[JUNE 25] Permanent failover to Flash model for OAuth users after persistent 429 errors (#1376)

Co-authored-by: Scott Densmore <scottdensmore@mac.com>

packages/core/src/utils/flashFallback.integration.test.ts

@@ -0,0 +1,144 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { Config } from '../config/config.js';
+import {
+  setSimulate429,
+  disableSimulationAfterFallback,
+  shouldSimulate429,
+  createSimulated429Error,
+  resetRequestCounter,
+} from './testUtils.js';
+import { DEFAULT_GEMINI_FLASH_MODEL } from '../config/models.js';
+import { retryWithBackoff } from './retry.js';
+import { AuthType } from '../core/contentGenerator.js';
+
+describe('Flash Fallback Integration', () => {
+  let config: Config;
+
+  beforeEach(() => {
+    config = new Config({
+      sessionId: 'test-session',
+      targetDir: '/test',
+      debugMode: false,
+      cwd: '/test',
+      model: 'gemini-2.5-pro',
+    });
+
+    // Reset simulation state for each test
+    setSimulate429(false);
+    resetRequestCounter();
+  });
+
+  it('should automatically accept fallback', async () => {
+    // Set up a minimal flash fallback handler for testing
+    const flashFallbackHandler = async (): Promise<boolean> => true;
+
+    config.setFlashFallbackHandler(flashFallbackHandler);
+
+    // Call the handler directly to test
+    const result = await config.flashFallbackHandler!(
+      'gemini-2.5-pro',
+      DEFAULT_GEMINI_FLASH_MODEL,
+    );
+
+    // Verify it automatically accepts
+    expect(result).toBe(true);
+  });
+
+  it('should trigger fallback after 3 consecutive 429 errors for OAuth users', async () => {
+    let fallbackCalled = false;
+    let fallbackModel = '';
+
+    // Mock function that simulates exactly 3 429 errors, then succeeds after fallback
+    const mockApiCall = vi
+      .fn()
+      .mockRejectedValueOnce(createSimulated429Error())
+      .mockRejectedValueOnce(createSimulated429Error())
+      .mockRejectedValueOnce(createSimulated429Error())
+      .mockResolvedValueOnce('success after fallback');
+
+    // Mock fallback handler
+    const mockFallbackHandler = vi.fn(async (_authType?: string) => {
+      fallbackCalled = true;
+      fallbackModel = DEFAULT_GEMINI_FLASH_MODEL;
+      return fallbackModel;
+    });
+
+    // Test with OAuth personal auth type, with maxAttempts = 3 to ensure fallback triggers
+    const result = await retryWithBackoff(mockApiCall, {
+      maxAttempts: 3,
+      initialDelayMs: 1,
+      maxDelayMs: 10,
+      shouldRetry: (error: Error) => {
+        const status = (error as Error & { status?: number }).status;
+        return status === 429;
+      },
+      onPersistent429: mockFallbackHandler,
+      authType: AuthType.LOGIN_WITH_GOOGLE_PERSONAL,
+    });
+
+    // Verify fallback was triggered
+    expect(fallbackCalled).toBe(true);
+    expect(fallbackModel).toBe(DEFAULT_GEMINI_FLASH_MODEL);
+    expect(mockFallbackHandler).toHaveBeenCalledWith(
+      AuthType.LOGIN_WITH_GOOGLE_PERSONAL,
+    );
+    expect(result).toBe('success after fallback');
+    // Should have: 3 failures, then fallback triggered, then 1 success after retry reset
+    expect(mockApiCall).toHaveBeenCalledTimes(4);
+  });
+
+  it('should not trigger fallback for API key users', async () => {
+    let fallbackCalled = false;
+
+    // Mock function that simulates 429 errors
+    const mockApiCall = vi.fn().mockRejectedValue(createSimulated429Error());
+
+    // Mock fallback handler
+    const mockFallbackHandler = vi.fn(async () => {
+      fallbackCalled = true;
+      return DEFAULT_GEMINI_FLASH_MODEL;
+    });
+
+    // Test with API key auth type - should not trigger fallback
+    try {
+      await retryWithBackoff(mockApiCall, {
+        maxAttempts: 5,
+        initialDelayMs: 10,
+        maxDelayMs: 100,
+        shouldRetry: (error: Error) => {
+          const status = (error as Error & { status?: number }).status;
+          return status === 429;
+        },
+        onPersistent429: mockFallbackHandler,
+        authType: AuthType.USE_GEMINI, // API key auth type
+      });
+    } catch (error) {
+      // Expected to throw after max attempts
+      expect((error as Error).message).toContain('Rate limit exceeded');
+    }
+
+    // Verify fallback was NOT triggered for API key users
+    expect(fallbackCalled).toBe(false);
+    expect(mockFallbackHandler).not.toHaveBeenCalled();
+  });
+
+  it('should properly disable simulation state after fallback', () => {
+    // Enable simulation
+    setSimulate429(true);
+
+    // Verify simulation is enabled
+    expect(shouldSimulate429()).toBe(true);
+
+    // Disable simulation after fallback
+    disableSimulationAfterFallback();
+
+    // Verify simulation is now disabled
+    expect(shouldSimulate429()).toBe(false);
+  });
+});