Module use_driver 

Generic item-effect application + bag/shop buy-sell flow (P0e).

This module owns only the control flow of using, buying, and selling items. It is 100% game-agnostic: it never decides what an item effect actually does. The engine routes; the game decides.

• UsageContext / ItemUseResult are neutral engine types.
• ItemProvider::apply_effect is an opaque dispatch hook: the game implements what healing / status-cure / PP-restore / vitamins / battle items / catch / etc. actually do. The engine never inspects the effect.
• use_item is the shared driver for field and battle use: it validates ownership and the usage context (ItemProvider::usable_in), dispatches to apply_effect, then consumes one unit from the Inventory iff the result says so. One place so field & battle share it.
• buy / sell perform pure money/inventory bookkeeping; prices and the sell rate come from ShopProvider (Gen-1 quirks stay game-side).

Structs

ShopReceipt

Summary of a completed shop transaction.

Enums

ItemUseResult

Neutral result of an item-use attempt, returned by ItemProvider::apply_effect and propagated by use_item.

ShopError

Error from a shop transaction. Nothing is mutated when an error is returned.

UsageContext

Where / whether an item may be used. A neutral engine enum — no game specifics. Returned by ItemProvider::usable_in and passed into ItemProvider::apply_effect / use_item as the active context.

Functions

buy

Buy quantity units of item at the shop’s ShopProvider::buy_price.

sell

Sell quantity units of item for the shop’s ShopProvider::sell_price.

use_item

Engine driver for using an item from the bag, shared by field and battle.