Function mysqlStore

Build the full MySQL-backed store on a connection pool the caller creates and owns — the mysql2 pool from createMysqlPool, or the pipelining mariadb pool from @pwngh/economy-lab/engines/mysql-mariadb; both fill the same MysqlPool seam and run the same SQL against the same schema.

transaction(work) borrows one connection, wraps work in START TRANSACTION ... COMMIT, and rolls back if work throws. Money transactions run at READ COMMITTED (set once per pooled connection); correctness comes from explicit FOR UPDATE row locks plus a GET_LOCK named lock per account. A transient InnoDB abort — deadlock, lock-wait timeout, named-lock deadlock, or a stale-head chain fork — committed nothing, so the whole unit of work is re-run in a fresh connection and transaction and callers never see it as an error. Every posting appends to a per-account hash chain, and the schema's triggers enforce conservation and chain continuity on every write. On the way out of a transaction every named lock the connection acquired is released, so a returned connection carries no leftover locks. Anything outside a transaction (plain reads/writes, plus the trust and checkpoint stores) runs directly on the pool and commits on its own.

The hash service defaults to the deterministic web-standard SHA-256; the clock defaults to wall-clock time. Pass a fixed clock when reproducible postedAt values matter. The velocity window defaults to one hour.