Writes a route, replacing any route with the same id.
The route to persist.
Nothing. Rejects when the transaction fails.
Reads one route.
Its identity.
The route, or null when there is none.
Every persisted route, newest first.
The routes.
Removes one route.
Its identity.
Nothing. Resolves even when nothing was stored under id — a delete that
reports "not found" makes callers write a read they do not need.
What this sub-module offers.