fix: make index weights configurable in SearchService

KNOWN-ISSUES.md

@@ -84,22 +84,6 @@ km search 'content:"user:password"'
 
 ---
 
-## Configuration Limitations
-
-### 4. Index Weights Not Configurable
-
-**Status:** Known limitation
-
-**Issue:** Index weights for reranking use hardcoded defaults instead of configuration.
-
-**Location:** `src/Core/Search/SearchService.cs:223`
-
-**Impact:** Cannot tune relevance scoring per index.
-
-**Fix Required:** Load index weights from configuration file.
-
----
-
 ## Testing Gaps
 
 These bugs were discovered through comprehensive E2E testing. Previous tests only verified:

src/Core/Search/SearchService.cs

@@ -14,18 +14,26 @@ namespace KernelMemory.Core.Search;
 public sealed class SearchService : ISearchService
 {
     private readonly Dictionary<string, NodeSearchService> _nodeServices;
+    private readonly Dictionary<string, Dictionary<string, float>>? _indexWeights;
     private readonly ISearchReranker _reranker;
 
     /// <summary>
     /// Initialize a new SearchService.
     /// </summary>
     /// <param name="nodeServices">Per-node search services.</param>
+    /// <param name="indexWeights">
+    /// Per-node, per-index weights for relevance scoring.
+    /// Outer key = node ID, Inner key = index ID, Value = weight multiplier.
+    /// If null or missing entries, defaults to SearchConstants.DefaultIndexWeight (1.0).
+    /// </param>
     /// <param name="reranker">Reranking implementation (default: WeightedDiminishingReranker).</param>
     public SearchService(
         Dictionary<string, NodeSearchService> nodeServices,
+        Dictionary<string, Dictionary<string, float>>? indexWeights = null,
         ISearchReranker? reranker = null)
     {
         this._nodeServices = nodeServices;
+        this._indexWeights = indexWeights;
         this._reranker = reranker ?? new WeightedDiminishingReranker();
     }
 
@@ -201,7 +209,7 @@ private void ValidateNodes(string[] nodeIds)
     }
 
     /// <summary>
-    /// Build reranking configuration from request and defaults.
+    /// Build reranking configuration from request, configured index weights, and defaults.
     /// </summary>
     private RerankingConfig BuildRerankingConfig(SearchRequest request, string[] nodeIds)
     {
@@ -219,15 +227,33 @@ private RerankingConfig BuildRerankingConfig(SearchRequest request, string[] nod
             }
         }
 
-        // Index weights: use defaults for now
-        // TODO: Load from configuration
+        // Index weights: use configured weights, fall back to defaults for missing entries
         var indexWeights = new Dictionary<string, Dictionary<string, float>>();
         foreach (var nodeId in nodeIds)
         {
-            indexWeights[nodeId] = new Dictionary<string, float>
+            // Check if we have configured index weights for this node
+            if (this._indexWeights?.TryGetValue(nodeId, out var configuredNodeIndexWeights) == true
+                && configuredNodeIndexWeights.Count > 0)
             {
-                ["fts-main"] = SearchConstants.DefaultIndexWeight
-            };
+                // Use configured weights, but ensure defaults for missing indexes
+                var nodeIndexWeights = new Dictionary<string, float>(configuredNodeIndexWeights);
+
+                // Ensure default FTS index has a weight (use configured or default)
+                if (!nodeIndexWeights.ContainsKey(SearchConstants.DefaultFtsIndexId))
+                {
+                    nodeIndexWeights[SearchConstants.DefaultFtsIndexId] = SearchConstants.DefaultIndexWeight;
+                }
+
+                indexWeights[nodeId] = nodeIndexWeights;
+            }
+            else
+            {
+                // No configured weights for this node, use default
+                indexWeights[nodeId] = new Dictionary<string, float>
+                {
+                    [SearchConstants.DefaultFtsIndexId] = SearchConstants.DefaultIndexWeight
+                };
+            }
         }
 
