Covers both behaviours end to end: a refused outbound URL and an exhausted
budget must skip the request entirely rather than fall through to httpx, the
remaining budget caps each hop's timeout, and an over-ceiling Content-Length
returns 413 without the body being parsed.
Verified against the pre-fix tree: the User-Agent was hardcoded, the endpoints
were literals, check_outbound_url was absent, both hops carried independent
12.0s timeouts, and an oversized declared body returned 422 after parsing
rather than 413 before it.
