[Naveen Chatlapalli (1aifanatic)]

Motivation & Context

The JSON options installed by AddAGUIServer cannot serialize interrupt request/response content inside a ChatMessage. This prevents callers using the configured options from round-tripping human-in-the-loop messages.

Description & Review Guide

• What are the major changes? Register the existing interrupt content resolver with the ASP.NET Core JSON options, and add request/response round-trip regression tests.
• What is the impact of these changes? Interrupt content retains its concrete type and payload when serialized through the server's configured options. No new public API or dependency.
• What do you want reviewers to focus on? Reusing AGUIJsonUtilities.RegisterInterruptContentTypes keeps this path consistent with the other AG-UI serializers. Both new tests failed before the change and pass afterward; all 14 tests in the affected project pass. The full .NET solution builds without warnings or errors. The full unit run had 9,167 passes, 69 skips, and three host-process failures; rerunning the affected LocalCodeAct and Shell projects separately passed all 120 and 118 tests respectively.

Related Issue

Addresses the interrupt-content serialization portion of #8962. The separate null-field serialization report is already covered by open PR #7920; this change does not duplicate it or claim to close the entire issue.

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change.

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused registration change resolves the reported serialization failure and is adequately covered by regression tests.

Review effort: Balanced
Findings: None

What changed in this PR

Registers AG-UI interrupt content types with ASP.NET Core JSON options, enabling human-in-the-loop messages to round-trip correctly.

Changes:

• Registers interrupt request and response content types.
• Adds regression tests covering both interrupt variants.

File	Description
dotnet/​src/​Microsoft.Agents.AI.Hosting.AGUI.AspNetCore/​ConfigureAGUIJsonOptions.cs	Registers interrupt content types with server JSON options.
dotnet/​tests/​Microsoft.Agents.AI.Hosting.AGUI.AspNetCore.UnitTests/​ConfigureAGUIJsonOptionsTests.cs	Tests request and response interrupt round-tripping.

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[Naveen Chatlapalli (1aifanatic)]

Rebased onto current main to resolve the conflict with #7920. Kept main's Insert(0/1, ...) resolver ordering and re-applied AGUIJsonUtilities.RegisterInterruptContentTypes(...) after it; the new interrupt round-trip tests sit alongside the omit-null-fields test. Microsoft.Agents.AI.Hosting.AGUI.AspNetCore.UnitTests passes locally (31/31, net10.0).