@actions/exec: convert to ESM module

packages/exec/__tests__/scripts/spawn-wait-for-file.cjs

@@ -0,0 +1,44 @@
+const childProcess = require('child_process')
+const path = require('path')
+
+// Parse args
+const args = {}
+for (const arg of process.argv.slice(2)) {
+  const idx = arg.indexOf('=')
+  if (idx !== -1) {
+    args[arg.slice(0, idx)] = arg.slice(idx + 1)
+  }
+}
+
+const filePath = args.file
+if (!filePath) {
+  throw new Error('file is not specified')
+}
+
+// Spawn wait-for-file.cjs with inherited stdio
+// This creates a grandchild process that holds the stdio handles open
+// after this process (the child) exits
+const waitScript = path.join(__dirname, 'wait-for-file.cjs')
+const isWindows = process.platform === 'win32'
+
+// On Windows, use detached:true to properly keep streams open
+// On Unix, detached:true also works and creates a new process group
+const child = childProcess.spawn(process.execPath, [waitScript, `file=${filePath}`], {
+  stdio: ['ignore', 'inherit', 'inherit'],
+  detached: true,
+  windowsHide: true
+})
+
+// Don't wait for child to exit
+child.unref()
+
+// Handle optional stderr output (must happen BEFORE we exit)
+if (args.stderr === 'true') {
+  process.stderr.write('hi')
+}
+
+// Small delay to ensure child has started and inherited handles
+setTimeout(() => {
+  const exitCode = args.exitCode ? parseInt(args.exitCode, 10) : 0
+  process.exit(exitCode)
+}, 50)