,71 @@
+"""Tests for #3690: LangGraphAGUIAgent stores Context as Pydantic objects instead of dicts."""
+
+import json
+from unittest.mock import MagicMock, patch
+from ag_ui.core import Context
+
+
+class TestAGUIContextSerialization:
+    """Verify that context items stored in state are JSON-serializable dicts, not Pydantic objects."""
+
+    def test_context_items_are_dicts_not_pydantic(self):
+        """Context from ag-ui properties should be model_dump'd before storage."""
+        from copilotkit.langgraph_agui_agent import LangGraphAGUIAgent
+
+        mock_graph = MagicMock()
+        mock_graph.get_state = MagicMock()
+        agent = LangGraphAGUIAgent(name="test", graph=mock_graph)
+
+        # Pydantic Context objects as they arrive from AG-UI
+        ctx1 = Context(name="user_info", description="User details", value="John")
+        ctx2 = Context(name="session", description="Session data", value="abc123")
+
+        merged_state = {
+            'ag-ui': {
+                'tools': [],
+                'context': [ctx1, ctx2],
+            },
+            'messages': [],
+        }
+
+        with patch.object(
+            type(agent).__mro__[1],  # LangGraphAgent (parent class)
+            "langgraph_default_merge_state",
+            return_value=merged_state
+        ):
+            result = agent.langgraph_default_merge_state({}, [], None)
+
+        # Context items must be plain dicts, not Pydantic objects
+        for item in result['copilotkit']['context']:
+            assert isinstance(item, dict), f"Expected dict, got {type(item)}"
+            json.dumps(item)  # Must be JSON-serializable
+
+    def test_context_with_mixed_types(self):
+        """If context contains both Pydantic objects and plain dicts, handle both."""
+        from copilotkit.langgraph_agui_agent import LangGraphAGUIAgent
+
+        mock_graph = MagicMock()
+        mock_graph.get_state = MagicMock()
+        agent = LangGraphAGUIAgent(name="test", graph=mock_graph)
+
+        ctx_pydantic = Context(name="key1", description="desc", value="val1")
+        ctx_dict = {"name": "key2", "description": "desc2", "value": "val2"}
+
+        merged_state = {
+            'ag-ui': {
+                'tools': [],
+                'context': [ctx_pydantic, ctx_dict],
+            },
+            'messages': [],
+        }
+
+        with patch.object(
+            type(agent).__mro__[1],
+            "langgraph_default_merge_state",
+            return_value=merged_state
+        ):
+            result = agent.langgraph_default_merge_state({}, [], None)
+
+        for item in result['copilotkit']['context']:
+            assert isinstance(item, dict), f"Expected dict, got {type(item)}"
+            json.dumps(item)