feat(rag): implement KM-RAG retrieval read-path, endpoints, query handlers, global Q&A panel, and unit tests

tests/NexusReader.Application.Tests/Queries/QueryTests.cs

@@ -148,6 +148,57 @@ public class QueryTests : IDisposable
         result.Value.First().ContentHash.Should().Be("hash-123");
     }
 
+    [Fact]
+    public async Task AskLibraryQuestionQuery_WithEmptyQuestion_ReturnsFailure()
+    {
+        // Arrange
+        var knowledgeServiceMock = new Mock<IKnowledgeService>();
+        var handler = new AskLibraryQuestionQueryHandler(knowledgeServiceMock.Object);
+        var query = new AskLibraryQuestionQuery("", "tenant-123");
+
+        // Act
+        var result = await handler.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.IsSuccess.Should().BeFalse();
+        result.Errors.First().Message.Should().Be("Question cannot be empty.");
+    }
+
+    [Fact]
+    public async Task AskLibraryQuestionQuery_WithValidQuestion_CallsKnowledgeService()
+    {
+        // Arrange
+        var knowledgeServiceMock = new Mock<IKnowledgeService>();
+        var expectedResponse = new GroundedResponseDto
+        {
+            Answer = "Based on the book, water boils at 100 degrees Celsius.",
+            Citations = new List<CitationDto>
+            {
+                new CitationDto
+                {
+                    CitationId = "chunk-1",
+                    Snippet = "Water boils at 100 degrees Celsius.",
+                    SourceBook = "Physics 101"
+                }
+            }
+        };
+
+        knowledgeServiceMock.Setup(s => s.AskQuestionAsync("what temp does water boil?", "tenant-123", null, 5, It.IsAny<CancellationToken>()))
+            .ReturnsAsync(Result.Ok(expectedResponse));
+
+        var handler = new AskLibraryQuestionQueryHandler(knowledgeServiceMock.Object);
+        var query = new AskLibraryQuestionQuery("what temp does water boil?", "tenant-123");
+
+        // Act
+        var result = await handler.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.IsSuccess.Should().BeTrue();
+        result.Value.Answer.Should().Be("Based on the book, water boils at 100 degrees Celsius.");
+        result.Value.Citations.Should().HaveCount(1);
+        result.Value.Citations.First().CitationId.Should().Be("chunk-1");
+    }
+
     public void Dispose()
     {
         _connection.Close();