Fix hidden battle UI overlay backgrounds

src/battle/UIVisibility.lua

@@ -0,0 +1,39 @@
+-- Shared visibility rules for battle-owned UI states.  Text and choice
+-- overlays live above BattleState on the state stack, but they are still part
+-- of its bottom UI layer and must inherit that layer's visibility.
+
+local Runtime = require("src.mods.Runtime")
+
+local UIVisibility = {}
+
+local function enclosingBattle(state)
+  local stack = state and state.game and state.game.stack
+  local states = stack and stack.states
+  local found = false
+  for i = #(states or {}), 1, -1 do
+    local candidate = states[i]
+    if candidate == state then found = true end
+    if found and candidate and candidate.isBattle then return candidate end
+  end
+  return nil
+end
+
+-- queryState keeps the existing TextBox contract: a mod may still decide
+-- visibility for that individual box.  ChoiceBox only inherits the enclosing
+-- battle decision, so field YES/NO prompts never become battle-hook states.
+function UIVisibility.bottomVisible(state, queryState)
+  if not Runtime.wantsHook("battle.bottom_ui_visible") then return true end
+  local battle = enclosingBattle(state)
+  if battle and battle ~= state
+      and Runtime.call("battle.bottom_ui_visible",
+                       function() return true end, battle) == false then
+    return false
+  end
+  if queryState or battle == state then
+    return Runtime.call("battle.bottom_ui_visible",
+                        function() return true end, state) ~= false
+  end
+  return true
+end
+
+return UIVisibility