Decide what to delegate in an expense routing feature

You are building a Python feature for your company's expense tool. A language model reads each submitted receipt and tags it with a category. Then routing rules decide who must approve it, based on the category, the amount and the employee's department.

Finance changes those rules about once a month. You want a coding agent to build most of it.

What do you delegate to the agent, what do you keep, and what principle decides the split?