Integrity check on Baidu BOS flags an object as corrupted — is it really?

We multipart-uploaded a 400 MiB file to Baidu Object Storage (BOS) and our
verifier compares the returned ETag against the local MD5:

  object:      datasets/train-04.tar
  provider:    Baidu BOS (bcebos.com endpoint)
  size:        419430400 bytes  (matches local file exactly)
  local md5:   9f2a1d4e6a7b8c901122334455667788
  BOS ETag:    "-3b1c9f0ad28e5f6471a2b3c4d5e6f708"   <-- note the LEADING dash

Our verifier marks it corrupted because the ETag != local md5 and it does not
match the AWS multipart pattern `<hex>-N` either. The same pipeline works fine
against AWS S3 and MinIO.

Is the object actually corrupted, or is the BOS ETag just formatted differently?
How should we verify integrity on BOS?
