Added a way to read what the AI received from your sources (#1100)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/MindWork AI Studio/Tools/Services/Indexing/IndexedDocumentIds.cs

@@ -26,25 +26,35 @@ internal static class IndexedDocumentIds
         CreateStableGuid($"{dataSourceId}:chunk:{source}:{chunkIndex}");
 
     /// <summary>
-    /// What the chunk ids of a document derive from: nearly always its fingerprint.
+    /// What the chunk ids of a document derive from: nearly always its fingerprint, and the generation of the chunks.
     /// </summary>
     /// <remarks>
     /// A moved file keeps its parent id and its chunk ids, but its fingerprint now names the new path.
     /// Another file may later appear at the old path with exactly the fingerprint those chunk ids came
     /// from, and the fingerprint alone would hand it the same ids. The two documents would then take
     /// over each other's chunks. Hence the parent id joins whenever a document is not stored under the
-    /// id its key gives, which only happens after a move. Every other document keeps the ids it has.
+    /// id its key gives, which only happens after a move. Every other document keeps the ids it has.<br/><br/>
+    /// Every time a document is indexed again, its chunks get the next generation, and with it new
+    /// ids, even where the fingerprint stays the same, as for a mail. So the new chunks never
+    /// overwrite the old ones, which keep their vectors until the new chunks are stored, cf.
+    /// ReusableVectors. The first indexing of a document is generation 0, which gives the ids
+    /// documents got before generations existed.
     /// </remarks>
     /// <param name="dataSourceId">The data source the document belongs to.</param>
     /// <param name="documentKey">The key of the document.</param>
     /// <param name="parentId">The id the document is stored under.</param>
     /// <param name="fingerprint">The fingerprint of the document as it is about to be read.</param>
+    /// <param name="generation">The generation of the chunks about to be written.</param>
     /// <returns>What to pass to CreateChunkId.</returns>
-    public static string CreateChunkIdSource(string dataSourceId, string documentKey, string parentId, string fingerprint) =>
-        string.Equals(parentId, CreateParentId(dataSourceId, documentKey), StringComparison.Ordinal)
+    public static string CreateChunkIdSource(string dataSourceId, string documentKey, string parentId, string fingerprint, int generation = 0)
+    {
+        var source = string.Equals(parentId, CreateParentId(dataSourceId, documentKey), StringComparison.Ordinal)
             ? fingerprint
             : $"{parentId}:{fingerprint}";
 
+        return generation is 0 ? source : $"{source}:generation:{generation}";
+    }
+
     /// <summary>
     /// The id of a document's row in the index store, which its chunks point at.
     /// </summary>