refactor: use json.dumps default parameter for non-serializable objects

- Replace manual serialization loop with json.dumps default parameter
- Use __qualname__ for better type representation
- Change format from <non-serializable> to <<non-serializable>>
- Update tests to match new serialization format
- Addresses PR feedback to simplify serialization approach

Author: cagataycali

src/strands/agent/agent.py

@@ -616,22 +616,10 @@ def _record_tool_execution(
             user_message_override: Optional custom message to include.
         """
         # Create user message describing the tool call
-
-        # Filter out non-serializable objects to prevent JSON serialization errors
-        serializable_input = {}
-        for key, value in tool["input"].items():
-            try:
-                json.dumps(value)  # Test if serializable
-                serializable_input[key] = value
-            except (TypeError, ValueError):
-                serializable_input[key] = f"<non-serializable: {type(value).__name__}>"
+        input_parameters = json.dumps(tool["input"], default=lambda o: f"<<non-serializable: {type(o).__qualname__}>>")
 
         user_msg_content: list[ContentBlock] = [
-            {
-                "text": (
-                    f"agent.tool.{tool['name']} direct tool call.\nInput parameters: {json.dumps(serializable_input)}\n"
-                )
-            }
+            {"text": (f"agent.tool.{tool['name']} direct tool call.\nInput parameters: {input_parameters}\n")}
         ]
 
         # Add override message if provided

tests/strands/agent/test_agent.py

@@ -1616,7 +1616,7 @@ def test_agent_tool_non_serializable_parameter_filtering(agent, mock_randint):
     tool_call_text = user_message["content"][1]["text"]
     assert "agent.tool.tool_decorated direct tool call." in tool_call_text
     assert '"random_string": "test_value"' in tool_call_text
-    assert '"non_serializable_agent": "<non-serializable: Agent>"' in tool_call_text
+    assert '"non_serializable_agent": "<<non-serializable: Agent>>"' in tool_call_text
 
 
 def test_agent_tool_multiple_non_serializable_types(agent, mock_randint):
@@ -1663,11 +1663,14 @@ def __init__(self, value):
     assert '"serializable_dict": {"key": "value"}' in tool_call_text
 
     # Verify non-serializable objects are replaced with descriptive strings
-    assert '"agent": "<non-serializable: Agent>"' in tool_call_text
-    assert '"custom_object": "<non-serializable: CustomClass>"' in tool_call_text
-    assert '"function": "<non-serializable: function>"' in tool_call_text
-    assert '"set_object": "<non-serializable: set>"' in tool_call_text
-    assert '"complex_number": "<non-serializable: complex>"' in tool_call_text
+    assert '"agent": "<<non-serializable: Agent>>"' in tool_call_text
+    assert (
+        '"custom_object": "<<non-serializable: test_agent_tool_multiple_non_serializable_types.<locals>.CustomClass>>"'
+        in tool_call_text
+    )
+    assert '"function": "<<non-serializable: function>>"' in tool_call_text
+    assert '"set_object": "<<non-serializable: set>>"' in tool_call_text
+    assert '"complex_number": "<<non-serializable: complex>>"' in tool_call_text
 
 
 def test_agent_tool_serialization_edge_cases(agent, mock_randint):
@@ -1705,7 +1708,7 @@ def test_agent_tool_serialization_edge_cases(agent, mock_randint):
     assert '"nested_dict_serializable": {"nested": {"key": "value"}}' in tool_call_text
 
     # Verify non-serializable nested structure is replaced
-    assert '"nested_list_with_non_serializable": "<non-serializable: list>"' in tool_call_text
+    assert '"nested_list_with_non_serializable": [1, 2, "<<non-serializable: Agent>>"]' in tool_call_text
 
 
 def test_agent_tool_no_non_serializable_parameters(agent, mock_randint):
@@ -1731,8 +1734,8 @@ def test_agent_tool_no_non_serializable_parameters(agent, mock_randint):
     # Verify normal parameter serialization (no filtering needed)
     assert "agent.tool.tool_decorated direct tool call." in tool_call_text
     assert '"random_string": "normal_call"' in tool_call_text
-    # Should not contain any "<non-serializable:" strings
-    assert "<non-serializable:" not in tool_call_text
+    # Should not contain any "<<non-serializable:" strings
+    assert "<<non-serializable:" not in tool_call_text
 
 
 def test_agent_tool_record_direct_tool_call_disabled_with_non_serializable(agent, mock_randint):