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

src/NexusReader.Application/Abstractions/Services/IKnowledgeService.cs

@@ -12,6 +12,7 @@ public interface IKnowledgeService
     Task<Result<List<RelevantContext>>> GetRelevantContextAsync(string query, string tenantId, CancellationToken cancellationToken = default);
     Task<Result<GroundednessResult>> VerifyGroundednessAsync(string answer, string context, string tenantId, CancellationToken cancellationToken = default);
     Task<Result<List<SemanticSearchResultDto>>> SearchLibrarySemanticallyAsync(string queryText, string tenantId, int limit, CancellationToken cancellationToken = default);
+    Task<Result<GroundedResponseDto>> AskQuestionAsync(string question, string tenantId, Guid? ebookId = null, int limit = 5, CancellationToken cancellationToken = default);
     Task<Result> ClearCacheAsync(CancellationToken cancellationToken = default);
 }
 

src/NexusReader.Application/DTOs/AI/GroundedResponseDto.cs

@@ -0,0 +1,16 @@
+using System.Collections.Generic;
+
+namespace NexusReader.Application.DTOs.AI;
+
+public class GroundedResponseDto
+{
+    public string Answer { get; set; } = string.Empty;
+    public List<CitationDto> Citations { get; set; } = new();
+}
+
+public class CitationDto
+{
+    public string CitationId { get; set; } = string.Empty; // e.g., chunk hash/ID
+    public string Snippet { get; set; } = string.Empty;    // Verified text snippet from context
+    public string SourceBook { get; set; } = string.Empty; // Book title or description
+}

src/NexusReader.Application/Queries/Library/AskLibraryQuestionQuery.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using FluentResults;
+using MediatR;
+using NexusReader.Application.Abstractions.Services;
+using NexusReader.Application.DTOs.AI;
+
+namespace NexusReader.Application.Queries.Library;
+
+public record AskLibraryQuestionQuery(string Question, string TenantId, Guid? EbookId = null, int Limit = 5) 
+    : IRequest<Result<GroundedResponseDto>>;
+
+public class AskLibraryQuestionQueryHandler : IRequestHandler<AskLibraryQuestionQuery, Result<GroundedResponseDto>>
+{
+    private readonly IKnowledgeService _knowledgeService;
+    
+    public AskLibraryQuestionQueryHandler(IKnowledgeService knowledgeService)
+    {
+        _knowledgeService = knowledgeService;
+    }
+
+    public async Task<Result<GroundedResponseDto>> Handle(AskLibraryQuestionQuery request, CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrWhiteSpace(request.Question))
+        {
+            return Result.Fail("Question cannot be empty.");
+        }
+
+        return await _knowledgeService.AskQuestionAsync(
+            request.Question, 
+            request.TenantId, 
+            request.EbookId, 
+            request.Limit, 
+            cancellationToken);
+    }
+}