Read the reported token usage in one place

app/MindWork AI Studio/Provider/OpenAI/ChatCompletionDeltaStreamLine.cs

@@ -34,10 +34,7 @@ public record ChatCompletionDeltaStreamLine(string Id, string Object, uint Creat
     public ContentStreamChunk GetContent() => new(this.Choices[0].Delta.Content, []);
 
     /// <inheritdoc />
-    public bool ContainsUsage() => this.GetUsage().IsKnown;
-
-    /// <inheritdoc />
-    public TokenUsage GetUsage() => this.Usage is null ? TokenUsage.UNKNOWN : TokenUsage.OfReported(this.Usage.PromptTokens, this.Usage.CompletionTokens);
+    public TokenUsage GetUsage() => this.Usage?.ToTokenUsage() ?? TokenUsage.UNKNOWN;
 
     #region Implementation of IAnnotationStreamLine
 

app/MindWork AI Studio/Provider/OpenAI/ChatCompletionUsage.cs

@@ -22,9 +22,12 @@ public sealed record ChatCompletionUsage
     public int? CompletionTokens { get; init; }
 
     /// <summary>
-    /// What the provider says both of them add up to. Read but not relied upon: it is the sum of
-    /// the other two wherever a provider fills all three, and this way a provider which sends only
-    /// this one is not a reason to throw the other numbers away.
+    /// States what this block reports, as far as it can be believed.
     /// </summary>
-    public int? TotalTokens { get; init; }
+    /// <remarks>
+    /// The one way from the wire to a usage, shared by every stream line which carries this block,
+    /// so that what counts as believable is decided in a single place.
+    /// </remarks>
+    /// <returns>The usage, or TokenUsage.UNKNOWN when the block states nothing usable.</returns>
+    public TokenUsage ToTokenUsage() => TokenUsage.OfReported(this.PromptTokens, this.CompletionTokens);
 }