pf1e-simulator/src/pf1e_simulator/combat.py

"""Deterministic combat engine: attacks, crits, DR, hp states, initiative, rounds.

Phase 0 documented deviations from PF1e (conventions):
- Action economy: a normal turn grants one standard action + one move action
  (or one full-round action), plus swift/free/immediate. The policy returns an
  ordered sequence of `Action` per turn; the engine enforces the budget on it
  (X4, `_action_economy_filter`): a cast_spell occupies the slot of its spell's
  casting time (long casts are dropped before the budget with
  `downgraded:cast_time`), surplus standards/moves/swifts and a full-round
  action conflicting with an already-spent standard/move are
  dropped in order (earliest legal prefix-subsequence kept) and reported as
  `downgraded:action_economy`; a move action may convert a still-free standard
  slot; the condition-specific filters then apply as
  before. The engine executes the remaining actions in order,
  stopping early if the actor drops or one side is wiped. `default_policy`
  returns `(full_attack,)` when already in range, `(charge,)` when a
  straight-line charge path exists, `(5foot_step, full_attack)` when a single
  step brings the target into range, or `(move, attack)` otherwise (move at
  full speed along the Dijkstra path, then single attack). Immediate actions
  (off-turn, consume next swift) are modeled via an opt-in ``reaction_policy``
  hook: each resolved attack, movement step, spell cast, and damage application
  emits a ``ReactionEvent``; the first combatant whose policy returns an
  ``Action(kind="immediate")`` executes it immediately, and its next turn's
  swift action is consumed. A readied action (``Action(kind="ready")``,
  standard) stores a carrier-field payload that fires off-turn through the
  same ``ReactionEvent`` machinery when its ``ready_trigger`` matches an
  enemy event, then is consumed. Flanking, full attack, charge, withdraw, and
  5-foot step are modeled; attacks of opportunity are resolved inline (see
  below).
- A weapon with `count` > 1 ("2x Talons") resolves `count` independent attacks
  in one attack action; remaining swings are lost once the target drops
  (down or dead) mid-routine. BAB iterative attacks (full-round action
  ``full_attack``): at BAB +6/+11/+16, additional attacks at -5/-10/-15 from
  the weapon's attack bonus; iteratives are only computed for weapons with
  ``count == 1`` (natural multi-attacks do not gain iteratives). Multiple
  natural weapons in a single full attack are not modeled.
- Natural 1 always misses; natural 20 always hits and threatens a crit.
- A confirmed crit multiplies the base damage (physical dice + flat bonus)
  by crit_mult; energy weapon-special-ability dice (flaming etc.) and
  precision dice are NOT multiplied (CRB Critical Hits exception).
- DR applies once, after crit multiplication, to the PHYSICAL portion of the
  damage only (bludgeoning/piercing/slashing dice, flat bonuses and precision
  dice) — energy damage dealt along with an attack is never reduced by DR
  (CRB "Damage Reduction"); a single bypass type defeats
  DR; a multi-component "and" bypass (e.g. "bludgeoning and magic") requires
  EVERY component (PF1e "DR X/Y and Z" notation).
- Death when negative hp reaches the Constitution score (hp <= -CON); PF1e
  has no -10 rule. At exactly 0 hp a living creature is disabled: active,
  staggered (one move OR standard action per round) at half speed, and a
  non-movement action costs 1 hp at its end (hp -> -1, dying).
  Optional rule (``monsters_die_at_zero``, CLI ``--simple-monster-death``):
  monster combatants die at hp <= 0 instead — player characters are never
  affected and the default (flag off) is the PF1e rule above, bit-identical.
- Initiative ties: higher initiative_mod first, then list order (no re-roll).
- Movement: a move action travels up to the combatant's speed in cells along
  the true shortest path (Dijkstra cost field from the target, 5-10-5
  diagonals), stopping adjacent to the nearest enemy; ties keep delta order.
  The speed budget is the best of land and fly speed (V4); flying over
  obstacles or difficult terrain is NOT modeled (grid costs still apply).
- Line of effect gates all attacks: a target fully behind blocking terrain
  cannot be attacked, and the policy moves to gain sight instead.
- Cover (corner rule) grants +4 AC on hit and crit-confirm rolls; melee and
  ranged reuse the same corner rule. Soft cover: active creatures between
  attacker and target also grant +4 AC on ranged attacks (CRB soft cover);
  melee attacks ignore creatures.
- Flanking: +2 on melee attack rolls (melee touch included) when an active
  ally THREATENS the target from the opposite border or corner — the ally
  must actually threaten the target's squares with a usable melee weapon
  (a reach weapon's 5-ft dead zone does not threaten) and must not be
  unable to act (stunned/paralyzed allies do not flank). Ranged attacks do
  not benefit from flanking; allies without melee weapons do not threaten.
- Attacks of opportunity: a combatant threatens the 8 adjacent squares if
  active and wielding a melee weapon. Two triggers are modeled: (1) moving
  out of a threatened square — movement is resolved step-by-step, and each
  enemy that threatens the current square gets one AoO before the mover
  leaves it; (2) making a ranged attack while in a threatened square — each
  threatening enemy gets one AoO before each ranged swing. One AoO per
  combatant per round by default (tracked in ``_aoo_used``, cleared at round
  start); the Combat Reflexes feat raises the allowance to ``max(1, 1 + DEX
  mod)`` per round. Moving out of more than one square threatened by the same
  opponent in the same round counts as ONE opportunity for that opponent
  (tracked in ``_move_aoo_provoked``, cleared at round start); the ranged,
  casting, stand-up and maneuver triggers are separate and each still
  provokes. AoOs always strike (PF1e allows declining, the simulator
  does not) — except that an opponent with cover or total concealment
  relative to the attacker cannot be struck at all (the opportunity is
  suppressed, not spent; CRB "Cover"/"Concealment"). A 5-foot step never
  provokes AoOs (it is not a move action); the
  withdraw action protects only the starting square (see below). A 5-foot
  step and any other movement (move, charge, withdraw) are mutually exclusive
  within the same turn (``moved_this_turn`` flag, cleared in ``_take_turn``).
- Charge: a full-round action that moves in a straight line (Bresenham) up to
  2x speed toward the closest square from which the charger can melee the
  target, then makes a single melee attack at +2. The charger takes -2 AC
  until the start of their next turn (tracked as a StatModifier in
  ``effects``, cleared in ``_take_turn``). The straight line must be clear of difficult terrain,
  obstacles, and creatures; minimum 2 cells (10 ft). ``default_policy``
  chooses a charge when the enemy is out of reach but a valid charge path
  exists.
- Withdraw: a full-round action that moves up to 2x speed away from the
  nearest enemy. The starting square is not threatened — no AoO when leaving
  it. Subsequent squares provoke AoOs normally (resolved step-by-step, as for
  move). The path is a greedy ascent of the Dijkstra cost field from the
  threat. ``default_policy`` does not choose withdraw (it is only available
  via a custom policy).
- 5-foot step: a free action that moves one square toward the nearest enemy
  without provoking AoOs. Mutually exclusive with any other movement (move,
  charge, withdraw) in the same turn — tracked via ``moved_this_turn``,
  cleared at the start of each turn in ``_take_turn``. ``default_policy``
  uses ``(5foot_step, full_attack)`` when a single step brings the target
  into weapon range.
- Ranged: cumulative -2 per full range increment beyond the first, up to 10
  range increments; the penalty applies to attack and crit-confirm rolls.
  Thrown weapons (5 increments max) are not distinguished.
"""

from __future__ import annotations

from collections.abc import Callable, Iterable
from dataclasses import asdict, dataclass, field
from itertools import pairwise
from pathlib import Path
from typing import TYPE_CHECKING, Literal

from pf1e_simulator.areas import cone_cells, line_cells
from pf1e_simulator.conditions import CONDITIONS_BY_NAME, Condition
from pf1e_simulator.dice import DiceExpr, dice_to_str
from pf1e_simulator.effects import ActiveBuff, ActiveCondition, StatModifier, resolve_modifiers
from pf1e_simulator.loaders.combatant import CombatantLoadError, load_combatant
from pf1e_simulator.models import PREDEFINED_SKILLS
from pf1e_simulator.spells import (
    AreaEffect,
    BuffEffect,
    CastTime,
    ConditionEffect,
    DamageEffect,
    HealEffect,
    PenaltyEffect,
    RecurringDamageSpec,
    SaveType,
    SpellEffect,
    SummonEffect,
    save_descriptors_for_effects,
    spell_range_ft,
    spell_save_descriptors,
)

if TYPE_CHECKING:
    from pf1e_simulator.grid import Grid
    from pf1e_simulator.map import Pos, TerrainType
    from pf1e_simulator.models import AttackSpec, Combatant, DamageReduction
    from pf1e_simulator.rng import Rng
    from pf1e_simulator.spells import SpellSpec

    TrickCondition = Literal[
        "dazzled", "blinded", "deafened", "entangled", "shaken", "sickened"
    ]

    ReadyTrigger = Literal[
        "enemy_enters_reach", "enemy_casts", "enemy_attacks", "enemy_hits_ally"
    ]

from pf1e_simulator.los import (
    cover_bonus_cells,
    has_line_of_effect_cells,
)

_SQUARE_FT = 5  # Phase 0 maps use 5-ft squares
_NATURAL_ONE = 1  # PF1e: natural 1 always misses
_NATURAL_TWENTY = 20  # PF1e: natural 20 always hits and threatens
_RANGE_INCREMENT_PENALTY = 2  # PF1e: -2 per full range increment beyond the first
_MAX_RANGE_INCREMENTS = 10  # PF1e: projectile weapons shoot up to 10 increments
_MAX_TOUCH_RANGE_INCREMENTS = 5  # PF1e: thrown/firearm touch weapons shoot up to 5 increments
_FLANK_BONUS = 2  # PF1e: +2 melee attack when ally threatens opposite side
_HIGH_GROUND_BONUS = 1  # PF1e: +1 melee attack when attacker stands higher than target
_ITERATIVE_PENALTY = 5  # PF1e: each BAB iterative is at -5 from the previous
_MAX_ITERATIVES = 4  # PF1e: BAB +16 gives 4 attacks (at +16, +11, +6, +1)
_WEAPON_DURABILITY = 10  # Accumulated sunder damage that destroys a weapon.
_CHARGE_ATTACK_BONUS = 2  # PF1e: +2 attack roll on a charge
_CHARGE_AC_PENALTY = 2  # PF1e: -2 AC until start of next turn after charging
_CHARGE_MIN_CELLS = 2  # PF1e: charge must move at least 10 ft (2 squares)
_UP_CLOSE_RANGE_FT = 30  # PF1e: Up Close and Deadly works within 30 ft
_GRAPPLED_CMB_PENALTY = 2  # PF1e: grappled/pinned -2 on non-grapple/escape CMB
_MINIMUM_HIT_DAMAGE = 1  # PF1e (CRB "Damage" - Minimum Damage): a hit deals >= 1
_DISARM_RETALIATION_MARGIN = 10  # PF1e SRD: disarm fails by 10 -> attacker drops
# PF1e: Point-Blank Shot grants +1/+1 within 30 ft with ranged weapons
_POINT_BLANK_RANGE_FT = 30
_FIRING_MELEE_PENALTY = -4  # PF1e: ranged attack into melee
_FIRING_MELEE_SAFE_FT = 10  # PF1e: 2 cells (10 ft) = the -4 penalty is avoided
_SNEAK_ATTACK_FEATURE = "Sneak Attack"  # PF1e: rogue class feature (precision dice)
_PRECISE_SHOT_FEATURE = "Precise Shot"  # PF1e: feat negating firing-into-melee penalty
_IMPROVED_CRITICAL_FEATURE = "Improved Critical"  # PF1e: feat doubling the threat range
_CRIT_RANGE_BASE = 21  # threat range top is 21 - min natural die (20 -> 20-20)
_DYING_DC = 10  # PF1e: DC of the per-round stabilization Constitution check
_DELAY_INITIATIVE_STEP = 0.5  # PF1e: a delay slots 0.5 below its anchor total
_TOTAL_DEFENSE_AC_BONUS = 4  # PF1e: total defense grants +4 dodge AC
_FIGHT_DEFENSIVELY_AC_BONUS = 2  # PF1e: fighting defensively grants +2 dodge AC
_FIGHT_DEFENSIVELY_ATTACK_PENALTY = -4  # PF1e: and -4 on attacks / crit confirms
_SPELL_COMBAT_ATTACK_PENALTY = -2  # PF1e: magus Spell Combat melee attacks at -2
_TOTAL_CONCEALMENT_PCT = 50  # PF1e: a blinded attacker's targets have total concealment
# PF1e (CRB Damage Reduction): DR does not negate energy damage dealt along
# with an attack — only these weapon damage types ride the DR path.
_PHYSICAL_DAMAGE_TYPES = frozenset({"bludgeoning", "piercing", "slashing"})
# PF1e confused d% table: 01-25 act normally, 26-50 babble, 51-75 hit self,
# 76-100 attack the nearest creature
_CONFUSED_ACT_NORMAL_MAX = 25
_CONFUSED_BABBLE_MAX = 50
_CONFUSED_SELF_DAMAGE_MAX = 75
_INVISIBLE_ATTACK_BONUS = 2  # PF1e: +2 attack rolls for an invisible attacker
_HELPLESS_MELEE_BONUS = 4  # PF1e: +4 melee attack rolls (and crit confirms) vs helpless
# PF1e: a helpless creature (paralyzed, held, bound, sleeping, unconscious —
# stunned is NOT helpless) has an effective Dexterity score of 0, i.e. a -5
# modifier for a Medium creature (CRB, Helpless condition).
_DEX_ZERO_MOD = -5
_HELPLESS_CONDITION_NAMES: frozenset[str] = frozenset(
    {"helpless", "paralyzed", "asleep", "unconscious"}
)
# PF1e (CRB, Disabled): at exactly 0 hp a creature takes only a single move
# or standard action (staggered, half speed); move-equivalent and free
# activities are not "strenuous" and cost no hp — everything else does.
# retrieve_weapon / repair_weapon are move actions (CRB: drawing or mending a
# weapon is a move action), so they belong here too.
_DISABLED_MOVE_KINDS: frozenset[str] = frozenset(
    {
        "move",
        "5foot_step",
        "stand_up",
        "drop_prone",
        "wait",
        "retrieve_weapon",
        "repair_weapon",
    }
)
# PF1e (CRB, Combat Maneuver): attempting a combat maneuver provokes an
# attack of opportunity from the target unless the attacker holds the
# Improved feat for that maneuver (escape never provokes).
_IMPROVED_MANEUVER_FEATS: dict[str, str] = {
    "trip": "Improved Trip",
    "disarm": "Improved Disarm",
    "bull_rush": "Improved Bull Rush",
    "sunder": "Improved Sunder",
    "grapple": "Improved Grapple",
    "overrun": "Improved Overrun",
    "dirty_trick": "Improved Dirty Trick",
    "steal": "Improved Steal",
    "reposition": "Improved Reposition",
    "drag": "Improved Drag",
}
# PF1e (CRB, Metamagic Feats): a metamagic spell occupies a slot of its
# level + the feat's adjustment. B7: applied per cast, never blanket-on.
# Heighten Spell's RAW adjustment is variable (the caster picks the
# heightened level); the engine's per-cast API carries feat names only, so
# it is modeled at its minimum +1 (documented simplification).
_METAMAGIC_SLOT_ADJUST: dict[str, int] = {
    "Empower Spell": 2,
    "Maximize Spell": 3,
    "Extend Spell": 1,
    "Heighten Spell": 1,
}
_COMBAT_CASTING_FEAT = "Combat Casting"  # PF1e: +4 concentration (defensive/grappled only)
# PF1e: skill checks that take Dexterity-based penalties (the "dex_skills"
# modifier target — grappled/pinned/blinded -4). Climb and Swim are the
# Strength skills the conformance adjudication groups with the Dex skills.
_DEX_BASED_SKILLS: frozenset[str] = frozenset(
    {
        "acrobatics", "climb", "disable_device", "escape_artist", "fly",
        "ride", "sleight_of_hand", "stealth", "swim",
    }
)
# PF1e (CRB): undead and constructs are immune to precision damage (sneak
# attack). Ooze/plant immunity is not modeled (the model has no such types).
_PRECISION_IMMUNE_TYPES: frozenset[str] = frozenset({"undead", "construct"})
_AID_ANOTHER_DC = 10  # PF1e: aid another is an attack roll against AC 10
_AID_ANOTHER_BONUS = 2  # PF1e: a successful aid grants +2 (next attack or AC)
_RUN_SPEED_FACTOR = 4  # PF1e: running is a full-round action at 4x speed
_OVERRUN_PRONE_MARGIN = 5  # PF1e: overrun knocks prone only on a 5+ CMB margin
_BULL_RUSH_EXTRA_PER_MARGIN = 5  # PF1e: +5 ft push per 5 points above CMD
_DIRTY_TRICK_EXTRA_ROUND_MARGIN = 5  # PF1e APG: +1 round per 5 points above CMD
# PF1e (APG "Dirty Trick"): "The penalty is limited to one of the following
# conditions: blinded, dazzled, deafened, entangled, shaken, or sickened."
_DIRTY_TRICK_CONDITIONS: frozenset[str] = frozenset(
    {"blinded", "dazzled", "deafened", "entangled", "shaken", "sickened"}
)
_REPOSITION_EXTRA_PER_MARGIN = 5  # PF1e APG: +5 ft move per 5 points above CMD
_DRAG_EXTRA_PER_MARGIN = 5  # PF1e APG: +5 ft drag per 5 points above CMD
_TRIP_RETALIATION_MARGIN = 10  # PF1e: trip failing by 10+ knocks the attacker prone
_MANEUVER_MAX_SIZE_DIFF = 2  # PF1e: 2+ size categories larger = unmaneuverable
_SAVE_DESCRIPTOR_CONDITIONS = frozenset({
    "fear", "cold", "electricity", "fey", "divination", "poison", "disease",
    "mind_affecting",
})


_SIZE_MODIFIERS: dict[str, int] = {
    "fine": -8, "diminutive": -4, "tiny": -2, "small": -1,
    "medium": 0, "large": 1, "huge": 2, "gargantuan": 4, "colossal": 8,
}

# PF1e (SRD Combat Maneuvers): creatures Tiny or smaller use their Dexterity
# modifier in place of their Strength modifier to determine their CMB.
_TINY_OR_SMALLER_SIZES: frozenset[str] = frozenset({"tiny", "diminutive", "fine"})

# PF1e size order, smallest first (SRD "Size").
_SIZE_ORDER: tuple[str, ...] = (
    "fine", "diminutive", "tiny", "small", "medium", "large", "huge",
    "gargantuan", "colossal",
)

# PF1e (SRD Trip / Bull Rush / Overrun; APG Reposition / Drag): "You can only
# [affect/reposition/drag] an opponent [who is] no more than one size category
# larger than you."
_SIZE_RESTRICTED_MANEUVERS: frozenset[str] = frozenset(
    {"trip", "bull_rush", "overrun", "reposition", "drag"}
)


def _size_rank(size: str) -> int:
    """Index in the PF1e size order; unknown sizes rank as Medium."""
    try:
        return _SIZE_ORDER.index(size.lower())
    except ValueError:
        return _SIZE_ORDER.index("medium")


def _weapon_filter_matches(weapon_filter: str, weapon_name: str | None) -> bool:
    """True when a feat's weapon_filter names the weapon being used.

