feat(mods): add battle menu auxiliary action

src/battle/BattleState.lua

@@ -21,6 +21,7 @@ local MoveEffects = require("src.battle.MoveEffects")
 local Party = require("src.pokemon.Party")
 local Pokemon = require("src.pokemon.Pokemon")
 local Runtime = require("src.mods.Runtime")
+local BattleSafety = require("src.battle.BattleSafety")
 local Screens = require("src.ui.Screens")
 local Status = require("src.battle.Status")
 local Timing = require("src.core.Timing")
@@ -1942,6 +1943,17 @@ function BattleState:update(dt)
       self:resolveTurn(locked)
       return
     end
+    -- START has no vanilla action at the settled ordinary player-decision
+    -- boundary.  A tool mod may claim this semantic auxiliary action through
+    -- the public hook, receiving only game plus a data-only kind.  The shared
+    -- safety predicate keeps every unsupported/forced/animated phase inert.
+    if input:wasPressed("start") and Runtime.wantsHook("battle.menu_auxiliary") then
+      local safe = BattleSafety.inspect(self.game, self)
+      if safe and Runtime.call("battle.menu_auxiliary", function() return false end,
+          self.game, { kind = self.kind }) == true then
+        return
+      end
+    end
     local col = (self.menuIndex - 1) % 2
     local row = math.floor((self.menuIndex - 1) / 2)
     if input:wasPressed("left") then