Python: Allow OpenAI function results without call IDs

[mikemikimike]

Motivation & Context

The OpenAI Responses API permits function_call_output items without a call_id, but Agent Framework currently requires one when constructing function-result content and serializes an absent value as "call_id": null. This makes adapting OpenAI-compatible SDK payloads unnecessarily difficult.

Description & Review Guide

• What are the major changes? Content.from_function_result now accepts an omitted call ID, and the OpenAI Responses serializer only includes call_id when one is provided.
• What is the impact of these changes? Function results without IDs can be represented and sent without a null field; existing function results with IDs retain their current payload.
• What do you want reviewers to focus on? Please review the optional-field boundary and the unchanged ID-preserving path. The function-calling specification matrix now names this provider scenario and links it to the regression test in packages/openai/tests/openai/test_openai_chat_client.py.
• Local checks: The OpenAI package's non-integration test suite passes, focused core factory tests pass, Ruff 0.16.3 checks pass, targeted Pyright passes for both changed source files, and both affected packages build successfully.
• Known environment limitation: The full core test and standard dependency type-checking sweeps require optional mcp, agent-hooks, and related workspace packages that are not installed in this checkout.
• Review status: This pull request remains a draft for maintainer confirmation of the function-calling contract.

Related Issue

Fixes #7922

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible (the focused core tests and full OpenAI package suite pass; the full core sweep is limited by optional workspace dependencies noted above)
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change.

[Copilot]

Pull request overview

Allows OpenAI Responses API function results to omit call_id instead of serializing it as null.

Changes:

• Makes Content.from_function_result accept an optional call ID.
• Conditionally serializes call_id.
• Adds regression tests for ID-less results.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
python/packages/core/agent_framework/_types.py	Makes result call IDs optional.
python/packages/core/tests/core/test_types.py	Tests ID-less result construction.
python/packages/openai/agent_framework_openai/_chat_client.py	Omits absent IDs from Responses payloads.
python/packages/openai/tests/openai/test_openai_chat_client.py	Tests serialization with no call ID.

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[mikemikimike]

Addressed in commit 69bba19: added the OpenAI function-result-without-call-ID row to docs/specs/004-python-function-calling-loop.md and linked it to test_prepare_content_for_openai_function_result_without_call_id.