Method handleFlashFallback

packages/core/src/core/client.ts:870–911

* Handles falling back to Flash model when persistent 429 errors occur for OAuth users. * Uses a fallback handler if provided by the config; otherwise, returns null.

(
    authType?: string,
    error?: unknown,
  )

   * Uses a fallback handler if provided by the config; otherwise, returns null.
   */
  private async handleFlashFallback(
    authType?: string,
    error?: unknown,
  ): Promise<string | null> {
    // Only handle fallback for OAuth users
    if (authType !== AuthType.LOGIN_WITH_GOOGLE) {
      return null;
    }

    const currentModel = this.config.getModel();
    const fallbackModel = DEFAULT_FALLBACK_MODEL;

    // Don't fallback if already using Flash model
    if (currentModel === fallbackModel) {
      return null;
    }

    // Check if config has a fallback handler (set by CLI package)
    const fallbackHandler = this.config.flashFallbackHandler;
    if (typeof fallbackHandler === 'function') {
      try {
        const accepted = await fallbackHandler(
          currentModel,
          fallbackModel,
          error,
        );
        if (accepted !== false && accepted !== null) {
          this.config.setModel(fallbackModel);
          this.config.setFallbackMode(true);
          return fallbackModel;
        }
        // Check if the model was switched manually in the handler
        if (this.config.getModel() === fallbackModel) {
          return null; // Model was switched but don't continue with current prompt
        }
      } catch (error) {
        console.warn('Flash fallback handler failed:', error);
      }
    }

    return null;
  }
}

export const TEST_ONLY = {