Python: fix(orchestrations): preserve multimodal content during agent handoff

[Manideep Malyala (manideep-malyala)]

Fixes #7822 (replaces #7823)

Summary

• Preserves semantic multimodal content (uri, data, hosted_file, hosted_vector_store) for user messages during orchestrator handoffs.
• Keeps assistant and other non-user messages text-only to prevent OpenAI API serialization failures.
• Strips runtime-only tool-control payloads (function_call, function_result, approval_response).
• Added unit tests in test_handoff.py covering all multimodal variants and regression test in test_sequential.py.

[Copilot]

🟡 Changes recommended

The sequential regression test iterates an input type that may be non-iterable, causing type-checking failure.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Preserves supported multimodal user content during orchestrator handoffs while removing runtime-only control payloads.

Changes:

• Adds role-aware semantic content filtering.
• Expands multimodal handoff tests.
• Adds sequential URI propagation coverage.

File summaries

File	Review
python/packages/orchestrations/tests/test_sequential.py	Requires narrowing AgentRunInputs before iteration to satisfy type checking.
python/packages/orchestrations/tests/test_handoff.py	Covers multimodal preservation and control-content filtering.
python/packages/orchestrations/agent_framework_orchestrations/_orchestrator_helpers.py	Preserves allowed user multimodal content during cleanup.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Balanced

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[Copilot]

🔵 Needs a closer look

The role-sensitive serialization changes require final human review.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 0 new
• Review effort level: Balanced