Copy entire chats & Rollback chats to certain message (#992)

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

app/MindWork AI Studio/Chat/ChatThread.cs

@@ -350,6 +350,48 @@ public sealed record ChatThread
         this.Blocks.Remove(block);
     }
 
+    /// <summary>
+    /// Rolls this chat thread back, so that the given content becomes the last block of the conversation.
+    /// </summary>
+    /// <remarks>
+    /// Every later block is removed in conversation order, which is the order of the time stamps and
+    /// the order in which the chat shows the blocks. That includes the blocks hidden from the user,
+    /// such as the prompts an assistant sends into a chat: the user can neither see nor remove them,
+    /// so leaving them behind would continue the chat with messages nobody knows about. Hidden blocks
+    /// before the content stay, e.g. the example conversation of a chat template. The managed
+    /// transcripts of the removed blocks are deleted with them.<br/><br/>
+    ///
+    /// The augmented data and the AI-selected data sources are reset, too. Both describe the last
+    /// retrieval, not a certain message, so after a rollback nobody knows whether they belong to a
+    /// kept or to a removed one. The next message with active data sources retrieves anew; without
+    /// active data sources, the chat continues without this context. The data source options stay,
+    /// because they are the user's choice rather than the result of a message.<br/><br/>
+    ///
+    /// What stays as well is everything the thread ratchets for security reasons, namely the data
+    /// security and the required provider confidence. Both only ever tighten, because the data which
+    /// raised them was seen by this thread. Removing the message that brought it in does not unsee
+    /// it, so the chat keeps demanding the same of every provider which continues it.
+    /// </remarks>
+    /// <param name="content">The content to keep as the last block.</param>
+    /// <returns>True when one or more later blocks were removed. False when the content is unknown or already the last block; the thread stays unchanged then.</returns>
+    public bool RollBackTo(IContent content)
+    {
+        var sortedBlocks = this.Blocks.OrderBy(x => x.Time).ToList();
+        var blockIndex = sortedBlocks.FindIndex(block => ReferenceEquals(block.Content, content));
+        if (blockIndex < 0 || blockIndex == sortedBlocks.Count - 1)
+            return false;
+
+        foreach (var block in sortedBlocks.Skip(blockIndex + 1))
+        {
+            DeleteManagedAttachments(block);
+            this.Blocks.Remove(block);
+        }
+
+        this.AugmentedData = string.Empty;
+        this.AISelectedDataSources = [];
+        return true;
+    }
+
     private static void DeleteManagedAttachments(ContentBlock block)
     {
         if (block.Content is not ContentText textContent)