Add PII redaction POC for secure LLM prompting.

Implements detect-redact-sanitize pipeline with regex, domain rules, and ONNX NER before the LLM boundary, plus NUnit tests and Xenovex push documentation.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/PiiRedaction.Infrastructure.Tests/Llm/MockLlmPromptServiceTests.cs

@@ -0,0 +1,62 @@
+using System.Runtime.CompilerServices;
+using FluentAssertions;
+using Microsoft.Extensions.AI;
+using PiiRedaction.Infrastructure.Llm;
+
+namespace PiiRedaction.Infrastructure.Tests.Llm;
+
+[TestFixture]
+public sealed class MockLlmPromptServiceTests
+{
+    [Test]
+    public async Task SendPromptAsync_ReturnsAssistantText()
+    {
+        var service = new MockLlmPromptService(new MockChatClient());
+
+        const string prompt = "Sanitized <EMAIL_1> content.";
+        var response = await service.SendPromptAsync(prompt);
+
+        response.Should().Contain("Mock LLM Response");
+        response.Should().Contain($"{prompt.Length} chars");
+    }
+
+    [Test]
+    public async Task SendPromptAsync_UsesUserRoleForOutboundMessage()
+    {
+        var capturingClient = new CapturingChatClient();
+        var service = new MockLlmPromptService(capturingClient);
+
+        await service.SendPromptAsync("Only placeholders <PHONE_1>.");
+
+        capturingClient.LastUserMessage.Should().Be("Only placeholders <PHONE_1>.");
+    }
+
+    private sealed class CapturingChatClient : IChatClient
+    {
+        public string? LastUserMessage { get; private set; }
+
+        public Task<ChatResponse> GetResponseAsync(
+            IEnumerable<ChatMessage> messages,
+            ChatOptions? options = null,
+            CancellationToken cancellationToken = default)
+        {
+            LastUserMessage = messages.LastOrDefault(message => message.Role == ChatRole.User)?.Text;
+            return Task.FromResult(new ChatResponse(new ChatMessage(ChatRole.Assistant, "ok")));
+        }
+
+        public async IAsyncEnumerable<ChatResponseUpdate> GetStreamingResponseAsync(
+            IEnumerable<ChatMessage> messages,
+            ChatOptions? options = null,
+            [EnumeratorCancellation] CancellationToken cancellationToken = default)
+        {
+            await GetResponseAsync(messages, options, cancellationToken);
+            yield break;
+        }
+
+        public object? GetService(Type serviceType, object? serviceKey = null) => null;
+
+        public void Dispose()
+        {
+        }
+    }
+}

tests/PiiRedaction.Infrastructure.Tests/Onnx/OnnxNerModelRunnerTests.cs

@@ -0,0 +1,53 @@
+using FluentAssertions;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using PiiRedaction.Core.Configuration;
+using PiiRedaction.Core.Models;
+using PiiRedaction.Infrastructure.Onnx;
+
+namespace PiiRedaction.Infrastructure.Tests.Onnx;
+
+[TestFixture]
+public sealed class OnnxNerModelRunnerTests
+{
+    [Test]
+    public void Constructor_MissingModel_IsModelUnavailable()
+    {
+        var path = Path.Combine(Path.GetTempPath(), $"missing-ner-{Guid.NewGuid():N}.onnx");
+        using var runner = CreateRunner(path);
+
+        runner.IsModelAvailable.Should().BeFalse();
+    }
+
+    [Test]
+    public void PredictEntities_WhenModelUnavailable_ReturnsEmpty()
+    {
+        var path = Path.Combine(Path.GetTempPath(), $"missing-ner-{Guid.NewGuid():N}.onnx");
+        using var runner = CreateRunner(path);
+
+        runner.PredictEntities("Customer Ravi Kumar").Should().BeEmpty();
+    }
+
+    [Test]
+    public void Constructor_InvalidModelFile_IsModelUnavailable()
+    {
+        var path = Path.Combine(Path.GetTempPath(), $"invalid-ner-{Guid.NewGuid():N}.onnx");
+        File.WriteAllText(path, "not-a-valid-onnx-model");
+
+        try
+        {
+            using var runner = CreateRunner(path);
+            runner.IsModelAvailable.Should().BeFalse();
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    private static OnnxNerModelRunner CreateRunner(string modelPath)
+    {
+        var options = Options.Create(new PiiRedactionOptions { OnnxModelPath = modelPath });
+        return new OnnxNerModelRunner(options, NullLogger<OnnxNerModelRunner>.Instance);
+    }
+}

tests/PiiRedaction.Infrastructure.Tests/Onnx/RealNerModelRunnerTests.cs

@@ -0,0 +1,51 @@
+using FluentAssertions;
+
+using PiiRedaction.Core.Models;
+
+using PiiRedaction.Tests.Shared;
+
+
+
+namespace PiiRedaction.Infrastructure.Tests.Onnx;
+
+
+
+[TestFixture]
+
+[Category("RealModel")]
+
+public sealed class RealNerModelRunnerTests : RealNerModelFixture
+
+{
+
+    [TestCase("Customer Ravi Kumar called about billing.", "Ravi", "Ravi Kumar")]
+
+    [TestCase("Mr. John Smith called about a duplicate debit.", "John", "John Smith")]
+
+    public void PredictEntities_DetectsPersonWithCorrectSpan(string prompt, string expectedNamePart, string expectedValue)
+
+    {
+
+        var entities = Runner.PredictEntities(prompt);
+
+
+
+        entities.Should().Contain(entity =>
+
+            entity.Type == PiiEntityType.Person &&
+
+            entity.Source == PiiDetectionSource.Ner &&
+
+            entity.Value.Contains(expectedNamePart, StringComparison.Ordinal) &&
+
+            prompt.AsSpan(entity.StartIndex, entity.Length).ToString() == entity.Value);
+
+
+
+        entities.Should().Contain(entity => entity.Value == expectedValue);
+
+    }
+
+}
+
+

tests/PiiRedaction.Infrastructure.Tests/PiiRedaction.Infrastructure.Tests.csproj

@@ -0,0 +1,34 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <LangVersion>latest</LangVersion>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="FluentAssertions" Version="8.10.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.0" />
+    <PackageReference Include="NUnit" Version="4.3.2" />
+    <PackageReference Include="NUnit.Analyzers" Version="4.7.0" />
+    <PackageReference Include="NUnit3TestAdapter" Version="5.0.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="NUnit.Framework" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Compile Include="..\TestSupport.Shared\RealNerModelPaths.cs" Link="TestSupport.Shared\RealNerModelPaths.cs" />
+    <Compile Include="..\TestSupport.Shared\RealNerModelFixture.cs" Link="TestSupport.Shared\RealNerModelFixture.cs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\PiiRedaction.Infrastructure\PiiRedaction.Infrastructure.csproj" />
+    <ProjectReference Include="..\..\src\PiiRedaction.Core\PiiRedaction.Core.csproj" />
+  </ItemGroup>
+
+</Project>