//! Module: ops::replay::ttl
//!
//! Responsibility: validate replay TTL bounds.
//! Does not own: receipt storage, command authorization, or replay decisions.
//! Boundary: replay guards call this before reserving receipts.
///
/// ReplayTtlError
///
/// Validation error emitted by replay TTL checks.
///
/// validate_replay_ttl
///
/// Enforce root replay TTL bounds as a pure mechanical check.
pub const