name: "shop"
category: "Interaction"
description: |
  Buy and sell items with shopkeeper NPCs, straight from the game prompt.

  Find a mob that runs a shop and use these commands in the room:

  list            Show the shop's inventory (item, stock, buy, sell prices)
  buy <item>      Buy an item by name (e.g. "buy fishing bait")
  buy <N> <item>  Buy a quantity (e.g. "buy 5 bait")
  buy all <item>  Buy as many as you can afford and carry
  sell <item>     Sell an item from your inventory (e.g. "sell bronze sword")
  sell <N> <item> Sell a quantity (e.g. "sell 3 logs")
  sell all <item> Sell your entire held stack of that item

  Partial names work: "buy bait" matches "fishing bait". If a name matches
  multiple items, a list is shown to disambiguate.

  If a room has more than one shopkeeper, name the one you mean:

  list <mob>
  buy <item> from <mob>
  sell <item> to <mob>

  Prices are based on each item's value. Shops sell items for 100% of their
  value. They buy items back for less, starting around 40% of value and paying
  less the more of that item they already hold (down to a floor of 10%). Buy
  low, sell where a shop is short on stock.

  Shops keep limited stock that refills over time. An item can sell out, and
  selling to a shop lowers what it will pay for the next one.