fix(e2e): wait for download file to be fully written before checking size

The save-large-labelmap test could fail on CI when the file watcher
resolved before Chrome finished flushing the download. Poll for non-zero
file size before asserting.

Author: PaulHax

tests/specs/save-large-labelmap.e2e.ts

@@ -159,6 +159,21 @@ describe('Save large labelmap', function () {
       throw new Error(`Save error:\n${errorDetails}`);
     }
 
+    // Wait for the file to be fully written (Chrome may create it before flushing)
+    await browser.waitUntil(
+      () => {
+        try {
+          return fs.statSync(downloadedPath).size > 0;
+        } catch {
+          return false;
+        }
+      },
+      {
+        timeout: 30_000,
+        interval: 500,
+        timeoutMsg: 'Downloaded file remained 0 bytes',
+      }
+    );
     const stat = fs.statSync(downloadedPath);
     expect(stat.size).toBeGreaterThan(0);
   });