Python: removed additional properties from messages sent to OAI responses and chat completions

[eavanvalkenburg]

Motivation and Context

The Responses API gives an error when additional properties are set on a chat message and some services did not send additional properties while Responses and OpenAI chat did, this removes that. The API docs for both also do not mention any other fields, but apparantely the Chat Completion API did not complain while Responses did.

Also adds a note on this to the docstring of ChatMessage.

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.

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
_types.py	945	99	89%	130–131, 149–150, 287, 289, 296, 315, 355, 401–402, 438, 588, 702–703, 705, 730, 737, 754–756, 829, 834–835, 837, 844–845, 847, 869, 876, 879–881, 886–887, 893–895, 1019, 1106–1109, 1117–1118, 1209, 1390, 1396, 1640–1642, 1648–1649, 1817, 1948, 1953, 1957, 1961, 2142, 2193–2197, 2207, 2212, 2671, 2757–2759, 2832, 2843–2844, 3018, 3022, 3034–3036, 3137–3139, 3141–3143, 3146, 3150, 3153, 3158, 3203–3204, 3211–3212, 3246–3248, 3263, 3279, 3307, 3314
packages/core/agent_framework/openai
_chat_client.py	234	43	81%	110–111, 115, 133, 143–144, 146, 157, 171, 173–176, 185, 197, 233, 264, 269–283, 290–292, 367, 374, 376, 378, 396–397, 403, 419
_responses_client.py	414	70	83%	144–145, 148–149, 155–156, 159, 166, 201, 231, 259–260, 287, 291, 308, 313, 355, 419, 494, 499, 503–505, 526, 541–542, 546–548, 596, 616–617, 630–631, 647–648, 686, 688, 726, 728, 737–738, 751, 753, 826–832, 849–854, 873, 891, 901, 903, 921–922, 924–926, 937–938, 941, 943
TOTAL	15036	2216	85%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2183	127 💤	0 ❌	0 🔥	57.513s ⏱️

[Copilot]

Pull Request Overview

This PR removes the mapping of ChatMessage.additional_properties to a "metadata" field when sending messages to OpenAI's Responses API and Chat Completions API. The Responses API rejects requests with additional properties on messages, causing errors. The PR also adds documentation clarifying that additional_properties are for internal Agent Framework use only and are not sent to external services.

• Removed code that was sending message.additional_properties as "metadata" to OpenAI services
• Added inline documentation to ChatMessage.__init__() overloads and class docstring
• Fixes API errors with the OpenAI Responses API

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
python/packages/core/agent_framework/openai/_responses_client.py	Removed lines that mapped message.additional_properties to args["metadata"] in the message parser
python/packages/core/agent_framework/openai/_chat_client.py	Removed lines that mapped message.additional_properties to args["metadata"] in the message parser
python/packages/core/agent_framework/_types.py	Added documentation to clarify that additional_properties are used within Agent Framework and are not sent to services