.NET: [Bug]: AGUIChatClient doesnt forward/populate AdditionalProperties

[MD-V]

Description

When the AGUIChatClient constructs the RunAgentInput it doesn't populate the ForwardedProperties property.

Currently there seems no way to supply those ForwardedProperties in any way.

Code Sample

AGUIChatClient:

// Create the input for the AGUI service
var input = new RunAgentInput
{
    // AG-UI requires a thread ID to work, but for FunctionInvokingChatClient that
    // implies the underlying client is managing the history.
    ThreadId = threadId,
    RunId = runId,
    Messages = messagesList.AsAGUIMessages(this._jsonSerializerOptions),
    State = state,
};

Error Messages / Stack Traces

Package Versions

Microsoft.Agents.AI.AGUI

.NET Version

.NET 10

Additional Context

No response

[github-actions]

🤖 Automated triage reproduction notes (agent-authored — trust but verify)

Agent analysis

Repro: AGUIChatClient.AGUIChatClientHandler.GetStreamingResponseAsync() in dotnet/src/Microsoft.Agents.AI.AGUI/AGUIChatClient.cs (lines 208-217) constructs RunAgentInput without ever setting ForwardedProperties, even when the caller provides them via ChatOptions.AdditionalProperties["ag_ui_forwarded_properties"]. The server-side equivalent in AGUIEndpointRouteBuilderExtensions.cs (line 140) already reads input.ForwardedProperties successfully, demonstrating the expected pattern. Minimal repro: create an AGUIChatClient, call GetStreamingResponseAsync with ChatOptions containing AditionalProperties["ag_ui_forwarded_properties"] = JsonElement, and observe the HTTP request body has no forwardedProps field.

• Failing test: dotnet/tests/Microsoft.Agents.AI.AGUI.UnitTests/AGUIChatClientForwardedPropertiesTests.cs
• Files examined: dotnet/src/Microsoft.Agents.AI.AGUI/AGUIChatClient.cs, dotnet/src/Microsoft.Agents.AI.AGUI/Shared/RunAgentInput.cs, dotnet/src/Microsoft.Agents.AI.Hosting.AGUI.AspNetCore/AGUIEndpointRouteBuilderExtensions.cs, dotnet/tests/Microsoft.Agents.AI.AGUI.UnitTests/AGUIChatClientTests.cs, dotnet/tests/Microsoft.Agents.AI.Hosting.AGUI.AspNetCore.IntegrationTests/ForwardedPropertiesTests.cs, dotnet/tests/Microsoft.Agents.AI.AGUI.UnitTests/TestHelpers.cs
• Tests run: dotnet/tests/Microsoft.Agents.AI.AGUI.UnitTests/AGUIChatClientForwardedPropertiesTests.cs