echo
----
db0.Txn(ctx, func(ctx context.Context, txn *kv.Txn) error {
  txn.SetIsoLevel(isolation.Serializable)
  txn.Del(ctx, tk(1) /* @s1 */) // <nil>
  txn.Del(ctx, tk(1) /* @s2 */) // <nil>
  return nil
}) // result is ambiguous: boom
/Table/100/"0000000000000001"/0.000000001,0 @ s1 <nil>
committed txn overwritten key had write: [d]/Table/100/"0000000000000001":0.000000001,0-><nil>@s1 [d]/Table/100/"0000000000000001":missing-><nil>@s2
