1 files changed, 48 insertions, 0 deletions
diff --git a/internal/world/mob_rekey_test.go b/internal/world/mob_rekey_test.go
index 8118059..af4dd5c 100644
--- a/internal/world/mob_rekey_test.go
+++ b/internal/world/mob_rekey_test.go
@@ -51,3 +51,51 @@ func TestRekeyRoomsUpdatesMobDespawnRooms(t *testing.T) {
 		t.Fatalf("despawn_rooms = %v, want [3 7]", got)
 	}
 }
+
+// TestSeedMobsKeysByDefOccurrenceAndPrunes: reordering a room's mobs list
+// must not orphan old instances (spawning duplicates) and removing an entry
+// must delete its seeded instance. Keys use a per-defID occurrence counter, so
+// the same declaration keeps the same key across reorders.
+func TestSeedMobsKeysByDefOccurrenceAndPrunes(t *testing.T) {
+	s := &MobStore{
+		defs: map[string]*MobDef{
+			"rat": {ID: "rat", Name: "rat"},
+			"bat": {ID: "bat", Name: "bat"},
+		},
+		instances: map[string]*MobInstance{
+			"rat_1_0": {InstanceID: "rat_1_0", DefID: "rat", RoomID: 1, HomeRoomID: 1, HP: 1, MaxHP: 1},
+			"bat_1_0": {InstanceID: "bat_1_0", DefID: "bat", RoomID: 1, HomeRoomID: 1, HP: 1, MaxHP: 1},
+		},
+	}
+	// Reorder and drop rat: bat keeps its key, rat is pruned, no duplicates.
+	s.SeedMobs(1, []RoomMob{{ID: "bat"}})
+	if s.instances["bat_1_0"] == nil {
+		t.Fatal("surviving declared mob was dropped")
+	}
+	if _, ok := s.instances["rat_1_0"]; ok {
+		t.Fatal("removed mob was not pruned")
+	}
+	if len(s.instances) != 1 {
+		t.Fatalf("instances = %v, want only bat_1_0", s.instances)
+	}
+}
+
+func TestSeedMobsReorderDoesNotDuplicate(t *testing.T) {
+	s := &MobStore{
+		defs: map[string]*MobDef{
+			"rat": {ID: "rat", Name: "rat"},
+			"bat": {ID: "bat", Name: "bat"},
+		},
+		instances: map[string]*MobInstance{
+			"rat_1_0": {InstanceID: "rat_1_0", DefID: "rat", RoomID: 1, HomeRoomID: 1, HP: 1, MaxHP: 1},
+			"bat_1_0": {InstanceID: "bat_1_0", DefID: "bat", RoomID: 1, HomeRoomID: 1, HP: 1, MaxHP: 1},
+		},
+	}
+	s.SeedMobs(1, []RoomMob{{ID: "bat"}, {ID: "rat"}})
+	if len(s.instances) != 2 {
+		t.Fatalf("reorder changed instance count: %v", s.instances)
+	}
+	if s.instances["rat_1_0"] == nil || s.instances["bat_1_0"] == nil {
+		t.Fatalf("reorder lost a declared mob: %v", s.instances)
+	}
+}