.NET: Implement Microsoft.Agents.AI.FoundryLocal package for C#

[DavidLuong98]

Motivation and Context

The existing Microsoft.Agents.AI.Foundry package only supports cloud-based Azure AI Foundry. There is no .NET support for AI Foundry Local. Microsoft's on-device model inference product that runs models locally via an OpenAI-compatible HTTP API.

A Python implementation already exists in this repo (python/packages/foundry_local/), but C# developers have no equivalent. This PR adds that parity.

Description

Adds a new Microsoft.Agents.AI.FoundryLocal package that enables on-device model inference through the Microsoft.AI.Foundry.Local SDK (v0.9.0).

Architecture: The Foundry Local SDK internally uses Betalgo.Ranul.OpenAI, which is incompatible with Microsoft.Extensions.AI.IChatClient. To solve this, we use the SDK for model management (catalog, download, load, web service lifecycle) but create the chat client by pointing the official OpenAI NuGet package at the SDK's local HTTP endpoint (localhost:5272/v1), the same approach the Python implementation uses.

Key classes:

• FoundryLocalChatClient - DelegatingChatClient with async CreateAsync factory that handles manager bootstrapping, model download/load, and web service startup
• FoundryLocalClientOptions - Configuration (model alias, bootstrap, prepare model, web service URL, env var support via FOUNDRY_LOCAL_MODEL)
• FoundryLocalChatClientExtensions 0 .AsAIAgent() extension methods matching the OpenAIChatClientExtensions pattern

Design decisions:

• No Azure dependencies - zero references to Azure.AI.Projects or Azure.Identity
• net9.0 only - constrained by the Microsoft.AI.Foundry.Local SDK's target framework
• Static async factory (CreateAsync) because SDK initialization requires async operations (model download, load, web service start)
• Default web service URL (http://localhost:5272) always configured, matching the Python SDK's default endpoint

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass (12/12), and I have added new tests where possible
• Is this a breaking change? Nope, this is a new package with no changes to existing code.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a new .NET package (Microsoft.Agents.AI.FoundryLocal) to enable AI Foundry Local on-device inference by managing models via Microsoft.AI.Foundry.Local while using the official OpenAI client against the local OpenAI-compatible HTTP endpoint.

Changes:

• Introduces FoundryLocalChatClient, FoundryLocalClientOptions, and FoundryLocalChatClientExtensions for Foundry Local-backed IChatClient / agent creation.
• Adds unit tests for options validation and basic factory/extension argument checks.
• Adds a standalone smoke test console project and wires the new package into the .NET solution + dependency versions.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
dotnet/src/Microsoft.Agents.AI.FoundryLocal/Microsoft.Agents.AI.FoundryLocal.csproj	New package project targeting net9.0 and referencing Foundry Local + OpenAI dependencies
dotnet/src/Microsoft.Agents.AI.FoundryLocal/FoundryLocalClientOptions.cs	Adds options object with env-var model resolution
dotnet/src/Microsoft.Agents.AI.FoundryLocal/FoundryLocalChatClient.cs	Implements async factory that bootstraps manager, resolves/downloads/loads model, starts service, and builds OpenAI chat client
dotnet/src/Microsoft.Agents.AI.FoundryLocal/FoundryLocalChatClientExtensions.cs	Adds .AsAIAgent() convenience extensions for FoundryLocalChatClient
dotnet/tests/Microsoft.Agents.AI.FoundryLocal.UnitTests/Microsoft.Agents.AI.FoundryLocal.UnitTests.csproj	Adds new unit test project for FoundryLocal package
dotnet/tests/Microsoft.Agents.AI.FoundryLocal.UnitTests/FoundryLocalClientOptionsTests.cs	Unit tests for model resolution and default option values
dotnet/tests/Microsoft.Agents.AI.FoundryLocal.UnitTests/FoundryLocalChatClientTests.cs	Unit tests for CreateAsync argument/option validation
dotnet/tests/Microsoft.Agents.AI.FoundryLocal.UnitTests/FoundryLocalChatClientExtensionsTests.cs	Unit tests for extension method null argument behavior
dotnet/tests/FoundryLocal.SmokeTest/FoundryLocal.SmokeTest.csproj	Adds a non-test executable project for manual local integration verification
dotnet/tests/FoundryLocal.SmokeTest/Program.cs	Smoke test that creates a client/agent and runs a prompt against a local model
dotnet/agent-framework-dotnet.slnx	Adds the new FoundryLocal project to the solution
dotnet/Directory.Packages.props	Pins Microsoft.AI.Foundry.Local dependency version (0.9.0)