fix backup restore: stream-peek gzip content instead of zlib.gunzipFile (node20 API)

server.js

@@ -186,7 +186,8 @@ app.put('/api/settings', requireAdmin, async (req, res) => {
 });
 
 // --- Backup / Restore ---
-const gunzipFile = require('util').promisify(require('zlib').gunzipFile);
+const gunzipAsync = require('util').promisify(require('zlib').gunzip);
+const zlib = require('zlib');
 const tar = require('tar');
 const os = require('os');
 const uploadBackup = multer({
@@ -347,14 +348,38 @@ function cleanupUpload(req) {
   } catch {}
 }
 
+function peekGunzip(filePath, n) {
+  return new Promise((resolve) => {
+    const gunz = zlib.createGunzip();
+    const bufs = [];
+    let total = 0;
+    let done = false;
+    gunz.on('data', (c) => {
+      if (done) return;
+      const need = n - total;
+      bufs.push(c.length > need ? c.subarray(0, need) : c);
+      total += Math.min(c.length, need);
+      if (total >= n) {
+        done = true;
+        gunz.destroy();
+      }
+    });
+    gunz.on('error', () => resolve(null));
+    gunz.on('close', () => resolve(Buffer.concat(bufs)));
+    fs.createReadStream(filePath).pipe(gunz);
+  });
+}
+
 app.post('/api/restore', requireAdmin, uploadBackup.single('backup'), async (req, res) => {
   if (!req.file) return res.status(400).json({ error: 'backup file required' });
   let data;
   let legacyPhotos = [];
   const staging = fs.mkdtempSync(path.join(os.tmpdir(), 'wido-rst-'));
   try {
-    const gunz = await gunzipFile(req.file.path).catch(() => null);
-    if (gunz && gunz[0] === 0x7b) {
+    const head = await peekGunzip(req.file.path, 8);
+    if (head && head[0] === 0x7b) {
+      const buf = await fs.promises.readFile(req.file.path);
+      const gunz = await gunzipAsync(buf);
       data = JSON.parse(gunz.toString('utf8'));
       legacyPhotos = data.photos || [];
     } else {