Read the reported token usage in one place

app/MindWork AI Studio/Provider/BaseProvider.cs

@@ -1123,11 +1123,12 @@ public abstract class BaseProvider : IProvider, ISecretId
                 // send it as the last line of the stream, with no choices at all. It is handled
                 // before the check below, which would otherwise drop it as an empty response.
                 //
-                if (providerResponse.ContainsUsage())
+                var usage = providerResponse.GetUsage();
+                if (usage.IsKnown)
                 {
                     yield return providerResponse.ContainsContent()
-                        ? providerResponse.GetContent() with { Usage = providerResponse.GetUsage() }
-                        : new(string.Empty, [], providerResponse.GetUsage());
+                        ? providerResponse.GetContent() with { Usage = usage }
+                        : new(string.Empty, [], usage);
 
                     continue;
                 }

app/MindWork AI Studio/Provider/Fireworks/ResponseStreamLine.cs

@@ -29,10 +29,7 @@ public readonly record struct ResponseStreamLine(string Id, string Object, uint
     public ChatCompletionUsage? Usage { get; init; }
 
     /// <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/IResponseStreamLine.cs

@@ -18,18 +18,16 @@ public interface IResponseStreamLine : IAnnotationStreamLine
     public ContentStreamChunk GetContent();
 
     /// <summary>
-    /// Checks whether the response line states what the request cost.
+    /// Gets what the provider said the request cost.
     /// </summary>
     /// <remarks>
     /// Answered here for every wire format which says nothing about it, which is most of them: a
     /// provider who reports no usage is the normal case, not a gap somebody has to fill in.
+    ///
+    /// Unlike content and sources, there is no separate check for whether a line carries it. This
+    /// never fails on a line without one, and whether the answer means anything is what IsKnown of
+    /// the returned usage says.
     /// </remarks>
-    /// <returns>True when the response line carries a token usage, false otherwise.</returns>
-    public bool ContainsUsage() => false;
-
-    /// <summary>
-    /// Gets what the provider said the request cost.
-    /// </summary>
     /// <returns>The usage, or TokenUsage.UNKNOWN when the line carries none.</returns>
     public TokenUsage GetUsage() => TokenUsage.UNKNOWN;
 }

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);
 }

app/MindWork AI Studio/Provider/Perplexity/ResponseStreamLine.cs

@@ -30,10 +30,7 @@ public readonly record struct ResponseStreamLine(string Id, string Object, uint
     public ChatCompletionUsage? Usage { get; init; }
 
     /// <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;
     
     /// <inheritdoc />
     public bool ContainsSources() => this != default && this.SearchResults.Count > 0;