radio notebook: verify checkpoint length

kaggle/notebook_radio.py

@@ -15,6 +15,12 @@ def main() -> None:
     pull(BUNDLE_REPO, BUNDLE, repo_type="dataset")
     if not (BUNDLE / "student4_rc.pt").exists():
         raise SystemExit("student4_rc.pt missing from the bundle")
+    # A truncated transfer looks like a present file and fails later inside
+    # torch.load, so check the byte count the run recorded.
+    expected = 206273737
+    got = (BUNDLE / "student4_rc.pt").stat().st_size
+    if got != expected:
+        raise SystemExit(f"student4_rc.pt is {got} bytes, expected {expected}")
     env = dict(os.environ, WORK_ROOT=str(ROOT), CUDA_VISIBLE_DEVICES="0")
     rc = subprocess.run([sys.executable, str(BUNDLE / "kaggle/radio_demo.py")],
                         env=env).returncode