Python: DevUI, Fix message serialization issue, improve tests

[victordibia]

Motivation and Context

Python: DevUI, Fix message serialization issue, improve tests .
Thanks @pamelafox

Description

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
TOTAL	16230	2540	84%

report-only-changed-files is enabled. No files were changed during this commit :)

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2322	130 💤	0 ❌	0 🔥	58.916s ⏱️

[Copilot]

Pull request overview

This PR fixes a critical message serialization bug in the Python DevUI package and significantly improves test coverage. The main issue was that ExecutorCompletedEvent.data could contain nested non-JSON-serializable objects (AgentExecutorResponse with AgentRunResponse and ChatMessage), which caused serialization failures when events were sent over Server-Sent Events (SSE).

Key Changes:

• Fixed serialization of ExecutorCompletedEvent by calling _serialize_value() on the result data before including it in the event
• Corrected ExecutorFailedEvent to use the details field instead of error field
• Added comprehensive regression tests using real agent_framework classes (not mocks) to ensure proper serialization
• Removed test skips and improved test organization with a new test_helpers.py module

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
python/packages/devui/agent_framework_devui/_mapper.py	Core serialization fix: calls _serialize_value() on ExecutorCompletedEvent.data; corrects field access for ExecutorFailedEvent from 'error' to 'details'
python/packages/devui/agent_framework_devui/_server.py	Improves error logging by adding exc_info=True for better debugging context
python/packages/devui/tests/test_mapper.py	Major refactoring with new comprehensive tests for serialization, executor events, workflow events, and edge cases using real classes
python/packages/devui/tests/test_helpers.py	New file providing reusable test utilities including mock clients, agents, and factory functions for test data
python/packages/devui/tests/test_execution.py	Extensive improvements with full pipeline tests, workflow execution tests, and proper fixtures using real ChatAgent with mock LLM
python/packages/devui/tests/test_server.py	Unskipped test and improved assertions for entity discovery
python/packages/devui/tests/test_discovery.py	Unskipped agent discovery test
python/packages/devui/tests/test_cleanup_hooks.py	Fixed field name from content to contents to match API
python/packages/devui/pyproject.toml	Added pythonpath configuration for test discovery