.NET: [Bug]: DEVUI Read unrecognized type discriminator id 'function_approval_response'.

[wyarcdev]

Description

DevUI HITL approval fails for workflow-as-agent (function_approval_response not recognized)

Description

Using a workflow exposed as an agent (workflow.AsAIAgent) in DevUI, tool approval reaches Awaiting approval but fails when clicking Approve.
The approval response appears to send a function-approval payload (function_approval_response), and the hosting pipeline rejects it during JSON deserialization.

Repro (minimal)

1. Register DevUI + OpenAI hosting endpoints.
2. Register workflow as agent (AddAIAgent(... Agent = workflow.AsAIAgent(...))).
3. Trigger a tool wrapped with ApprovalRequiredAIFunction.
4. Click Approve in DevUI.

Expected
Approval response is accepted and execution resumes.

Actual
Request fails (400). Approval cannot resume execution.

Notes

• Tool invocation works.
• Pending approval state is reached.
• Failure occurs on approval response handling path.

Code Sample

Error Messages / Stack Traces

fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
      An unhandled exception has occurred while executing the request.
      Microsoft.AspNetCore.Http.BadHttpRequestException: Failed to read parameter "CreateResponse request" from the request body as JSON.
       ---> System.Text.Json.JsonException: Read unrecognized type discriminator id 'function_approval_response'. Path: $[0] | LineNumber: 0 | BytePositionInLine: 51.
         at System.Text.Json.ThrowHelper.ThrowJsonException(String message)
         at System.Text.Json.ThrowHelper.ThrowJsonException_UnrecognizedTypeDiscriminator(Object typeDiscriminator)
         at System.Text.Json.Serialization.Metadata.PolymorphicTypeResolver.TryGetDerivedJsonTypeInfo(Object typeDiscriminator, JsonTypeInfo& jsonTypeInfo)
         at System.Text.Json.Serialization.JsonConverter.ResolvePolymorphicConverter(J

Package Versions

• Microsoft.Agents.AI — 1.6.1 • Microsoft.Agents.AI.DevUI — 1.6.1-preview.260514.1 • Microsoft.Agents.AI.Hosting — 1.6.1-preview.260514.1 • Microsoft.Agents.AI.Hosting.OpenAI — 1.6.1-alpha.260514.1 • Microsoft.Agents.AI.Workflows — 1.6.1

.NET Version

NET 10

Additional Context

No response

[github-actions]

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

Agent analysis

Repro: POST to the Responses API (CreateResponseAsync in ResponsesHttpHandler.cs) with input containing {"type":"function_approval_response",...} returns 400 because ResponseInputJsonConverter.Read() in ResponseInput.cs deserializes the input array as List which requires role+content properties. No FunctionApprovalResponseItemParam class exists in ItemParam.cs, and ItemParamConverter.cs has no case for "function_approval_response". Minimal repro: create a test server via ConformanceTestBase.CreateTestServerAsync and POST a CreateResponse JSON with input array containing a function_approval_response item — assert the status code is not 400.

• Failing test: dotnet/tests/Microsoft.Agents.AI.Hosting.OpenAI.UnitTests/FunctionApprovalResponseDeserializationTests.cs
• Files examined: dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/Models/ResponseInput.cs, dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/Models/ItemParam.cs, dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/Converters/ItemParamConverter.cs, dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/Models/StreamingResponseEvent.cs, dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/ResponsesHttpHandler.cs, dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/Models/CreateResponse.cs, dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/OpenAIHostingJsonUtilities.cs, dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/Models/ItemParamExtensions.cs
• Tests run: dotnet/tests/Microsoft.Agents.AI.Hosting.OpenAI.UnitTests/FunctionApprovalResponseDeserializationTests.cs
• Reported version: 1.6.1-preview.260514.1