fix(plan): sandbox path resolution in Plan Mode to prevent hallucinations (#22737)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

packages/core/src/tools/edit.test.ts

@@ -131,8 +131,10 @@ describe('EditTool', () => {
       isInteractive: () => false,
       getDisableLLMCorrection: vi.fn(() => true),
       getExperiments: () => {},
+      isPlanMode: vi.fn(() => false),
       storage: {
         getProjectTempDir: vi.fn().mockReturnValue('/tmp/project'),
+        getPlansDir: vi.fn().mockReturnValue('/tmp/plans'),
       },
       isPathAllowed(this: Config, absolutePath: string): boolean {
         const workspaceContext = this.getWorkspaceContext();
@@ -1299,4 +1301,42 @@ function doIt() {
       );
     });
   });
+
+  describe('plan mode', () => {
+    it('should allow edits to plans directory when isPlanMode is true', async () => {
+      const mockProjectTempDir = path.join(tempDir, 'project');
+      fs.mkdirSync(mockProjectTempDir);
+      vi.mocked(mockConfig.storage.getProjectTempDir).mockReturnValue(
+        mockProjectTempDir,
+      );
+
+      const plansDir = path.join(mockProjectTempDir, 'plans');
+      fs.mkdirSync(plansDir);
+
+      vi.mocked(mockConfig.isPlanMode).mockReturnValue(true);
+      vi.mocked(mockConfig.storage.getPlansDir).mockReturnValue(plansDir);
+
+      const filePath = path.join(rootDir, 'test-file.txt');
+      const planFilePath = path.join(plansDir, 'test-file.txt');
+      const initialContent = 'some initial content';
+      fs.writeFileSync(planFilePath, initialContent, 'utf8');
+
+      const params: EditToolParams = {
+        file_path: filePath,
+        instruction: 'Replace initial with new',
+        old_string: 'initial',
+        new_string: 'new',
+      };
+
+      const invocation = tool.build(params);
+      const result = await invocation.execute(new AbortController().signal);
+
+      expect(result.llmContent).toMatch(/Successfully modified file/);
+
+      // Verify plan file is written with new content
+      expect(fs.readFileSync(planFilePath, 'utf8')).toBe('some new content');
+
+      fs.rmSync(plansDir, { recursive: true, force: true });
+    });
+  });
 });