In both change collections and pre-images collections, truncates are issued based on the 'lastRecord' of a given marker.

Truncate markers are updated when there are inserts into each collection asynchronously. On secondaries, they may even be applied out of order. However, for each collection there is a separate remover thread. If the 'lastRecord' is not actually durable, we could accidentally truncate records before they have been made durable (applies to both primaries and secondaries). Additionally, on secondaries, truncates should be limited to ranges < lastApplied to guarantee a consistent state of the data within its range.