## 1. Add Semantic Kernel Dependencies

- [x] 1.1 Add `Microsoft.SemanticKernel` and `Microsoft.SemanticKernel.Connectors.OpenAI` NuGet packages to `ChatAgent.Api`
- [x] 1.2 Remove the `OpenAI` SDK package if no longer needed after migration

## 2. Define Extraction Schema

- [x] 2.1 Create `ExtractedFields` class in `ChatAgent.Shared/Models/` with the predefined set of key-value fields (placeholder fields until real schema is provided)
- [x] 2.2 Create `ValidationResult` class in `ChatAgent.Shared/Models/` with `IsValid`, `Errors` properties

## 3. Create Extraction Plugin

- [x] 3.1 Create `ExtractionPlugin` class in `ChatAgent.Api/Plugins/` with a `[KernelFunction]` validation method that checks `ExtractedFields` for required fields and type correctness
- [x] 3.2 Add inline tutorial comments explaining SK plugin concepts (`[KernelFunction]`, `[Description]`, auto-invocation)

## 4. Wire Semantic Kernel in Program.cs

- [x] 4.1 Register `OpenAIChatCompletionService` in DI using `ResponsesApi:BaseUrl` and `ResponsesApi:Model` from config
- [x] 4.2 Register `Kernel` with `AddKernel()` and import `ExtractionPlugin`
- [x] 4.3 Add inline tutorial comments explaining kernel setup, connectors, and plugin registration

## 5. Rewrite ChatController

- [x] 5.1 Replace `IHttpClientFactory` and `IConfiguration` injection with `Kernel` injection
- [x] 5.2 Replace manual HTTP proxy logic with `IChatCompletionService.GetStreamingChatMessageContentsAsync()` using the conversation history from the request
- [x] 5.3 Configure `OpenAIPromptExecutionSettings` with `FunctionChoiceBehavior.Auto()` and `autoInvokeMaxCallCount = 3`
- [x] 5.4 Re-emit streaming content as the existing SSE format (`data: {"text":"..."}\n\n` and `data: [DONE]\n\n`)
- [x] 5.5 Add inline tutorial comments explaining streaming chat completion, execution settings, and tool call behavior

## 6. Update Tests

- [x] 6.1 Update `ChatControllerTests` to mock `IChatCompletionService` instead of upstream HTTP calls
- [x] 6.2 Add tests for the validation plugin (`ExtractionPlugin` returns correct pass/fail results)
- [x] 6.3 Add a test verifying the agent escalates to the user after max retries

## 7. Verify

- [x] 7.1 Run `dotnet build` to confirm no errors
- [x] 7.2 Run `dotnet test` to confirm all tests pass
- [ ] 7.3 Manual smoke test: send a chat message and verify streaming still works end-to-end through SK