Python: fix circular reference error in KernelArguments.dumps() during OTel diagnostics

python/semantic_kernel/functions/kernel_arguments.py

@@ -1,6 +1,7 @@
 # Copyright (c) Microsoft. All rights reserved.
 
 import json
+import logging
 from typing import TYPE_CHECKING, Any
 
 from pydantic import BaseModel
@@ -14,6 +15,8 @@
 
     from semantic_kernel.connectors.ai.prompt_execution_settings import PromptExecutionSettings
 
+logger: logging.Logger = logging.getLogger(__name__)
+
 
 class KernelArguments(dict):
     """The arguments sent to the KernelFunction."""
@@ -108,15 +111,45 @@ def __ior__(self, value: "SupportsKeysAndGetItem[Any, Any] | Iterable[tuple[Any,
         return self
 
     def dumps(self, include_execution_settings: bool = False) -> str:
-        """Serializes the KernelArguments to a JSON string."""
+        """Serializes the KernelArguments to a JSON string.
+
+        Handles arguments that contain objects with circular references (e.g.,
+        KernelProcessStepContext) by falling back to their string representation.
+        """
         data = dict(self)
         if include_execution_settings and self.execution_settings:
             data["execution_settings"] = self.execution_settings
 
-        def default(obj):
+        seen: set[int] = set()
+
+        def default(obj: Any) -> Any:
+            obj_id = id(obj)
+            if obj_id in seen:
+                return f"<circular ref: {type(obj).__name__}>"
+            seen.add(obj_id)
+
             if isinstance(obj, BaseModel):
-                return obj.model_dump()
+                try:
+                    return obj.model_dump()
+                except Exception:
+                    return f"<{type(obj).__name__}>"
 
             return str(obj)
 
-        return json.dumps(data, default=default)
+        try:
+            return json.dumps(data, default=default)
+        except ValueError:
+            # Catch circular reference errors that json.dumps raises when
+            # model_dump() produces dicts with internal circular references.
+            # This can happen with complex runtime objects like
+            # KernelProcessStepContext whose step_message_channel holds
+            # back-references to the process graph.
+            logger.debug("Circular reference detected while serializing KernelArguments, using string fallback.")
+            safe_data: dict[str, Any] = {}
+            for key, value in data.items():
+                try:
+                    json.dumps(value, default=default)
+                    safe_data[key] = value
+                except (ValueError, TypeError):
+                    safe_data[key] = f"<{type(value).__name__}>"
+            return json.dumps(safe_data, default=default)

python/tests/unit/functions/test_kernel_arguments.py

@@ -179,3 +179,47 @@ def test_kernel_arguments_ror_operator_with_invalid_type(lhs):
     """Test the __ror__ operator with an invalid type raises TypeError."""
     with pytest.raises(TypeError):
         lhs | KernelArguments()
+
+
+def test_kernel_arguments_dumps_basic():
+    """Test basic dumps serialization."""
+    kargs = KernelArguments(name="test", value=42)
+    result = kargs.dumps()
+    import json
+
+    parsed = json.loads(result)
+    assert parsed == {"name": "test", "value": 42}
+
+
+def test_kernel_arguments_dumps_with_pydantic_model():
+    """Test dumps serialization with a Pydantic model argument."""
+    from pydantic import BaseModel
+
+    class SimpleModel(BaseModel):
+        field: str = "hello"
+
+    kargs = KernelArguments(model=SimpleModel())
+    result = kargs.dumps()
+    import json
+
+    parsed = json.loads(result)
+    assert parsed == {"model": {"field": "hello"}}
+
+
+def test_kernel_arguments_dumps_with_circular_reference():
+    """Test dumps handles arguments with circular references gracefully.
+
+    This reproduces the bug from issue #13393 where KernelProcessStepContext
+    (which contains a step_message_channel that references back to the process
+    graph) caused 'Circular reference detected' errors during OTel diagnostics.
+    """
+    # Create a dict with a circular reference to simulate what happens
+    # when model_dump() produces circular structures
+    circular: dict = {"key": "value"}
+    circular["self"] = circular
+
+    kargs = KernelArguments(data=circular)
+    # This should not raise ValueError: Circular reference detected
+    result = kargs.dumps()
+    assert isinstance(result, str)
+    assert "data" in result