I get that, the nondeterminism would come from the completion order of the join set. If the children sleep appropriately, they'll race to be inserted after completing, and order of the result set will depend on the specifics of the implementation. It's possible this could happen deterministically, but probably not reasonably.
The actual order in which child workflows finish and their results hit the persistence layer is indeed nondeterministic in real-time execution. Trying to force deterministic completion order would likely be complex and defeat the purpose of parallelism, as you noted.
However, this external nondeterminism is outside the scope of the workflow execution's determinism required for replay.
When the workflow replays, it doesn't re-run the race. It consumes events from the log. The `-await-next` operation during replay simply reads the next recorded result, based on the fixed order. Since the log provides the same sequence of results every time, the workflow's internal logic proceeds identically, making the same decisions based on that recorded history.
Determinism is maintained within the replay context by reading the persisted, ordered outcomes of those nondeterministic races.
