.NET: Include ReasoningEncryptedContent by default when stored output disabled with Responses

[westey-m]

Motivation and Context

When a reasoning model is used and reasoning content items are returned, they do not necessarily contain any content, but only the ids. When coupled with store=false, this causes a failure during a multi-turn conversation, since the service doesn't have the reasoning content that the id refers to. The caller must opt in to returning the reasoning content. This change makes this the default behavior, with an opt out, if the user doesn't care about multi-turn conversations and want to save on the response payload size.

#4562

Description

• Include ReasoningEncryptedContent by default for responses when switching off service chat history storage
• Allow users to not include it, which reduces the response payload, but doesn't work with multi-turn conversations

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

Updates the OpenAI Responses client extension used by Agent Framework to support optionally including encrypted reasoning tokens when using the Responses API in a stateless configuration (store/stored output disabled).

Changes:

• Added includeReasoningEncryptedContent (default true) to AsIChatClientWithStoredOutputDisabled and conditionally adds ReasoningEncryptedContent to IncludedProperties.
• Added unit tests verifying default/true/false behavior and that the inner ResponsesClient remains accessible.
• Added a test helper that extracts CreateResponseOptions from the configured options pipeline via reflection.

Reviewed changes

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

File	Description
dotnet/src/Microsoft.Agents.AI.OpenAI/Extensions/OpenAIResponseClientExtensions.cs	Adds the new parameter and conditional CreateResponseOptions configuration when stored output is disabled.
dotnet/tests/Microsoft.Agents.AI.OpenAI.UnitTests/Extensions/OpenAIResponseClientExtensionsTests.cs	Adds coverage for the new parameter and validates the configured CreateResponseOptions via reflection.