feat(core): add prePlanMode tracking to restore previous approval mode

When entering plan mode, Config now saves the previous approval mode
(e.g. AUTO_EDIT, YOLO) so it can be restored when exiting. Previously,
/plan execute and ExitPlanModeTool both hardcoded a return to DEFAULT,
losing the user's prior mode.

Changes:
- Config: add prePlanMode field, getPrePlanMode(), auto-track in
  setApprovalMode()
- planCommand: /plan execute restores prePlanMode instead of DEFAULT
- ExitPlanModeTool: ProceedOnce restores prePlanMode instead of DEFAULT
- Tests: 4 new Config tests, 1 new planCommand test, 1 new
  ExitPlanModeTool test

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/cli/src/ui/commands/planCommand.test.ts

@@ -18,6 +18,7 @@ describe('planCommand', () => {
       services: {
         config: {
           getApprovalMode: vi.fn().mockReturnValue(ApprovalMode.DEFAULT),
+          getPrePlanMode: vi.fn().mockReturnValue(ApprovalMode.DEFAULT),
           setApprovalMode: vi.fn(),
         } as unknown as import('@qwen-code/qwen-code-core').Config,
       },
@@ -116,6 +117,30 @@ describe('planCommand', () => {
     });
   });
 
+  it('should restore pre-plan mode when executing from plan mode', async () => {
+    if (!planCommand.action) {
+      throw new Error('The plan command must have an action.');
+    }
+
+    (mockContext.services.config?.getApprovalMode as Mock).mockReturnValue(
+      ApprovalMode.PLAN,
+    );
+    (mockContext.services.config?.getPrePlanMode as Mock).mockReturnValue(
+      ApprovalMode.AUTO_EDIT,
+    );
+
+    const result = await planCommand.action(mockContext, 'execute');
+
+    expect(mockContext.services.config?.setApprovalMode).toHaveBeenCalledWith(
+      ApprovalMode.AUTO_EDIT,
+    );
+    expect(result).toEqual({
+      type: 'message',
+      messageType: 'info',
+      content: 'Exited plan mode. The agent will now execute the plan.',
+    });
+  });
+
   it('should return error when execute is used but not in plan mode', async () => {
     if (!planCommand.action) {
       throw new Error('The plan command must have an action.');

packages/cli/src/ui/commands/planCommand.ts

@@ -45,7 +45,7 @@ export const planCommand: SlashCommand = {
         };
       }
       try {
-        config.setApprovalMode(ApprovalMode.DEFAULT);
+        config.setApprovalMode(config.getPrePlanMode());
       } catch (e) {
         return {
           type: 'message',