Market backend

Concurrency

• Serialize every mutation of an item's order book with the shared RedisMutex in src/utils/functions/economy/market.ts. Use the item ID as its key.
• Acquire through withMarketLock() so release always happens in finally.
• Keep the thin lock-acquiring public wrappers together near the top of market.ts; leave their unlocked implementations in the relevant backend sections.
• Never restore the legacy local Set, MARKET_IN_TRANSACTION Redis key, recursive polling, or timeout-based forced unlocks.
• Let exported mutation entry points acquire the lock. Helpers called within them, including settleMarketFill(), must assume the caller already holds it; RedisMutex is not reentrant.
• After waiting for the lock, re-read mutable rows before changing them. Cancellation follows this pattern so a fill that won the race returns false instead of deleting stale state.
• Keep Discord requests and other slow post-mutation effects outside the locked section when they do not protect order-book state.

Settlement

• Treat balance, inventory, escrow, and market-row changes as one settlement boundary.
• createMarketOrder() owns initial escrow; command and interaction callers must not deduct balance or inventory themselves. Keep escrow deduction, order insertion, matching, and remainder updates in one serializable transaction.
• Atomic creation holds the Redis item mutex, a transaction-scoped PostgreSQL advisory item lock, locks matching market rows in deterministic ID order with FOR UPDATE, and locks existing affected inventory and balance rows in deterministic user-ID order before settlement.
• Keep market-row state/history, escrow consumption, wallet/inventory transfers, buyer refunds, and tax-bank credits together in market/settlement.ts using the provided Prisma transaction client.
• Cancellation holds the Redis item mutex and the same PostgreSQL locks as settlement, then re-reads, deletes, and refunds the active order in one serializable transaction. Callers must not refund the escrow themselves.
• For balance and inventory debits, use update with the resulting value selected and throw if it is negative; the transaction rollback restores the original value. Avoid conditional updateMany guards for these debits.
• Calculate tax from the executed value and the actual seller's premium tier, regardless of which side owns the resting order.
• Invalidate balance, inventory, item-existence, and gem caches only after commit. Run acquisition autosell after commit as a separate follow-up so it cannot escape or invalidate the market transaction.
• Keep stats, transaction logs, DMs, watcher notifications, and Discord message updates outside the database transaction. Derive them from a committed structured result.
• Preserve season-interim and alt-account history behavior unless the task explicitly changes it.

Matching

• Keep price-time selection and quote arithmetic pure in src/utils/functions/economy/market/matching.ts. Database functions should fetch candidate rows and pass them to quoteMarketOrder() rather than implementing their own loops.
• Use one matcher for direct fills and newly crossed orders.
• Match incoming buys against lowest sell price then oldest ID; match incoming sells against highest buy price then oldest ID.
• Execute at the resting order's price. Calculate tax from the executed value and explicitly refund unused buy-side reservation.
• Add invariant tests for conservation of money/items, price limits, FIFO, partial fills, refunds, and rollback before changing settlement behavior.

Run make check after changes.