Python: Fix OpenAI Responses streaming to propagate created_at from final response.completed event

[moonbox3]

Motivation and Context

When using OpenAIChatClient with stream=True, the final streamed response had created_at=None even though the raw response.completed event contains a valid timestamp. This caused noisy warnings in durabletask persistence and incorrect metadata on streamed responses.

Fixes #5347

Description

The root cause was that _parse_chunk_from_openai extracted response_id, conversation_id, and model from the response.completed event but never read created_at. The fix adds extraction of event.response.created_at (a Unix timestamp), formats it as an ISO 8601 UTC string, and passes it through to the returned ChatResponseUpdate. A dedicated unit test verifies the timestamp is correctly propagated and formatted.

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.

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Note: PR autogenerated by moonbox3's agent

[moonbox3]

Automated Code Review

Reviewers: 4 | Confidence: 92% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage, Design Approach

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Automated review by moonbox3's agents

[moonbox3]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/openai/agent_framework_openai
_chat_client.py	916	121	86%	522–525, 529–530, 536–537, 572–578, 599, 607, 630, 748, 847, 906, 908, 910, 912, 978, 992, 1072, 1082, 1087, 1130, 1246, 1427, 1432, 1436–1438, 1442–1443, 1509, 1538, 1544, 1554, 1560, 1565, 1571, 1576–1577, 1596, 1686, 1708–1709, 1724–1725, 1743–1744, 1787, 1953, 1991–1992, 2008, 2010, 2090–2098, 2128, 2238, 2273, 2288, 2308–2318, 2331, 2342–2346, 2360, 2374–2385, 2394, 2426–2429, 2439–2440, 2451–2453, 2467–2469, 2479–2480, 2486, 2501
TOTAL	28468	3304	88%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
5688	30 💤	0 ❌	0 🔥	1m 30s ⏱️

[Copilot]

Pull request overview

Fixes OpenAI Responses streaming so the final response.completed event propagates created_at into the final ChatResponse/AgentResponse, addressing missing timestamps that caused durabletask persistence warnings and incorrect response metadata.

Changes:

• Extract event.response.created_at in _parse_chunk_from_openai() for response.completed events and set it on ChatResponseUpdate.
• Add a unit test asserting created_at is propagated and formatted as ISO-8601 UTC (...Z) for streaming completion.
• Adjust optional orjson imports in conversation samples with a type-ignore annotation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
python/packages/openai/agent_framework_openai/_chat_client.py	Propagates created_at from response.completed streaming events into ChatResponseUpdate.
python/packages/openai/tests/openai/test_openai_chat_client.py	Adds/updates tests to validate streamed created_at propagation and formatting.
python/samples/02-agents/conversations/file_history_provider.py	Updates optional orjson import with a type-ignore comment.
python/samples/02-agents/conversations/file_history_provider_conversation_persistence.py	Updates optional orjson import with a type-ignore comment.

[moonbox3]

Automated Code Review

Reviewers: 4 | Confidence: 94% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage, Design Approach

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Automated review by moonbox3's agents