feat(telemetry): Update API response in telemetry

Adds the text content of the API response to the  telemetry event. This provides more context for debugging and analysis without logging the entire, potentially large, response object.

- Adds an optional  field to the  type.
- Updates  to include the  field in the logged attributes.
- Modifies the  to extract the response text using  and pass it to the logger.
- Adds a new test file for the telemetry loggers, including tests for the  function to verify the new functionality.

packages/core/src/core/client.ts

@@ -250,6 +250,7 @@ export class GeminiClient {
         response.usageMetadata?.cachedContentTokenCount ?? 0,
       thoughts_token_count: response.usageMetadata?.thoughtsTokenCount ?? 0,
       tool_token_count: response.usageMetadata?.toolUsePromptTokenCount ?? 0,
+      response_text: getResponseText(response),
     });
   }
 

packages/core/src/telemetry/loggers.test.ts

@@ -0,0 +1,119 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { logs } from '@opentelemetry/api-logs';
+import { SemanticAttributes } from '@opentelemetry/semantic-conventions';
+import { Config } from '../config/config.js';
+import { EVENT_API_RESPONSE } from './constants.js';
+import { logApiResponse } from './loggers.js';
+import * as metrics from './metrics.js';
+import * as sdk from './sdk.js';
+import { vi, describe, beforeEach, it, expect } from 'vitest';
+
+describe('logApiResponse', () => {
+  const mockConfig = {
+    getSessionId: () => 'test-session-id',
+  } as Config;
+
+  const mockLogger = {
+    emit: vi.fn(),
+  };
+
+  const mockMetrics = {
+    recordApiResponseMetrics: vi.fn(),
+    recordTokenUsageMetrics: vi.fn(),
+  };
+
+  beforeEach(() => {
+    vi.spyOn(sdk, 'isTelemetrySdkInitialized').mockReturnValue(true);
+    vi.spyOn(logs, 'getLogger').mockReturnValue(mockLogger);
+    vi.spyOn(metrics, 'recordApiResponseMetrics').mockImplementation(
+      mockMetrics.recordApiResponseMetrics,
+    );
+    vi.spyOn(metrics, 'recordTokenUsageMetrics').mockImplementation(
+      mockMetrics.recordTokenUsageMetrics,
+    );
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('2025-01-01T00:00:00.000Z'));
+  });
+
+  it('should log an API response with all fields', () => {
+    const event = {
+      model: 'test-model',
+      status_code: 200,
+      duration_ms: 100,
+      attempt: 1,
+      output_token_count: 50,
+      cached_content_token_count: 10,
+      thoughts_token_count: 5,
+      tool_token_count: 2,
+      response_text: 'test-response',
+    };
+
+    logApiResponse(mockConfig, event);
+
+    expect(mockLogger.emit).toHaveBeenCalledWith({
+      body: 'API response from test-model. Status: 200. Duration: 100ms.',
+      attributes: {
+        'session.id': 'test-session-id',
+        'event.name': EVENT_API_RESPONSE,
+        'event.timestamp': '2025-01-01T00:00:00.000Z',
+        [SemanticAttributes.HTTP_STATUS_CODE]: 200,
+        model: 'test-model',
+        status_code: 200,
+        duration_ms: 100,
+        attempt: 1,
+        output_token_count: 50,
+        cached_content_token_count: 10,
+        thoughts_token_count: 5,
+        tool_token_count: 2,
+        response_text: 'test-response',
+      },
+    });
+
+    expect(mockMetrics.recordApiResponseMetrics).toHaveBeenCalledWith(
+      mockConfig,
+      'test-model',
+      100,
+      200,
+      undefined,
+    );
+
+    expect(mockMetrics.recordTokenUsageMetrics).toHaveBeenCalledWith(
+      mockConfig,
+      'test-model',
+      50,
+      'output',
+    );
+  });
+
+  it('should log an API response with an error', () => {
+    const event = {
+      model: 'test-model',
+      duration_ms: 100,
+      attempt: 1,
+      error: 'test-error',
+      output_token_count: 50,
+      cached_content_token_count: 10,
+      thoughts_token_count: 5,
+      tool_token_count: 2,
+      response_text: 'test-response',
+    };
+
+    logApiResponse(mockConfig, event);
+
+    expect(mockLogger.emit).toHaveBeenCalledWith({
+      body: 'API response from test-model. Status: N/A. Duration: 100ms.',
+      attributes: {
+        'session.id': 'test-session-id',
+        ...event,
+        'event.name': EVENT_API_RESPONSE,
+        'event.timestamp': '2025-01-01T00:00:00.000Z',
+        'error.message': 'test-error',
+      },
+    });
+  });
+});

packages/core/src/telemetry/loggers.ts

@@ -195,6 +195,9 @@ export function logApiResponse(
     'event.name': EVENT_API_RESPONSE,
     'event.timestamp': new Date().toISOString(),
   };
+  if (event.response_text) {
+    attributes.response_text = event.response_text;
+  }
   if (event.error) {
     attributes['error.message'] = event.error;
   } else if (event.status_code) {

packages/core/src/telemetry/types.ts

@@ -53,6 +53,7 @@ export interface ApiResponseEvent {
   cached_content_token_count: number;
   thoughts_token_count: number;
   tool_token_count: number;
+  response_text?: string;
 }
 
 export interface CliConfigEvent {