@tomconnolly, but what is stopping you from creating the (nearly) exact copy of the bpmn pattern you shown in the first post? → Each order received by the Message start event waits for a message of completion. And Daily you execute your batch process.
something like this:
would be a few different ways to build the setup depending on your needs.
But essentially it’s: Each order is a process instance. You query for those instances and then send a message to each order instance to mark that they are part of a batch. (you could remove this step depending on your Retry scenario and data loss scenario). And once the batch is executed, you message each instance that was part of the batch.
This might also be a good pattern for the external task worker pattern.