Right now, when we pass around timestamps and transaction IDs, it's always "oldest-start-ts, newest-durable-ts, newest-stop-ts, oldest-start-txn, newest-stop-txn", which isn't easy to read because "durable" sort of shows up in the middle. (This happened because of the order in which I did the work, when I was anticipating that the durable timestamp would always appear between the start & stop timestamps.)

Absent making strong guarantees about newest-durable-ts vs. oldest-start-ts, I'd rather move to "durable-ts, start/stop-ts, start/stop-txn", just because I think it will make it easier to spot mistakes in the code.

It might be interesting to consider if stronger (internal) typing of transaction IDs would make it easier to catch places where timestamps and transaction IDs are used incorrectly, where the other should have been used.