Why: Parallel unpublished candidates reused numeric versions, so version-only checks could reinterpret a different schema after combination.
Evidence: SQLite ledger and source-copy mismatch tests failed before the guard and pass now; PostgreSQL store/migrator and full Go suites pass.
Impact: Fail closed on version-name mismatch before opening a migration target or serving a database.
Refs: feature/rdm-two-trees-latest-templates Backend combination probe