feat(mods): add battle menu auxiliary action

tests/engine/battle_menu_auxiliary.lua

@@ -0,0 +1,91 @@
+-- Public battle auxiliary actions are a narrow semantic entry point for tool
+-- mods.  They run only at the same settled ordinary decision boundary as a
+-- battle checkpoint, consume no FIGHT/PKMN/ITEM/RUN action, and receive no
+-- live BattleState object.
+
+package.path = "./?.lua;./?/init.lua;" .. package.path
+love = love or require("tests.love_stub")
+
+local T = require("tests.harness").suite("battle menu auxiliary action")
+local Fixtures = require("tests.modkit").fixtures
+local BattleState = require("src.battle.BattleState")
+local Hooks = require("src.mods.Hooks")
+local Runtime = require("src.mods.Runtime")
+local Pokemon = require("src.pokemon.Pokemon")
+local SaveData = require("src.core.SaveData")
+local StateStack = require("src.core.StateStack")
+
+local Data = Fixtures.fresh()
+
+local function makeGame(kind)
+  local save = SaveData.newGame()
+  save.meta.playthroughId = "battle-menu-playthrough"
+  save.party = { Pokemon.new(Data, "FIXMON_A", 20) }
+  local stack = setmetatable({ states = {} }, { __index = StateStack })
+  local overworld = {
+    map = { id = save.player.map },
+    player = { cellX = save.player.x, cellY = save.player.y, facing = save.player.facing },
+    runner = { isRunning = function() return false end },
+    parallelRunners = {}, pendingScripts = {}, parallelQueue = {}, scriptMoves = {},
+  }
+  local game = { data = Data, save = save, stack = stack }
+  game.input = { wasPressed = function(_, button) return button == "start" end }
+  game.overworld = overworld
+  stack.states[1] = overworld
+  local battle = kind == "trainer"
+    and BattleState.newTrainer(game, "OPP_FIX_YOUNGSTER", 1)
+    or BattleState.newWild(game, "FIXMON_B", 12)
+  battle.phase, battle.queue = "menu", {}
+  battle.checkpointOrigin = kind == "trainer"
+    and { kind = "trainer_encounter", map = save.player.map, npcId = "TRAINER_1",
+      trainerClass = "OPP_FIX_YOUNGSTER", partyIndex = 1, event = "EVENT_BEAT_TRAINER_1" }
+    or { kind = "wild_encounter", map = save.player.map }
+  battle.onFinish = function() end
+  stack.states[2] = battle
+  return game, battle
+end
+
+local oldHooks = Runtime.hooks
+local hooks = Hooks.new()
+Runtime.hooks = hooks
+
+local game, battle = makeGame("wild")
+local calls = 0
+hooks:wrap("battle.menu_auxiliary", function(nextFn, liveGame, context)
+  calls = calls + 1
+  T.check(liveGame == game, "auxiliary action receives the live game")
+  T.same(context, { kind = "wild" }, "auxiliary action receives only data-only battle context")
+  return true
+end, 0, "tool_fixture")
+
+local originalIndex = battle.menuIndex
+battle:update(1 / 60)
+T.eq(calls, 1, "START reaches the public auxiliary action at a wild decision")
+T.eq(battle.phase, "menu", "handled auxiliary action does not advance the battle")
+T.eq(battle.menuIndex, originalIndex, "handled auxiliary action preserves cursor")
+T.eq(#battle.queue, 0, "handled auxiliary action does not enqueue a turn")
+
+hooks:removeOwner("tool_fixture")
+local trainerGame, trainer = makeGame("trainer")
+local trainerCalls = 0
+hooks:wrap("battle.menu_auxiliary", function(_, liveGame, context)
+  trainerCalls = trainerCalls + 1
+  T.check(liveGame == trainerGame, "trainer action receives its live game")
+  T.same(context, { kind = "trainer" }, "trainer context remains data-only")
+  return true
+end, 0, "trainer_fixture")
+trainer:update(1 / 60)
+T.eq(trainerCalls, 1, "START reaches the public auxiliary action at a trainer decision")
+hooks:removeOwner("trainer_fixture")
+
+local unsafeGame, unsafe = makeGame("wild")
+unsafe.phase = "messages"
+local unsafeCalls = 0
+hooks:wrap("battle.menu_auxiliary", function() unsafeCalls = unsafeCalls + 1 return true end,
+  0, "unsafe_fixture")
+unsafe:update(1 / 60)
+T.eq(unsafeCalls, 0, "messages never expose the auxiliary action")
+hooks:removeOwner("unsafe_fixture")
+
+Runtime.hooks = oldHooks
+T.finish()