Added the page of a passage to what the AI is told about it

app/MindWork AI Studio/Tools/RAG/IRetrievalContextExtensions.cs

@@ -8,7 +8,36 @@ namespace AIStudio.Tools.RAG;
 public static class IRetrievalContextExtensions
 {
     private static readonly ILogger<IRetrievalContext> LOGGER = Program.LOGGER_FACTORY.CreateLogger<IRetrievalContext>();
-    
+
+    /// <summary>
+    /// Writes what the AI is told about a retrieval context, before its content follows.
+    /// </summary>
+    /// <remarks>
+    /// The location is what lets the AI say where an answer comes from. Naming only the file is
+    /// not enough in a document of two hundred pages, and we know the page: it travels from the
+    /// runtime through the index into the context. A slide or a sheet has no page, and then
+    /// nothing is claimed rather than something made up.
+    /// </remarks>
+    /// <param name="contextBuilder">The builder to write into.</param>
+    /// <param name="retrievalContext">The context to describe.</param>
+    internal static void AppendContextDescription(StringBuilder contextBuilder, IRetrievalContext retrievalContext)
+    {
+        contextBuilder.AppendLine($"Data source name: {retrievalContext.DataSourceName}");
+        contextBuilder.AppendLine($"Content category: {retrievalContext.Category}");
+        contextBuilder.AppendLine($"Content type: {retrievalContext.Type}");
+        contextBuilder.AppendLine($"Content path: {retrievalContext.Path}");
+
+        if(retrievalContext is RetrievalTextContext { PageNumber: > 0 } locatedContext)
+            contextBuilder.AppendLine($"Content location: page {locatedContext.PageNumber}");
+
+        if(retrievalContext.Links.Count is 0)
+            return;
+
+        contextBuilder.AppendLine("Additional links:");
+        foreach(var link in retrievalContext.Links)
+            contextBuilder.AppendLine($"- {link}");
+    }
+
     public static async Task<string> AsMarkdown(this IReadOnlyList<IRetrievalContext> retrievalContexts, StringBuilder? sb = null, CancellationToken token = default)
     {
         sb ??= new StringBuilder();
@@ -49,17 +78,7 @@ public static class IRetrievalContextExtensions
                 break;
         }
         
-        contextBuilder.AppendLine($"Data source name: {retrievalContext.DataSourceName}");
-        contextBuilder.AppendLine($"Content category: {retrievalContext.Category}");
-        contextBuilder.AppendLine($"Content type: {retrievalContext.Type}");
-        contextBuilder.AppendLine($"Content path: {retrievalContext.Path}");
-            
-        if(retrievalContext.Links.Count > 0)
-        {
-            contextBuilder.AppendLine("Additional links:");
-            foreach(var link in retrievalContext.Links)
-                contextBuilder.AppendLine($"- {link}");
-        }
+        AppendContextDescription(contextBuilder, retrievalContext);
 
         var guardService = Program.SERVICE_PROVIDER.GetRequiredService<PromptInjectionGuardService>();
         var source = PromptInjectionSource.RetrievalContext(retrievalContext.DataSourceName, retrievalContext.Path);

app/MindWork AI Studio/Tools/RAG/RetrievalTextContext.cs

@@ -50,4 +50,14 @@ public sealed class RetrievalTextContext : IRetrievalContext
     /// Optional link used when this context is displayed as a source reference.
     /// </summary>
     public string ReferenceLink { get; init; } = string.Empty;
+
+    /// <summary>
+    /// The page this passage was found on, or null when it has none.
+    /// </summary>
+    /// <remarks>
+    /// Kept as a number rather than only inside the reference title: the AI is told the page so it
+    /// can say where an answer comes from, and a source has to name a page a program can be sent
+    /// to. A slide or a sheet has no page and leaves this empty.
+    /// </remarks>
+    public int? PageNumber { get; init; }
 }

app/MindWork AI Studio/Tools/Services/DataSourceLocalRetrievalService.cs

@@ -395,6 +395,7 @@ public sealed class DataSourceLocalRetrievalService(
             SurroundingContent = [],
             ReferenceTitle = BuildReferenceTitle(hit),
             ReferenceLink = referenceLink,
+            PageNumber = hit.PageNumber is > 0 ? hit.PageNumber : null,
         };
     }
 
