Constant CONTRACT_SCHEMA_VERSION 

pub const CONTRACT_SCHEMA_VERSION: u32 = crate::contract::schema::KNOWN_SCHEMA_VERSION; // 1u32

The OSS-RELEASE.md contract-document schema version this build reads and emits. Distinct from the JSON-envelope crate::SCHEMA_VERSION: this versions the contract document (SCHEMA.md §4), that versions the wire envelope. Both are 1 today. A breaking change to the §4 shape bumps this (and crate::contract::schema::KNOWN_SCHEMA_VERSION, its enforcement twin), never silently (migration rule).