feat(core): implement native Windows sandboxing with restricted tokens

packages/core/scripts/compile-windows-sandbox.js

@@ -0,0 +1,119 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { spawnSync } from 'node:child_process';
+import path from 'node:path';
+import fs from 'node:fs';
+import os from 'node:os';
+import { fileURLToPath } from 'node:url';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+/**
+ * Compiles the GeminiSandbox C# helper on Windows.
+ * This is used to provide native restricted token sandboxing.
+ */
+function compileWindowsSandbox() {
+  if (os.platform() !== 'win32') {
+    return;
+  }
+
+  const srcHelperPath = path.resolve(
+    __dirname,
+    '../src/services/scripts/GeminiSandbox.exe',
+  );
+  const distHelperPath = path.resolve(
+    __dirname,
+    '../dist/src/services/scripts/GeminiSandbox.exe',
+  );
+  const sourcePath = path.resolve(
+    __dirname,
+    '../src/services/scripts/GeminiSandbox.cs',
+  );
+
+  if (!fs.existsSync(sourcePath)) {
+    console.error(`Sandbox source not found at ${sourcePath}`);
+    return;
+  }
+
+  // Ensure directories exist
+  [srcHelperPath, distHelperPath].forEach((p) => {
+    const dir = path.dirname(p);
+    if (!fs.existsSync(dir)) {
+      fs.mkdirSync(dir, { recursive: true });
+    }
+  });
+
+  // Find csc.exe (C# Compiler) which is built into Windows .NET Framework
+  const systemRoot = process.env['SystemRoot'] || 'C:\\Windows';
+  const cscPaths = [
+    'csc.exe', // Try in PATH first
+    path.join(
+      systemRoot,
+      'Microsoft.NET',
+      'Framework64',
+      'v4.0.30319',
+      'csc.exe',
+    ),
+    path.join(
+      systemRoot,
+      'Microsoft.NET',
+      'Framework',
+      'v4.0.30319',
+      'csc.exe',
+    ),
+  ];
+
+  let csc = undefined;
+  for (const p of cscPaths) {
+    if (p === 'csc.exe') {
+      const result = spawnSync('where', ['csc.exe'], { stdio: 'ignore' });
+      if (result.status === 0) {
+        csc = 'csc.exe';
+        break;
+      }
+    } else if (fs.existsSync(p)) {
+      csc = p;
+      break;
+    }
+  }
+
+  if (!csc) {
+    console.warn(
+      'Windows C# compiler (csc.exe) not found. Native sandboxing will attempt to compile on first run.',
+    );
+    return;
+  }
+
+  console.log(`Compiling native Windows sandbox helper...`);
+  // Compile to src
+  let result = spawnSync(
+    csc,
+    [`/out:${srcHelperPath}`, '/optimize', sourcePath],
+    {
+      stdio: 'inherit',
+    },
+  );
+
+  if (result.status === 0) {
+    console.log('Successfully compiled GeminiSandbox.exe to src');
+    // Copy to dist if dist exists
+    const distDir = path.resolve(__dirname, '../dist');
+    if (fs.existsSync(distDir)) {
+      const distScriptsDir = path.dirname(distHelperPath);
+      if (!fs.existsSync(distScriptsDir)) {
+        fs.mkdirSync(distScriptsDir, { recursive: true });
+      }
+      fs.copyFileSync(srcHelperPath, distHelperPath);
+      console.log('Successfully copied GeminiSandbox.exe to dist');
+    }
+  } else {
+    console.error('Failed to compile Windows sandbox helper.');
+  }
+}
+
+compileWindowsSandbox();