Python: Add executor I/O data to ExecutorInvokedEvent and ExecutorCompletedEvent

[moonbox3]

Motivation and Context

Enables observing executor input/output without modifying executor code:

• ExecutorInvokedEvent.data now contains the input message received by the executor
• ExecutorCompletedEvent.data now contains messages sent via ctx.send_message()
• Added WorkflowContext.get_sent_messages() to track sent messages during handler execution

This aligns Python behavior with .NET, where these events already carry I/O data.

Description

• Closes Python: Executor with decorator doesn't generate AgentRunUpdateEvent event #2536
• Added unit tests for executor event data
• Added executor_io_observation.py sample demonstrating the feature
• Fixed fragile test in test_handoff.py to use AgentRunEvent type check

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
_executor.py	142	6	95%	208, 326, 341, 343, 458, 468
_workflow_context.py	168	26	84%	60–61, 69, 73, 87, 163, 188, 298, 403, 412, 417, 438–440, 442, 444–445, 447–448, 457–459, 461–463, 465
TOTAL	15891	2416	84%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2286	130 💤	0 ❌	0 🔥	58.509s ⏱️

[Copilot]

Pull request overview

This PR adds executor input/output data to workflow events, enabling observability of executor I/O without modifying executor code. The implementation tracks messages sent via ctx.send_message() and exposes them through ExecutorInvokedEvent.data and ExecutorCompletedEvent.data, aligning Python behavior with the .NET implementation.

Key changes:

• Added WorkflowContext._sent_messages tracking and get_sent_messages() method to capture messages sent during handler execution
• Updated ExecutorInvokedEvent to include the input message as event data
• Updated ExecutorCompletedEvent to include sent messages as event data (or None if no messages were sent)

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
python/samples/getting_started/workflows/observability/executor_io_observation.py	New sample demonstrating executor I/O observation through streaming events with two executors and helper formatting function
python/samples/getting_started/workflows/README.md	Added documentation entry for the new executor I/O observation sample
python/packages/core/tests/workflow/test_handoff.py	Improved test robustness by using explicit AgentRunEvent type check and removing fragile attribute checks
python/packages/core/tests/workflow/test_executor.py	Added comprehensive unit tests covering input data in invoked events, sent messages in completed events, and complex message types
python/packages/core/agent_framework/_workflows/_workflow_context.py	Implemented _sent_messages tracking in send_message() and added get_sent_messages() method; added type ignore comment to existing deprecated method
python/packages/core/agent_framework/_workflows/_executor.py	Updated executor event creation to include input message in ExecutorInvokedEvent and sent messages in ExecutorCompletedEvent