Python: restore WorkflowAgent pending request state across AgentSession resume

[Copilot]

Motivation and Context

Magentic workflows that pause on request_info (human plan review) could not be resumed after AgentSession serialization/restore, even when replying with the original request_id. The resumed run lost pending-request correlation and failed instead of continuing execution.

Description

• Pending request persistence in AgentSession

  • WorkflowAgent now stores pending request_info metadata in session.state["workflow_agent"]["pending_request_info_events"] and rehydrates it on subsequent runs.

• Resume path now supports restore+response in one call

  • When pending requests exist, WorkflowAgent forwards checkpoint_id and checkpoint_storage together with responses into workflow.run(...), so checkpoint restore and request fulfillment happen on the same execution path.

• Pending-response input handling

  • While resolving pending requests, the agent uses current input messages (approval/function responses) rather than full history payloads, preventing non-response content from being misinterpreted during resume.

• Regression coverage

  • Added a focused workflow-agent test for:
    • emit request_info
    • serialize/deserialize AgentSession
    • restore from checkpoint
    • resume with same request_id
    • verify completion path advances

# restored session + same request_id + checkpoint restore
result = await restored_agent.run(
    response_message,
    session=restored_session,
    checkpoint_id=checkpoint_with_request.checkpoint_id,
    checkpoint_storage=checkpoint_storage,
)

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.

[TaoChenOSU]

@copilot why is this needed?

[Copilot]

Good catch — it wasn’t required for functionality. I reverted that simplification and restored the previous explicit form in commit aee043d.