1 files changed, 55 insertions, 0 deletions
diff --git a/internal/game/polish_shop_merge_test.go b/internal/game/polish_shop_merge_test.go
new file mode 100644
index 0000000..8851464
--- /dev/null
+++ b/internal/game/polish_shop_merge_test.go
@@ -0,0 +1,55 @@
+package game
+
+// Regression: giveShopItems used to merge a purchase into any inventory slot
+// holding the same item id, ignoring Quality/MaxQuality, while every other
+// merge site (craft, harvest, ammo return, pickup) merges only into a stack
+// with the properties a fresh stack gets (stackProps). A purchase could
+// therefore merge into a differently qualified stack. shopInvCapacity had the
+// same blind spot, which mattered because the buy path charges for the
+// quantity capacity reports as placeable.
+
+import (
+	"path/filepath"
+	"testing"
+
+	"thehouseoficarus/internal/player"
+)
+
+func TestGiveShopItemsDoesNotMergeIntoDifferentQualityStack(t *testing.T) {
+	h := newHarness(t)
+	h.seedAccount("alice")
+	p := h.seedCharacter("alice", "alice")
+	writeSeedFile(t, filepath.Join(h.dir, "items", "polish_shop_gem.yaml"),
+		[]byte("id: polish_shop_gem\nname: polish shop gem\nstackable: true\nmax_quality: 5\nvalue: 1\n"))
+
+	h.g.RunOnOwner(func() {
+		h.g.ItemStore.Reload(h.dir)
+		def := mustLoadItem(t, h.g, "polish_shop_gem")
+
+		// A differently qualified stack is not a merge target: with no free
+		// slot, capacity must report 0 and the purchase must not be placed.
+		p.SetInvSlot(0, &player.InventorySlot{ItemID: def.ID, Quantity: 10, Quality: 1, MaxQuality: 5})
+		fillInventoryExcept(p)
+		if got := h.g.shopInvCapacity(p, def.ID, def); got != 0 {
+			t.Fatalf("shopInvCapacity = %d, want 0 (the only stack has a different quality)", got)
+		}
+		h.g.giveShopItems(p, def.ID, 3, def)
+		if slot := p.InvSlot(0); slot.Quantity != 10 || slot.Quality != 1 || slot.MaxQuality != 5 {
+			t.Errorf("purchase merged into a differently qualified stack: %+v", slot)
+		}
+		if got := p.CountItem(def.ID); got != 10 {
+			t.Errorf("gems carried = %d, want 10 (nothing should have been delivered)", got)
+		}
+
+		// The same full inventory accepts the purchase once the stack carries
+		// the properties a fresh stack gets.
+		p.SetInvSlot(0, &player.InventorySlot{ItemID: def.ID, Quantity: 10, Quality: 5, MaxQuality: 5})
+		if got := h.g.shopInvCapacity(p, def.ID, def); got == 0 {
+			t.Fatalf("shopInvCapacity = %d, want room for a matching stack", got)
+		}
+		h.g.giveShopItems(p, def.ID, 3, def)
+		if slot := p.InvSlot(0); slot.Quantity != 13 || slot.Quality != 5 || slot.MaxQuality != 5 {
+			t.Errorf("matched stack = %+v, want quantity 13 at quality 5", slot)
+		}
+	})
+}