fix: truly detach Windows update batch via spawn+unref instead of exec

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/native/updater.ts

@@ -1,5 +1,5 @@
 import { Notification, app, ipcMain } from "electron";
-import { exec } from "child_process";
+import { exec, spawn } from "child_process";
 import { createWriteStream, mkdirSync, writeFileSync } from "fs";
 import { dirname, join } from "path";
 import { tmpdir } from "os";
@@ -118,8 +118,13 @@ async function downloadAndInstall(url: string, version: string) {
     ].join("\r\n");
     writeFileSync(batchPath, bat);
 
-    // Launch batch detached so it outlives this process
-    exec(`cmd /C start /B "" "${batchPath}"`);
+    // Spawn batch truly detached so it outlives this process
+    const child = spawn("cmd.exe", ["/C", batchPath], {
+      detached: true,
+      stdio: "ignore",
+      windowsHide: false,
+    });
+    child.unref();
     setUpdateReady(version); // restart button will just app.exit(0) — batch relaunches
   } else {
     await new Promise<void>((resolve, reject) => {