//! Soothfast docs engine.
//!
//! Four rot channels, four mechanisms:
//! - signatures can't rot: the API surface is read from rustdoc JSON
//! ([`surface`], [`mod@reference`], [`diff`]);
//! - prose can't rot silently: bind blocks fingerprint the code they
//! describe, locked in `soothfast.lock` ([`markdown`], [`lockfile`]);
//! - examples can't rot: every markdown `rust` block becomes a generated
//! test, capture blocks become runnable examples ([`gentests`]);
//! - numbers can't rot: quantitative claims in prose evaluate against the
//! latest measurement baseline ([`claims`]).