fix: handle windows background execution errors and add tests

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

@@ -831,4 +831,33 @@ describe('ShellTool', () => {
       expect(shellTool.description).toMatchSnapshot();
     });
   });
+
+  describe('Windows background execution', () => {
+    it('should detect immediate failure in Windows background task', async () => {
+      vi.mocked(os.platform).mockReturnValue('win32');
+      const mockAbortSignal = new AbortController().signal;
+
+      const invocation = shellTool.build({
+        command: 'invalid_command',
+        is_background: true,
+      });
+
+      const promise = invocation.execute(mockAbortSignal);
+
+      // Wait a tick to ensure mockShellOutputCallback is assigned
+      await new Promise((resolve) => setTimeout(resolve, 0));
+
+      if (mockShellOutputCallback) {
+        mockShellOutputCallback({
+          type: 'data',
+          chunk:
+            "'invalid_command' is not recognized as an internal or external command,\r\noperable program or batch file.\r\n",
+        });
+      }
+
+      const result = await promise;
+      expect(result.error).toBeDefined();
+      expect(result.llmContent).toContain('Command failed to start');
+    });
+  });
 });