Every backup on galactus died with: mysqldump: unknown variable 'set-gtid-purged=OFF' respaldo incompleto eliminado Alpine's mysql-client is MariaDB's, so `mysqldump` inside the API container is a shim over `mariadb-dump`, which has no --set-gtid-purged. That took out BACKUP and, because they take a safety dump first, SYNC and REIMPORT too. Probe `mysqldump --help` and pass the flag only when it is advertised, calling `mariadb-dump` directly otherwise — MariaDB writes no GTID state unless asked with --gtid, so there is nothing to suppress. Testing whether mariadb-dump merely exists would be wrong: on a host carrying both clients it would shadow a perfectly good MySQL mysqldump. The probe uses a command substitution rather than `--help | grep -q` because PIPEFAIL is in effect for these commands and grep closing the pipe early would report a supported flag as unsupported. pre-migrate-backup.mjs is unaffected — it dumps from a real mysql:8.4 image, not from the API container. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>