database/sql discards a poisoned connection and retries on a fresh one.
newEngine installs a Times(1)ConnDrop rule on OpSQL. The adapter maps
ConnDrop to driver.ErrBadConn, which makes database/sql discard that
connection and retry on a new one — so a single Exec succeeds while the
fake driver opens two connections.
Command db-conn-pool shows database/sql discarding a poisoned connection and
transparently retrying on a fresh one when chaos injects a connection drop.
Run with `go run .`.