ByPriorityTaskSelection

Higher priority first, ties broken by how long the task has waited.

The tie-break is not decoration. Priority classes are usually few and tasks many, so ties are the common case rather than the exception, and a rule that left them to whatever order the list happened to be in would make the model's behaviour depend on an implementation detail of the queue. Falling back to age also means that within a priority class this degrades to FIFO, which is what a modeller expects "priority" to mean.