    PF1e Weapon Focus is taken by weapon GROUP ("Pistol"), while sheets name
    individual weapons ("Braises d'Automne (pistolet ?)"), so the match is a
    case-insensitive substring test of the filter against the weapon name.
    A None weapon name (no weapon context) never matches a filtered modifier.
    """
    if weapon_name is None:
        return False
    return weapon_filter.lower() in weapon_name.lower()

# PF1e natural reach for tall creatures (simplification: no long/quadruped
# distinction). Tiny, Diminutive and Fine have a natural reach of 0 ft (SRD
# "Big and Little Creatures in Combat"): "Creatures that take up less than 1
# square of space typically have a natural reach of 0 feet, meaning they can't
# reach into adjacent squares." Unknown sizes fall back to 5 ft (the historical
# behavior).
_SIZE_NATURAL_REACH_FT: dict[str, int] = {
    "Fine": 0,
    "Diminutive": 0,
    "Tiny": 0,
    "Small": 5,
    "Medium": 5,
    "Large": 10,
    "Huge": 15,
    "Gargantuan": 20,
    "Colossal": 30,
}

# PF1e co-occupancy (SRD "Big and Little Creatures in Combat"): "Very small
# creatures take up less than 1 square of space. This means that more than one
# such creature can fit into a single square" and "They must enter an
# opponent's square to attack in melee" — a Tiny-or-smaller creature shares a
# square with a strictly larger one (and the larger one may move through and
# end in the smaller's square). Small and larger creatures occupy a full
# square and never share. The rank ceiling for "takes up less than 1 square".
_TINY_OR_SMALLER_MAX_RANK: int = _size_rank("Tiny")

# SRD "Moving Through a Square": "Any creature can move through a square
# occupied by a creature three size categories larger than itself." The
# minimum size-rank gap that opens the pass-through gate.
_PASS_THROUGH_MIN_SIZE_GAP: int = 3


def _can_cooccupy(size_a: str, size_b: str) -> bool:
    """True when two sizes may share a single grid square (PF1e co-occupancy).

    Only a Tiny-or-smaller creature ("less than 1 square") and a STRICTLY
    larger creature share; two same-size creatures never do.
    """
    rank_a = _size_rank(size_a)
    rank_b = _size_rank(size_b)
    if rank_a == rank_b:
        return False
    return min(rank_a, rank_b) <= _TINY_OR_SMALLER_MAX_RANK


def _can_pass_through(size_a: str, size_b: str) -> bool:
    """True when a creature of ``size_a`` may move THROUGH a square occupied by ``size_b``.

    PF1e (SRD "Movement, Position, and Distance" / "Moving Through a Square"):
    "You can move through a square occupied by a creature three size categories
    larger than you" and "A big creature can move through a square occupied by
    a creature three size categories smaller than it" — the size ranks must
    differ by at least three categories. The pass-through may cross the
    occupied square but never END on it (``_blocked`` keeps the
    co-occupancy-only end gate; SRD: "You can't end your movement in the same
    square as another creature unless it is helpless").
    """
    return abs(_size_rank(size_a) - _size_rank(size_b)) >= _PASS_THROUGH_MIN_SIZE_GAP

# Number of grid cells per side of a creature's footprint (square footprint).
# Unknown sizes fall back to 1 (the historical single-cell behavior).
SIZE_CELLS: dict[str, int] = {
    "Small": 1,
    "Medium": 1,
    "Large": 2,
    "Huge": 3,
    "Gargantuan": 4,
    "Colossal": 6,
}

# Row-major scan order of the 8 adjacent cells, used by reposition.
_NEIGHBOR_OFFSETS: tuple[tuple[int, int], ...] = (
    (-1, -1), (-1, 0), (-1, 1), (0, -1), (0, 1), (1, -1), (1, 0), (1, 1),
)


# PF1e (SRD Combat Maneuver Defense): the AC bonus types a creature may add
# to its CMD. Penalties and other bonus types (armor, shield, natural,
# enhancement, competence, untyped) stay out of the CMD.
_CMD_AC_BONUS_TYPES: frozenset[str] = frozenset({
    "circumstance", "deflection", "dodge", "insight", "luck", "morale",
    "profane", "sacred",
})


def _save_label(result: SaveResult | None) -> str:
    if result is None:
        return "NO SAVE"
    return "SAVED" if result.success else "FAILED"


def _burst_center(
    target: CombatantState | None, center_pos: tuple[int, int] | None
) -> tuple[int, int] | None:
    """AoE center: the U7b point-targeting override wins over the target cell."""
    if center_pos is not None:
        return center_pos
    if target is not None:
        return target.pos
    return None


def _spell_effect_summary(effect: SpellEffect) -> str:
    """Short serializable summary of one spell effect (never the description)."""
    if isinstance(effect, (DamageEffect, PenaltyEffect)):
        tags = effect.types if isinstance(effect, DamageEffect) else effect.targets
        parts = [dice_to_str(effect.formula), *tags]
        if effect.half_on_save:
            parts.append("half on save")
        return " ".join(parts)
    if isinstance(effect, ConditionEffect):
        return f"{effect.condition_name} {effect.duration_rounds}r"
    if isinstance(effect, HealEffect):
        return f"heal {dice_to_str(effect.formula)}"
    if isinstance(effect, BuffEffect):
        return f"buff {effect.duration_rounds}r"
    if isinstance(effect, AreaEffect):
        return f"area {effect.radius_ft}ft"
    return f"summon {effect.creature}"


def _spell_summary(spell: SpellSpec) -> str:
    """Short serializable summary of a spell's effects, joined with ', '."""
    return ", ".join(_spell_effect_summary(e) for e in spell.effects)


def _stat_modifier_dict(mod: StatModifier) -> dict[str, object]:
    """Serialize one StatModifier to a JSON-safe dict."""
    return {
        "target": mod.target,
        "value": mod.value,
        "bonus_type": mod.bonus_type,
        "condition": mod.condition,
        "weapon_filter": mod.weapon_filter,
    }


def _condition_definition_dict(cond: Condition) -> dict[str, object]:
    """Serialize one Condition definition (mods + behavioral flags)."""
    flags = [
        name
        for name, value in (
            ("denies_dex_to_ac", cond.denies_dex_to_ac),
            ("cant_act", cond.cant_act),
            ("cant_move", cond.cant_move),
            ("cant_attack", cond.cant_attack),
            ("cant_charge", cond.cant_charge),
            ("cant_aoo", cond.cant_aoo),
            ("must_flee", cond.must_flee),
        )
        if value
    ]
    return {
        "mods": [_stat_modifier_dict(m) for m in cond.modifiers],
        "flags": flags,
        "speed_mult": cond.speed_mult,
        "miss_chance": cond.miss_chance,
    }


def _spell_half_on_save(spell: SpellSpec) -> bool:
    """True if any effect grants half damage on a successful save."""
    for effect in spell.effects:
        if isinstance(effect, DamageEffect) and effect.half_on_save:
            return True
        if isinstance(effect, PenaltyEffect) and effect.half_on_save:
            return True
        if isinstance(effect, AreaEffect) and effect.save_for_half:
            return True
    return False


def _spell_declares_projectiles(spell: SpellSpec) -> bool:
    """True when a top-level damage effect carries a projectile-scaling spec.

    Such spells (Magic Missile, Scorching Ray) resolve EVERY projectile's
    attack roll inside ``_apply_damage_effect`` — even a single-ray Scorching
    Ray — so the one-shot delivery-gate ranged touch attack is skipped for
    them. Rays without a projectile spec (Acid Arrow, Ray of Frost) keep the
    single delivery attack unchanged.
    """
    return any(
        isinstance(e, DamageEffect) and e.projectiles is not None
        for e in spell.effects
    )


def _spell_area_dict(spell: SpellSpec) -> dict[str, object] | None:
    """Structured area template of a spell, or None if it has no top-level AreaEffect.

    Returns ``{"shape": str, "radius_ft": int}`` for the FIRST AreaEffect found
    in ``spell.effects`` (a spell may declare several effects; only the first
    area is exposed, and effects nested inside an AreaEffect are not scanned).
    """
    for effect in spell.effects:
        if isinstance(effect, AreaEffect):
            return {"shape": effect.shape, "radius_ft": effect.radius_ft}
    return None


_STEP_DELTAS: tuple[Pos, ...] = (
    (-1, -1),
    (-1, 0),
    (-1, 1),
    (0, -1),
    (0, 1),
    (1, -1),
    (1, 0),
    (1, 1),
)


def _effective_reach_ft(state: CombatantState, weapon: AttackSpec) -> int:
    """Outer edge, in feet, of a melee attack's usable reach zone.

    PF1e distinguishes two cases (CRB "Big and Little Creatures in Combat"):
    a creature's NATURAL reach is a disk, while a reach weapon doubles that
    natural reach but cannot strike at the wielder's natural reach or less
    (a ring). See ``_melee_reach_zone_cells`` for the full zone.
    """
    natural_ft = _SIZE_NATURAL_REACH_FT.get(state.combatant.size, 5)
    if weapon.reach_weapon:
        return 2 * natural_ft
    return max(natural_ft, weapon.reach_ft)


def _melee_reach_zone_cells(state: CombatantState, weapon: AttackSpec) -> tuple[int, int]:
    """Inclusive grid-cell reach zone ``(inner, outer)`` of one melee attack.

    PF1e, CRB "Big and Little Creatures in Combat": "Unlike when someone
    uses a reach weapon, a creature with greater than normal natural reach
    (more than 5 feet) still threatens squares adjacent to it" — natural
    reach is a DISK, so the zone is ``0 .. max(natural, weapon.reach_ft)``
    (a natural attack's ``reach_ft`` IS the creature's natural reach). A
    reach weapon instead "can strike up to double their natural reach but
    can't strike at their natural reach or less" — the zone is the RING
    ``natural+1 .. 2 * natural``, whose dead zone is the wielder's natural
    reach.
    """
    natural_cells = _SIZE_NATURAL_REACH_FT.get(state.combatant.size, 5) // _SQUARE_FT
    inner_cells = natural_cells + 1 if weapon.reach_weapon else 0
    outer_cells = _effective_reach_ft(state, weapon) // _SQUARE_FT
    return inner_cells, outer_cells


def _speed_ft(state: CombatantState) -> int:
    """Movement budget in feet: the best of the combatant's land and fly speed.

    Simplification (V4): a creature that has a fly speed is assumed to use it;
    flying OVER obstacles or difficult terrain is NOT modeled — the grid's
    passability and terrain costs still apply to the whole budget. No
    fly maneuverability, no 3D flight. Swim/climb/burrow speeds do not exist
    in the model (fly only).
    """
    return max(state.combatant.speed_land_ft, state.combatant.speed_fly_ft or 0)


def _bresenham_line(start: Pos, end: Pos) -> list[Pos]:
    """Integer Bresenham line from start to end (exclusive of start, inclusive of end)."""
    r0, c0 = start
    r1, c1 = end
    dr = abs(r1 - r0)
    dc = abs(c1 - c0)
    sr = 1 if r1 > r0 else -1
    sc = 1 if c1 > c0 else -1
    err = dr - dc
    path: list[Pos] = []
    r, c = r0, c0
    while (r, c) != (r1, c1):
        e2 = 2 * err
        if e2 > -dc:
            err -= dc
            r += sr
        if e2 < dr:
            err += dr
            c += sc
        path.append((r, c))
    return path


@dataclass(frozen=True)
class CombatantStats:
    """Aggregated outcomes for one combatant over a battle."""

    hits: int = 0
    crits: int = 0
    damage_dealt: int = 0
    damage_taken: int = 0


_PC_SOURCE_PREFIX = "fiches_personnages/"


def _is_pc_combatant(combatant: Combatant) -> bool:
    """True for player characters, False for monsters (X5 classification).

    The unified loader records each combatant's origin in ``source``: every
    PC JSON (``data/pcs/*.json``) points at its Foundry sheet under
    ``fiches_personnages/`` (README convention), while monster JSONs carry
    bestiary/summon sources. ``side`` is a user-chosen faction name and
    ``cr``/``xp`` are absent from some monster files, so ``source`` is the
    only robust per-combatant marker that survives loading without a schema
    change.
    """
    return combatant.source.startswith(_PC_SOURCE_PREFIX)


@dataclass(frozen=True)
class RecurringDamage:
    """One active damage-over-time source on a combatant (S2c, Acid Arrow).

    - ``formula``: dice rolled each recurring round (2d4)
    - ``types``: energy types, reduced by resistance/immunity (never DR)
    - ``rounds_left``: rounds this source still deals damage (decremented and
      removed at the start of the owner's turn once it ticks)
    - ``source``: human-readable origin for the transcript
    """

    formula: DiceExpr
    types: frozenset[str]
    rounds_left: int
    source: str


@dataclass(frozen=True)
class PendingCast:
    """A one-round cast begun this turn, to be resolved next turn.

    PF1e (SRD "Casting Time"): "A spell that takes 1 round to cast is a
    full-round action. It comes into effect just before the beginning of
    your turn in the round after you began casting the spell. You then act
    normally after the spell is completed." Everything the delivery still
    needs is frozen at the start of the casting (the slot is already
    spent): ``slot_level`` carries the metamagic-inflated level (B7) that
    drives the concentration checks and the Heighten Spell DC (other
    metamagic does not raise the DC - see _spell_dc), ``hp_at_cast`` is the
    caster's hp when the casting began
    — the net hp lost before resolution is the interruption damage that
    forces the concentration check (CRB "Concentration": injured while
    casting, DC 10 + damage + spell level).
    """

    spell_name: str
    target_id: str | None
    center_pos: tuple[int, int] | None
    metamagic: tuple[str, ...]
    slot_level: int
    cast_defensively: bool
    hp_at_cast: int


@dataclass(frozen=True)
class HeldCharge:
    """A touch spell whose melee touch attack missed - the charge is held.

