refactor(core,cli): useAlternateBuffer read from config (#20346)

Co-authored-by: Jacob Richman <jacob314@gmail.com>

packages/cli/src/ui/components/ExitPlanModeDialog.test.tsx

@@ -167,6 +167,7 @@ Implement a comprehensive authentication system with multiple providers.
             readTextFile: vi.fn(),
             writeTextFile: vi.fn(),
           }),
+          getUseAlternateBuffer: () => options?.useAlternateBuffer ?? true,
         } as unknown as import('@google/gemini-cli-core').Config,
       },
     );
@@ -443,6 +444,7 @@ Implement a comprehensive authentication system with multiple providers.
                 readTextFile: vi.fn(),
                 writeTextFile: vi.fn(),
               }),
+              getUseAlternateBuffer: () => useAlternateBuffer ?? true,
             } as unknown as import('@google/gemini-cli-core').Config,
           },
         );

packages/cli/src/ui/components/ToolConfirmationQueue.test.tsx

@@ -51,6 +51,7 @@ describe('ToolConfirmationQueue', () => {
     storage: {
       getPlansDir: () => '/mock/temp/plans',
     },
+    getUseAlternateBuffer: () => false,
   } as unknown as Config;
 
   beforeEach(() => {