From 153acb7f644d755c45533b7c5311e3ffa47e8973 Mon Sep 17 00:00:00 2001
From: historia <[not public]>
Date: Fri, 18 Sep 2026 05:31:09 -0400
Subject: fix: harden engine across casino, economy, concurrency, security, and
 content

---
 internal/game/cmd_shop.go | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

(limited to 'internal/game/cmd_shop.go')

diff --git a/internal/game/cmd_shop.go b/internal/game/cmd_shop.go
index 7299ad3..f3211e0 100644
--- a/internal/game/cmd_shop.go
+++ b/internal/game/cmd_shop.go
@@ -366,8 +366,13 @@ func (g *Game) doShopSell(sess *net.Session, mob *world.MobInstance, input strin
 // shopInvCapacity reports how many of an item the player can still carry.
 func (g *Game) shopInvCapacity(p *player.Player, itemID string, def *item.ItemDef) int {
 	if def != nil && def.Stackable {
+		quality, maxQuality := stackProps(def)
 		for i := 0; i < 28; i++ {
-			if slot := p.InvSlot(i); slot != nil && slot.ItemID == itemID {
+			// Capacity must agree with giveShopItems: only a stack with the
+			// properties a fresh stack gets can absorb a purchase (see
+			// stackProps). Counting a differently qualified stack here would
+			// let the caller charge for items the delivery path cannot place.
+			if slot := p.InvSlot(i); slot != nil && slot.ItemID == itemID && slot.Quality == quality && slot.MaxQuality == maxQuality {
 				return 1 << 30
 			}
 		}
@@ -383,8 +388,13 @@ func (g *Game) shopInvCapacity(p *player.Player, itemID string, def *item.ItemDe
 // possible. Callers must ensure capacity via shopInvCapacity first.
 func (g *Game) giveShopItems(p *player.Player, itemID string, qty int, def *item.ItemDef) {
 	if def != nil && def.Stackable {
+		// Merge only into a stack with the properties this purchase would
+		// itself receive (stackProps/newInventorySlot), matching craft,
+		// harvest, ammo return and pickup: a differently qualified stack is
+		// not a merge target.
+		quality, maxQuality := stackProps(def)
 		for i := 0; i < 28; i++ {
-			if slot := p.InvSlot(i); slot != nil && slot.ItemID == itemID {
+			if slot := p.InvSlot(i); slot != nil && slot.ItemID == itemID && slot.Quality == quality && slot.MaxQuality == maxQuality {
 				slot.Quantity += qty
 				return
 			}
-- 
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