    PF1e (SRD "Cast a Spell - Touch Attacks", Holding the Charge): "If you
    don't discharge the spell in the round when you cast the spell, you can
    hold the charge indefinitely. You can continue to make touch attacks
    round after round." A missed melee touch therefore does NOT expend the
    spell (the slot was spent at the cast; the spell itself survives to be
    re-attempted). Casting another spell dissipates it ("If you cast another
    spell, the touch spell dissipates"). Ranged touch attacks are NOT held:
    SRD "Ranged Touch Spells in Combat" - "ranged touch attacks cannot be
    held until a later turn".
    """

    spell_name: str
    target_id: str
    metamagic: tuple[str, ...]
    slot_level: int


@dataclass
class CombatantState:
    """Mutable runtime state of one combatant on the grid."""

    combatant: Combatant
    side: str
    pos: Pos
    hp: int
    # Old fields for backwards compatibility with tests
    effects: list[StatModifier] = field(default_factory=list)
    conditions: list[Condition] = field(default_factory=list)
    # New duration-tracked fields
    active_buffs: list[ActiveBuff] = field(default_factory=list)
    active_conditions: list[ActiveCondition] = field(default_factory=list)
    resources_left: dict[str, int] = field(default_factory=dict)
    spell_slots_left: dict[int, int] = field(default_factory=dict)
    moved_this_turn: bool = False
    power_attack: bool = False
    grappled_with: str | None = None
    deed_up_close_and_deadly: bool = False
    immediate_used: bool = False
    # PF1e (SRD Immediate Actions): an immediate used ON your turn counts as
    # your swift action for that turn; it also caps the round at one
    # immediate. Reset at the start of your next turn (like moved_this_turn).
    swift_used_this_turn: bool = False
    summon_duration: int = 0
    summon_caster_id: str | None = None
    # Runtime weapon durability (not in the frozen data model): accumulated
    # sunder damage per weapon id, and the set of weapon ids rendered unusable.
    weapon_damage: dict[str, int] = field(default_factory=dict)
    weapon_broken: set[str] = field(default_factory=set)
    # Runtime weapon theft (not in the frozen data model): weapon ids taken by
    # steal maneuvers.
    weapon_stolen: set[str] = field(default_factory=set)
    # Runtime disarmed weapons (not in the frozen data model): weapon ids the
    # combatant DROPPED on a failed disarm maneuver (SRD Disarm: "your
    # opponent drops the weapon"). A retrieve_weapon move action picks the
    # weapon back up.
    weapon_dropped: set[str] = field(default_factory=set)
    # Dying & stabilization (not in the frozen data model): the hp at which
    # this combatant stabilized while dying; None = not stabilized.
    stabilized_hp: int | None = None
    # Simple monster death (X5, not in the frozen data model): set by the
    # engine when ``monsters_die_at_zero`` is on, for monster combatants only
    # — the combatant dies at hp <= 0 instead of the PF1e hp <= -CON rule.
    dies_at_zero: bool = False
    # Action feedback (not in the frozen data model): the ActionResults of the
    # PREVIOUS turn, assigned at the end of each turn so the Observation built
    # at the next policy invocation can expose them.
    last_action_results: list[ActionResult] = field(default_factory=list)
    # Delay action (not in the frozen data model): set when the combatant took
    # the delay action this round; delay_before is the id of the combatant it
    # chose to act just before (None = end of the round). Reset at round start.
    delayed_this_round: bool = False
    delay_before: str | None = None
    # Ready action (not in the frozen data model): the concrete payload the
    # combatant prepared with its standard action, and the trigger event that
    # fires it. Cleared when the readied action executes (one-shot).
    readied: Action | None = None
    readied_trigger: ReadyTrigger | None = None
    # Defensive actions (not in the frozen data model): the dodge AC bonus
    # granted by total defense (+4) and fighting defensively (+2), and the
    # fighting-defensively flag (-4 on attack and crit confirm). Both reset
    # at the start of the combatant's NEXT turn, so they last through the
    # opponents' turns in between. The total_defense flag additionally marks
    # that the combatant is using total defense — PF1e (SRD "Total Defense"):
    # "You can't make attacks of opportunity while using total defense."
    defensive_ac_bonus: int = 0
    fight_defensively: bool = False
    total_defense: bool = False
    # Aid another & run (not in the frozen data model): aid bonuses granted to
    # this combatant by an ally's aid another — aid_attack_bonus is consumed by
    # its next attack roll, aid_ac_bonus applies against the next attack that
    # targets it. PF1e (SRD "Aid Another"): the +2 lasts "as long as that
    # attack comes before the beginning of your next turn" — YOUR = the AIDER,
    # so each grant is tracked on the aider (target id, mode) and expires at
    # the start of the aider's next turn. The running flag denies the Dex
    # bonus to AC until the runner's next turn.
    aid_attack_bonus: int = 0
    aid_ac_bonus: int = 0
    aid_grants: list[tuple[str, str]] = field(default_factory=list)
    running: bool = False
    # Bleeding (V5b, not in the frozen data model): damage taken at the start
    # of each turn; any effect that restores hit points clears it.
    bleed_damage: int = 0
    # PF1e recurring spell damage (S2c, not in the frozen data model): each
    # entry is one damage-over-time source (Acid Arrow's lingering acid) that
    # deals its dice at the start of this combatant's turn for `rounds_left`
    # rounds, reduced by energy resistance/immunity (never DR).
    recurring_damage: list[RecurringDamage] = field(default_factory=list)
    # PF1e one-round casting (SRD "Casting Time", not in the frozen data
    # model): the spell begun on this combatant's turn, resolved just before
    # its NEXT turn begins; None when no casting is in progress.
    pending_cast: PendingCast | None = None
    # PF1e held touch charge (SRD "Cast a Spell - Touch Attacks", Holding the
    # Charge, not in the frozen data model): a touch spell whose melee touch
    # attack missed; re-attempted at the start of each later turn of this
    # combatant while the target lives and stands in reach, dissipated when
    # this combatant casts another spell. None when no charge is held.
    held_charge: HeldCharge | None = None

    def usable_attacks(self) -> list[AttackSpec]:
        return [
            w
            for w in self.combatant.attacks
            if w.id not in self.weapon_broken
            and w.id not in self.weapon_stolen
            and w.id not in self.weapon_dropped
        ]

    def occupied_cells(self) -> frozenset[Pos]:
        """The set of grid cells this creature occupies (its footprint).

        ``pos`` is the anchor (top-left corner); the footprint is an n x n
        square where n = SIZE_CELLS[size]. A 1x1 creature occupies {pos}.
        """
        n = SIZE_CELLS.get(self.combatant.size, 1)
        r, c = self.pos
        return frozenset(
            (r + dr, c + dc) for dr in range(n) for dc in range(n)
        )

    def __post_init__(self) -> None:
        if not self.spell_slots_left:
            self.spell_slots_left = dict(self.combatant.spell_slots)

    def spend_resource(self, name: str, n: int = 1) -> bool:
        """Spend n points of a resource. Returns True if successful, False if insufficient."""
        current = self.resources_left.get(name, 0)
        if current < n:
            return False
        self.resources_left[name] = current - n
        return True

    def spend_spell_slot(self, level: int) -> bool:
        """Spend one spell slot of ``level``. Returns True if a slot was spent."""
        current = self.spell_slots_left.get(level, 0)
        if current <= 0:
            return False
        self.spell_slots_left[level] = current - 1
        return True

    @property
    def active(self) -> bool:
        """PF1e: hp > 0 acts normally; hp == 0 is DISABLED (CRB, Effects of
        Death: a living creature at exactly 0 hp can still take a single move
        or standard action), so it remains active. hp < 0 is dying/dead.
        Under the simple monster-death rule (``dies_at_zero``) hp <= 0 is
        dead, so the disabled band never applies."""
        return self.hp >= 0 and not self.dead

    @property
    def dead(self) -> bool:
        return self.hp <= self.death_threshold

    @property
    def death_threshold(self) -> int:
        """PF1e (CRB): death when negative hp reaches the CON score (no -10 rule).
        Undead and constructs have no Constitution score and are "immediately
        destroyed when reduced to 0 hit points or fewer" (SRD Undead/Construct
        traits). The optional simple monster-death rule raises the threshold to 0."""
        if self.dies_at_zero:
            return 0
        if self.combatant.creature_type in ("undead", "construct"):
            return 0
        return -self.combatant.abilities.con_score


@dataclass(frozen=True)
class AttackResult:
    """Outcome of one attack roll, including the raw rolls for the log."""

    hit: bool
    crit: bool
    damage: int
    roll: int
    total: int
    ac: int
    penalty: int = 0
    flank_bonus: int = 0
    high_ground_bonus: int = 0
    base_bonus: int = 0
    melee_penalty: int = 0


@dataclass(frozen=True)
class ChargeResult:
    """Outcome of a charge feasibility check (public, for policy/LLM reading).

    weapon is the melee weapon that would be used when the charge is possible
    (reason None); otherwise weapon is None and reason explains the failure.
    distance_ft is 0 on failure.
    """

    weapon: AttackSpec | None
    distance_ft: int
    reason: str | None


@dataclass(frozen=True)
class Observation:
    """Serializable snapshot of combat state for a policy/LLM.

    Built by the engine at the point of policy invocation; the snapshot is the
    ONLY source of information for an ``LLMPolicy`` — it never exposes
    ``engine.*`` callables nor mutable references to live state. All collections
    are copied (tuples/dicts) so the snapshot is frozen and JSON-serializable.

    ``combatants`` holds one dict per combatant in ``self._states`` order;
    ``pairs`` holds one dict per (acting combatant x each other combatant) with
    ``target_index`` disambiguating the target. ``terrain`` and ``elevation``
    are height x width layers aligned on the same dimensions (``elevation`` is
    ``()`` when the grid has no elevation layer). ``threatened`` is a height x
    width boolean grid whose cells are True when threatened by at least one
    ENEMY of the acting combatant (active, opposite side, with a melee
    weapon); the union is bounded to the grid — out-of-grid threatened cells
    are dropped. ``ranged_threatened`` is a height x width boolean grid whose
    cells are True when under enemy RANGED fire: reachable within a usable
    ranged-style weapon (``ranged``, or ``touch`` with a range increment) of
    an active enemy of the acting combatant, with a line of effect from that
    enemy's occupied cells; bounded to the grid. PF1e ranged weapons do NOT
    threaten for attacks of opportunity — this is a tactical field-of-fire
    map, not an AoO threat, and it leaves ``threatened`` untouched.
    ``terrain_semantics`` is one dict per distinct terrain type
    on the map (sorted by type for determinism), carrying
    ``{type, move_cost, blocks_los, cover}`` — derived from
    ``grid.terrain_at((r, c))`` over the entire map (the Grid does not expose
    ``MapSpec.legend``). ``initiative_order`` lists the combatant ids in the
    current round's initiative order (``_build_round_order()``, read-only,
    no RNG): the first entry acts next this round.
    """

    round: int
    acting_combatant: int
    combatants: tuple[dict[str, object], ...]
    pairs: tuple[dict[str, object], ...]
    terrain: tuple[tuple[str | None, ...], ...]
    elevation: tuple[tuple[int, ...], ...]
    threatened: tuple[tuple[bool, ...], ...] = ()
    ranged_threatened: tuple[tuple[bool, ...], ...] = ()
    terrain_semantics: tuple[dict[str, object], ...] = ()
    condition_definitions: tuple[tuple[str, dict[str, object]], ...] = ()
    initiative_order: tuple[str, ...] = ()

    def to_dict(self) -> dict[str, object]:
        """Return a JSON-serializable dict with the pinned top-level keys."""
        return {
            "round": self.round,
            "acting_combatant": self.acting_combatant,
            "combatants": self.combatants,
            "pairs": self.pairs,
            "terrain": self.terrain,
            "elevation": self.elevation,
            "threatened": self.threatened,
            "ranged_threatened": self.ranged_threatened,
            "terrain_semantics": self.terrain_semantics,
            "condition_definitions": self.condition_definitions,
            "initiative_order": self.initiative_order,
        }


@dataclass(frozen=True)
class SaveResult:
    """Outcome of one saving throw roll."""

    success: bool
    roll: int
    total: int
    dc: int


@dataclass(frozen=True)
class Action:
    """What a policy wants a combatant to do this turn.

    Kinds map to PF1e action types: ``attack`` is a standard action
    (single attack, highest BAB only — no iteratives), ``move`` is a move
    action, ``full_attack`` is a full-round action (BAB iteratives), ``charge``
    is a special full-round action (2x speed, straight line, +2 attack, -2
    AC), ``5foot_step`` is a free action (one square, no AoO, mutually
    exclusive with move/charge/withdraw), ``swift`` and ``free`` are minor
    actions, ``immediate`` is an off-turn reaction (deferred). ``wait`` is a
    no-op. ``delay`` is a standard action that forgoes the turn to act later
    in the same round (end of order, or just before ``target_id``). The engine
    executes a policy-returned sequence per turn. ``ready`` is a standard
    action that prepares the carrier-field payload (spell / maneuver / attack
    on ``target_id``) to fire off-turn when ``ready_trigger`` matches a
    ``ReactionEvent``; the readied action is then consumed.
    ``total_defense`` and ``fight_defensively`` are standard defensive actions
    granting a temporary dodge AC bonus until the combatant's next turn;
    ``fight_defensively`` also takes -4 on its attacks. ``stand_up`` is a move
    action ending the prone condition (it provokes an AoO from each enemy
    threatening the combatant); ``drop_prone`` is a free action going prone
    until the combatant stands up. ``move`` and ``5foot_step`` accept an
    explicit ``destination`` cell ``(row, col)``: with one they walk to that
    cell instead of auto-pathing toward ``target_id`` (the 5-foot step's
    destination must be exactly one cell away). ``attack`` and ``full_attack``
    accept ``weapon_id`` to strike with THAT weapon instead of the
    auto-selected one; a choice that is unknown, broken, stolen, or unable to
    hit the target (range / line of effect) is rejected
    (``weapon_unavailable``).
    ``cast_spell`` accepts ``target_pos``: an explicit ``(row, col)`` cell to
    center the spell's ``AreaEffect`` on instead of the target creature's
    position (a point-targeted Fireball). It is meaningful only for spells
    with a top-level ``AreaEffect`` — for every other effect the resolved
    target is used exactly as before, and ``target_pos`` is ignored. A point
    outside the map or without line of effect from the caster is rejected
    (``invalid_destination``); with ``target_pos`` and no resolved target the
    spell is cast on the point and every creature in the area rolls its own
    save.     ``aid_another`` is a standard action helping a resolved ally: the
    aider makes an attack roll (d20 + its first usable melee weapon's bonus)
    against AC 10; on success the ally gains +2 on its next attack roll
    (``aid_mode`` "attack" or None) or +2 AC against the next attack
    targeting it (``aid_mode`` "ac"). ``run`` is a full-round action moving
    up to 4x speed toward ``target_id`` or an explicit ``destination`` (U5c),
    reusing the move machinery (step-by-step, AoO-provoking); it sets
    ``running``, which lasts until the runner's next turn and denies the
    runner its Dexterity bonus to AC.
    ``cast_spell`` accepts ``metamagic`` (B7): the metamagic feats to apply
    to THIS cast — PF1e metamagic is chosen per cast, so only the feats
    listed here AND known by the caster (in ``Combatant.metamagic_feats``)
    apply; the spell then occupies a slot of base level + adjustment
    (Empower +2, Maximize +3, Extend +1) and its save DC uses that slot
    level. Without ``metamagic``, casting is unchanged. ``cast_spell`` also
    accepts ``cast_defensively`` (B24): the caster forgoes the casting AoO
    but must pass a concentration check (DC 15 + 2 x spell level, +4 with
    Combat Casting) or the spell fizzles.
    """

    kind: Literal[
        "attack", "move", "wait", "swift", "free", "immediate", "full_round",
        "full_attack", "charge", "withdraw", "5foot_step", "cast_spell",
        "maneuver", "channel_energy", "hex", "deed", "spell_combat",
        "inspire_courage", "retrieve_weapon", "repair_weapon",
        "activate_power_attack", "delay", "ready",
        "total_defense", "fight_defensively", "stand_up", "drop_prone",
        "aid_another", "run",
    ]
    target_id: str | None = None
    spell_name: str | None = None
    maneuver: str | None = None  # "trip", "disarm", "bull_rush", "sunder",
    # "grapple", "escape", "overrun", "dirty_trick", "steal", "reposition", "drag"
    hex_name: str | None = None  # "evil_eye", "slumber", "cackle"
    deed_name: str | None = None  # "up_close_and_deadly", "quick_clear"
    class_ability: str | None = None  # "deed"|"spell_combat"|"inspire_courage"|"hex"|"channel"
    channel_mode: Literal["heal", "harm"] | None = None  # channel energy polarity for this use
    direction: tuple[int, int] | None = None  # steering for directional maneuvers
    trick_condition: TrickCondition | None = None  # dirty trick condition choice
    # weapon id for attack / full_attack / retrieve_weapon / repair_weapon
    weapon_id: str | None = None
    ready_trigger: ReadyTrigger | None = None  # ready action trigger event
    destination: tuple[int, int] | None = None  # explicit (row, col) cell for move / 5foot_step
    target_pos: tuple[int, int] | None = None  # explicit (row, col) AoE center for cast_spell
    aid_mode: Literal["attack", "ac"] | None = None  # aid another: bonus to grant (default attack)
    # B7: metamagic feats to apply to THIS cast (only known ones apply)
    metamagic: tuple[str, ...] = ()
    # B24: cast defensively — no AoO, but a concentration check or the spell fizzles
    cast_defensively: bool = False


# Normalized action-result reason vocabulary. U1 emits ok, unsupported_kind,
# missing_target and the downgraded:* reasons; no_weapon, out_of_range,
# no_line_of_effect are reused by U6b to explain, per pair, why an attack or
# a charge is unavailable. no_slot and insufficient_resource are declared
# here for the deeper execution-feedback package. U3 adds delayed /
# already_delayed for the delay action. U4 adds ready for the ready action.
# U5b adds not_prone / already_prone for the prone actions. U5c adds
# unreachable_destination for move / 5foot_step with an explicit destination.
# U5d adds weapon_unavailable for attack / full_attack with an explicit
# weapon_id that cannot be honoured. U7b adds invalid_destination for
# cast_spell with an explicit target_pos that cannot be honoured. U5e reuses
# no_weapon (aid another without a usable melee weapon) and
# unreachable_destination (run to an unhonourable destination). X4 adds
# downgraded:action_economy for actions the general per-turn budget filter
# drops from the policy sequence (second standard, second move when no
# standard is left to convert, second swift, full-round conflicting with
# standard+move). The cast-time package adds downgraded:cast_time for
# cast_spell actions whose spell has a long casting time (more than 1 round): the
# engine cannot schedule them within a turn, so they are dropped before the
# budget filter runs. S3a adds downgraded:surprise for actions the surprise
# round allowance (SRD "Surprise": one standard OR move plus free) drops from
# an aware combatant's sequence during the surprise round.
ACTION_RESULT_REASONS: frozenset[str] = frozenset({
    "ok", "unsupported_kind", "missing_target", "no_weapon", "out_of_range",
    "no_line_of_effect", "no_slot", "insufficient_resource",
    "downgraded:staggered", "downgraded:nauseated",
    "downgraded:action_economy", "downgraded:cast_time",
    "downgraded:surprise",
    "delayed", "already_delayed", "ready",
    "not_prone", "already_prone", "unreachable_destination",
    "weapon_unavailable", "invalid_destination", "cannot_combine",
})
_REASON_OK = "ok"
_REASON_UNSUPPORTED_KIND = "unsupported_kind"
_REASON_MISSING_TARGET = "missing_target"
_REASON_DOWNGRADED_STAGGERED = "downgraded:staggered"
_REASON_DOWNGRADED_NAUSEATED = "downgraded:nauseated"
_REASON_DOWNGRADED_IMMEDIATE_SWIFT = "downgraded:immediate_swift"
_REASON_DOWNGRADED_ACTION_ECONOMY = "downgraded:action_economy"
_REASON_DOWNGRADED_CAST_TIME = "downgraded:cast_time"
_REASON_DOWNGRADED_SURPRISE = "downgraded:surprise"
_REASON_DELAYED = "delayed"
_REASON_ALREADY_DELAYED = "already_delayed"
_REASON_READY = "ready"
_REASON_NOT_PRONE = "not_prone"
_REASON_ALREADY_PRONE = "already_prone"
_REASON_UNREACHABLE_DESTINATION = "unreachable_destination"
_REASON_WEAPON_UNAVAILABLE = "weapon_unavailable"
_REASON_INVALID_DESTINATION = "invalid_destination"
_REASON_NO_WEAPON = "no_weapon"
_REASON_OUT_OF_RANGE = "out_of_range"
_REASON_NO_LINE_OF_EFFECT = "no_line_of_effect"
_REASON_CANNOT_COMBINE = "cannot_combine"

# Action kinds that are declared but have no engine dispatch (U1 surfaces
# them as explicit rejections instead of silent no-ops).
_UNSUPPORTED_ACTION_KINDS: frozenset[str] = frozenset({"swift", "free", "full_round"})
# Action kinds whose helper is a silent no-op (or worse) without a resolved
# target; _execute rejects them up front with missing_target instead.
# move / 5foot_step / run are exempt when an explicit destination is provided
# (U5c / U5e).
_TARGET_REQUIRED_ACTION_KINDS: frozenset[str] = frozenset({
    "attack", "full_attack", "charge", "withdraw", "move", "5foot_step",
    "cast_spell", "maneuver", "aid_another", "run",
})


@dataclass(frozen=True)
class ActionResult:
    """Explicit outcome of executing one Action (feedback for the policy).