@@ -413,11 +414,19 @@ public sealed class DataSourceLocalRetrievalService(
         return $"{sourceName} ({location})";
     }
 
+    /// <remarks>
+    /// A known page is written as the fragment `#page=N`, which is what the PDF open parameters
+    /// call for: a program which understands them opens the document where the passage is. Without
+    /// a page there is nothing to send a program to, and the chunk stays in the link so the
+    /// reference still points at something.
+    /// </remarks>
     private static string BuildReferenceLink(string path, LocalRetrievalHit hit)
     {
         var link = NormalizeLocalReferencePath(path);
         var separator = link.Contains('#', StringComparison.Ordinal) ? "&" : "#";
-        return $"{link}{separator}chunk={hit.ChunkIndex}";
+        return hit.PageNumber is > 0
+            ? $"{link}{separator}page={hit.PageNumber}"
+            : $"{link}{separator}chunk={hit.ChunkIndex}";
     }
 
     private static string NormalizeLocalReferencePath(string path)

app/Tests/Tools/RetrievalContextDescriptionTests.cs

@@ -0,0 +1,84 @@
+using System.Text;
+
+using AIStudio.Tools.RAG;
+
+namespace AIStudio.Tests.Tools;
+
+/// <summary>
+/// Checks what the AI is told about a passage before it reads it.
+/// </summary>
+/// <remarks>
+/// The page a passage sits on travels from the runtime through the index into the retrieval
+/// context, but it used to stop there: the AI was given the file and nothing else, so an answer
+/// could name the document it rests on but never the place in it. A source which has no page, a
+/// slide for instance, must stay silent rather than claim one.
+/// </remarks>
+[TestFixture]
+public sealed class RetrievalContextDescriptionTests
+{
+    [Test]
+    public void AKnownPageIsPartOfWhatTheAIIsTold()
+    {
+        var description = Describe(TextContext(pageNumber: 12));
+
+        Assert.That(description, Does.Contain("Content location: page 12"), "The AI is told the page, so it can say where an answer comes from.");
+    }
+
+    [Test]
+    public void APassageWithoutAPageClaimsNone()
+    {
+        var description = Describe(TextContext(pageNumber: null));
+
+        Assert.That(description, Does.Not.Contain("Content location"), "A slide or a sheet has no page, and none is invented for it.");
+    }
+
+    /// <remarks>
+    /// The location belongs to the document, so it is stated with it and before the passage itself
+    /// follows further down.
+    /// </remarks>
+    [Test]
+    public void ThePageIsStatedWithTheDocumentItBelongsTo()
+    {
+        var description = Describe(TextContext(pageNumber: 12));
+        var lines = description.Split('\n').Select(line => line.Trim()).Where(line => line.Length > 0).ToArray();
+
+        Assert.That(lines, Is.EqualTo(new[]
+        {
+            "Data source name: Handbooks",
+            "Content category: TEXT",
+            "Content type: TEXT_DOCUMENT",
+            "Content path: /docs/handbook.pdf",
+            "Content location: page 12",
+        }), "Name, kind, path and place of the document, in that order.");
+    }
+
+    [Test]
+    public void AdditionalLinksStillFollowTheLocation()
+    {
+        var description = Describe(TextContext(pageNumber: 12, links: ["https://example.com/handbook"]));
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(description, Does.Contain("Additional links:"), "The links a data source delivers are still passed on.");
+            Assert.That(description.IndexOf("Content location", StringComparison.Ordinal), Is.LessThan(description.IndexOf("Additional links", StringComparison.Ordinal)), "The place inside the document is stated before links pointing elsewhere.");
+        });
+    }
+
+    private static string Describe(IRetrievalContext retrievalContext)
+    {
+        var builder = new StringBuilder();
+        IRetrievalContextExtensions.AppendContextDescription(builder, retrievalContext);
+        return builder.ToString();
+    }
+
+    private static RetrievalTextContext TextContext(int? pageNumber, IReadOnlyList<string>? links = null) => new()
+    {
+        DataSourceName = "Handbooks",
+        Category = RetrievalContentCategory.TEXT,
+        Type = RetrievalContentType.TEXT_DOCUMENT,
+        Path = "/docs/handbook.pdf",
+        Links = links ?? [],
+        MatchedText = "The mixing console is described here.",
+        PageNumber = pageNumber,
+    };
+}