  ok  18 moves the data mount to /var/lib/postgresql
  ok  18 leaves the redis mount alone
  ok  16 keeps /var/lib/postgresql/data
  ok  back from 18 to 16 restores /data
  ok  pg_conversion names the one moving service
  ok  within a major is no conversion
  ok  pgvector's pg16 tag reads 16
  ok  an entry with a good mark is well-formed
  ok  a mark naming a service outside `to` is refused
  ok  a mark going DOWN is refused
pg conversion tests: 0 failed
