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

@rogerbarreto is already working on this.

Since Jun 16, 2026.

### 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

```markdown

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### Error Messages / Stack Traces

```markdown
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_