    ``ok`` is True only when the action was dispatched to its helper;
    rejections (``unsupported_kind``, ``missing_target``) and filter
    downgrades (``downgraded:*``) carry ok=False and a reason drawn from
    ``ACTION_RESULT_REASONS``. ``detail`` is reserved for future packages.
    """

    kind: str
    ok: bool
    reason: str = ""
    detail: str = ""


@dataclass(frozen=True)
class ReactionEvent:
    """An off-turn event a ``reaction_policy`` may react to.

    ``kind`` describes what just happened: ``attack_resolved`` (a swing was
    resolved, ``actor`` is the attacker, ``target`` the defender, ``damage``
    the damage dealt), ``movement_step`` (``actor`` moved one cell),
    ``spell_cast`` (``actor`` finished casting at ``target``), or
    ``damage_taken`` (``target`` lost ``damage`` hp from a non-attack source
    such as a spell or channel energy). ``action`` is reserved for future
    use (the triggering action is not threaded through the engine today).
    """

    kind: Literal["attack_resolved", "movement_step", "spell_cast", "damage_taken"]
    actor: CombatantState
    target: CombatantState | None = None
    damage: int = 0
    action: Action | None = None


@dataclass(frozen=True)
class CombatResult:
    """Outcome of a full battle: winner, rounds, log, and per-combatant stats."""

    winner: str | None
    rounds: int
    transcript: tuple[str, ...]
    stats: dict[str, CombatantStats]


@dataclass
class _LiveStats:
    hits: int = 0
    crits: int = 0
    damage_dealt: int = 0
    damage_taken: int = 0


@dataclass
class _ManeuverRoll:
    """Roll context shared by all combat-maneuver handlers."""
    roll: int
    attacker_cmb: int
    total: int
    target_cmd: int
    success: bool


class CombatEngine:
    """Runs one battle to completion on a grid with a single RNG stream."""

    def __init__(
        self,
        rng: Rng,
        grid: Grid,
        states: list[CombatantState],
        *,
        round_cap: int = 100,
        policy: Policy | None = None,
        llm_policy: LLMPolicy | None = None,
        spell_registry: dict[str, SpellSpec] | None = None,
        reaction_policy: ReactionPolicy | None = None,
        monsters_die_at_zero: bool = False,
    ) -> None:
        if policy is not None and llm_policy is not None:
            msg = "policy and llm_policy are mutually exclusive"
            raise ValueError(msg)
        self._rng = rng
        self._grid = grid
        self._states = states
        self._round_cap = round_cap
        if llm_policy is not None:
            self._policy = self._llm_adapter(llm_policy)
        else:
            self._policy = policy if policy is not None else default_policy
        self._spell_registry = spell_registry or {}
        self._reaction_policy = reaction_policy
        self._monsters_die_at_zero = monsters_die_at_zero
        if monsters_die_at_zero:
            for st in states:
                self._apply_simple_monster_death(st)
        self._in_reaction = False
        # The combatant currently executing `_take_turn` (None between turns):
        # lets an immediate action tell in-turn from off-turn use (SRD
        # Immediate Actions).
        self._turn_actor: CombatantState | None = None
        self._transcript: list[str] = []
        self._stats: dict[str, _LiveStats] = {s.combatant.id: _LiveStats() for s in states}
        self._current_round = 0
        self._aoo_used: dict[str, int] = {}
        # Movement-triggered opportunities already taken this round, keyed by
        # mover id: PF1e counts leaving several squares threatened by the same
        # opponent as ONE opportunity for that opponent.
        self._move_aoo_provoked: dict[str, set[str]] = {}
        self._initiative_keys: dict[str, tuple[float, int, int]] = {}
        self._pending_summons: list[CombatantState] = []
        # True while the surprise round runs (SRD "Surprise"): the turn filter
        # then degrades every aware combatant's sequence to a single standard
        # OR move action plus free actions.
        self._surprise_round = False

    @property
    def states(self) -> list[CombatantState]:
        """The live list of combatant states in initiative order."""
        return self._states

    @property
    def grid(self) -> Grid:
        """The combat grid."""
        return self._grid

    @property
    def spell_registry(self) -> dict[str, SpellSpec]:
        """The spell registry used for spell lookups."""
        return self._spell_registry

    def _apply_simple_monster_death(self, state: CombatantState) -> None:
        """Opt-in X5 rule: with ``monsters_die_at_zero``, monster combatants
        die at hp <= 0 (no dying/disabled band); PCs are never marked."""
        if self._monsters_die_at_zero and not _is_pc_combatant(state.combatant):
            state.dies_at_zero = True

    def _llm_adapter(self, llm_policy: LLMPolicy) -> Policy:
        """Wrap an ``LLMPolicy`` into a ``Policy``.

        At the point of invocation (``actions = self._policy(self, state)`` in
        ``_take_turn``), the Observation is built for the current state and
        delegated to ``llm_policy(observation, state)``. The adapter consumes
        no RNG and mutates no state.
        """

        def adapter(_engine: CombatEngine, state: CombatantState) -> tuple[Action, ...]:
            observation = self._build_observation(state)
            return llm_policy(observation, state)

        return adapter

    def _build_observation(self, state: CombatantState) -> Observation:
        """Build a frozen, serializable snapshot of the current combat state.

        Pure read: never mutates state nor consumes RNG. ``state`` is the
        acting combatant (the one whose turn it is).
        """
        acting_index = self._states.index(state)
        combatants = tuple(self._combatant_snapshot(s) for s in self._states)
        pairs = tuple(
            self._pair_snapshot(state, target)
            for target in self._states
            if target is not state
        )
        terrain = tuple(
            tuple(self._grid.terrain_at((r, c)).type for c in range(self._grid.width))
            for r in range(self._grid.height)
        )
        has_elevation = getattr(self._grid, "_elevation", None) is not None
        if has_elevation:
            elevation = tuple(
                tuple(
                    self._grid.elevation_at((r, c)) for c in range(self._grid.width)
                )
                for r in range(self._grid.height)
            )
        else:
            elevation = ()
        threatened = self._threat_grid(state)
        ranged_threatened = self._ranged_threat_grid(state)
        terrain_semantics = self._terrain_semantics()
        condition_definitions = tuple(
            (name, _condition_definition_dict(cond))
            for name, cond in sorted(CONDITIONS_BY_NAME.items())
        )
        initiative_order = tuple(
            s.combatant.id for s in self._build_round_order()
        )
        return Observation(
            round=self._current_round,
            acting_combatant=acting_index,
            combatants=combatants,
            pairs=pairs,
            terrain=terrain,
            elevation=elevation,
            threatened=threatened,
            ranged_threatened=ranged_threatened,
            terrain_semantics=terrain_semantics,
            condition_definitions=condition_definitions,
            initiative_order=initiative_order,
        )

    def _threat_grid(self, state: CombatantState) -> tuple[tuple[bool, ...], ...]:
        """Build the height x width bool grid of cells threatened by enemies.

        Union of ``threatened_squares(e)`` for every enemy ``e`` of ``state``
        (active, opposite side, with a usable melee weapon). The union is
        bounded to the grid: cells produced by the public helper that lie
        outside the map are dropped (helper output is in 5-ft-square coords
        and may overflow on small maps).
        """
        enemies = (
            s for s in self._states
            if s is not state
            and s.active
            and s.side != state.side
            and any(w.kind == "melee" for w in s.usable_attacks())
        )
        threatened: set[Pos] = set()
        for enemy in enemies:
            threatened |= self.threatened_squares(enemy)
        return tuple(
            tuple((r, c) in threatened for c in range(self._grid.width))
            for r in range(self._grid.height)
        )

    def _ranged_threat_grid(self, state: CombatantState) -> tuple[tuple[bool, ...], ...]:
        """Build the height x width bool grid of cells under enemy ranged fire.

        Sibling of ``_threat_grid`` for RANGED weapons: the union over every
        active enemy ``e`` of ``state`` (opposite side) of the cells each of
        e's usable ranged-style weapons can reach (see
        ``_cell_under_ranged_fire``). Bounded to the grid. Read-only, no RNG.
        PF1e ranged weapons grant no attacks of opportunity — this is a
        tactical field-of-fire map, not an AoO threat; the melee
        ``threatened`` grid is unchanged by it.
        """
        covered = self._ranged_covered_cells(state)
        return tuple(
            tuple((r, c) in covered for c in range(self._grid.width))
            for r in range(self._grid.height)
        )

    def _ranged_covered_cells(self, state: CombatantState) -> set[Pos]:
        """Cells covered by any usable ranged-style weapon of state's enemies."""
        covered: set[Pos] = set()
        for enemy in self._states:
            if enemy is state or not enemy.active or enemy.side == state.side:
                continue
            weapons = [w for w in enemy.usable_attacks() if self._is_ranged_attack(w)]
            if not weapons:
                continue
            occupied = enemy.occupied_cells()
            for r in range(self._grid.height):
                for c in range(self._grid.width):
                    cell = (r, c)
                    if cell not in covered and self._cell_under_ranged_fire(
                        occupied, cell, weapons
                    ):
                        covered.add(cell)
        return covered

    def _cell_under_ranged_fire(
        self,
        occupied: frozenset[Pos],
        cell: Pos,
        weapons: list[AttackSpec],
    ) -> bool:
        """True if some ranged weapon in ``weapons`` reaches ``cell`` with LoE.

        Reach uses the same maximum-range rule as ``_weapon_usable_against``:
        ``range_increment_ft`` x 10 increments (x 5 for touch), measured from
        the shooter's closest occupied cell under the 5-10-5 rule; the line of
        effect runs from the shooter's footprint to the bare cell.
        """
        dist_ft = (
            min(self._grid.distance(from_cell, cell) for from_cell in occupied)
            * _SQUARE_FT
        )
        for weapon in weapons:
            increment = weapon.range_increment_ft
            if increment is None:
                continue
            max_increments = (
                _MAX_TOUCH_RANGE_INCREMENTS
                if weapon.kind == "touch"
                else _MAX_RANGE_INCREMENTS
            )
            if dist_ft > increment * max_increments:
                continue
            if has_line_of_effect_cells(self._grid, occupied, frozenset({cell})):
                return True
        return False

    def _terrain_semantics(self) -> tuple[dict[str, object], ...]:
        """One dict per distinct ``TerrainType`` on the map (sorted by type).

        Derived by deduplicating ``grid.terrain_at`` over the entire map: the
        Grid stores resolved ``TerrainType`` objects in ``_cells`` but does
        not expose ``MapSpec.legend`` directly, so iterating the cells is
        the safest source. The Grid is guaranteed to hold at least one
        cell (constructor enforces non-empty ``cells``).
        """
        seen: dict[str, TerrainType] = {}
        for r in range(self._grid.height):
            for c in range(self._grid.width):
                cell = self._grid.terrain_at((r, c))
                seen.setdefault(cell.type, cell)
        return tuple(
            {
                "type": cell.type,
                "move_cost": cell.move_cost,
                "blocks_los": cell.blocks_los,
                "cover": cell.cover,
                "cover_bonus": cell.cover_bonus,
            }
            for cell in (seen[name] for name in sorted(seen))
        )

    def _combatant_snapshot(self, state: CombatantState) -> dict[str, object]:
        """One per-combatant dict for the Observation (frozen copies)."""
        conditions = tuple(
            (c.condition.name, c.rounds_left) for c in state.active_conditions
        ) + tuple((c.name, 0) for c in state.conditions)
        resources = dict(state.resources_left)
        for level, count in state.spell_slots_left.items():
            resources[f"spell_slot_{level}"] = count
        dr = None
        if state.combatant.dr is not None:
            dr = {
                "amount": state.combatant.dr.amount,
                "bypass": ",".join(sorted(state.combatant.dr.bypass)),
            }
        return {
            "id": state.combatant.id,
            "side": state.side,
            "pos": state.pos,
            "occupied_cells": tuple(sorted(state.occupied_cells())),
            "hp": state.hp,
            "hp_max": state.combatant.hp_max,
            "active": state.active,
            "dead": state.dead,
            "dying": state.hp < 0 and not state.dead,
            "stabilized": state.stabilized_hp is not None,
            "conditions": conditions,
            "resources_left": resources,
            "weapon_broken": tuple(sorted(state.weapon_broken)),
            "weapon_stolen": tuple(sorted(state.weapon_stolen)),
            "weapon_dropped": tuple(sorted(state.weapon_dropped)),
            "grappled_with": state.grappled_with,
            "moved_this_turn": state.moved_this_turn,
            "power_attack": state.power_attack,
            "defensive_ac_bonus": state.defensive_ac_bonus,
            "fight_defensively": state.fight_defensively,
            "aid_attack_bonus": state.aid_attack_bonus,
            "aid_ac_bonus": state.aid_ac_bonus,
            "running": state.running,
            "bleed_damage": state.bleed_damage,
            "recurring_damage": [
                {
                    "formula": dice_to_str(entry.formula),
                    "types": tuple(sorted(entry.types)),
                    "rounds_left": entry.rounds_left,
                }
                for entry in state.recurring_damage
            ],
            "aoo_remaining": max(
                0,
                self._aoo_allowance(state) - self._aoo_used.get(state.combatant.id, 0),
            ),
            "name": state.combatant.name,
            "level": state.combatant.level,
            "size": state.combatant.size,
            "natural_reach_ft": _SIZE_NATURAL_REACH_FT.get(state.combatant.size, 5),
            "aware": state.combatant.aware,
            "creature_type": state.combatant.creature_type,
            "bab": state.combatant.bab,
            "initiative_mod": state.combatant.initiative_mod,
            "initiative_total": self._initiative_keys.get(
                state.combatant.id, (0, 0, -999)
            )[0],
            "casting_ability": (
                state.combatant.casting_ability if state.combatant.spells else None
            ),
            "dr": dr,
            "abilities": {
                "str": state.combatant.abilities.str_score,
                "dex": state.combatant.abilities.dex_score,
                "con": state.combatant.abilities.con_score,
                "int": state.combatant.abilities.int_score,
                "wis": state.combatant.abilities.wis_score,
                "cha": state.combatant.abilities.cha_score,
            },
            "skills": {
                name: {
                    "rank": rank.rank,
                    "class_skill": rank.class_skill,
                    "armor_penalty": rank.armor_penalty,
                }
                for name, rank in state.combatant.skills.items()
                if rank.rank > 0
            },
            "metamagic_feats": tuple(sorted(state.combatant.metamagic_feats)),
            "weapon_damage": dict(state.weapon_damage),
            "summon_duration": state.summon_duration or None,
            "immediate_used": state.immediate_used,
            "deed_up_close_and_deadly": state.deed_up_close_and_deadly,
            "active_buffs": tuple(
                {
                    "source": buff.source,
                    "rounds_left": buff.rounds_left,
                    "mods": tuple(
                        {
                            "target": mod.target,
                            "value": mod.value,
                            "bonus_type": mod.bonus_type,
                        }
                        for mod in buff.modifiers
                    ),
                }
                for buff in state.active_buffs
            ),
            "speed_land_ft": state.combatant.speed_land_ft,
            "speed_fly_ft": state.combatant.speed_fly_ft,
            "speed_effective_ft": _speed_ft(state),
            "ac": {
                "total": state.combatant.ac.total,
                "touch": state.combatant.ac.touch,
                "flat_footed": state.combatant.ac.flat_footed,
            },
            "saves": {
                "fort": state.combatant.saves.fort,
                "ref": state.combatant.saves.ref,
                "will": state.combatant.saves.will,
            },
            "cmb": self._maneuver_cmb(state),
            "cmd": self._maneuver_cmd(state),
            "attacks": tuple(
                {
                    "id": attack.id,
                    "name": attack.name,
                    "kind": attack.kind,
                    "attack_bonus": attack.attack_bonus,
                    "damage": tuple(
                        {
                            "formula": dice_to_str(component.formula),
                            "types": tuple(component.types),
                        }
                        for component in attack.damage
                    ),
                    "damage_bonus": attack.damage_bonus,
                    "crit_range": attack.crit_range,
                    "crit_mult": attack.crit_mult,
                    "reach_ft": attack.reach_ft,
                    "range_increment_ft": attack.range_increment_ft,
                    "count": attack.count,
                    "firearm": attack.firearm,
                }
                for attack in state.combatant.attacks
            ),
            "features": tuple(sorted(f.name for f in state.combatant.features)),
            "feature_details": tuple(
                {
                    "name": feature.name,
                    "category": feature.category,
                    "source_detail": feature.source_detail,
                    "effects": tuple(
                        _stat_modifier_dict(mod) for mod in feature.effects
                    ),
                }
                for feature in sorted(
                    state.combatant.features, key=lambda f: f.name
                )
            ),
            "spells": tuple(
                self._spell_snapshot(state, name) for name in state.combatant.spells
            ),
            "spell_resistance": state.combatant.spell_resistance,
            "resistances": dict(state.combatant.resistances),
            "immunities": tuple(state.combatant.immunities),
            "sneak_dice": (
                (state.combatant.level + 1) // 2
                if self._has_feat(state, _SNEAK_ATTACK_FEATURE)
                else 0
            ),
            "engaged_in_melee": self._engaged_in_melee(state),
            "last_turn_results": tuple(
                {"kind": r.kind, "ok": r.ok, "reason": r.reason}
                for r in state.last_action_results
            ),
            "readied": (
                {"kind": state.readied.kind, "trigger": state.readied_trigger}
                if state.readied is not None
                else None
            ),
            "pending_cast": (
                None
                if state.pending_cast is None
                else {
                    "spell_name": state.pending_cast.spell_name,
                    "target_id": state.pending_cast.target_id,
                    "slot_level": state.pending_cast.slot_level,
                }
            ),
        }

