fix(gen2): refresh caches missing trainer HUD balls

src/import/RomImporter.lua

@@ -136,6 +136,9 @@ local VERSION_REQUIRED_FILES_OVERRIDE = {
     -- costs nothing on a current cache and is the difference between every
     -- trainer battle opening with a picture and opening with none.
     "assets/generated/battle/trainers/falkner.png",
+    -- BattleStart_TrainerHuds cannot draw its party rows from a cache made
+    -- before the four ball tiles were extracted (#1502).
+    "assets/generated/battle/hud/balls.png",
     "assets/generated/audio/programs.bin",
   },
 }

tests/engine/rom_importer_source_tree_test.lua

@@ -26,5 +26,7 @@ check(helperStart ~= nil, "requiredFilesFor helper exists")
 local helper = src:sub(helperStart, start)
 check(helper:find("VERSION_REQUIRED_FILES_OVERRIDE", 1, true) ~= nil,
   "requiredFilesFor consults VERSION_REQUIRED_FILES_OVERRIDE")
+check(src:find('"assets/generated/battle/hud/balls.png"', 1, true) ~= nil,
+  "Gold caches require the trainer HUD ball sheet")
 
 T.finish()