Refactor the worker, it's a mess!

[Matir]

The worker is a mess of spaghetti. Let's clean it up.

[Matir]

Step 1: instead of mangling in the worker, we could pass the task to an expander that feeds into the workqueue.
Step 2: refactor the decision on whether to add dependent work into a separate function
Step 3: split error handling & result building into new functions