acquire() made sure a row existed and then raced on a conditional UPDATE,
two statements the registrar wrapped in a transaction of its own. lint:tx
cannot follow a repository reached through a local variable, so it
reported the method. One INSERT ... ON CONFLICT DO UPDATE ... WHERE now
takes a free lease, renews the holder's and leaves anyone else's alone,
atomically on SQLite and on Postgres, and needs no transaction.
Maurice
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