[Agents] ChatCompletionAgent.InvokeAsync<T> — expose IChatClient structured output through the agent layer

[ericstj]

Problem

IChatClient (M.E.AI preview) supports GetResponseAsync<T>() for structured output via JSON schema. ChatCompletionAgent in SK 1.45 doesn't surface this, so developers who want typed responses from a named agent must bypass the agent abstraction entirely.

This creates a choice: use M.E.AI IChatClient directly (typed output, no agent identity) or use SK ChatCompletionAgent (agent identity, no typed output). Symphony and similar orchestration patterns need both.

Proposed API

var pow = await agent.InvokeAsync<ProofOfWork>(prompt);
// where ProofOfWork is a [JSonSerializable] C# record

Cross-provider coverage

• OpenAI: response_format: json_schema ✅
• Azure OpenAI: same ✅
• Google Gemini: response_schema ✅
• Anthropic Claude: tool-use workaround ⚠️

Reference

• Symphony spec: https://github.com/openai/symphony/blob/main/SPEC.md §2 "proof of work"
• M.E.AI IChatClient: https://learn.microsoft.com/en-us/dotnet/ai/ai-extensions-overview
• POC: https://github.com/microsoft/dotnet-app-plat-sideops/issues/38

[stephentoub]

I'm not understanding this issue. Did you intend to open one in the agent framework repo instead? You mention SK, but SK agents have been superceded by agent framework, and agent framework does expose structured output support now.