fix invalid 6x69 command checks

src/CommandFormats.hh

@@ -4573,13 +4573,14 @@ struct G_CreateTelepipe_6x68 {
 } __packed__;
 
 // 6x69: NPC control
+// Note: NPCs cannot be destroyed with 6x69; 6x1C is used instead for that.
 
 struct G_NPCControl_6x69 {
   G_UnusedHeader header;
-  le_uint16_t state = 0;
-  le_uint16_t npc_entity_id = 0;
+  le_uint16_t param1; // Commands 0/3: state; commands 1/2: npc_entity_id
+  le_uint16_t param2; // Commands 0/3: npc_entity_id; commands 1/2: unused
   le_uint16_t command = 0; // 0 = create follower NPC, 1 = stop acting, 2 = start acting, 3 = create attacker NPC
-  le_uint16_t npc_template_index = 0; // Specifies which NPC to create if command == 0 or 3; unused otherwise
+  le_uint16_t param3; // Commands 0/3: npc_template_index; commands 1/2: unused
 } __packed__;
 
 // 6x6A: Use boss warp (not valid on Episode 3)

src/ReceiveSubcommands.cc

@@ -1025,11 +1025,26 @@ static void on_npc_control(shared_ptr<Client> c, uint8_t command, uint8_t flag,
   // Don't allow NPC control commands if there is a player in the relevant slot
   const auto& l = c->require_lobby();
   if (!l->is_game()) {
-    throw runtime_error("cannot create NPCs in the lobby");
+    throw runtime_error("cannot create or modify NPC in the lobby");
   }
-  if ((cmd.npc_entity_id < 4) && l->clients[cmd.npc_entity_id]) {
-    throw runtime_error("cannot overwrite existing player with NPC");
+
+  uint16_t npc_entity_id = 0xFFFF;
+  switch (cmd.command) {
+    case 0:
+    case 3:
+      npc_entity_id = cmd.param2;
+      break;
+    case 1:
+    case 2:
+      npc_entity_id = cmd.param1;
+      break;
+    default:
+      throw runtime_error("invalid 6x69 command");
   }
+  if ((npc_entity_id < 4) && l->clients[npc_entity_id]) {
+    throw runtime_error("cannot create or modify NPC in existing player slot");
+  }
+
   forward_subcommand(c, command, flag, data, size);
 }