Fixed the exact token count outliving the conversation it was reported for

app/MindWork AI Studio/Chat/ChatThread.cs

@@ -392,6 +392,48 @@ public sealed record ChatThread
         return true;
     }
 
+    /// <summary>
+    /// Finds what a provider reported for this conversation, as long as the report still describes it.
+    /// </summary>
+    /// <remarks>
+    /// A report describes one request: the conversation up to the answer which carries it. It is
+    /// worth something only while the thread still is that conversation, so only the last block is
+    /// asked, and no earlier answer ever stands in for it. Whatever came after an older report -- a
+    /// message whose request was turned down, an answer which is still being written, an answer
+    /// without a report of its own -- is missing from that report's number, and the estimate is
+    /// closer to the truth than a figure which leaves it out. Answers written while tools were
+    /// offered carry no report yet, so for them the estimate always takes over.<br/><br/>
+    ///
+    /// A report also stops counting when the thread holds a different number of blocks than the
+    /// request did, which means an earlier message was deleted, and when the next request goes to
+    /// another model, which counts the same conversation with another tokenizer. Editing the last
+    /// message or rolling the chat back makes an earlier answer the last block again, with exactly
+    /// the blocks it was reported for, so its report counts once more.<br/><br/>
+    ///
+    /// What goes unnoticed is a change beside the messages: another system prompt, profile, or
+    /// selection of tools. That shows only with the next answer. Noticing it would take a
+    /// fingerprint of the system prompt as it was sent, after the data sources added to it, which
+    /// is a lot of machinery for a number which corrects itself one answer later.
+    /// </remarks>
+    /// <param name="model">The model the next request would go to.</param>
+    /// <returns>What the provider reported, or unknown when no report describes this conversation.</returns>
+    public TokenUsage ReportedUsageFor(Model model)
+    {
+        if (this.Blocks.Count is 0)
+            return TokenUsage.UNKNOWN;
+
+        if (this.Blocks[^1].Content is not ContentText { IsStreaming: false, ReportedUsage: { } reported })
+            return TokenUsage.UNKNOWN;
+
+        if (reported.BlockCount != this.Blocks.Count)
+            return TokenUsage.UNKNOWN;
+
+        if (!string.Equals(reported.ModelId, model.Id, StringComparison.Ordinal))
+            return TokenUsage.UNKNOWN;
+
+        return reported.ToTokenUsage();
+    }
+
     private static void DeleteManagedAttachments(ContentBlock block)
     {
         if (block.Content is not ContentText textContent)

app/MindWork AI Studio/Chat/ContentText.cs

@@ -58,10 +58,12 @@ public sealed class ContentText : IContent
     /// <remarks>
     /// Kept on the answer rather than beside the chat, so that it is stored, loaded, and exported
     /// with the message it belongs to -- and so that it goes away when the message does. An edited
-    /// or regenerated answer removes its block, which removes these numbers with it, and the chat
-    /// falls back to the estimate instead of carrying a figure for a conversation which no longer
-    /// exists. Null for every answer written before this was recorded, and at every provider which
-    /// reports nothing.
+    /// or regenerated answer removes its block, which removes these numbers with it. Null for every
+    /// answer written before this was recorded, and at every provider which reports nothing.
+    ///
+    /// Having a report is not the same as the report still being true. Whether it still describes
+    /// the conversation is decided by ChatThread.ReportedUsageFor, which looks at the thread around
+    /// the answer, not just at the answer.
     /// </remarks>
     public ReportedTokenUsage? ReportedUsage { get; set; }
 
@@ -121,7 +123,8 @@ public sealed class ContentText : IContent
     /// </remarks>
     /// <param name="usage">What the current chunk of the stream says, which is mostly nothing.</param>
     /// <param name="modelId">The model the request went to.</param>
-    public void RecordReportedUsage(TokenUsage usage, string modelId)
+    /// <param name="blockCount">How many blocks the conversation had when the request went out, this answer included.</param>
+    public void RecordReportedUsage(TokenUsage usage, string modelId, int blockCount)
     {
         if (!usage.IsKnown)
             return;
@@ -131,6 +134,7 @@ public sealed class ContentText : IContent
             PromptTokens = usage.PromptTokens,
             CompletionTokens = usage.CompletionTokens,
             ModelId = modelId,
+            BlockCount = blockCount,
         };
     }
 
@@ -194,7 +198,10 @@ public sealed class ContentText : IContent
 
         // Get the settings manager:
         var settings = Program.SERVICE_PROVIDER.GetService<SettingsManager>()!;
-        
+
+        // What the request carries, for telling later whether a report still describes this chat:
+        var blocksSent = chatThread.Blocks.Count;
+
         // Start another thread by using a task to uncouple
         // the UI thread from the AI processing:
         try
@@ -224,7 +231,7 @@ public sealed class ContentText : IContent
                         this.Sources.MergeSources(contentStreamChunk.Sources);
 
                         // Keep what the provider says the request cost:
-                        this.RecordReportedUsage(contentStreamChunk.Usage, chatModel.Id);
+                        this.RecordReportedUsage(contentStreamChunk.Usage, chatModel.Id, blocksSent);
 
                         // Notify the UI that the content has changed,
                         // depending on the energy saving mode:
@@ -349,6 +356,12 @@ public sealed class ContentText : IContent
     }
 
     /// <inheritdoc />
+    /// <remarks>
+    /// The reported usage stays behind on purpose. A clone continues somewhere else -- as the
+    /// example conversation of a chat template, or as an assistant's conversation carried over into
+    /// a chat -- with another system prompt around it, and what the provider stated was for the
+    /// request this answer came out of.
+    /// </remarks>
     public IContent DeepClone() => new ContentText
     {
         Text = this.Text,

app/MindWork AI Studio/Chat/ReportedTokenUsage.cs

@@ -37,6 +37,20 @@ public sealed record ReportedTokenUsage
     /// </remarks>
     public string ModelId { get; init; } = string.Empty;
 
+    /// <summary>
+    /// How many blocks the conversation had when the request went out, this answer included.
+    /// </summary>
+    /// <remarks>
+    /// What tells an outdated report apart without anybody having to remember anything about it.
+    /// Blocks are only ever added at the end, so while this answer is the last block, a thread with
+    /// the same count is the thread the provider saw. A lower count means an earlier message was
+    /// deleted, and that message is still inside the reported number.
+    ///
+    /// Taken when the request is sent rather than when the report arrives: whatever is deleted
+    /// while the answer streams in was still part of what the provider counted.
+    /// </remarks>
+    public int BlockCount { get; init; }
+
     /// <summary>
     /// States the stored numbers as a usage again.
     /// </summary>