.NET: Pass AdditionalProperties from parent to child when exposing an agent as a FunctionTool

[westey-m]

Motivation and Context

#3127

Description

• Pass AdditionalProperties from parent to child when exposing an agent as a FunctionTool

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

This PR enables the propagation of AdditionalProperties from a parent agent to a child agent when the child is exposed as a FunctionTool. This allows custom properties set on the parent agent's run context to flow through to nested agent invocations.

Changes:

• Modified AgentExtensions.AsAIFunction to extract AdditionalProperties from the parent agent's FunctionInvokingChatClient context and pass them to the child agent via AgentRunOptions
• Added a comprehensive unit test to verify that AdditionalProperties are correctly passed from parent to child agent
• Added a helper method in the test class to use reflection for setting the FunctionInvokingChatClient's CurrentContext for testing purposes

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
dotnet/src/Microsoft.Agents.AI/AgentExtensions.cs	Modified InvokeAgentAsync to propagate AdditionalProperties from FunctionInvokingChatClient.CurrentContext to child agent options
dotnet/tests/Microsoft.Agents.AI.UnitTests/AgentExtensionsTests.cs	Added test for AdditionalProperties propagation and helper method for setting CurrentContext via reflection; enhanced TestAgent to track received AgentRunOptions

[rogerbarreto]

We might be missing the ChatOptions here.

I would addtionally check if the agent is a ChatClientAgent and provide the FunctionInvokingChatClient.CurrentContext?.Options as new ChatClientAgentRunOptions { ChatOptions = options } and if not use the current proposed code approach.

Suggest adding an additional test UT to covering ChatClientAgent (and non-chatclientagents, which seems a bit odd as I think this is exclusive to ChatClientAgents and FICC scenarios..)

[westey-m]

I'm not sure that we can pick the entire ChatOptions and pass it down.
E.g. we shouldn't be passing tools, conversation id, instructions, AllowBackgroundResponses, ContinuationToken or ResponseFormat, since all of these would be based on the behavior and underlying service of the parent agent, and may cause the child agent to behave incorrectly.

[rogerbarreto]

I'm not sure that we can pick the entire ChatOptions and pass it down.
E.g. we shouldn't be passing tools, conversation id, instructions, AllowBackgroundResponses, ContinuationToken or ResponseFormat, since all of these would be based on the behavior and underlying service of the parent agent, and may cause the child agent to behave incorrectly.

I'm trying to understand why AdditionalProperties have a different criteria compared to other Properties, sound a bit inconsistent.

[westey-m]

The main difference is that they are not used by the AF/MEAI stack, but customers may need them to pass their data down the stack.