.NET: Enable access to hosted AIAgents via OpenAI Responses (#947)

* init

* wip

* wip wip wip

* wip wip

* open up API

* enable for multiple agents

* more wip

* make frontend respond.

* wip

* not sure if proper setup

* define type

* cleanup

* frontend streaming wip

* use System.Net.ServerSentEvents

* usings

* reformat via ichatclient

* merge main renaming + refactor

* fix main merge + fix sample (a2a change)

* fix sample

* some rebase (not working yet)

* make it at least build somehow

* make non-stream work without internal types

* Input without custom models

* implement streaming

* test frontend

* enable alerts and fix

* build fixes & rereview

* Update dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI.Responses/Microsoft.Agents.AI.Hosting.OpenAI.Responses.csproj

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI.Responses/Utils/ResponseItemJsonConverter.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* fix agent discovery

* rename

* rename project into Microsoft.Agents.AI.Hosting.OpenAI (no responses in name)

* PR address comments x1

* address PR comments x2

* correctly instantiate OpenAIResponse

* address PR comments x3

* reconfigure JSON serialization & handle AOT warnings

* fix build

* proper ref

* check update differently

* correct check

* exclude dotnet format diagnostics for IL2026 and IL3050

* space  :)

* re-review

* add comments

* remove unnecessary using

* always take last openai response item

* set responseItem Id explicitly

* add agent.name validation for uri

* cleanup

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: SergeyMenshykh <68852919+SergeyMenshykh@users.noreply.github.com>

dotnet/src/Microsoft.Agents.AI.Workflows/TurnToken.cs

@@ -1,10 +1,12 @@
 // Copyright (c) Microsoft. All rights reserved.
 
+using Microsoft.Extensions.AI;
+
 namespace Microsoft.Agents.AI.Workflows;
 
 /// <summary>
 /// Sent to an <see cref="AIAgent"/>-based executor to request
-/// a response to accumulated <see cref="Extensions.AI.ChatMessage"/>.
+/// a response to accumulated <see cref="ChatMessage"/>.
 /// </summary>
 /// <param name="emitEvents">Whether to raise AgentRunEvents for this executor.</param>
 public class TurnToken(bool? emitEvents = null)