//! Cloud doors (spec/auth.md AUTH-10 `host`, AUTH-11 signing).
//!
//! - [`hosts`]: settings resolution, base-URL rendering and the host's
//! closed set of request rewrites (`lm15/cloud/hosts.py`).
//! - [`sigv4`]: AWS Signature Version 4 (`lm15/cloud/sigv4.py`), pinned
//! byte for byte by `auth/sigv4-vectors.json`.
//!
//! `chains` (native builds) resolves the vendor chains or deterministic named
//! subsets and records their provenance. The pure signer accepts an explicit
//! `AwsCredentials` value, including in codec-only builds.