ServerSystem

Fixes three things found while testing against a real MySQL server and a connected client.

MySQL storage never worked. CREATE INDEX IF NOT EXISTS is SQLite syntax; MySQL answers with a syntax error, so the schema stopped after the first table and the plugin refused to enable. Anyone who set storage.type to mysql got a startup failure and nothing else. Indexes are now created through information_schema on MySQL. Checked against MySQL 8.4.6: ten tables, six indexes, homes, warps, mail and the transaction log written and read back, and a second save updating the row rather than adding one.

Vault lookups blocked the server thread. Accounts were fetched through a future with a two second timeout, called from the tick. A shop plugin walking a list of offline accounts could stall the server for that long. Vault's API is synchronous and there is no correct way to answer it asynchronously, so the read now happens inline as one indexed query and is cached afterwards. A warning is logged if one ever takes longer than 25ms.

/pay could destroy money. The transfer ignored the result of the withdrawal, so a failed deposit left the amount in neither account. The move is now serialised and the deposit is compensated if it fails.

Two servers sharing one MySQL database can still race the balance ceiling check. That needs row locking and has not been done.