fix(core): prefer pwsh.exe over Windows PowerShell 5.1 (#25859) (#25900)

Co-authored-by: Tommaso Sciortino <sciortino@gmail.com>

packages/core/src/services/shellExecutionService.test.ts

@@ -213,7 +213,7 @@ describe('ShellExecutionService', () => {
     mockSerializeTerminalToObject.mockReturnValue([]);
     mockIsBinary.mockReturnValue(false);
     mockPlatform.mockReturnValue('linux');
-    mockResolveExecutable.mockImplementation(async (exe: string) => exe);
+    mockResolveExecutable.mockImplementation((exe: string) => exe);
     process.env['PATH'] = '/test/path';
     mockGetPty.mockResolvedValue({
       module: { spawn: mockPtySpawn },
@@ -2064,7 +2064,7 @@ describe('ShellExecutionService environment variables', () => {
       sandboxManager: mockSandboxManager,
     };
 
-    mockResolveExecutable.mockResolvedValue('/bin/bash/resolved');
+    mockResolveExecutable.mockReturnValue('/bin/bash/resolved');
     const mockChild = new EventEmitter() as unknown as ChildProcess;
     mockChild.stdout = new EventEmitter() as unknown as Readable;
     mockChild.stderr = new EventEmitter() as unknown as Readable;

packages/core/src/services/shellExecutionService.ts

@@ -414,8 +414,7 @@ export class ShellExecutionService {
       executable = 'cmd.exe';
     }
 
-    const resolvedExecutable =
-      (await resolveExecutable(executable)) ?? executable;
+    const resolvedExecutable = resolveExecutable(executable) ?? executable;
 
     const guardedCommand = ensurePromptvarsDisabled(commandToExecute, shell);
     const spawnArgs = [...argsPrefix, guardedCommand];

packages/core/src/services/shellExecutionService.windows.integration.test.ts

@@ -0,0 +1,89 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import os from 'node:os';
+import { ShellExecutionService } from './shellExecutionService.js';
+import { NoopSandboxManager } from './sandboxManager.js';
+
+const isWindows = os.platform() === 'win32';
+
+/**
+ * Real-shell integration tests that reproduce the regression class from
+ * issue #25859: commands with inline double quotes executed on Windows
+ * lose their quotes when they reach the native executable, because
+ * Windows PowerShell 5.1 mangles embedded " during native-command
+ * argument passing. PowerShell 7 (pwsh.exe) passes arguments correctly.
+ *
+ * These tests exercise the full pipeline end-to-end. They pass when
+ * gemini-cli selects pwsh.exe from PATH; they fail when the pipeline
+ * routes through Windows PowerShell 5.1.
+ */
+describe.skipIf(!isWindows)(
+  'ShellExecutionService Windows quoting (real shell)',
+  () => {
+    const baseConfig = {
+      sanitizationConfig: {
+        allowedEnvironmentVariables: [],
+        blockedEnvironmentVariables: [],
+        enableEnvironmentVariableRedaction: false,
+      },
+      sandboxManager: new NoopSandboxManager(),
+    };
+
+    async function runReal(command: string) {
+      const controller = new AbortController();
+      const handle = await ShellExecutionService.execute(
+        command,
+        process.cwd(),
+        () => {},
+        controller.signal,
+        false,
+        baseConfig,
+      );
+      const result = await handle.result;
+      return { result, output: result.output };
+    }
+
+    it('should preserve inline double quotes through node -e', async () => {
+      const { result, output } = await runReal(
+        `node -e 'console.log("preserved")'`,
+      );
+      expect(result.exitCode).toBe(0);
+      expect(output).toBe('preserved');
+    });
+
+    it('should preserve double quotes inside JSON output', async () => {
+      const { result, output } = await runReal(
+        `node -e 'console.log(JSON.stringify({ok:"yes"}))'`,
+      );
+      expect(result.exitCode).toBe(0);
+      expect(output).toBe('{"ok":"yes"}');
+    });
+
+    it('should handle quoted argument containing a space', async () => {
+      const { result, output } = await runReal(
+        `node -e "console.log('hello world')"`,
+      );
+      expect(result.exitCode).toBe(0);
+      expect(output).toBe('hello world');
+    });
+
+    it('should handle a mixed-quote regex literal', async () => {
+      const { result, output } = await runReal(
+        `node -e 'console.log(String("a").match(/"/))'`,
+      );
+      expect(result.exitCode).toBe(0);
+      expect(output).toBe('null');
+    });
+
+    it('should pass a literal double-quote byte through to stdout', async () => {
+      const { result, output } = await runReal(`node -e 'console.log("\\"")'`);
+      expect(result.exitCode).toBe(0);
+      expect(output).toBe('"');
+    });
+  },
+);