.NET: Fix AG-UI forwardedProps JSON property name

[javiercn]

Summary

Fixes the incorrect JSON property name for forwarded properties in the AG-UI protocol implementation.

Problem

The RunAgentInput.ForwardedProperties property in dotnet/src/Microsoft.Agents.AI.AGUI/Shared/RunAgentInput.cs was using the wrong JsonPropertyName attribute value:

• Before: "forwardedProperties"
• After: "forwardedProps"

This caused AG-UI clients to be unable to pass forwarded properties to agents since the JSON key didn't match the protocol specification.

Solution

Changed the JsonPropertyName attribute from "forwardedProperties" to "forwardedProps" to match the AG-UI protocol specification.

- [JsonPropertyName("forwardedProperties")]
+ [JsonPropertyName("forwardedProps")]
  [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
  public JsonElement ForwardedProperties { get; set; }

Testing

Added comprehensive integration tests in ForwardedPropertiesTests.cs that verify:

Test	Description
ForwardedProps_AreParsedAndPassedToAgent_WhenProvidedInRequestAsync	Basic forwarded props parsing
ForwardedProps_WithNestedObjects_AreCorrectlyParsedAsync	Nested JSON objects
ForwardedProps_WithArrays_AreCorrectlyParsedAsync	JSON arrays
ForwardedProps_WhenEmpty_DoesNotCauseErrorsAsync	Empty {} object
ForwardedProps_WhenNotProvided_AgentStillWorksAsync	Missing forwardedProps
ForwardedProps_ReturnsValidSSEResponse_WithTextDeltaEventsAsync	Full SSE response flow
ForwardedProps_WithMixedTypes_AreCorrectlyParsedAsync	Mixed JSON value types

All 7 tests pass successfully.

Fixes

Closes #2468

[Copilot]

Pull request overview

This pull request fixes a JSON property name mismatch in the AG-UI protocol implementation that was preventing clients from properly passing forwarded properties to agents. The property name has been corrected from "forwardedProperties" to "forwardedProps" to align with the AG-UI protocol specification.

• Changed JsonPropertyName attribute from "forwardedProperties" to "forwardedProps" in the RunAgentInput class
• Added comprehensive integration tests covering various scenarios including basic parsing, nested objects, arrays, empty objects, missing properties, SSE responses, and mixed types

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
dotnet/src/Microsoft.Agents.AI.AGUI/Shared/RunAgentInput.cs	Corrected the JSON property name for ForwardedProperties from "forwardedProperties" to "forwardedProps"
dotnet/tests/Microsoft.Agents.AI.Hosting.AGUI.AspNetCore.IntegrationTests/ForwardedPropertiesTests.cs	Added comprehensive integration tests to verify forwarded properties are correctly parsed and passed to agents

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