Fix backup restore failing on large zips with Z_BUF_ERROR

unzipper.Extract().promise() has a race condition on large zip files
where the promise resolves before write buffers are flushed, causing
zlib to see a premature end-of-stream. Switch both backup restore and
Obsidian import to unzipper.Open.file() which reads the central
directory first and is reliable for large archives.

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

Author: alexmicuplusfour

server/src/routes/backup.js

@@ -305,9 +305,10 @@ async function streamRestoreFromZip(req, res, zipPath, displayName, { deleteSour
     console.log('[RESTORE] Extracting backup:', displayName);
 
     await fs.mkdir(extractDir, { recursive: true });
-    await require('fs').createReadStream(zipPath)
-      .pipe(unzipper.Extract({ path: extractDir }))
-      .promise();
+    // Open via central directory (more reliable for large zips than the
+    // streaming Extract().promise() which can resolve before writes flush).
+    const zipDir = await unzipper.Open.file(zipPath);
+    await zipDir.extract({ path: extractDir, concurrency: 4 });
 
     const sqlFilePath = path.join(extractDir, 'database.sql');
     const extractedUploadsPath = path.join(extractDir, 'uploads');

server/src/routes/import-obsidian.js

@@ -126,9 +126,8 @@ router.post('/', blockInDemo, upload.fields([
       fs.mkdirSync(extractDir, { recursive: true });
 
       send('status', { message: 'Extracting archive...' });
-      await fs.createReadStream(zipPath)
-        .pipe(unzipper.Extract({ path: extractDir }))
-        .promise();
+      const zipDir = await unzipper.Open.file(zipPath);
+      await zipDir.extract({ path: extractDir, concurrency: 4 });
 
       importFiles = collectMdFiles(extractDir);
       resourceMap = buildResourceMap(extractDir);