allow $unset to remove assist cards too

src/ChatCommands.cc

@@ -2697,8 +2697,12 @@ ChatCommandDefinition cc_unset(
         throw precondition_failed("$C6Battle has not\nyet begun");
       }
 
-      size_t index = stoull(a.text) - 1;
-      l->ep3_server->force_destroy_field_character(a.c->lobby_client_id, index);
+      size_t index = stoull(a.text);
+      if (index == 0) {
+        l->ep3_server->force_replace_assist_card(a.c->lobby_client_id, 0xFFFF);
+      } else {
+        l->ep3_server->force_destroy_field_character(a.c->lobby_client_id, index - 1);
+      }
       co_return;
     });
 

src/Episode3/Server.cc

@@ -592,7 +592,14 @@ void Server::force_replace_assist_card(uint8_t client_id, uint16_t card_id) {
   if (!ps) {
     throw runtime_error("player does not exist");
   }
-  ps->replace_assist_card_by_id(card_id);
+  if (card_id == 0xFFFF) {
+    ps->discard_set_assist_card();
+    this->check_for_destroyed_cards_and_send_6xB4x05_6xB4x02();
+    this->check_for_battle_end();
+
+  } else {
+    ps->replace_assist_card_by_id(card_id);
+  }
 }
 
 void Server::force_destroy_field_character(uint8_t client_id, size_t visible_index) {