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Python: [Bug]: SerializationMixin does not recursively serialize nested containers #7788
Description
Description
SerializationMixin.to_dict() serializes framework objects when they are direct list items or dictionary values, but it stops after one container level. A SerializationProtocol object nested inside a combination such as dict -> list -> dict remains in the returned mapping. As a result, SerializationMixin.to_json() raises TypeError for otherwise supported nested state.
Expected: supported objects are recursively converted at any list/dictionary depth, while unsupported values keep the existing behavior of being skipped.
Actual: nested supported objects are returned unchanged and cannot be JSON encoded.
Code Sample
from agent_framework._serialization import SerializationMixin
class Item(SerializationMixin):
def __init__(self, value: str):
self.value = value
class Container(SerializationMixin):
def __init__(self, payload: dict):
self.payload = payload
container = Container({"groups": [{"items": [Item("example")]}]})
container.to_json()Error Messages / Stack Traces
TypeError: Object of type Item is not JSON serializable
Package Versions
agent-framework-core: 1.14.0 and current main (ab6c4d2dc8573071d7f73fd8c94a8cb15a2c78a2)
Python Version
Python 3.12.14
Additional Context
The same behavior occurs for list -> dict and deeper nested dictionaries. Direct list items and direct dictionary values already serialize correctly.
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github-actions commentedon Aug 21, 2026
🤖 Automated triage reproduction notes (agent-authored — trust but verify)
Agent analysis
Repro:
python/packages/core/agent_framework/_serialization.py::SerializationMixin.to_dictat lines 345-389 stops traversing when a list or dictionary contains another container, andto_jsonfails at line 416. Trigger it with aSerializationMixinattribute shaped asdict -> list -> dict -> list -> SerializationMixin; the focused test constructs that shape and observesTypeError: Object of type Item is not JSON serializable.python/packages/core/tests/core/test_serializable_mixin.py::TestSerializationMixin::test_to_json_with_serialization_protocol_in_nested_containers1.14.01.14.0