[Naveen Chatlapalli (1aifanatic)]

Motivation & Context

An AG-UI endpoint can stream normal replies without any visible reasoning when the agent has not requested a provider-supported summary. The sample README does not explain where to configure this or how to distinguish a provider configuration issue from a frontend rendering issue.

Description & Review Guide

• What are the major changes? Add a reasoning-summary section with ChatClientAgentOptions.ChatOptions.Reasoning, the equivalent Harness configuration, provider/API compatibility guidance, and a three-stage diagnostic path from TextReasoningContent to SSE to the frontend.
• What is the impact of these changes? Documentation only. The sample's default model connection and behavior are unchanged. The guide distinguishes reasoning effort from summary output and links to the existing Responses-based Harness sample.
• What do you want reviewers to focus on? Whether the setup and diagnostic steps answer the reported documentation gap. The C# example compiles against current repository projects; a provider-free smoke check with the pinned AGUI.Server package emitted REASONING_MESSAGE_CONTENT with the expected summary, followed by normal text and a successful run finish. Harness reasoning options also compile. No live model call or frontend test was performed; no new framework behavior is claimed.

Related Issue

Fixes #8426. The reporter confirmed that existing reasoning options work and requested documentation. No competing PR was found in issue cross-references or PR searches.

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• 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]

Copilot review overview

🟢 Approval recommended

The documentation accurately reflects the current agent, Harness, and AG-UI streaming APIs.

Review effort: Balanced
Findings: None

What changed in this PR

Documents how AG-UI reasoning summaries are configured and diagnosed.

Changes:

• Adds standard and Harness agent configuration guidance.
• Explains provider/API compatibility and troubleshooting steps.

File	Description
dotnet/​samples/​02-agents/​AGUI/​README.md	Adds reasoning-summary setup and diagnostics.

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