Add Microsoft.Extensions.AI implementations for dotnet SDK

[Meir017]

I would be really useful being able to use the CopilotClient as an IChatClient

similar to:

• Google feat: Add Microsoft.Extensions.AI implementations to Google.GenAI googleapis/dotnet-genai#81
• Anthropics - Add Microsoft.Extensions.AI support anthropics/anthropic-sdk-csharp#10
• Mistral - Add Microsoft.Extensions.AI IChatClient / IEmbeddingGenerator implementations tghamm/Mistral.SDK#6
• OpenAI - https://www.nuget.org/packages/Microsoft.Extensions.AI.OpenAI

FYI @stephentoub

[github-actions]

Thank you for opening this issue, @Meir017!

I've labeled this as an enhancement for the dotnet SDK. This is a well-documented request to add IChatClient implementation from Microsoft.Extensions.AI, similar to other SDK providers you've referenced.

The request is clear with good context and examples. The team will review this feature request.

AI generated by Issue Triage Agent

[SteveSandersonMS]

Thanks for the suggestion. We've been discussing it with the .NET team (and for context, I was one of the creators of Microsoft.Extensions.AI along with @stephentoub so I'm very familiar).

At the moment we think AIAgent might be the closer-matching abstraction for GitHub Copilot SDK's agents since our APIs don't follow a request-response model. But maybe the right design is for us to have helpers in the .NET SDK here that can map between Copilot SDK and AIContent types in both directions, and then it is almost trivial for external code to create either an IChatClient or an AIAgent that wraps Copilot SDK sessions using whatever rules it wants about the request-response correlations.

[stephentoub]

For reference, there's also a PR adding a copilot SDK-based AIAgent to the Agent Framework repo here:
microsoft/agent-framework#3395

[Meir017]

@SteveSandersonMS maybe the dotnet section of this repo should mention the integration in the agent framework repo?