From #68969 (review).

We need to do some extra work in kv.Txn to respect the deadline when NegotiateAndSend is used. We'll just use the same max_timestamp_bound mechanism with some code in NegotiateAndSend like:

if txn.mu.deadline != nil {
    ba.BoundedStaleness.MaxTimestampBound.Backward(*txn.mu.deadline)
}

I didn't see you create an issue, so opening this for tracking :)