test(core): improve testing for API request/response parsing (#21227)

integration-tests/api-resilience.responses

@@ -0,0 +1 @@
+{"method":"generateContentStream","response":[{"candidates":[{"content":{"parts":[{"text":"Part 1. "}],"role":"model"},"index":0}]},{"usageMetadata":{"promptTokenCount":100,"candidatesTokenCount":10,"totalTokenCount":110}},{"candidates":[{"content":{"parts":[{"text":"Part 2."}],"role":"model"},"index":0}],"finishReason":"STOP"}]}

integration-tests/api-resilience.test.ts

@@ -0,0 +1,50 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { TestRig } from './test-helper.js';
+import { join, dirname } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+describe('API Resilience E2E', () => {
+  let rig: TestRig;
+
+  beforeEach(() => {
+    rig = new TestRig();
+  });
+
+  afterEach(async () => {
+    await rig.cleanup();
+  });
+
+  it('should not crash when receiving metadata-only chunks in a stream', async () => {
+    await rig.setup('api-resilience-metadata-only', {
+      fakeResponsesPath: join(
+        dirname(fileURLToPath(import.meta.url)),
+        'api-resilience.responses',
+      ),
+      settings: {
+        planSettings: { modelRouting: false },
+      },
+    });
+
+    // Run the CLI with a simple prompt.
+    // The fake responses will provide a stream with a metadata-only chunk in the middle.
+    // We use gemini-3-pro-preview to minimize internal service calls.
+    const result = await rig.run({
+      args: ['hi', '--model', 'gemini-3-pro-preview'],
+    });
+
+    // Verify the output contains text from the normal chunks.
+    // If the CLI crashed on the metadata chunk, rig.run would throw.
+    expect(result).toContain('Part 1.');
+    expect(result).toContain('Part 2.');
+
+    // Verify telemetry event for the prompt was still generated
+    const hasUserPromptEvent = await rig.waitForTelemetryEvent('user_prompt');
+    expect(hasUserPromptEvent).toBe(true);
+  });
+});