    def _pair_snapshot(
        self, state: CombatantState, target: CombatantState
    ) -> dict[str, object]:
        """One per-pair dict (acting combatant x target) for the Observation."""
        distance_ft = self.creature_distance(state, target) * _SQUARE_FT
        weapon = self.weapon_for(state, target)
        weapon_name = weapon.name if weapon is not None else None
        range_penalty = (
            self.range_penalty(weapon, distance_ft) if weapon is not None else 0
        )
        charge = self.can_charge(state, target)
        can_charge = charge is not None and charge.weapon is not None
        occupied = state.occupied_cells()
        line_of_effect = has_line_of_effect_cells(
            self._grid, occupied, target.occupied_cells()
        )
        weapon_reason = self._weapon_failure_reason(
            state, weapon, line_of_effect=line_of_effect
        )
        charge_reason: str | None = None
        if not can_charge:
            # can_charge() returns None only when no melee weapon is usable.
            charge_reason = charge.reason if charge is not None else _REASON_NO_WEAPON
        target_threatens_me = bool(
            target.active
            and any(w.kind == "melee" for w in target.usable_attacks())
            and self.threatened_squares(target) & occupied
        )
        threatening_enemies: set[str] = set()
        for cell in occupied:
            for enemy in self.enemies_threatening(state, cell):
                threatening_enemies.add(enemy.combatant.id)
        cover_bonus = 0
        if weapon is not None:
            others = frozenset(
                cell
                for s in self._states
                if s.active and s is not state and s is not target
                for cell in s.occupied_cells()
            )
            cover_bonus = cover_bonus_cells(
                self._grid,
                state.occupied_cells(),
                target.occupied_cells(),
                ranged=self._is_ranged_attack(weapon),
                occupied=others,
            )
        return {
            "target_index": self._states.index(target),
            "distance_ft": distance_ft,
            "weapon_for": weapon_name,
            "weapon_reason": weapon_reason,
            "range_penalty": range_penalty,
            "can_charge": can_charge,
            "charge_reason": charge_reason,
            "can_step5_to_attack": self.can_step5_to_attack(state, target),
            "has_line_of_effect": line_of_effect,
            "flanking": self._flanking_bonus(state, target) > 0,
            "movement_cost_ft": self.movement_cost_ft(state, target),
            "target_threatens_me": target_threatens_me,
            "enemies_threatening_me": len(threatening_enemies),
            "cover_bonus": cover_bonus,
        }

    def _weapon_failure_reason(
        self,
        attacker: CombatantState,
        weapon: AttackSpec | None,
        *,
        line_of_effect: bool,
    ) -> str | None:
        """Why ``weapon_for`` found no weapon against a target, or None if it did.

        U6b: the cause is drawn from the ``ACTION_RESULT_REASONS`` vocabulary
        — no usable weapon at all, no line of effect, or every usable weapon
        out of range — so a policy learns which obstacle to remove.
        """
        if weapon is not None:
            return None
        if not attacker.usable_attacks():
            return _REASON_NO_WEAPON
        if not line_of_effect:
            return _REASON_NO_LINE_OF_EFFECT
        return _REASON_OUT_OF_RANGE

    def _resolve_pending_cast(self, caster: CombatantState) -> None:
        """PF1e (SRD "Casting Time"): a one-round cast "comes into effect just
        before the beginning of your turn in the round after you began casting
        the spell. You then act normally after the spell is completed." The
        caster is busy casting through the intervening round: net hp lost
        between the start of the casting and this moment forces the
        injured-while-casting concentration check (CRB "Concentration":
        DC 10 + damage + spell level, no Combat Casting bonus) or the spell
        is lost.
        Bounded model (documented): interruption is measured as NET hp loss
        at resolution instead of a hook at every damage site, so healing in
        between can mask damage taken.
        """
        pending = caster.pending_cast
        if pending is None:
            return
        caster.pending_cast = None
        spell = self._spell_registry.get(pending.spell_name)
        if spell is None:
            return
        damage = max(0, pending.hp_at_cast - caster.hp)
        if damage > 0 and not self._check_concentration(
            caster, pending.slot_level, damage
        ):
            dc = self._concentration_dc(caster, pending.slot_level, damage)
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"one-round cast of {pending.spell_name} interrupted: "
                f"concentration check failed (DC {dc}), spell fizzles"
            )
            return
        self._log(
            f"round {self._current_round} {caster.combatant.id}: "
            f"finishes casting {pending.spell_name}"
        )
        target = (
            next(
                (s for s in self._states if s.combatant.id == pending.target_id),
                None,
            )
            if pending.target_id is not None
            else None
        )
        self._deliver_cast(
            caster, target, spell, pending.spell_name, pending.center_pos,
            metamagic=pending.metamagic, slot_level=pending.slot_level,
        )

    def _resolve_held_charge(self, caster: CombatantState) -> None:
        """PF1e (SRD "Cast a Spell - Touch Attacks", Holding the Charge): a
        missed melee touch attack leaves the charge held - "You can continue
        to make touch attacks round after round." Re-attempt it at the start
        of each of the caster's later turns while the held target is alive
        and within the spell's touch range; a miss re-sets the charge, a hit
        delivers through the normal gates, and an SR suppression consumes it
        (the spell discharges into the resistance).

        Documented simplifications: the re-attempt is engine-driven at turn
        start instead of costing a standard action; discharge-on-any-touch
        and unarmed-attack interactions while holding are not modeled; the
        charge is not exposed in the Observation."""
        held = caster.held_charge
        if held is None:
            return
        spell = self._spell_registry.get(held.spell_name)
        if spell is None:
            caster.held_charge = None
            return
        target = next(
            (s for s in self._states if s.combatant.id == held.target_id), None
        )
        if target is None or not target.active:
            caster.held_charge = None
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"held charge of {held.spell_name} dissipates (target gone)"
            )
            return
        dist_ft = self.creature_distance(caster, target) * _SQUARE_FT
        if dist_ft > spell_range_ft(spell, caster.combatant.level):
            return  # out of reach: still holding, re-attempt a later turn
        caster.held_charge = None  # consumed by this attempt; a miss re-sets
        self._log(
            f"round {self._current_round} {caster.combatant.id}: "
            f"re-attempts held charge {held.spell_name}"
        )
        self._deliver_cast(
            caster, target, spell, held.spell_name, None,
            metamagic=held.metamagic, slot_level=held.slot_level,
        )

    def _forfeit_pending_cast(self, caster: CombatantState) -> None:
        """PF1e (SRD "Casting Time"): "you must continue the concentration
        from the current round to just before your turn in the next round
        [...] If you lose concentration before the casting is complete, you
        lose the spell." A caster that reaches its initiative slot unable to
        act (dead or dying) never gets to resolve the casting."""
        pending = caster.pending_cast
        if pending is None:
            return
        caster.pending_cast = None
        self._log(
            f"round {self._current_round} {caster.combatant.id}: "
            f"one-round cast of {pending.spell_name} lost (cannot act)"
        )

    def _take_turn(self, state: CombatantState) -> bool:
        """Execute one combatant's full turn; return True if the battle is over."""
        # A freshly-delayed combatant is re-inserted into the round order and
        # ``_take_turn`` runs a second time in the SAME round. The start-of-turn
        # block below (duration decrement, the bleed/confusion/cant_act gate,
        # the fear aura and the per-turn flag resets) must run only ONCE per
        # round, so it is skipped when ``delayed_this_round`` is already set at
        # entry (it was cleared at round start and only a delay action sets it).
        # The delayed turn still gets its policy call, budget and execution.
        if not state.delayed_this_round:
            self._expire_readied_action(state)
            self._decrement_durations(state)
            # SRD "Casting Time": the one-round cast "comes into effect just
            # before the beginning of your turn" — resolved here, before the
            # start-of-turn gate, then the turn proceeds normally.
            self._resolve_pending_cast(state)
            gate = self._turn_gate(state)
            if gate is not None:
                # A start-of-turn effect (bleed, confusion, cant_act) forfeited
                # the turn; the value is the battle-over flag.
                state.last_action_results = []
                return gate
            # SRD "Holding the Charge": a held touch spell is re-attempted at
            # the start of a later turn (before the caster acts).
            self._resolve_held_charge(state)
            self._apply_fear_aura(state)
            state.moved_this_turn = False
            state.power_attack = False
            state.defensive_ac_bonus = 0
            state.fight_defensively = False
            state.total_defense = False
            self._expire_aid_grants(state)
            state.running = False
            state.swift_used_this_turn = False
        original = self._policy(self, state)
        results: list[ActionResult] = []
        actions = self._filter_turn_actions(state, original, results)
        before = len(self._transcript)
        was_delayed = state.delayed_this_round
        disabled = self._is_disabled(state)
        self._turn_actor = state
        try:
            for action in actions:
                if not state.active:
                    break
                if state.swift_used_this_turn and (
                    _effective_slot(action, self._cast_time_of) == "swift"
                ):
                    # PF1e (SRD Immediate Actions): the in-turn immediate
                    # already spent this turn's swift slot.
                    results.append(
                        ActionResult(
                            kind=action.kind,
                            ok=False,
                            reason=_REASON_DOWNGRADED_IMMEDIATE_SWIFT,
                        )
                    )
                    continue
                results.append(self._execute(state, action))
                if disabled and state.hp == 0 and action.kind not in _DISABLED_MOVE_KINDS:
                    # PF1e (CRB, Disabled): completing a standard (or otherwise
                    # strenuous) action costs 1 hp — the creature slips to -1 and
                    # is dying. Simplification: if the action itself healed the
                    # creature above 0 hp the cost is not applied.
                    state.hp -= 1
                    self._log(
                        f"round {self._current_round} {state.combatant.id}: "
                        f"disabled: strenuous action costs 1 hp (hp 0 -> -1, dying)"
                    )
                if state.delayed_this_round and not was_delayed:
                    # A fresh delay forfeits the rest of the turn.
                    break
                if self._winner_side() is not None:
                    break
        finally:
            self._turn_actor = None
        if state.active and len(self._transcript) == before:
            self._log(f"round {self._current_round} {state.combatant.id}: wait")
        # Assigned at the END of the turn (never reset at the start): the
        # Observation is built inside the policy call at the START of the next
        # turn, so it must still see THIS turn's results at that moment.
        state.last_action_results = results
        return self._winner_side() is not None

    def _cast_time_of(self, action: Action) -> CastTime:
        """Resolve a cast_spell action's casting time from the registry.

        Unknown spell names (and non-cast actions) default to "standard".
        Future hook (out of scope here): for a spontaneous caster this
        closure would read state.combatant.spontaneous_caster and
        action.metamagic — a spontaneous cast with a non-empty metamagic
        feat and no Quickened Spell becomes full_round (unless the spell is
        already one_round or long). The Callable[[Action], CastTime]
        resolver signature already accommodates the state-aware variant.
        """
        spell = self._spell_registry.get(action.spell_name or "")
        return spell.cast_time if spell is not None else "standard"

    def _filter_turn_actions(
        self,
        state: CombatantState,
        actions: tuple[Action, ...],
        results: list[ActionResult],
    ) -> tuple[Action, ...]:
        """Downgrade the policy's action sequence to the legal action economy.

        Composition order: a cast-time pre-pass first drops every cast_spell
        whose spell has a long casting time (more than 1 round — the engine cannot
        schedule it within a turn; reported as downgraded:cast_time). Then
        the general per-turn budget (CRB, "Actions in Combat": one standard
        + one move, or one full-round, plus one swift; a move action may be
        taken instead of the standard) is enforced on every sequence, with
        each cast_spell occupying the slot of its resolved casting time. The
        condition-specific specializations then run on the budget-legal
        remainder (their output is a single action, so the budget never
        re-drops it). Swift consumed by an immediate action; PF1e (CRB,
        Disabled): a creature at exactly 0 hp is staggered — one move OR one
        standard action per round, no full-round actions (including
        full-round and one-round casts and spell_combat); nauseated: single
        move only. Dropped kinds are reported into ``results``.
        """
        schedulable = tuple(
            a
            for a in actions
            if not (a.kind == "cast_spell" and self._cast_time_of(a) == "long")
        )
        results.extend(
            ActionResult(kind="cast_spell", ok=False, reason=_REASON_DOWNGRADED_CAST_TIME)
            for _ in range(len(actions) - len(schedulable))
        )
        actions = schedulable
        # PF1e (SRD "Move Actions"): "If you have a base attack bonus of +1 or
        # higher, you may draw a weapon as a free action combined with a
        # regular move." The draw rides the turn's move action instead of
        # consuming the move slot.
        free_draw = state.combatant.bab >= 1 and any(
            a.kind == "move" for a in actions
        )
        kept = _action_economy_filter(
            actions, cast_time=self._cast_time_of, free_draw=free_draw
        )
        results.extend(
            ActionResult(
                kind=kind, ok=False, reason=_REASON_DOWNGRADED_ACTION_ECONOMY
            )
            for kind in _dropped_kinds_multiset(actions, kept)
        )
        actions = kept
        if self._surprise_round:
            # PF1e (SRD "Surprise"): the surprise round allowance replaces the
            # normal budget — one standard OR move action plus free actions.
            kept = _surprise_filter(
                actions, cast_time=self._cast_time_of, free_draw=free_draw
            )
            results.extend(
                ActionResult(kind=kind, ok=False, reason=_REASON_DOWNGRADED_SURPRISE)
                for kind in _dropped_kinds(actions, kept)
            )
            return kept
        if state.immediate_used:
            kept = _without_swift_bonus(actions, cast_time=self._cast_time_of)
            results.extend(
                ActionResult(kind=kind, ok=False, reason=_REASON_DOWNGRADED_IMMEDIATE_SWIFT)
                for kind in _dropped_kinds(actions, kept)
            )
            actions = kept
            state.immediate_used = False
        if self._is_staggered_limited(state):
            kept = _staggered_filter(
                actions, cast_time=self._cast_time_of, free_draw=free_draw
            )
            results.extend(
                ActionResult(kind=kind, ok=False, reason=_REASON_DOWNGRADED_STAGGERED)
                for kind in _dropped_kinds(actions, kept)
            )
            return kept
        if self.has_condition_flag(state, "cant_attack"):
            kept = _nauseated_filter(actions)
            results.extend(
                ActionResult(kind=kind, ok=False, reason=_REASON_DOWNGRADED_NAUSEATED)
                for kind in _dropped_kinds(actions, kept)
            )
            return kept
        return actions

    def has_condition_flag(self, state: CombatantState, flag: str) -> bool:
        """Check if any active condition has the given behavioral flag set to True."""
        for ac in state.active_conditions:
            if getattr(ac.condition, flag, False):
                return True
        # Also check old conditions field for backwards compatibility
        return any(getattr(cond, flag, False) for cond in state.conditions)

    def _has_condition_named(self, state: CombatantState, name: str) -> bool:
        """Check if the state has an active or old condition with the given name."""
        return (
            any(ac.condition.name == name for ac in state.active_conditions)
            or any(cond.name == name for cond in state.conditions)
        )

    def _is_disabled(self, state: CombatantState) -> bool:
        """PF1e (CRB, Effects of Death): a living creature at exactly 0 hp is
        disabled — staggered, half speed, and a strenuous action costs 1 hp."""
        return state.hp == 0

    def _is_staggered_limited(self, state: CombatantState) -> bool:
        """True when the creature is limited to one move OR one standard
        action per round (CRB "Conditions — Staggered"; a disabled creature
        at 0 hp is staggered). Such a creature cannot take full-round actions
        — except Restricted Withdraw (SRD "Full-Round Actions"), which it may
        take as a standard action moving up to its speed."""
        return self._is_disabled(state) or self._has_condition_named(
            state, "staggered"
        )

    def _is_helpless(self, state: CombatantState) -> bool:
        """PF1e (CRB): helpless = paralyzed, held, bound, sleeping, unconscious.

        Stunned is NOT helpless. A helpless creature has effective Dexterity 0
        and melee attackers gain +4 (resolve_attack)."""
        return any(
            self._has_condition_named(state, name)
            for name in _HELPLESS_CONDITION_NAMES
        )

    def _modifier_condition_holds(
        self,
        _state: CombatantState,
        condition_name: str,
        *,
        weapon: AttackSpec | None = None,
        dist_ft: int | None = None,
        save_descriptors: frozenset[str] = frozenset(),
    ) -> bool:
        """Evaluate whether a StatModifier's runtime condition holds.