         return new RerankingConfig

src/Main/CLI/Commands/SearchCommand.cs

@@ -455,6 +455,7 @@ private void FormatSearchResultsHuman(SearchResponse response, SearchCommandSett
     private SearchService CreateSearchService()
     {
         var nodeServices = new Dictionary<string, NodeSearchService>();
+        var indexWeights = new Dictionary<string, Dictionary<string, float>>();
 
         foreach (var (nodeId, nodeConfig) in this.Config.Nodes)
         {
@@ -478,9 +479,21 @@ private SearchService CreateSearchService()
             );
 
             nodeServices[nodeId] = nodeSearchService;
+
+            // Extract index weights from configuration
+            if (nodeConfig.SearchIndexes.Count > 0)
+            {
+                var nodeIndexWeights = new Dictionary<string, float>();
+                foreach (var searchIndex in nodeConfig.SearchIndexes)
+                {
+                    // Use the configured weight for each search index
+                    nodeIndexWeights[searchIndex.Id] = searchIndex.Weight;
+                }
+                indexWeights[nodeId] = nodeIndexWeights;
+            }
         }
 
-        return new SearchService(nodeServices);
+        return new SearchService(nodeServices, indexWeights);
     }
 
     /// <summary>

tests/Core.Tests/Search/SearchServiceIndexWeightsTests.cs

@@ -0,0 +1,266 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using KernelMemory.Core.Search;
+using KernelMemory.Core.Search.Models;
+using KernelMemory.Core.Storage;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using Moq;
+
+namespace KernelMemory.Core.Tests.Search;
+
+/// <summary>
+/// Tests for SearchService with configurable index weights.
+/// Verifies that index weights from configuration are used in reranking.
+/// This test class tests the fix for Known Issue 4: Index Weights Not Configurable.
+/// </summary>
+public sealed class SearchServiceIndexWeightsTests : IDisposable
+{
+    private readonly string _tempDir;
+    private readonly ContentStorageService _storage;
+    private readonly ContentStorageDbContext _context;
+    private readonly SqliteFtsIndex _ftsIndex;
+
+    public SearchServiceIndexWeightsTests()
+    {
+        this._tempDir = Path.Combine(Path.GetTempPath(), $"km-index-weights-test-{Guid.NewGuid():N}");
+        Directory.CreateDirectory(this._tempDir);
+
+        var mockStorageLogger = new Mock<ILogger<ContentStorageService>>();
+        var mockFtsLogger = new Mock<ILogger<SqliteFtsIndex>>();
+        var cuidGenerator = new CuidGenerator();
+
+        // Create storage
+        var contentDbPath = Path.Combine(this._tempDir, "content.db");
+        var options = new DbContextOptionsBuilder<ContentStorageDbContext>()
+            .UseSqlite($"Data Source={contentDbPath}")
+            .Options;
+        this._context = new ContentStorageDbContext(options);
+        this._context.Database.EnsureCreated();
+
+        // Create FTS index
+        var ftsDbPath = Path.Combine(this._tempDir, "fts.db");
+        this._ftsIndex = new SqliteFtsIndex(ftsDbPath, enableStemming: true, mockFtsLogger.Object);
+
+        var searchIndexes = new Dictionary<string, ISearchIndex> { ["fts"] = this._ftsIndex };
+        this._storage = new ContentStorageService(this._context, cuidGenerator, mockStorageLogger.Object, searchIndexes);
+    }
+
+    public void Dispose()
+    {
+        this._ftsIndex.Dispose();
+        this._context.Dispose();
+
+        try
+        {
+            if (Directory.Exists(this._tempDir))
+            {
+                Directory.Delete(this._tempDir, true);
+            }
+        }
+        catch (IOException)
+        {
+            // Ignore cleanup errors
+        }
+    }
+
+    [Fact]
+    public async Task SearchService_WithConfiguredIndexWeights_UsesConfiguredWeights()
+    {
+        // Arrange: Insert test data
+        await this._storage.UpsertAsync(new KernelMemory.Core.Storage.Models.UpsertRequest
+        {
+            Content = "Test document about Docker containers",
