For full description, see https://docs.google.com/document/d/1-tO_27qZAEHuTL7rMKe-5PUVQZsyJ61aZ0KdNYBOCM0

Dev note

A few test scenarios to try and check how routing and stats behave:

1. Isolated backends: each backend has its own path without overlapping – Nothing weird should happen here; it's just to set a reliable base for comparing behaviors later.
2. Empty path: one backend trivially overlaps the others by using an empty path
3. Path extension: one of the paths extends another backend’s path with a slash plus something to make it unique
4. Product mapping rules overriding backend mapping rules
5. Catch-all mapping rule at product level
6. Catch-all mapping rule at backend level