feat: capture data-only battle checkpoints

src/core/BattleCheckpoint.lua

@@ -0,0 +1,140 @@
+-- Semantic, data-only capture for settled single-player battle checkpoints.
+-- Reconstruction lives here too; public mods only see the opaque checkpoint
+-- facade in Loader.
+
+local BattleCheckpoint = {}
+
+local BATTLER_FIELDS = {
+  "shownHP", "shownStatus", "stages", "curStats", "curTypes", "curMoves",
+  "sleepTurns", "confusedTurns", "disabledSlot", "disabledTurns",
+  "toxicCounter", "substituteHP", "bideDamage", "bideTurns", "boundTurns",
+  "charging", "chargeReady", "invulnerable", "mustRecharge", "thrashMove",
+  "thrashTurns", "thrashAnnounced", "rageMove", "focusEnergy", "leechSeeded",
+  "lightScreen", "reflect", "mist", "xAccuracy", "lastMove", "flinched",
+  "skipMove", "hazeStatReset", "drainFloor", "drainHold", "trappingTurns",
+  "trapMove", "trapDamage", "fainted",
+}
+
+local BATTLE_FIELDS = {
+  "oppClass", "partyIndex", "enemyIndex", "turnCount", "menuIndex",
+  "moveIndex", "moveSwapIndex", "aiUses", "runAttempts", "payDay",
+  "sideToxic", "isGymLeader", "musicKind", "lastBall", "lockedBall",
+  "lowHealthAlarmDisabled", "lowHealthAlarmOn", "victoryMusicPlayed",
+  "endBattleText",
+}
+
+local function partyIndex(party, mon)
+  for index, candidate in ipairs(party or {}) do
+    if candidate == mon then return index end
+  end
+end
+
+local function indexSet(set, party)
+  local out = {}
+  for mon, present in pairs(set or {}) do
+    if present then
+      local index = partyIndex(party, mon)
+      if index then out[#out + 1] = index end
+    end
+  end
+  table.sort(out)
+  return out
+end
+
+local function captureBattler(battler, index, copy)
+  local out = { index = index }
+  for _, field in ipairs(BATTLER_FIELDS) do
+    if battler[field] ~= nil then out[field] = battler[field] end
+  end
+  return copy(out)
+end
+
+local function captureExtensions(battle, copy)
+  local sides = {}
+  for i = 1, 2 do
+    local side = battle.sides and battle.sides[i] or {}
+    local encoded, err = copy({
+      index = i,
+      screens = side.screens or {},
+      hazards = side.hazards or {},
+      tokens = side.tokens or {},
+    })
+    if not encoded then return nil, err end
+    sides[i] = encoded
+  end
+  local field, err = copy({
+    weather = battle.field and battle.field.weather or nil,
+    tokens = battle.field and battle.field.tokens or {},
+  })
+  if not field then return nil, err end
+  return sides, field
+end
+
+function BattleCheckpoint.capture(game, battle, progress, copy)
+  local getState = love and love.math and love.math.getRandomState
+  local setState = love and love.math and love.math.setRandomState
+  if type(getState) ~= "function" or type(setState) ~= "function" then
+    return nil, "rng_state_unavailable",
+      "This runtime cannot preserve deterministic battle randomness."
+  end
+  local ok, rngState = pcall(getState)
+  if not ok or type(rngState) ~= "string" or rngState == "" then
+    return nil, "rng_state_unavailable",
+      "The gameplay random-number state could not be captured."
+  end
+
+  local origin, originErr = copy(battle.checkpointOrigin)
+  if not origin then
+    return nil, "battle_origin_unsupported",
+      "The battle completion path is not data-only: " .. tostring(originErr)
+  end
+  local sides, fieldOrErr = captureExtensions(battle, copy)
+  if not sides then
+    return nil, "battle_extension_unsafe",
+      "Battle extension state is not data-only: " .. tostring(fieldOrErr)
+  end
+  local field = fieldOrErr
+
+  local liveParty = game.save.party
+  local playerIndex = partyIndex(liveParty, battle.player.mon)
+  if not playerIndex then
+    return nil, "battle_state_invalid",
+      "The active player battler is not in the current party."
+  end
+
+  local model = {
+    kind = battle.kind,
+    origin = origin,
+    player = captureBattler(battle.player, playerIndex, copy),
+    participants = indexSet(battle.participants, liveParty),
+    leveledUp = indexSet(battle.leveledUp, liveParty),
+    sides = sides,
+    field = field,
+  }
+  if battle.kind == "trainer" then
+    model.enemyParty = copy(battle.enemyParty)
+    model.enemy = captureBattler(battle.enemy, battle.enemyIndex, copy)
+  else
+    model.enemyMon = copy(battle.enemy.mon)
+    model.enemy = captureBattler(battle.enemy, 1, copy)
+  end
+  for _, fieldName in ipairs(BATTLE_FIELDS) do
+    if battle[fieldName] ~= nil then model[fieldName] = battle[fieldName] end
+  end
+
+  model = copy(model)
+  if not model then
+    return nil, "battle_state_invalid",
+      "Battle state contains non-serializable runtime data."
+  end
+  local player = progress.player
+  return {
+    overworld = {
+      map = player.map, x = player.x, y = player.y,
+      facing = player.facing, surfing = player.surfing and true or false,
+    },
+    battle = model,
+  }, { love = rngState }
+end
+
+return BattleCheckpoint

src/core/Checkpoint.lua

@@ -5,6 +5,7 @@ local SaveSerializer = require("src.core.SaveSerializer")
 local SaveData = require("src.core.SaveData")
 local Version = require("src.core.Version")
 local BattleState = require("src.battle.BattleState")
+local BattleCheckpoint = require("src.core.BattleCheckpoint")
 
 local Checkpoint = {}
 
@@ -172,6 +173,25 @@ function Checkpoint.capture(game)
       .. tostring(err)
   end
 
+  if capability.kind == "battle" then
+    local battle = game.stack:top()
+    local runtime, rngOrCode, battleMessage =
+      BattleCheckpoint.capture(game, battle, progress, dataCopy)
+    if not runtime then return nil, rngOrCode, battleMessage end
+    return {
+      format = Checkpoint.FORMAT,
+      kind = "battle",
+      identity = {
+        engineVersion = Version.engine,
+        gameVersion = game.save.version,
+        playthroughId = game.save.meta.playthroughId,
+      },
+      save = progress,
+      runtime = runtime,
+      rng = rngOrCode,
+    }
+  end
+
   local player = game.overworld.player
   return {
     format = Checkpoint.FORMAT,