+            MimeType = "text/plain"
+        }, CancellationToken.None).ConfigureAwait(false);
+
+        // Configure custom index weights (0.5 instead of default 1.0)
+        var indexWeights = new Dictionary<string, Dictionary<string, float>>
+        {
+            ["test-node"] = new Dictionary<string, float>
+            {
+                [SearchConstants.DefaultFtsIndexId] = 0.5f  // Custom weight
+            }
+        };
+
+        var nodeService = new NodeSearchService("test-node", this._ftsIndex, this._storage);
+        var nodeServices = new Dictionary<string, NodeSearchService> { ["test-node"] = nodeService };
+
+        // Create SearchService with custom index weights
+        var searchService = new SearchService(nodeServices, indexWeights: indexWeights);
+
+        var request = new SearchRequest
+        {
+            Query = "docker",
+            Limit = 10,
+            MinRelevance = 0.0f
+        };
+
+        // Act
+        var response = await searchService.SearchAsync(request, CancellationToken.None).ConfigureAwait(false);
+
+        // Assert
+        Assert.NotEmpty(response.Results);
+        // With default weight 1.0, a result with BaseRelevance ~1.0 would have Relevance ~1.0
+        // With weight 0.5, the same result should have Relevance ~0.5
+        // Since we set index weight to 0.5, relevance should be reduced by factor of 0.5
+        var result = response.Results.First();
+        Assert.True(result.Relevance <= 0.6f,
+            $"Expected relevance <= 0.6 (due to 0.5 index weight), got {result.Relevance}");
+    }
+
+    [Fact]
+    public async Task SearchService_WithoutConfiguredIndexWeights_UsesDefaultWeight()
+    {
+        // Arrange: Insert test data
+        await this._storage.UpsertAsync(new KernelMemory.Core.Storage.Models.UpsertRequest
+        {
+            Content = "Test document about Kubernetes orchestration",
+            MimeType = "text/plain"
+        }, CancellationToken.None).ConfigureAwait(false);
+
+        var nodeService = new NodeSearchService("test-node", this._ftsIndex, this._storage);
+        var nodeServices = new Dictionary<string, NodeSearchService> { ["test-node"] = nodeService };
+
+        // Create SearchService WITHOUT custom index weights (should use defaults)
+        var searchService = new SearchService(nodeServices);
+
+        var request = new SearchRequest
+        {
+            Query = "kubernetes",
+            Limit = 10,
+            MinRelevance = 0.0f
+        };
+
+        // Act
+        var response = await searchService.SearchAsync(request, CancellationToken.None).ConfigureAwait(false);
+
+        // Assert
+        Assert.NotEmpty(response.Results);
+        // With default weight 1.0, result should maintain its base relevance
+        var result = response.Results.First();
+        Assert.True(result.Relevance > 0.5f,
+            $"Expected relevance > 0.5 (using default 1.0 weight), got {result.Relevance}");
+    }
+
+    [Fact]
+    public async Task SearchService_WithIndexWeightsForMultipleIndexes_UsesCorrectWeights()
+    {
+        // This test verifies that when index weights are configured for multiple indexes,
+        // each index uses its correct weight for reranking.
+
+        // Arrange: Insert test data
+        await this._storage.UpsertAsync(new KernelMemory.Core.Storage.Models.UpsertRequest
+        {
+            Content = "Machine learning and artificial intelligence concepts",
+            MimeType = "text/plain"
+        }, CancellationToken.None).ConfigureAwait(false);
+
+        // Configure weights for multiple indexes
+        var indexWeights = new Dictionary<string, Dictionary<string, float>>
+        {
+            ["test-node"] = new Dictionary<string, float>
+            {
+                [SearchConstants.DefaultFtsIndexId] = 0.7f,  // FTS index weight
+                ["vector-main"] = 0.3f  // Vector index weight (not used here, but configured)
+            }
+        };
+
