.NET: Pass ChatClientAgent tools per run only rather than setting on FICC

[westey (westey-m)]

Motivation & Context

Setting tools both on FICC and passing them on ChatOptions duplicates the tools.

Description & Review Guide

• What are the major changes?
• What is the impact of these changes?
• What do you want reviewers to focus on?

Related Issue

Fixes #

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]

🟡 Changes recommended

Four existing Anthropic tests retain assertions that will fail under the new tool-scoping behavior.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Scopes ChatClientAgent tools per agent run, preventing duplication and leakage through shared clients.

Changes:

• Removes tool assignment to shared FunctionInvokingChatClient.AdditionalTools.
• Adds coverage for tool isolation between agents.

File summaries

File	Description
dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientExtensionsTests.cs	Tests shared-client tool isolation.
dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientExtensions.cs	Keeps tools in per-agent chat options.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

[github-actions]

MAF Automated Review — Iteration 1

Result: Findings reported
Scope: full PR (1 commit(s)): eb91ee35bbd9
Model: gpt-5.6-sol-fast

Overview

The PR removes agent-specific tools from shared FunctionInvokingChatClient state and relies on the existing per-run ChatOptions.Tools merge path instead. Constructor cloning, request-level merging, streaming and non-streaming forwarding, and the new shared-client regression test support that runtime contract. However, four tests in the active Anthropic unit-test project still require tools in AdditionalTools, so the current change deterministically breaks that suite.

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/ChatClientExtensions.cs