A System One client independent of any runtime or HTTP stack.
The policy lives here, once: retries and their budget, per-attempt
timeouts, "never sent" redials, request ids on every error, and error
classification. It reaches the world through two ports, [Transport]
(send one request) and [Runtime] (time and randomness), which an
adapter implements: postjevsql-pg over a Postgres WaitEventSet,
or a fake in tests, where time is virtual and runs deterministically.
An [Observer] hears each attempt, retry, redial and answer.
10#![forbid(unsafe_code)]