feat: add chebyshev, novaTargets and Polymorph.pool

src/phases.lua

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+-- A boss's second, harder-won escalation beyond bosses.lua's enrage. Enrage
+-- is a single instantaneous stat bump that never costs the boss a turn; a
+-- desperation phase is a two-turn state machine that consumes both turns
+-- outright once the boss is battered all the way down to its catalog
+-- desperateAt threshold:
+--   1. brace  - the boss telegraphs for one full turn, a visible defense
+--      spike (desperateDefenseBonus) warning the player something is coming
+--      without yet hurting anyone.
+--   2. unleash - on its very next turn the boss reverts that defense spike
+--      and detonates a single cataclysm, dealing novaDamage to the player
+--      and to every companion, hireling or thrall still within novaRadius.
+-- The cataclysm fires at most once per boss: novaSpent latches permanently
+-- the moment it lands, so a fight survived past it settles back into the
+-- boss's ordinary ability/ai behaviour (abilities.lua) for good. A boss with
+-- no desperateAt in its catalog entry (none outside bosses.lua today) never
+-- enters this state machine at all.
+--
+-- Bracing and unleashing both consume the boss's entire turn - the caller
+-- (Game:takeMonsterTurn) must skip Stealth.tick, Abilities.tryAct and
+-- Ai.act whenever Phases.tick reports the turn consumed, exactly as it
+-- already skips them all under Status.skipsTurn.
+
+local Bosses = require("bosses")
+
+local Phases = {}
+
+local function chebyshev(ax, ay, bx, by)
+  return math.max(math.abs(ax - bx), math.abs(ay - by))
+end
+
+-- Everyone the cataclysm can reach: the player when in range, plus every
+-- living companion, hireling or thrall within the same radius - the same
+-- three-way ally kind the rest of the engine treats as a single "player's
+-- own side" (see game.lua's isPlayerAlly, infighting.lua, and the noise/
+-- confuse/blind symmetry work across companions.lua/mercenaries.lua/
+-- reanimation.lua). A wild monster caught nearby is never a target - a
+-- boss's desperate gambit is aimed at the party that cornered it, not at
+-- whatever else happens to be on the floor (mirrors Bosses itself only ever
+-- threatening the player's side).
+local function novaTargets(game, monster, radius)
+  local targets = {}
+  if chebyshev(game.player.x, game.player.y, monster.x, monster.y) <= radius then
+    targets[#targets + 1] = game.player
+  end
+  for _, other in ipairs(game.level.entities) do
+    if other:isAlive() and (other.kind == "companion" or other.kind == "hireling" or other.kind == "thrall")
+      and chebyshev(other.x, other.y, monster.x, monster.y) <= radius then
+      targets[#targets + 1] = other
+    end
+  end
+  return targets
+end
+
+-- Called once per boss turn, at the same point Bosses.tryEnrage already
+-- runs in Game:takeMonsterTurn (after status/hazard/regen, before every
+-- other action). Returns (line, consumedTurn); consumedTurn true means the
+-- caller must skip everything else this turn, bracing and unleashing both
+-- being the entire point of the turn they happen on.
+function Phases.tick(game, monster)
+  if not monster.isBoss or not monster:isAlive() then return nil, false end
+  local spec = Bosses.byKey[monster.bossKey]
+  if not spec or not spec.desperateAt then return nil, false end
+
+  if monster.channeling then
+    monster.channeling = false
+    monster.novaSpent = true
+    monster.defense = monster.defense - spec.desperateDefenseBonus
+    monster.baseDefense = monster.baseDefense - spec.desperateDefenseBonus
+    local hit = {}
+    for _, victim in ipairs(novaTargets(game, monster, spec.novaRadius)) do
+      victim.hp = victim.hp - spec.novaDamage
+      hit[#hit + 1] = victim == game.player and "you" or victim.name
+    end
+    if #hit == 0 then
+      return string.format("%s unleashes a cataclysm that finds no one in range", monster.name), true
+    end
+    return string.format("%s unleashes a cataclysm on %s for %d", monster.name,
+      table.concat(hit, ", "), spec.novaDamage), true
+  end
+
+  if monster.novaSpent or monster.desperate then return nil, false end
+  if monster.hp > monster.maxHp * spec.desperateAt then return nil, false end
+
+  monster.desperate = true
+  monster.channeling = true
+  monster.defense = monster.defense + spec.desperateDefenseBonus
+  monster.baseDefense = monster.baseDefense + spec.desperateDefenseBonus
+  return string.format("%s reels and begins channeling a desperate cataclysm", monster.name), true
+end
+
+return Phases

src/polymorph.lua

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+-- Rewrites an entity's very body into a different bestiary species mid-run.
+-- Unlike affixes.lua or runewords.lua, which layer bonuses on top of a fixed
+-- body, a polymorph replaces the body outright: name, glyph, ai behaviour,
+-- attack, defense, speed, resistances, faction and any ability tag all come
+-- from the new species wholesale, the same fields Monsters.create stamps
+-- onto a fresh spawn. Only the current hp fraction survives the swap, so a
+-- polymorph is never a cheap full heal and never an outright kill either.
+-- Mutation happens in place on the entity table already held everywhere
+-- else (the turn scheduler, level.entities, a live nemesis reference), so
+-- nothing needs to re-look-up or re-insert anything after a transform.
+
+local Monsters = require("monsters")
+
+local Polymorph = {}
+
+-- Species a polymorph may land on at `depth`, in Monsters.species order so a
+-- given rng draw is deterministic. Excludes the shopkeeper outright: its
+-- "vend" behaviour idles forever once out of the shop context a polymorphed
+-- body would never occupy, leaving it neither hostile nor useful to anyone.
+function Polymorph.pool(depth)
+  local eligible = {}
+  for _, spec in ipairs(Monsters.species) do
+    if spec.key ~= "shopkeeper" and spec.minDepth <= depth then
+      eligible[#eligible + 1] = spec
+    end
+  end
+  return eligible
+end
+
+-- Transforms `entity` in place into a random species drawn from `pool`,
+-- excluding whatever species it already is so a polymorph always changes
+-- something. Returns the species table it became, or nil (entity untouched)
+-- if `pool` has nothing left to offer once the current species is excluded.
+function Polymorph.transform(entity, rng, pool)
+  local choices = {}
+  for _, spec in ipairs(pool) do
+    if spec.key ~= entity.species then choices[#choices + 1] = spec end
+  end
+  if #choices == 0 then return nil end
+  local spec = choices[rng:range(1, #choices)]
+  local fraction = entity.maxHp > 0 and (entity.hp / entity.maxHp) or 1
+  entity.glyph = spec.glyph
+  entity.name = spec.name
+  entity.species = spec.key
+  entity.ai = spec.ai
+  entity.maxHp = spec.hp
+  entity.hp = math.max(1, math.floor(spec.hp * fraction + 0.5))
+  entity.attack = spec.attack
+  entity.defense = spec.defense
+  entity.speed = spec.speed
+  entity.range = spec.range or 0
+  entity.regen = spec.regen
+  entity.onDeath = spec.onDeath
+  entity.breath = spec.breath
+  entity.ability = spec.ability
+  entity.summonSpecies = spec.summonSpecies
+  entity.cooldown = 0
+  entity.resist = spec.resist
+  entity.faction = spec.faction
+  return spec
+end
+
+return Polymorph