        Unknown/unresolvable conditions return False (modifier excluded).
        Supported: "target_within_30ft_ranged" (ranged-style weapon, <= 30 ft),
        "axe" (weapon name contains "axe"), and save-descriptor names (fear,
        cold, ...) that are present in the save's descriptor set.
        """
        if condition_name == "target_within_30ft_ranged":
            return (
                weapon is not None
                and dist_ft is not None
                and self._is_ranged_attack(weapon)
                and dist_ft <= _POINT_BLANK_RANGE_FT
            )
        if condition_name == "axe":
            return weapon is not None and "axe" in weapon.name.lower()
        if condition_name in _SAVE_DESCRIPTOR_CONDITIONS:
            return condition_name in save_descriptors
        return False

    def _get_speed_mult(self, state: CombatantState) -> float:
        """Get the minimum speed multiplier from all active conditions.

        PF1e (CRB, Disabled): a disabled creature (exactly 0 hp) moves at
        half speed.
        """
        speed_mult = 0.5 if state.hp == 0 else 1.0
        for ac in state.active_conditions:
            if ac.condition.speed_mult != 1.0:
                speed_mult = min(speed_mult, ac.condition.speed_mult)
        for cond in state.conditions:
            if cond.speed_mult != 1.0:
                speed_mult = min(speed_mult, cond.speed_mult)
        return speed_mult

    def _decrement_durations(self, state: CombatantState) -> None:
        """Decrement duration rounds for buffs and conditions; remove expired ones.

        A bleeding condition's last round ends with its bleed tick: the DoT
        lives on ``bleed_damage`` (CRB Conditions — bleeding), so the final
        damage is applied as the last condition instance expires and the
        field is cleared (mirrors ``_stop_bleeding`` on healing).
        """
        state.active_buffs[:] = [
            ActiveBuff(modifiers=b.modifiers, rounds_left=b.rounds_left - 1, source=b.source)
            for b in state.active_buffs
            if b.rounds_left > 1
        ]
        kept_conditions = [
            ActiveCondition(condition=c.condition, rounds_left=c.rounds_left - 1, source=c.source)
            for c in state.active_conditions
            if c.rounds_left > 1
        ]
        bleeding_expired = (
            any(ac.condition.name == "bleeding" for ac in state.active_conditions)
            and not any(ac.condition.name == "bleeding" for ac in kept_conditions)
        )
        state.active_conditions[:] = kept_conditions
        if bleeding_expired and state.bleed_damage > 0:
            self._apply_bleed_damage(state)
            state.bleed_damage = 0

    def _turn_gate(self, state: CombatantState) -> bool | None:
        """Start-of-turn effects: bleed tick, recurring spell damage, confused
        d% roll, cant_act flag.

        Returns None when the turn proceeds to the policy; otherwise the turn
        is forfeited and the value is the battle-over flag.
        """
        self._apply_bleed_damage(state)
        self._apply_recurring_damage(state)
        if not state.active:
            # Bleeding / acid knocked the combatant out (dying or dead); the
            # winner check covers the death case.
            return self._winner_side() is not None
        confused_over = self._apply_confusion(state)
        if confused_over is not None:
            return confused_over
        if self.has_condition_flag(state, "cant_act"):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot act)")
            return self._winner_side() is not None
        return None

    def _apply_bleed_damage(self, state: CombatantState) -> None:
        """PF1e bleeding: take ``bleed_damage`` at the beginning of the turn (CRB)."""
        if state.bleed_damage <= 0:
            return
        old_hp = state.hp
        state.hp -= state.bleed_damage
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"bleed {state.bleed_damage} (hp {old_hp}->{state.hp})"
        )

    def _apply_recurring_damage(self, state: CombatantState) -> None:
        """PF1e recurring spell damage (S2c, Acid Arrow): at the start of the
        owner's turn each active source rolls its dice, is reduced by energy
        resistance/immunity (never DR — it is spell damage), deals that damage,
        then loses one round; sources that reach 0 rounds are cleared."""
        if not state.recurring_damage:
            return
        remaining: list[RecurringDamage] = []
        for entry in state.recurring_damage:
            raw = entry.formula.roll(self._rng)
            dmg = self._apply_energy_resistance(raw, entry.types, state)
            old_hp = state.hp
            state.hp -= dmg
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"{entry.source} {dmg} (hp {old_hp}->{state.hp})"
            )
            if entry.rounds_left > 1:
                remaining.append(
                    RecurringDamage(
                        formula=entry.formula,
                        types=entry.types,
                        rounds_left=entry.rounds_left - 1,
                        source=entry.source,
                    )
                )
        state.recurring_damage[:] = remaining

    def _apply_confusion(self, state: CombatantState) -> bool | None:
        """PF1e confused: roll d% at the start of the turn to act randomly (CRB).

        Returns None when the subject acts normally (01-25, the turn proceeds);
        otherwise the turn is consumed and the value is the battle-over flag.
        Simplification: the "if attacked, attack the attacker" clause is
        reduced to attacking the nearest creature.
        """
        if not self._has_condition_named(state, "confused"):
            return None
        pct = self._rng.d100()
        if pct <= _CONFUSED_ACT_NORMAL_MAX:
            return None
        if pct <= _CONFUSED_BABBLE_MAX:
            self._log(
                f"round {self._current_round} {state.combatant.id}: confused: babbles"
            )
        elif pct <= _CONFUSED_SELF_DAMAGE_MAX:
            self._confused_self_damage(state)
        else:
            self._confused_attack_nearest(state)
        return self._winner_side() is not None

    def _confused_self_damage(self, state: CombatantState) -> None:
        """Confused 51-75: 1d8 + Str modifier damage to self with item in hand."""
        dmg = self._rng.roll_die(8) + state.combatant.abilities.str_mod
        old_hp = state.hp
        state.hp -= dmg
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"confused: hits self for {dmg} (hp {old_hp}->{state.hp})"
        )

    def _confused_attack_nearest(self, state: CombatantState) -> None:
        """Confused 76-100: attack the nearest creature (friend OR foe) once."""
        target = self._nearest_creature(state)
        weapon = None
        if target is not None:
            weapon = next(
                (
                    w
                    for w in state.usable_attacks()
                    if w.kind == "melee" and self._melee_weapon_usable(state, target, w)
                ),
                None,
            )
        if target is None or weapon is None:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"confused: attacks nearest but nothing in reach"
            )
            return
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"confused: attacks {target.combatant.id}"
        )
        self._single_attack(state, target, weapon)

    def _nearest_creature(self, state: CombatantState) -> CombatantState | None:
        """Closest active creature — friend OR foe — by grid distance."""
        others = [s for s in self._states if s is not state and s.active]
        if not others:
            return None
        return min(
            others,
            key=lambda s: (self.creature_distance(state, s), self._states.index(s)),
        )

    def _stop_bleeding(self, state: CombatantState) -> None:
        """PF1e: applying a spell that cures hit point damage stops bleeding (CRB).

        Simplification: the DC 15 Heal check alternative is not modeled
        (the engine has no Heal skill action).
        """
        state.bleed_damage = 0
        state.active_conditions[:] = [
            ac for ac in state.active_conditions if ac.condition.name != "bleeding"
        ]
        state.conditions[:] = [
            cond for cond in state.conditions if cond.name != "bleeding"
        ]

    def run(self) -> CombatResult:
        """Run the battle and return the final result and transcript."""
        self._roll_initiative()
        if self._surprise_round_applies():
            self._run_surprise_round()
        round_no = 1
        while round_no <= self._round_cap:
            self._current_round = round_no
            self._aoo_used.clear()
            self._move_aoo_provoked.clear()
            self._expire_summons()
            if self._run_round():
                break
            round_no += 1
        winner = self._winner_side()
        if winner is not None:
            self._log(f"battle over: {winner} win in {round_no} rounds")
        else:
            self._log(f"battle over: draw after {self._round_cap} rounds")
        stats = {cid: CombatantStats(**asdict(live)) for cid, live in self._stats.items()}
        return CombatResult(
            winner=winner,
            rounds=round_no if winner is not None else self._round_cap,
            transcript=tuple(self._transcript),
            stats=stats,
        )

    def _surprise_round_applies(self) -> bool:
        """PF1e (SRD "Surprise"): "If some but not all of the combatants are
        aware of their opponents, a surprise round happens before regular
        rounds begin"; if no one or everyone is surprised, none occurs."""
        active = [s for s in self._states if s.active]
        return any(not s.combatant.aware for s in active) and any(
            s.combatant.aware for s in active
        )

    def _run_surprise_round(self) -> None:
        """PF1e (SRD "Surprise"): one partial round before round 1. In
        initiative order (highest to lowest), aware combatants each take a
        standard OR move action plus free actions (``_surprise_filter``);
        "Combatants who are unaware at the start of battle don't get to act
        in the surprise round."
        Simplification: unaware combatants are not flagged flat-footed during
        the surprise round — the engine never injects the flat-footed
        condition itself (see README limitations).
        """
        self._current_round = 0
        self._aoo_used.clear()
        self._move_aoo_provoked.clear()
        self._log("surprise round")
        self._surprise_round = True
        try:
            for state in self._build_round_order():
                if not state.active:
                    continue
                if not state.combatant.aware:
                    self._log(
                        f"round 0 {state.combatant.id}: unaware — "
                        "no action in surprise round"
                    )
                    continue
                if self._take_turn(state):
                    return
        finally:
            self._surprise_round = False

    def _run_round(self) -> bool:
        """Execute one round; return True if the battle ended.

        The round order is mutable: a combatant that took a fresh delay action
        is re-inserted right before its ``delay_before`` target when that
        target is still ahead, otherwise at the end of the round.
        """
        for state in self._states:
            state.delayed_this_round = False
        order = self._build_round_order()
        i = 0
        while i < len(order):
            state = order[i]
            if not state.active:
                self._forfeit_pending_cast(state)
                self._process_dying(state)
                i += 1
                continue
            was_delayed = state.delayed_this_round
            if self._take_turn(state):
                return True
            if self._drive_pending_summons():
                return True
            i += 1
            if (
                state.delayed_this_round
                and not was_delayed
                and state not in order[i:]
            ):
                self._reinsert_delayed(order, i, state)
        self._pending_summons.clear()
        return self._winner_side() is not None

    def _reinsert_delayed(
        self, order: list[CombatantState], start: int, state: CombatantState
    ) -> None:
        """Put a freshly-delayed combatant back into the round order.

        Inserted immediately before its ``delay_before`` target if that target
        still has to act (search from ``start``); appended at the end otherwise.
        """
        insert_at = len(order)
        if state.delay_before is not None:
            for j in range(start, len(order)):
                if order[j].combatant.id == state.delay_before:
                    insert_at = j
                    break
        order.insert(insert_at, state)

    def _drive_pending_summons(self) -> bool:
        """Give summoned creatures their turn immediately; return True if battle ended."""
        while self._pending_summons:
            summoned = self._pending_summons.pop(0)
            if (
                summoned in self._states
                and summoned.active
                and self._take_turn(summoned)
            ):
                return True
        return False

    def _process_dying(self, state: CombatantState) -> None:
        """Advance the dying condition on the creature's own initiative slot.

        PF1e dying: a combatant below 0 hp but not dead is unconscious and, on
        its turn each round, makes a DC 10 Constitution check
        (d20 + Con modifier - negative hp total); a natural 20 auto-succeeds.
        Failure bleeds 1 more hp; success stabilizes (no further loss while
        stable). New damage below the stabilizing hp resumes dying; healing to
        hp >= 0 resets stabilization for any future downing. A creature taking
        continuous damage (bleed) instead ticks the bleed and AUTOMATICALLY
        FAILS the check (CRB, Stable Characters and Recovery).
        """
        if state.dead:
            return
        if state.hp >= 0:
            state.stabilized_hp = None
            return
        if state.stabilized_hp is not None:
            if state.hp >= state.stabilized_hp:
                return
            state.stabilized_hp = None
        # PF1e (CRB, Stable Characters and Recovery): "Characters taking
        # continuous damage, such as from an acid arrow or a bleed effect,
        # automatically fail all Constitution checks made to stabilize. Such
        # characters lose 1 hit point per round in addition to the continuous
        # damage." This is the inactive creature's once-per-round slot (the
        # active path already ticked bleed in _turn_gate), so the bleed damage
        # is applied here and the d20 check is skipped (auto-fail).
        if state.bleed_damage > 0:
            self._apply_bleed_damage(state)
            hp_before = state.hp
            state.hp -= 1
            self._log(
                f"round {self._current_round} {state.combatant.id}: dying — continuous "
                f"damage auto-fails the Constitution check, loses 1 hp "
                f"(hp {hp_before} -> {state.hp})"
            )
            return
        con_mod = (state.combatant.abilities.con_score - 10) // 2
        penalty = -state.hp
        roll = self._rng.d20()
        total = roll + con_mod - penalty
        check = f"d20({roll}) + CON({con_mod}) - {penalty} = {total} vs DC {_DYING_DC}"
        if roll == _NATURAL_TWENTY or total >= _DYING_DC:
            state.stabilized_hp = state.hp
            nat20 = " — natural 20" if roll == _NATURAL_TWENTY else ""
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"stabilized ({check}{nat20})"
            )
        else:
            hp_before = state.hp
            state.hp -= 1
            self._log(
                f"round {self._current_round} {state.combatant.id}: dying — Constitution "
                f"check {check} failed, loses 1 hp (hp {hp_before} -> {state.hp})"
            )

    def _blocked(self, *exclude: CombatantState) -> frozenset[Pos]:
        """Occupied cells that block the mover (the first excluded state).

        Union of the active creatures' cells except those in ``exclude``. PF1e
        co-occupancy (SRD "Big and Little Creatures in Combat") lets a
        Tiny-or-smaller creature share a square with a strictly larger one, so
        a co-occupiable creature's cells do NOT block the mover (it may move
        through and end on them); two same-size creatures (or two Small-or-
        larger) never share, so their cells still block.
        """
        mover = exclude[0] if exclude else None
        blocked: set[Pos] = set()
        for s in self._states:
            if not s.active or any(s is e for e in exclude):
                continue
            if mover is not None and _can_cooccupy(
                mover.combatant.size, s.combatant.size
            ):
                continue
            blocked |= set(s.occupied_cells())
        return frozenset(blocked)

    def _blocked_hostile(self, mover: CombatantState) -> frozenset[Pos]:
        """Hostile-occupied cells that block the mover's path.

        A hostile creature's square blocks movement (SRD "Movement" /
        "Moving Through a Square"), except when the mover may co-occupy it
        (``_can_cooccupy``, SRD "Big Creatures and Smaller Creatures") or may
        pass through it (``_can_pass_through``, SRD "Moving Through a Square" :
        "You can move through a square occupied by a creature three size
        categories larger than you").  The distinction between ``_blocked_hostile``
        (through-gate) and ``_blocked`` (end-gate) ensures pass-through
        candidates are walkable but not valid endpoints.
        """
        return frozenset(
            cell
            for s in self._states
            if s.active
            and s is not mover
            and s.side != mover.side
            and not _can_cooccupy(mover.combatant.size, s.combatant.size)
            and not _can_pass_through(mover.combatant.size, s.combatant.size)
            for cell in s.occupied_cells()
        )

    def creature_distance(self, a: CombatantState, b: CombatantState) -> int:
        """Minimum grid distance between any occupied cell of ``a`` and ``b``."""
        cells_b = b.occupied_cells()
        return min(
            self._grid.distance(cell_a, cell_b)
            for cell_a in a.occupied_cells()
            for cell_b in cells_b
        )

    def _elevation(self, state: CombatantState) -> int:
        """Height of the creature's anchor cell (0 when no elevation layer)."""
        return self._grid.elevation_at(state.pos)

    def _cells_free(self, cells: Iterable[Pos], mover: CombatantState) -> bool:
        """True if every cell is in bounds, passable, and unoccupied by others."""
        blocked = self._blocked(mover)
        return all(
            self._grid.passable(cell) and cell not in blocked for cell in cells
        )

    def _cells_walkable(self, cells: Iterable[Pos], mover: CombatantState) -> bool:
        """True if a move/run path may enter these cells (allies allowed).

        Inbounds, passable, and not occupied by a hostile creature; a
        friendly creature's square may be crossed through (SRD Movement),
        though the movement may not END there (``_cells_free`` gates that).
        """
        hostile = self._blocked_hostile(mover)
        return all(
            self._grid.passable(cell) and cell not in hostile for cell in cells
        )

    def _footprint_at(self, anchor: Pos, state: CombatantState) -> frozenset[Pos]:
        """The cells ``state`` would occupy if its anchor were at ``anchor``."""
        n = SIZE_CELLS.get(state.combatant.size, 1)
        r, c = anchor
        return frozenset(
            (r + dr, c + dc) for dr in range(n) for dc in range(n)
        )

    def _footprint_cost(
        self, footprint: frozenset[Pos], cost_field: dict[Pos, int]
    ) -> int | None:
        """Minimum cost over footprint cells present in the cost field."""
        costs = [cost_field[cell] for cell in footprint if cell in cost_field]
        return min(costs) if costs else None

    def nearest_enemy(self, state: CombatantState) -> CombatantState | None:
        """Closest active enemy by grid distance; ties keep list order."""
        enemies = [s for s in self._states if s.side != state.side and s.active]
        if not enemies:
            return None
        return min(
            enemies,
            key=lambda s: (self.creature_distance(state, s), self._states.index(s)),
        )

    def weapon_for(self, attacker: CombatantState, target: CombatantState) -> AttackSpec | None:
        """First weapon usable against the target at this range and with clear LoE."""
        for weapon in attacker.usable_attacks():
            if self._weapon_usable_against(attacker, target, weapon):
                return weapon
        return None

    def _weapon_usable_against(
        self, attacker: CombatantState, target: CombatantState, weapon: AttackSpec
    ) -> bool:
        """True if ``weapon`` can strike ``target`` at this range with clear LoE.

