Surface NER routing provenance (ModelOrigin, NerModelsInvoked) through the pipeline and WPF harness so English/Tamil routing is observable during POC validation. Consolidate docs into solution-guide and add NER logs, topic filtering, and batch UI fixes in the test harness.

tests/PiiRedaction.Core.Tests/Detection/OnnxNerPiiDetectorTests.cs

@@ -46,6 +46,36 @@ public sealed class OnnxNerPiiDetectorTests
         action.Should().Throw<ArgumentException>();
     }
 
+    [Test]
+    public void Detect_ModelAvailable_RecordsInvokedModels()
+    {
+        var runner = new FakeOnnxNerModelRunner
+        {
+            IsModelAvailable = true,
+            InvokedModelsToReturn = [NerModelOrigin.English, NerModelOrigin.Tamil]
+        };
+
+        var detector = new OnnxNerPiiDetector(runner);
+        detector.Detect("Mixed prompt");
+
+        detector.LastInvokedModels.Should().Equal(NerModelOrigin.English, NerModelOrigin.Tamil);
+    }
+
+    [Test]
+    public void Detect_ModelUnavailable_ClearsInvokedModels()
+    {
+        var runner = new FakeOnnxNerModelRunner
+        {
+            IsModelAvailable = false,
+            InvokedModelsToReturn = [NerModelOrigin.English]
+        };
+
+        var detector = new OnnxNerPiiDetector(runner);
+        detector.Detect("Any text");
+
+        detector.LastInvokedModels.Should().BeEmpty();
+    }
+
     private static OnnxNerPiiDetector CreateDetector(bool modelAvailable)
     {
         var runner = new FakeOnnxNerModelRunner { IsModelAvailable = modelAvailable };