fix(maf): populate total token usage

src/CodexSdk.MAF/CodexAIAgent.cs

@@ -100,7 +100,7 @@ protected override async Task<AgentResponse> RunCoreAsync(
                 switch (threadEvent)
                 {
                     case TurnCompletedEvent turnCompleted:
-                        usage = CreateUsageDetails(turnCompleted.Usage);
+                        usage = turnCompleted.Usage.ToUsageDetails();
                         break;
 
                     case TurnFailedEvent turnFailed:
@@ -200,16 +200,6 @@ await NotifyThreadStartedIfNeededAsync(
         await SaveNewMessagesAsync(safeSession, mergedMessages, responseMessages, cancellationToken);
     }
 
-    private static UsageDetails CreateUsageDetails(Usage usage)
-    {
-        return new UsageDetails
-        {
-            InputTokenCount = usage.InputTokens,
-            CachedInputTokenCount = usage.CachedInputTokens,
-            OutputTokenCount = usage.OutputTokens,
-        };
-    }
-
     private async ValueTask<bool> NotifyThreadStartedIfNeededAsync(
         CodexAgentSession session,
         string? threadId,

src/CodexSdk.MAF/Internal/ThreadEventExtensions.cs

@@ -35,6 +35,18 @@ internal static class ThreadEventExtensions
         return update;
     }
 
+    public static UsageDetails ToUsageDetails(this Usage usage)
+    {
+        return new UsageDetails
+        {
+            InputTokenCount = usage.InputTokens,
+            CachedInputTokenCount = usage.CachedInputTokens,
+            OutputTokenCount = usage.OutputTokens,
+            ReasoningTokenCount = usage.ReasoningOutputTokens,
+            TotalTokenCount = (long)usage.InputTokens + usage.OutputTokens,
+        };
+    }
+
     private static AgentResponseUpdate CreateLifecycleUpdate(string eventType)
     {
         return new AgentResponseUpdate
@@ -61,13 +73,7 @@ private static AgentResponseUpdate CreateUsageUpdate(Usage usage)
             },
             Contents =
             [
-                new UsageContent(new UsageDetails
-                {
-                    InputTokenCount = usage.InputTokens,
-                    CachedInputTokenCount = usage.CachedInputTokens,
-                    OutputTokenCount = usage.OutputTokens,
-                    ReasoningTokenCount = usage.ReasoningOutputTokens,
-                })
+                new UsageContent(usage.ToUsageDetails())
             ],
         };
     }

tests/CodexSdk.MAF.Tests/ThreadEventExtensionsTests.cs

@@ -92,6 +92,34 @@ public void ToAgentResponseUpdate_WhenTurnStarts_ReturnsVisibleSystemContent()
         Assert.False(update.ShouldSaveAsResponseMessage());
     }
 
+    [Fact]
+    public void ToAgentResponseUpdate_WhenTurnCompletes_MapsCompleteUsage()
+    {
+        // Arrange
+        var threadEvent = new TurnCompletedEvent
+        {
+            Usage = new Usage
+            {
+                InputTokens = 100,
+                CachedInputTokens = 60,
+                OutputTokens = 30,
+                ReasoningOutputTokens = 20,
+            },
+        };
+
+        // Act
+        var update = threadEvent.ToAgentResponseUpdate();
+
+        // Assert
+        Assert.NotNull(update);
+        var usage = Assert.IsType<UsageContent>(Assert.Single(update.Contents)).Details;
+        Assert.Equal(100L, usage.InputTokenCount);
+        Assert.Equal(60L, usage.CachedInputTokenCount);
+        Assert.Equal(30L, usage.OutputTokenCount);
+        Assert.Equal(20L, usage.ReasoningTokenCount);
+        Assert.Equal(130L, usage.TotalTokenCount);
+    }
+
     [Fact]
     public void ToAgentResponseUpdate_WhenCommandExecutionCompletedEvent_ReturnsFunctionResultContent()
     {