        The per-weapon half of ``weapon_for``'s auto-selection, exposed for
        the explicit weapon choice of ``attack`` / ``full_attack`` (U5d):
        melee/touch reach (with the reach dead zone) or ranged/touch range
        within the max increments, behind a line-of-effect gate.
        """
        if not has_line_of_effect_cells(
            self._grid, attacker.occupied_cells(), target.occupied_cells()
        ):
            return False
        dist_ft = self.creature_distance(attacker, target) * _SQUARE_FT
        if weapon.kind in ("melee", "touch"):
            inner_cells, outer_cells = _melee_reach_zone_cells(attacker, weapon)
            if inner_cells * _SQUARE_FT <= dist_ft <= outer_cells * _SQUARE_FT:
                return True
        max_increments = (
            _MAX_TOUCH_RANGE_INCREMENTS
            if weapon.kind == "touch"
            else _MAX_RANGE_INCREMENTS
        )
        return (
            weapon.kind in ("ranged", "touch")
            and weapon.range_increment_ft is not None
            and dist_ft <= weapon.range_increment_ft * max_increments
        )

    def _is_ranged_attack(self, weapon: AttackSpec) -> bool:
        """Ranged-style attack: projectile, or touch thrown/fired from a distance.

        Melee touch attacks (no range increment) are not ranged-style.
        """
        return weapon.kind == "ranged" or (
            weapon.kind == "touch" and weapon.range_increment_ft is not None
        )

    def _is_melee_attack(self, weapon: AttackSpec) -> bool:
        """PF1e: a melee touch attack (kind "touch" with no range increment,
        e.g. the lich's Paralyzing Touch) is a melee attack — it gains the
        melee benefits (flanking, high ground, vs-helpless +4, sneak attack).
        """
        return weapon.kind == "melee" or (
            weapon.kind == "touch" and weapon.range_increment_ft is None
        )

    def range_penalty(self, weapon: AttackSpec, dist_ft: int) -> int:
        """PF1e: -2 per full range increment beyond the first, zero within it."""
        if weapon.kind not in ("ranged", "touch") or weapon.range_increment_ft is None:
            return 0
        increments = dist_ft // weapon.range_increment_ft
        if dist_ft % weapon.range_increment_ft != 0:
            increments += 1
        return -_RANGE_INCREMENT_PENALTY * max(0, increments - 1)

    def _flanking_bonus(self, attacker: CombatantState, target: CombatantState) -> int:
        """+2 if an active ally threatens the target from the opposite side (CRB flanking).

        The opposite side is the mirror of every attacker cell across every
        target cell; an ally occupying any mirrored cell flanks. PF1e (CRB):
        the ally must actually THREATEN the target — a usable melee weapon
        whose reach covers a target square (a reach weapon's 5-ft dead zone
        does not), and no condition that stops it from acting (stunned,
        paralyzed, ...).
        """
        opposite = {
            (2 * tr - ar, 2 * tc - ac)
            for ar, ac in attacker.occupied_cells()
            for tr, tc in target.occupied_cells()
        }
        for ally in self._states:
            if ally is attacker or ally is target:
                continue
            if not ally.active or ally.side != attacker.side:
                continue
            if self.has_condition_flag(ally, "cant_act"):
                continue
            if not (ally.occupied_cells() & opposite):
                continue
            if self.threatened_squares(ally) & target.occupied_cells():
                return _FLANK_BONUS
        return 0

    def _stat_modifiers(
        self,
        state: CombatantState,
        target: str,
        *,
        weapon_name: str | None = None,
        weapon: AttackSpec | None = None,
        dist_ft: int | None = None,
        save_descriptors: frozenset[str] = frozenset(),
    ) -> list[StatModifier]:
        """Collect all StatModifiers for ``target`` from all sources.

        ``weapon_name`` filters out modifiers with a ``weapon_filter`` that
        doesn't match (e.g. Weapon Focus (Pistol) only applies to weapons
        whose name contains "Pistol", case-insensitively — see
        ``_weapon_filter_matches``). Modifiers without a ``weapon_filter``
        are always included.

        Modifiers whose ``condition`` is set are only included when the named
        runtime condition holds for ``state`` (evaluated via
        ``_modifier_condition_holds``, which consumes the weapon/range/save
        context threaded from the action being resolved).  Unsupported
        condition names are treated as NOT holding (modifier excluded).
        """
        mods: list[StatModifier] = []
        # Old effects field (backwards compatibility)
        mods.extend(m for m in state.effects if m.target == target)
        # Old conditions field (backwards compatibility)
        for cond in state.conditions:
            mods.extend(m for m in cond.modifiers if m.target == target)
        # New active buffs
        for buff in state.active_buffs:
            mods.extend(m for m in buff.modifiers if m.target == target)
        # New active conditions
        for ac in state.active_conditions:
            mods.extend(m for m in ac.condition.modifiers if m.target == target)
        # Features
        for feat in state.combatant.features:
            mods.extend(
                m
                for m in feat.effects
                if m.target == target
                and (
                    m.weapon_filter is None
                    or _weapon_filter_matches(m.weapon_filter, weapon_name)
                )
            )
        # PF1e: prone and helpless (paralyzed/asleep/unconscious) AC
        # adjustments depend on the weapon kind and are applied in
        # resolve_attack, where it is known — not unconditionally here.
        return [
            m
            for m in mods
            if m.condition is None
            or self._modifier_condition_holds(
                state,
                m.condition,
                weapon=weapon,
                dist_ft=dist_ft,
                save_descriptors=save_descriptors,
            )
        ]

    def _has_feat(self, state: CombatantState, feat_name: str) -> bool:
        """True if the combatant has a feature with the given name."""
        return any(f.name == feat_name for f in state.combatant.features)

    def _is_paralyzing_touch(self, attacker: CombatantState, weapon: AttackSpec) -> bool:
        """True if a hit with this weapon should apply the Lich's paralyzing touch.

        Robust check: the attacker has the "Paralyzing Touch" feature and the
        weapon is a touch attack (or is literally named "Paralyzing Touch").
        """
        if not self._has_feat(attacker, "Paralyzing Touch"):
            return False
        return weapon.kind == "touch" or weapon.name == "Paralyzing Touch"

    _FEAR_AURA_DC = 22
    _FEAR_AURA_RANGE_FT = 30
    _FEAR_AURA_ROUNDS = 1

    def _apply_fear_aura(self, state: CombatantState) -> None:
        """Apply the Lich's Fear Aura: enemies within 30 ft save Will (DC 22) or become shaken.

        Triggered at the start of the aura-bearer's turn (simplification of the
        PF1e "on range entry" trigger — the lich acts first each round, so this
        covers entry into range). Only enemies within range who are not already
        shaken are tested, so the effect does not re-roll on the same enemy each
        turn. Shaken lasts a fixed 1 round.
        """
        if not self._has_feat(state, "Fear Aura"):
            return
        for enemy in self._states:
            if (
                not enemy.active
                or enemy.side == state.side
                or self._has_condition_named(enemy, "shaken")
            ):
                continue
            dist_ft = self.creature_distance(state, enemy) * _SQUARE_FT
            if dist_ft > self._FEAR_AURA_RANGE_FT:
                continue
            save = self.resolve_save(
                enemy, "will", self._FEAR_AURA_DC, save_descriptors=frozenset({"fear"})
            )
            if save.success:
                self._log(
                    f"round {self._current_round} {state.combatant.id}: fear aura on "
                    f"{enemy.combatant.id} -> SAVED"
                )
                continue
            enemy.active_conditions.append(
                ActiveCondition(
                    condition=CONDITIONS_BY_NAME["shaken"],
                    rounds_left=self._FEAR_AURA_ROUNDS,
                    source=f"monster ability: fear aura by {state.combatant.id}",
                )
            )
            self._log(
                f"round {self._current_round} {state.combatant.id}: fear aura on "
                f"{enemy.combatant.id} -> shaken ({self._FEAR_AURA_ROUNDS}r)"
            )



    def _aoo_allowance(self, state: CombatantState) -> int:
        """Number of AoOs allowed per round for a combatant.

        Base is 1. Combat Reflexes adds the DEX modifier on top (clamped to >= 1
        so a non-positive DEX mod never reduces the normal single AoO).
        PF1e (SRD "Total Defense"): "You can't make attacks of opportunity
        while using total defense" — the allowance drops to 0 while the
        total-defense bonus is active (until the start of the next turn).
        """
        if state.total_defense:
            return 0
        if not self._has_feat(state, "Combat Reflexes"):
            return 1
        return max(1, 1 + ((state.combatant.abilities.dex_score - 10) // 2))

    def _power_attack_amt(self, attacker: CombatantState) -> int:
        """Power Attack exchange amount: X = BAB//4 + 1 (min 1). Returns 0 if inactive."""
        if not attacker.power_attack or not self._has_feat(attacker, "Power Attack"):
            return 0
        return max(1, attacker.combatant.bab // 4 + 1)

    def _attack_ac_mods(
        self, target: CombatantState, weapon: AttackSpec
    ) -> list[StatModifier]:
        """AC modifiers for one attack — the weapon-kind-dependent ones included.

        PF1e (CRB): a prone defender takes -4 AC against melee attacks but
        gains +4 AC against ranged attacks; a helpless defender (paralyzed,
        asleep, unconscious, helpless) has an effective Dexterity score of 0,
        so its whole Dex modifier gives way to the Dex-0 penalty (-5). The
        flat-footed base already excludes ALL Dex (bonus and penalty alike),
        so the mod is exactly -5 there; on the touch base the stored Dex
        modifier is stripped at the base (see resolve_attack) before this
        -5 is added."""
        mods = self._stat_modifiers(target, "ac")
        if self._has_condition_named(target, "prone"):
            mods.append(
                StatModifier(
                    target="ac", value=4 if self._is_ranged_attack(weapon) else -4
                )
            )
        if self._is_helpless(target):
            mods.append(StatModifier(target="ac", value=_DEX_ZERO_MOD))
        return mods

    def resolve_attack(
        self,
        attacker: CombatantState,
        target: CombatantState,
        weapon: AttackSpec,
        *,
        bonus_override: int | None = None,
    ) -> AttackResult:
        """Roll one attack (with crit confirm and damage) and apply it."""
        roll = self._rng.d20()
        dist_ft = self.creature_distance(attacker, target) * _SQUARE_FT
        penalty = self.range_penalty(weapon, dist_ft)
        # PF1e: melee touch attacks are melee attacks — flanking and high
        # ground apply to them (see _is_melee_attack).
        flank = self._flanking_bonus(attacker, target) if self._is_melee_attack(weapon) else 0
        high_ground = (
            _HIGH_GROUND_BONUS
            if self._is_melee_attack(weapon)
            and self._elevation(attacker) > self._elevation(target)
            else 0
        )
        base_bonus = bonus_override if bonus_override is not None else weapon.attack_bonus
        fim_penalty = (
            self._firing_into_melee_penalty(attacker, target)
            if self._is_ranged_attack(weapon)
            else 0
        )
        atk_mods = self._stat_modifiers(
            attacker, "attack", weapon_name=weapon.name, weapon=weapon, dist_ft=dist_ft
        )
        # PF1e (CRB): a prone attacker takes -4 on melee attack rolls. Ranged
        # weapons cannot be used while prone at all, EXCEPT crossbows, which
        # stay usable at -4. The model cannot tell a crossbow from a bow, so
        # every ranged weapon is treated as the crossbow-exempt case: usable,
        # but at -4 (documented simplification).
        if self._has_condition_named(attacker, "prone"):
            atk_mods.append(StatModifier(target="attack", value=-4))
        # PF1e: an invisible attacker strikes from an unknown direction (+2 on
        # attack and crit confirmation, target loses its Dex bonus to AC).
        if self._has_condition_named(attacker, "invisible"):
            atk_mods.append(StatModifier(target="attack", value=_INVISIBLE_ATTACK_BONUS))
        # PF1e (CRB): melee attacks (melee touch included) against a helpless
        # target gain +4; the helpless state includes paralyzed, asleep and
        # unconscious (stunned is NOT helpless). Ranged attacks gain no bonus.
        if self._is_melee_attack(weapon) and self._is_helpless(target):
            atk_mods.append(StatModifier(target="attack", value=_HELPLESS_MELEE_BONUS))
        attack_mod = resolve_modifiers(atk_mods)
        # PF1e (CRB Power Attack): the -X penalty rides ALL melee attack rolls
        # — a melee touch (no range increment) is a melee attack. The damage
        # bonus it buys stays weapon-only (see _resolve_hit_damage).
        pa_amt = (
            self._power_attack_amt(attacker) if self._is_melee_attack(weapon) else 0
        )
        fd_penalty = (
            _FIGHT_DEFENSIVELY_ATTACK_PENALTY if attacker.fight_defensively else 0
        )
        total = (
            roll + base_bonus + penalty + flank + high_ground + attack_mod - pa_amt
            + fim_penalty + fd_penalty + attacker.aid_attack_bonus
        )
        # Check if target denies DEX to AC (flat-footed); a running target
        # loses its DEX bonus too (U5e), reusing the same AC path. An
        # invisible attacker also denies the target's DEX bonus to AC.
        denies_dex = (
            self.has_condition_flag(target, "denies_dex_to_ac")
            or target.running
            or self._has_condition_named(attacker, "invisible")
        )
        full_ac_base = (
            target.combatant.ac.flat_footed
            if denies_dex
            else target.combatant.ac.total
        )
        # Touch resolves vs touch AC; firearms beyond their first increment use full AC.
        if weapon.kind == "touch":
            if (
                weapon.firearm
                and weapon.range_increment_ft is not None
                and dist_ft > weapon.range_increment_ft
            ):
                base_ac = full_ac_base
            elif denies_dex:
                # A flat-footed defender loses only a POSITIVE Dex bonus (a
                # Dex penalty stays on touch AC); a HELPLESS defender has an
                # effective Dex score of 0, so its whole stored Dex modifier
                # is stripped here and the exact -5 Dex-0 penalty is added by
                # _attack_ac_mods.
                dex_mod = target.combatant.abilities.dex_mod
                strip = dex_mod if self._is_helpless(target) else max(0, dex_mod)
                base_ac = target.combatant.ac.touch - strip
            else:
                base_ac = target.combatant.ac.touch
        else:
            base_ac = full_ac_base
        ac_mods = self._attack_ac_mods(target, weapon)
        ac = base_ac + resolve_modifiers(ac_mods)
        ac += target.defensive_ac_bonus
        ac += target.aid_ac_bonus
        ac += self._attack_cover_bonus(
            attacker, target, ranged=self._is_ranged_attack(weapon)
        )
        hit = roll == _NATURAL_TWENTY or (roll != _NATURAL_ONE and total >= ac)
        # PF1e (Ultimate Combat, Firearm Rules — Misfires): "If the natural
        # result of your attack roll falls within a firearm's misfire value,
        # that shot misses [...] When a firearm misfires, it gains the broken
        # condition." The model uses the minimum misfire value (1): a natural
        # 1 with a firearm (``firearm: true``) breaks the weapon — it joins
        # ``weapon_broken`` and is unusable until Quick Clear or a repair.
        # Bounded to firearms; the exploding-early-firearm and increased
        # misfire-value rules are not modeled (a broken gun cannot be fired
        # again here, so it cannot misfire twice).
        if weapon.firearm and roll == _NATURAL_ONE:
            attacker.weapon_broken.add(weapon.id)
            self._log(
                f"round {self._current_round} {attacker.combatant.id}: "
                f"{weapon.name} MISFIRE (broken)"
            )
        damage = 0
        concealment_miss = False
        crit = False
        if hit:
            crit, concealment_miss, damage = self._resolve_hit_damage(
                attacker, target, weapon, roll=roll, ac=ac, base_bonus=base_bonus,
                penalty=penalty, flank=flank, high_ground=high_ground,
                attack_mod=attack_mod, pa_amt=pa_amt, fim_penalty=fim_penalty,
                dist_ft=dist_ft, denies_dex=denies_dex,
            )
        if not concealment_miss:
            target.hp -= damage
            damage = self._consume_up_close_and_deadly(
                attacker, target, weapon, dist_ft, damage, hit=hit
            )
        attacker.aid_attack_bonus = 0
        return AttackResult(
            hit=hit, crit=crit, damage=damage, roll=roll, total=total, ac=ac,
            penalty=penalty, flank_bonus=flank, high_ground_bonus=high_ground,
            base_bonus=base_bonus, melee_penalty=fim_penalty,
        )

    def _resolve_hit_damage(
        self,
        attacker: CombatantState,
        target: CombatantState,
        weapon: AttackSpec,
        *,
        roll: int,
        ac: int,
        base_bonus: int,
        penalty: int,
        flank: int,
        high_ground: int,
        attack_mod: int,
        pa_amt: int,
        fim_penalty: int,
        dist_ft: int,
        denies_dex: bool,
    ) -> tuple[bool, bool, int]:
        """Resolve a successful attack roll: crit confirm, concealment miss
        chance, sneak attack dice, then damage (PF1e order).

