Tool grouping

[MackinnonBuck]

Summary

This PR demonstrates a prototype middleware that allows grouping related tools. Groups are hidden from the inner chat client by default, but a well-known "expand" function can be called to expand one group at a time. By reducing the number of tools available to the model at a time, its ability to select the correct tool improves.

Following is an overview of the changes in this PR:

• Add ToolGroupingChatClient, which provides tool grouping and expansion functionality.
• Introduce AIToolGroup to model stable, named batches of tools.
• Add integration tests validating the feasibility of approach.

Usage example

using Microsoft.Extensions.AI;

var travelUtilities = AIToolGroup.Create(
    "TravelUtilities",
    "Travel planning helpers that generate itinerary tokens.",
    [generateItinerary, summarizePacking]);

var financeUtilities = AIToolGroup.Create(
    name: "FinanceUtilities",
    description: "Budgeting helpers.",
    tools: [budgetTool]));

var options = new ChatOptions
{
    Tools = [travelUtilities, financeUtilities]
};

IChatClient client = baseClient
    .AsBuilder()
    .UseToolGrouping(/* ... */)
    .UseToolReduction(/* ... */) // Optionally further reduce the set of available tools
    .UseFunctionInvocation()
    .Build();

var response = await client.GetResponseAsync("Plan a weekend getaway to Lisbon and include a budget tip.");
// ...

Implementation notes

This middleware contains a lot of the same complexities present in FunctionInvokingChatClient: cloning options, honoring ConversationId, aggregating Usage across inner calls, and replaying tool-result messages into the history. The expansion loop is deliberately limited to one active group per top-level request to prevent degradation of tool selection as the number of expanded groups increases.

Microsoft Reviewers: Open in CodeFlow