[ai] Expose totalUsage and finishReason on DurableAgent stream result

.changeset/durable-agent-stream-result-totalusage.md

@@ -0,0 +1,5 @@
+---
+"@workflow/ai": minor
+---
+
+Expose `totalUsage` and `finishReason` on the `DurableAgent.stream()` result, mirroring the AI SDK's `GenerateTextResult`/`StreamTextResult` and the existing `onFinish` event payload.

packages/ai/src/agent/durable-agent-compat.test.ts

@@ -1348,6 +1348,30 @@ describe('DurableAgent (ToolLoopAgent compat)', () => {
           }
         `);
       });
+
+      it('should expose finishReason and totalUsage on the stream result', async () => {
+        const agent = new DurableAgent({
+          model: asModelFactory(mockModel),
+        });
+
+        const { writable } = createMockWritable();
+        const result = await agent.stream({
+          messages: [{ role: 'user' as const, content: 'test' }],
+          writable,
+        });
+
+        expect({
+          finishReason: result.finishReason,
+          inputTokens: result.totalUsage.inputTokens,
+          outputTokens: result.totalUsage.outputTokens,
+        }).toMatchInlineSnapshot(`
+          {
+            "finishReason": "stop",
+            "inputTokens": 3,
+            "outputTokens": 10,
+          }
+        `);
+      });
     });
   });
 

packages/ai/src/agent/durable-agent.ts

@@ -735,6 +735,16 @@ export interface DurableAgentStreamResult<
    */
   toolResults: ToolResult[];
 
+  /**
+   * The finish reason from the last step.
+   */
+  finishReason: FinishReason;
+
+  /**
+   * The total token usage across all steps.
+   */
+  totalUsage: LanguageModelUsage;
+
   /**
    * The generated structured output. It uses the `experimental_output` specification.
    * Only available when `experimental_output` is specified.
@@ -980,6 +990,8 @@ export class DurableAgent<TBaseTools extends ToolSet = ToolSet> {
         steps,
         toolCalls: [],
         toolResults: [],
+        finishReason: 'other',
+        totalUsage: aggregateUsage(steps),
         experimental_output: undefined as OUTPUT,
         uiMessages: undefined,
       };
@@ -1168,15 +1180,17 @@ export class DurableAgent<TBaseTools extends ToolSet = ToolSet> {
             // resolved tool results), so callers can resume the conversation.
             // Cast matches the existing pattern used at the end of stream().
             const messages = iterMessages as unknown as ModelMessage[];
+            const lastStep = steps[steps.length - 1];
+            const totalUsage = aggregateUsage(steps);
+            const finishReason = lastStep?.finishReason ?? 'other';
 
             if (mergedOnFinish && !wasAborted) {
-              const lastStep = steps[steps.length - 1];
               await mergedOnFinish({
                 steps,
                 messages,
                 text: lastStep?.text ?? '',
-                finishReason: lastStep?.finishReason ?? 'other',
-                totalUsage: aggregateUsage(steps),
+                finishReason,
+                totalUsage,
                 experimental_context: experimentalContext,
                 experimental_output: undefined as OUTPUT,
               });
@@ -1191,6 +1205,8 @@ export class DurableAgent<TBaseTools extends ToolSet = ToolSet> {
               steps,
               toolCalls: allToolCalls,
               toolResults: allToolResults,
+              finishReason,
+              totalUsage,
               experimental_output: undefined as OUTPUT,
               uiMessages,
             };
@@ -1328,15 +1344,18 @@ export class DurableAgent<TBaseTools extends ToolSet = ToolSet> {
       }
     }
 
+    const lastStep = steps[steps.length - 1];
+    const totalUsage = aggregateUsage(steps);
+    const finishReason = lastStep?.finishReason ?? 'other';
+
     // Call onFinish callback if provided (always call, even on errors, but not on abort)
     if (mergedOnFinish && !wasAborted) {
-      const lastStep = steps[steps.length - 1];
       await mergedOnFinish({
         steps,
         messages: messages as ModelMessage[],
         text: lastStep?.text ?? '',
-        finishReason: lastStep?.finishReason ?? 'other',
-        totalUsage: aggregateUsage(steps),
+        finishReason,
+        totalUsage,
         experimental_context: experimentalContext,
         experimental_output: experimentalOutput,
       });
@@ -1358,6 +1377,8 @@ export class DurableAgent<TBaseTools extends ToolSet = ToolSet> {
       steps,
       toolCalls: lastStepToolCalls,
       toolResults: lastStepToolResults,
+      finishReason,
+      totalUsage,
       experimental_output: experimentalOutput,
       uiMessages,
     };