+        var nodeService = new NodeSearchService("test-node", this._ftsIndex, this._storage);
+        var nodeServices = new Dictionary<string, NodeSearchService> { ["test-node"] = nodeService };
+
+        var searchService = new SearchService(nodeServices, indexWeights: indexWeights);
+
+        var request = new SearchRequest
+        {
+            Query = "machine learning",
+            Limit = 10,
+            MinRelevance = 0.0f
+        };
+
+        // Act
+        var response = await searchService.SearchAsync(request, CancellationToken.None).ConfigureAwait(false);
+
+        // Assert
+        Assert.NotEmpty(response.Results);
+        // With index weight 0.7 (not default 1.0), relevance should be scaled by 0.7
+        var result = response.Results.First();
+        Assert.True(result.Relevance <= 0.75f,
+            $"Expected relevance <= 0.75 (due to 0.7 index weight), got {result.Relevance}");
+    }
+
+    [Fact]
+    public async Task SearchService_WithMissingIndexWeight_UsesDefaultWeight()
+    {
+        // Tests that if an index weight is not configured for a specific index,
+        // the default weight is used.
+
+        // Arrange: Insert test data
+        await this._storage.UpsertAsync(new KernelMemory.Core.Storage.Models.UpsertRequest
+        {
+            Content = "Database optimization techniques",
+            MimeType = "text/plain"
+        }, CancellationToken.None).ConfigureAwait(false);
+
+        // Configure weights but NOT for the FTS index used
+        var indexWeights = new Dictionary<string, Dictionary<string, float>>
+        {
+            ["test-node"] = new Dictionary<string, float>
+            {
+                ["some-other-index"] = 0.5f  // Different index, not the one used
+            }
+        };
+
+        var nodeService = new NodeSearchService("test-node", this._ftsIndex, this._storage);
+        var nodeServices = new Dictionary<string, NodeSearchService> { ["test-node"] = nodeService };
+
+        var searchService = new SearchService(nodeServices, indexWeights: indexWeights);
+
+        var request = new SearchRequest
+        {
+            Query = "database",
+            Limit = 10,
+            MinRelevance = 0.0f
+        };
+
+        // Act
+        var response = await searchService.SearchAsync(request, CancellationToken.None).ConfigureAwait(false);
+
+        // Assert
+        Assert.NotEmpty(response.Results);
+        // Since fts-main is not in the configured weights, default weight 1.0 should be used
+        var result = response.Results.First();
+        Assert.True(result.Relevance > 0.5f,
+            $"Expected relevance > 0.5 (using default 1.0 weight for unconfigured index), got {result.Relevance}");
+    }
+
+    [Fact]
+    public void SearchService_Constructor_AcceptsNullIndexWeights()
+    {
+        // Verify that SearchService can be created with null index weights
+        var nodeService = new NodeSearchService("test-node", this._ftsIndex, this._storage);
+        var nodeServices = new Dictionary<string, NodeSearchService> { ["test-node"] = nodeService };
+
+        // Act - should not throw
+        var searchService = new SearchService(nodeServices, indexWeights: null);
+
+        // Assert - service was created successfully
+        Assert.NotNull(searchService);
+    }
+
+    [Fact]
+    public void SearchService_Constructor_AcceptsEmptyIndexWeights()
+    {
+        // Verify that SearchService works with empty index weights dictionary
+        var nodeService = new NodeSearchService("test-node", this._ftsIndex, this._storage);
+        var nodeServices = new Dictionary<string, NodeSearchService> { ["test-node"] = nodeService };
+
+        var emptyWeights = new Dictionary<string, Dictionary<string, float>>();
+
+        // Act - should not throw
+        var searchService = new SearchService(nodeServices, indexWeights: emptyWeights);
+
+        // Assert - service was created successfully
+        Assert.NotNull(searchService);
+    }
+}