Python: Emit ExecutorFailedEvent before WorkflowFailedEvent when executor throws exception

[moonbox3]

Motivation and Context

When an executor throws an exception, the ExecutorFailedEvent is queued via context.add_event() but never yielded to the stream. This happens because when the start executor fails, it runs before run_until_convergence(), so the exception bypasses the runner's event draining logic entirely.

The fix is to drain any pending events from the context before yielding WorkflowFailedEvent in the exception handler of _run_workflow_with_tracing().

Description

• Fixes Python: [Bug] Missing ExecutorFailedEvent in workflow if an executor throws exception #2508
• Add unit tests for coverage

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
packages/core/agent_framework/_workflows
_workflow.py	250	18	92%	94, 267–269, 271–272, 290, 314, 316, 413, 662, 696, 701, 704, 723–725, 790
TOTAL	15863	2416	84%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2266	130 💤	0 ❌	0 🔥	55.356s ⏱️

[Copilot]

Pull request overview

This PR fixes an issue where ExecutorFailedEvent was not being emitted before WorkflowFailedEvent when an executor throws an exception. The fix ensures that pending events queued via context.add_event() are drained and yielded before WorkflowFailedEvent in the exception handler.

• Added event draining logic in the exception handler of _run_workflow_with_tracing() to ensure ExecutorFailedEvent is emitted before WorkflowFailedEvent
• Added comprehensive test coverage for both start executor failures and non-start executor failures in a chain
• Added test assertions to verify the correct event ordering

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
python/packages/core/agent_framework/_workflows/_workflow.py	Added logic to drain pending events from context before yielding WorkflowFailedEvent in the exception handler
python/packages/core/tests/workflow/test_workflow_states.py	Added test coverage for event ordering, including a new PassthroughExecutor class and test_executor_failed_event_from_second_executor_in_chain() test case

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