X_DB_COMMIT_UNKNOWN

the connection was lost while COMMIT was in flight

the socket closed after COMMIT was sent and before the server answered, so the transaction is either durable or rolled back and this process cannot tell which; neither onCommit effects nor onRollback undos ran. Only the data can say which: a row the transaction wrote is present if it committed and absent if it did not

psql "$DATABASE_URL" — a session on that database: select a row the transaction wrote, and re-run the unit of work only when it is absent