Python: OpenAI Clients accepting api_key callback

[giles17]

Motivation and Context

Closes #1070

Description

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.

[Copilot]

Pull Request Overview

Adds support for supplying OpenAI API keys via a callable (sync or async) to enable dynamic token refresh. Implements a refresh hook invoked before each request/stream across Chat, Responses, and Assistants clients, and adds corresponding tests.

• Extend api_key parameters/types to accept callables returning str or Awaitable[str]
• Add _refresh_api_key logic and invoke it before request/stream calls
• Add tests for callable API key initialization and refresh behavior

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
python/packages/core/agent_framework/openai/_shared.py	Introduces callable/awaitable API key support and refresh mechanism in shared base classes.
python/packages/core/agent_framework/openai/_responses_client.py	Integrates API key refresh into responses client request/stream paths; updates constructor to accept callable key.
python/packages/core/agent_framework/openai/_chat_client.py	Adds refresh calls and callable api_key handling to chat client.
python/packages/core/agent_framework/openai/_assistants_client.py	Adds refresh call for streaming and callable api_key handling to assistants client.
python/packages/core/tests/openai/test_openai_responses_client.py	Adds tests for callable API key and refresh sequence (responses client).
python/packages/core/tests/openai/test_openai_chat_client.py	Adds tests for callable API key and refresh sequence (chat client).
python/packages/core/tests/openai/test_openai_assistants_client.py	Adds tests for callable API key and refresh sequence (assistants client).

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[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework/openai
_assistants_client.py	201	28	86%	175, 188, 191, 197–198, 201, 204, 207–208, 237, 239, 241, 243, 246, 249, 252, 256, 266, 350, 387, 423, 452–455, 505–506, 508
_chat_client.py	231	45	80%	106–107, 111, 129, 139–140, 142, 153, 160, 164, 166–169, 218, 249, 254–268, 275–277, 354, 357, 359, 361, 384–385, 391, 407, 439, 441, 452
_responses_client.py	403	64	84%	141–142, 145–146, 152–153, 156, 163, 195, 204, 216, 246, 274–275, 298, 319, 381, 476, 479, 494–495, 499–501, 549, 569–570, 583–584, 600–601, 634, 636, 680, 684, 686, 695, 697, 706–707, 720, 722, 795–801, 818–823, 842, 860, 870, 872, 890–891, 893–895
_shared.py	93	12	87%	65, 71–74, 139, 152, 154, 161, 163, 237, 261
TOTAL	10267	1701	83%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
1246	98 💤	0 ❌	0 🔥	28.036s ⏱️