.NET: Remove AGUI history special cases from ChatClientAgent

[Javier Calvarro Nelson (javiercn)]

Motivation & Context

ChatClientAgent contains provider-name checks that exempt AG-UI clients from the normal conversation ID and chat-history rules. Current AGUI.Client follows Microsoft.Extensions.AI service-managed-history semantics: it keeps AG-UI thread identity on protocol events and does not return a ConversationId. The framework no longer needs an AG-UI-specific workaround.

Description & Review Guide

• What are the major changes? Removed the AG-UI provider constant and both AG-UI-specific branches from ChatClientAgent, restoring the normal provider-agnostic conversation ID and ChatHistoryProvider logic. Strengthened the real AGUI.Client two-turn integration test to verify that no service-managed ConversationId is exposed and that the default InMemoryChatHistoryProvider retains both turns.
• What is the impact of these changes? AG-UI-backed agents continue using local history because AGUI.Client returns no ConversationId, while any chat client that does return one now follows the same service-managed-history conflict and provider-disengagement behavior regardless of provider name. Validation passed for the focused AG-UI regression on net8.0, net9.0, and net10.0; the ChatClient history-management tests and the full Microsoft.Agents.AI.UnitTests project passed on net10.0 and net472 (2,039 and 1,903 tests respectively).
• What do you want reviewers to focus on? Confirm that removing the provider-name gates fully restores the intended provider-agnostic semantics and that the two-turn AG-UI test captures the service-managed-history contract.

Related Issue

Fixes #7299

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. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

Pull request overview

Removes AG-UI-specific history handling so ChatClientAgent consistently applies provider-agnostic conversation and history semantics.

Changes:

• Removed AG-UI provider-name checks from conversation ID conflict and history-provider resolution.
• Expanded AG-UI integration coverage to verify local two-turn history and absent conversation IDs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgent.cs	Removes AG-UI history special cases.
dotnet/tests/Microsoft.Agents.AI.Hosting.AGUI.AspNetCore.IntegrationTests/BasicStreamingTests.cs	Verifies AG-UI local history across two turns.

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[github-actions]

MAF Automated Review — Iteration 1

Result: Findings reported
Scope: full PR (1 commit(s)): abe5e0d8ba34
Model: gpt-5.6-sol

Overview

The change restores provider-agnostic history ownership for current AGUI.Client, backed by a real-client two-turn integration test that verifies null conversation IDs and four locally retained messages. The generic service-managed-history guards remain well covered. However, removing the provider gate also changes the established contract for the previously published AG-UI client, whose returned thread ID did not mean that it stored history.

Reviewed the supplied pull-request change set across correctness, security/reliability, architecture, and failure behavior.
1 verified finding remained after source verification (1 medium) across 1 file. Details are attached to the affected lines below.

Affected areas: dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgent.cs

[westey (westey-m)]

Thanks for making the end to end updates Javier Calvarro Nelson (@javiercn)!