sync-rebuilds followed PUBLISHED_ARCHES (x86_64 by default), so the scheduled
run skipped every aarch64-only package, and it read aarch64 triggers from Arch
Linux ARM even when this repository carries them. It now follows the
architectures a merge builds (CI_ARCHES, shared with build-matrix), and reads a
carried trigger from its recipe once edge publishes that version; until then
its dependents wait. Published databases are verified before use and loaded
once per run.