fix(devui): Fix serialization of dataclass events in workflow mapper

[moti-malka]

Summary

This PR fixes a serialization bug in the devui package that causes PydanticSerializationError when using workflows with group chat orchestrators.

Problem

When running devui with a workflow that uses AgentBasedGroupChatOrchestrator, users encounter:

PydanticSerializationError: Unable to serialize unknown type: <class 'agent_framework._types.AgentResponse'>

Root Cause

The _convert_workflow_event method in _mapper.py handles legacy workflow events by serializing their data field. The original implementation only checked for to_dict() method:

if raw_event_data is not None and hasattr(raw_event_data, "to_dict"):
    serialized_event_data = raw_event_data.to_dict()

However, GroupChatResponseReceivedEvent.data contains AgentExecutorResponse, which is a dataclass (not a SerializationMixin). This dataclass contains nested AgentResponse objects that Pydantic cannot serialize directly.

Solution

The MessageMapper class already has a _serialize_value() method that properly handles:

• SerializationMixin objects (via to_dict())
• Dataclasses (via recursive field serialization)
• Nested structures
• Primitive types

Changed to use this existing method instead of the limited to_dict() check.

Testing

• Tested with devui . --log-level DEBUG running a workflow with AgentBasedGroupChatOrchestrator
• Verified GroupChatResponseReceivedEvent serializes correctly without errors

Changes

File	Change
python/packages/devui/agent_framework_devui/_mapper.py	Use _serialize_value() for legacy event serialization

Backwards Compatibility

✅ Fully backwards compatible - This change:

• Uses an existing internal method already used elsewhere in the class
• Doesn't change any public APIs
• Objects with to_dict() still serialize correctly via _serialize_value()
• Adds support for dataclasses that were previously failing

[Copilot]

Pull request overview

This PR fixes two runtime bugs in the devui package that occur when running workflows with AgentBasedGroupChatOrchestrator:

1. Serialization error: The mapper was using to_dict() to serialize event data, but GroupChatResponseReceivedEvent.data contains AgentExecutorResponse, a dataclass that doesn't have to_dict(). The fix switches to the existing _serialize_value() method which properly handles dataclasses, SerializationMixin objects, and nested structures.

2. ChatMessage constructor: Changed from positional to keyword argument for contents parameter, making the code more explicit and resilient to API changes.

Changes:

• Fixed serialization of dataclass events in mapper by using _serialize_value() instead of to_dict()
• Fixed ChatMessage constructor call to use keyword argument for contents

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
python/packages/devui/agent_framework_devui/_mapper.py	Use _serialize_value() for legacy event serialization to handle dataclasses like AgentExecutorResponse
python/packages/devui/agent_framework_devui/_executor.py	Use keyword argument for ChatMessage contents parameter for clarity

[moti-malka]

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