        Returns ``(crit, concealment_miss, damage)``. Sneak precision dice are
        added after the crit multiplier and before DR / energy resistance.
        Improved Critical doubles the threat range of every weapon (engine
        simplification: no per-weapon-type feat selection); it never affects
        the confirmation roll.
        """
        crit = False
        threat_range = weapon.crit_range
        if self._has_feat(attacker, _IMPROVED_CRITICAL_FEATURE):
            threat_range = _CRIT_RANGE_BASE - 2 * (_CRIT_RANGE_BASE - weapon.crit_range)
        if roll != _NATURAL_ONE and roll >= threat_range:
            confirm = self._rng.d20()
            confirm_total = (
                confirm + base_bonus + penalty + flank + high_ground
                + attack_mod - pa_amt + fim_penalty + attacker.aid_attack_bonus
                + (_FIGHT_DEFENSIVELY_ATTACK_PENALTY if attacker.fight_defensively else 0)
            )
            # PF1e (CRB): the confirmation roll is an attack roll — a natural
            # 20 on it is an automatic hit (auto-confirm), a natural 1 miss.
            crit = confirm == _NATURAL_TWENTY or (
                confirm != _NATURAL_ONE and confirm_total >= ac
            )
        concealment = self._concealment_chance(target)
        # PF1e: a blinded character's opponents count as having total
        # concealment against it — the blinded attacker itself misses 50%.
        attacker_blinded = self._has_condition_named(attacker, "blinded")
        miss_chance = (
            max(concealment, _TOTAL_CONCEALMENT_PCT) if attacker_blinded else concealment
        )
        if miss_chance > 0:
            pct = self._rng.d100()
            missed = pct <= miss_chance
            source = "attacker blinded" if attacker_blinded else "concealment"
            self._log(
                f"round {self._current_round} {attacker.combatant.id}: "
                f"{source} vs {target.combatant.id}: "
                f"d100({pct}) {'<=' if missed else '>'} {miss_chance}% "
                f"— attack {'misses' if missed else 'lands'}"
            )
            if missed:
                return False, True, 0
        sneak_total = 0
        sneak_dice = self._sneak_attack_dice(
            attacker, target, weapon, dist_ft=dist_ft,
            denies_dex=denies_dex, concealment=concealment,
        )
        if sneak_dice > 0:
            sneak_total = sum(self._rng.roll_die(6) for _ in range(sneak_dice))
            self._log(
                f"round {self._current_round} {attacker.combatant.id}: "
                f"sneak attack vs {target.combatant.id}: "
                f"{sneak_dice}d6 = {sneak_total} precision damage"
            )
        dmg_mods = self._stat_modifiers(
            attacker, "damage", weapon_name=weapon.name, weapon=weapon, dist_ft=dist_ft
        )
        rolls = [c.formula.roll(self._rng) for c in weapon.damage]
        # PF1e (CRB, Critical Hits): "Precision damage ... and additional
        # damage dice from weapon special abilities (such as flaming) are not
        # multiplied when you score a critical hit." Only the base physical
        # dice ride the multiplier with the flat bonuses; energy-typed
        # component dice (flaming/frost/shock/...) are added at 1x.
        physical_dice = sum(
            roll
            for comp, roll in zip(weapon.damage, rolls, strict=True)
            if _PHYSICAL_DAMAGE_TYPES.issuperset(comp.types)
        )
        energy_dice = sum(rolls) - physical_dice
        damage = physical_dice + weapon.damage_bonus
        damage += resolve_modifiers(dmg_mods)
        # PF1e (CRB Power Attack): +2X damage with a melee weapon, +3X (the
        # bonus increased by half) with a two-handed weapon, a one-handed
        # weapon used in two hands, or a primary natural with 1.5x Strength
        # (modeled via the weapon's `two_handed` flag). The off-hand /
        # secondary-natural halving (-50%, +1X) is NOT modeled: two-weapon
        # fighting is not in the engine (documented simplification). The
        # bonus damage never applies to touch attacks (CRB), which is why
        # this gate is kind == "melee" while the -X penalty also rides melee
        # touch rolls.
        if weapon.kind == "melee":
            damage += pa_amt * (3 if weapon.two_handed else 2)
        if crit:
            damage *= weapon.crit_mult
        damage += sneak_total + energy_dice
        # PF1e (CRB Damage Reduction): "Damage reduction does not negate ...
        # energy damage dealt along with an attack" — DR reduces only the
        # non-energy share of the damage (physical dice, flat bonuses and
        # precision dice); energy components are cut solely by energy
        # resistance/immunity in the per-component step below. The energy
        # share is its 1x dice: special-ability dice never ride the crit
        # multiplier (CRB Critical Hits exception).
        energy_share = sum(
            roll
            for comp, roll in zip(weapon.damage, rolls, strict=True)
            if not _PHYSICAL_DAMAGE_TYPES.issuperset(comp.types)
        )
        physical = max(0, damage - energy_share)
        damage = self._apply_dr(physical, weapon, target) + energy_share
        final = self._apply_energy_resistance_per_component(
            damage, weapon, rolls, target=target
        )
        # PF1e (CRB "Damage" — Minimum Damage): "If penalties reduce the
        # damage result to less than 1, a hit still deals 1 point of
        # nonlethal damage." The engine has no nonlethal damage track
        # (documented approximation): the floor is applied as 1 point of
        # normal damage on a landed hit.
        return crit, False, max(_MINIMUM_HIT_DAMAGE, final)

    def _attack_cover_bonus(
        self, attacker: CombatantState, target: CombatantState, *, ranged: bool
    ) -> int:
        """Cover the target has against one attack from ``attacker`` (terrain +
        soft cover from interposed creatures on ranged lines only)."""
        occupied = frozenset(
            cell
            for s in self._states
            if s.active and s is not attacker and s is not target
            for cell in s.occupied_cells()
        )
        return cover_bonus_cells(
            self._grid,
            attacker.occupied_cells(),
            target.occupied_cells(),
            ranged=ranged,
            occupied=occupied,
        )

    def _concealment_chance(self, target: CombatantState) -> int:
        """Highest miss chance (%) among the target's active concealment conditions."""
        chances = [ac.condition.miss_chance for ac in target.active_conditions]
        chances += [cond.miss_chance for cond in target.conditions]
        return max((c for c in chances if c > 0), default=0)

    def _sneak_attack_dice(
        self,
        attacker: CombatantState,
        target: CombatantState,
        weapon: AttackSpec,
        *,
        dist_ft: int,
        denies_dex: bool,
        concealment: int,
    ) -> int:
        """Sneak attack d6 count for this swing (0 when the sneak does not apply).

        PF1e: precision damage when the target is flanked (melee only, melee
        touch included) or denied its Dex bonus to AC (melee, or ranged within
        30 ft); dice = (level + 1) // 2. ANY concealment (miss chance > 0)
        denies the sneak attack (SRD rogue "Sneak Attack": "A rogue cannot
        sneak attack while striking a creature with concealment" — the rogue
        must see the target well enough to pick a vital spot). A BLINDED
        attacker faces total concealment against ALL its opponents (CRB
        "Conditions — Blinded": "All opponents are considered to have total
        concealment (50% miss chance) against the blinded character"), so it
        cannot sneak attack either — same max(target, 50) convention as
        _resolve_hit_damage.
        PF1e (CRB): undead and constructs are immune to precision damage —
        ooze/plant immunity is not modeled (no such creature types exist in
        the data model).
        """
        effective_concealment = concealment
        if self._has_condition_named(attacker, "blinded"):
            effective_concealment = max(concealment, _TOTAL_CONCEALMENT_PCT)
        if (
            effective_concealment > 0
            or not self._has_feat(attacker, _SNEAK_ATTACK_FEATURE)
        ):
            return 0
        if target.combatant.creature_type.lower() in _PRECISION_IMMUNE_TYPES:
            return 0
        dice = (attacker.combatant.level + 1) // 2
        is_melee = self._is_melee_attack(weapon)
        if is_melee and self._flanking_bonus(attacker, target) > 0:
            return dice
        if denies_dex and (
            is_melee
            or (self._is_ranged_attack(weapon) and dist_ft <= _POINT_BLANK_RANGE_FT)
        ):
            return dice
        return 0

    def _firing_into_melee_penalty(
        self, attacker: CombatantState, target: CombatantState
    ) -> int:
        """PF1e firing into melee: -4 on a ranged attack whose target is
        engaged in melee, avoided entirely (0) when the target stands 10+ ft
        from every friendly character of the attacker. Precise Shot removes
        it.

        PF1e (SRD "Attack" — Shooting or Throwing into a Melee): "If your
        target (or the part of your target you're aiming at, if it's a big
        target) is at least 10 feet away from the nearest friendly character,
        you can avoid the -4 penalty" — the exemption is measured from the
        TARGET to the attacker's nearest friendly character (a creature on
        the attacker's side other than the attacker), NOT from the attacker's
        own position; an archer 30 ft away still takes the -4 when the target
        is locked in melee with one of the archer's allies at 5 ft. The 10+
        ft clause is therefore 0, not -2. The -2 applies only when the target
        is two size categories larger than the friendly characters it is
        engaged with (and 0 at three or more): size-category reduction is
        NOT modeled (documented simplification).

        The target is engaged when an active enemy of the target (not the
        attacker itself) threatens the target's occupied cells with a melee
        weapon.
        """
        if self._has_feat(attacker, _PRECISE_SHOT_FEATURE):
            return 0
        threats = [
            s
            for s in self._states
            if s is not attacker
            and s.active
            and s.side != target.side
            and self.threatened_squares(s) & target.occupied_cells()
        ]
        if not threats:
            return 0
        allies = [
            s
            for s in self._states
            if s is not attacker and s.active and s.side == attacker.side
        ]
        if all(
            self.creature_distance(target, ally) * _SQUARE_FT
            >= _FIRING_MELEE_SAFE_FT
            for ally in allies
        ):
            return 0
        return _FIRING_MELEE_PENALTY

    def _engaged_in_melee(self, state: CombatantState) -> bool:
        """True when an active enemy with a melee weapon threatens this
        combatant's occupied cells (same threat machinery as AoO/flanking)."""
        occupied = state.occupied_cells()
        return any(
            self.threatened_squares(s) & occupied
            for s in self._states
            if s is not state and s.active and s.side != state.side
        )

    def _consume_up_close_and_deadly(
        self,
        attacker: CombatantState,
        target: CombatantState,
        weapon: AttackSpec,
        dist_ft: int,
        damage: int,
        *,
        hit: bool,
    ) -> int:
        """Consume the Up Close and Deadly deed on the first attack resolved.

        The deed applies +1d6 to a FIREARM attack that hits a target within
        30 ft (Ultimate Combat "Deeds - Up Close and Deadly": "makes a
        successful attack with a firearm against a target within 30 feet");
        the flag is reset after the first attack in all cases (the benefit is
        lost if the attack misses, is not a firearm, is out of range or is
        not ranged at all).
        """
        if not attacker.deed_up_close_and_deadly:
            return damage
        if (
            hit
            and weapon.firearm
            and self._is_ranged_attack(weapon)
            and dist_ft <= _UP_CLOSE_RANGE_FT
        ):
            bonus = self._rng.roll_die(6)
            damage += bonus
            target.hp -= bonus
        attacker.deed_up_close_and_deadly = False
        return damage

    def _dr_bypassed(self, dr: DamageReduction, types: frozenset[str]) -> bool:
        """PF1e (CRB): "DR X/Y and Z" requires EVERY listed component to bypass.

        A single-component bypass behaves as before (that type defeats the
        DR); a multi-component bypass is an "and" list — all components must
        be present on the attack. Documented gap: the weapon model exposes no
        "magic" property, so a bypass list containing "magic" (the lich's
        DR 15/bludgeoning and magic) can never be satisfied by a mundane
        weapon — correctly, a non-magical weapon must NOT bypass it.
        """
        if not dr.bypass:
            return False
        return dr.bypass <= types

    def _apply_dr(self, damage: int, weapon: AttackSpec, target: CombatantState) -> int:
        dr: DamageReduction | None = target.combatant.dr
        if dr is None:
            return damage
        types = frozenset(t for comp in weapon.damage for t in comp.types)
        if self._dr_bypassed(dr, types):
            return damage
        return max(0, damage - dr.amount)

    def _apply_dr_for_types(
        self, damage: int, damage_types: frozenset[str], target: CombatantState
    ) -> int:
        dr: DamageReduction | None = target.combatant.dr
        if dr is None:
            return damage
        if self._dr_bypassed(dr, damage_types):
            return damage
        return max(0, damage - dr.amount)

    def _check_spell_resistance(
        self, caster: CombatantState, target: CombatantState
    ) -> bool:
        """SR check: d20 + caster level vs target spell_resistance.

        Returns True if the spell affects the target (SR passed or no SR).
        Returns False if the target resists the spell (all effects skipped).
        """
        sr = target.combatant.spell_resistance
        if sr == 0:
            return True
        caster_level = caster.combatant.level
        roll = self._rng.d20()
        total = roll + caster_level
        if total >= sr:
            return True
        self._log(
            f"round {self._current_round} {caster.combatant.id}: "
            f"spell resistance {target.combatant.id}: "
            f"d20({roll}) + CL({caster_level}) = {total} vs SR {sr} "
            f"— resisted"
        )
        return False

    def _apply_energy_resistance_per_component(
        self,
        damage: int,
        weapon: AttackSpec,
        rolls: list[int],
        *,
        target: CombatantState,
    ) -> int:
        """Energy resistance / immunity applied PER DAMAGE COMPONENT (B21).

        PF1e (CRB "Energy Resistance"/"Immunity to Energy Damage"): each
        damage type's resistance reduces only the dice of that type — a
        weapon dealing 1d6 slashing + 1d6 fire against fire resistance 5
        loses only its fire portion; the slashing dice, the flat bonuses
        (damage_bonus, ability/damage modifiers, Power Attack) and the
        untyped sneak precision dice are never eaten by energy resistance.
        Each component's share of the final damage is its own roll at 1x:
        energy (weapon special ability) dice are never multiplied on a crit
        (CRB Critical Hits exception), so no crit factor rides this step.
        A component carrying several energy types uses the largest matching
        resistance (documented simplification: one die roll cannot be split
        across the listed types). Physical-only components match nothing in
        the target's resistance/immunity maps — they rode the DR path just
        before this step, which reduces only the non-energy share of the
        damage (CRB: DR does not negate energy damage dealt along with an
        attack); single-component weapons keep the exact arithmetic of the
        old lumped-total path.
        """
        for comp, roll in zip(weapon.damage, rolls, strict=True):
            damage -= self._energy_reduction(roll, frozenset(comp.types), target)
        return max(0, damage)

    def _energy_reduction(
        self, damage: int, damage_types: frozenset[str], target: CombatantState
    ) -> int:
        """Reduction the target's immunity/resistance applies to one
        damage portion of the given types, capped at the portion itself."""
        immunities = target.combatant.immunities
        if immunities and damage_types & frozenset(immunities):
            return damage
        resistances = target.combatant.resistances
        if not resistances:
            return 0
        max_resist = max(
            (resistances[t] for t in damage_types if t in resistances),
            default=0,
        )
        return min(damage, max_resist)

    def _apply_energy_resistance(
        self,
        damage: int,
        damage_types: frozenset[str],
        target: CombatantState,
    ) -> int:
        """Energy resistance / immunity applied to one whole damage portion.

        Used by the spell-damage path: a ``DamageEffect`` is a single
        component (one formula, one type list), so the per-component rule
        (see ``_apply_energy_resistance_per_component``) reduces to exactly
        this. Immunity: if any damage type matches → 0. Resistance:
        subtract the max resistance among matching energy types, floored
        at 0. Physical types (slashing/piercing/bludgeoning/physical) are
        ignored — they stay on the DR path.
        """
        return max(0, damage - self._energy_reduction(damage, damage_types, target))

    def resolve_save(
        self,
        state: CombatantState,
        save_type: Literal["fort", "ref", "will"],
        dc: int,
        *,
        save_descriptors: frozenset[str] = frozenset(),
    ) -> SaveResult:
        """Roll a saving throw (fort/ref/will) against ``dc``.

        PF1e: natural 1 = automatic failure, natural 20 = automatic success.
        Effect modifiers and condition modifiers (StatModifier with matching
        target) are applied via ``resolve_modifiers`` — same bonus-type
        stacking rules as attacks.  ``save_descriptors`` (e.g. {"fear"},
        {"poison"}) gates conditional modifiers like Bitter or Born Damned.
        """
        roll = self._rng.d20()
        base = getattr(state.combatant.saves, save_type)
        bonus = resolve_modifiers(
            self._stat_modifiers(state, save_type, save_descriptors=save_descriptors)
        )
        total = roll + base + bonus
        success = roll != _NATURAL_ONE and (roll == _NATURAL_TWENTY or total >= dc)
        return SaveResult(success=success, roll=roll, total=total, dc=dc)

    def resolve_skill(
        self, state: CombatantState, skill: str, dc: int
    ) -> SaveResult:
        """Roll a skill check against ``dc``."""

        roll = self._rng.d20()
        bonus = self._skill_static_bonus(state, skill)
        total = roll + bonus
        # Natural 1/20 are not auto-fail/success for skills
        success = total >= dc
        return SaveResult(success=success, roll=roll, total=total, dc=dc)

    def _skill_static_bonus(self, state: CombatantState, skill: str) -> int:
        """Return a skill's static bonus (no d20). Shared by resolve_skill."""
        skill_spec = PREDEFINED_SKILLS.get(skill)
        if skill_spec is None:
            msg = f"Unknown skill: {skill}"
            raise ValueError(msg)

        skill_rank = state.combatant.skills.get(skill, None)
        rank = skill_rank.rank if skill_rank else 0
        # Class skill bonus
        class_bonus = 3 if skill_rank and skill_rank.class_skill else 0
        # Armor check penalty
        armor_penalty = skill_rank.armor_penalty if skill_rank else 0
        if armor_penalty and skill_spec.armor_check_penalty:
            armor_penalty = -abs(armor_penalty)
        else:
            armor_penalty = 0
        # Ability modifier
        ability_name = skill_spec.ability
        ability_score = getattr(state.combatant.abilities, f"{ability_name}_score")
        ability_mod = (ability_score - 10) // 2
        # Effect/condition modifiers. PF1e: modifiers targeting "dex_skills"
        # (grappled/pinned/blinded -4) apply to the Dexterity-based skills
        # listed in _DEX_BASED_SKILLS — they are stored under that aggregate
        # target, not the concrete skill name, so collect them explicitly.
        mods = self._stat_modifiers(state, skill)
        if skill in _DEX_BASED_SKILLS:
            mods.extend(self._stat_modifiers(state, "dex_skills"))
        mod_bonus = resolve_modifiers(mods)
        return rank + class_bonus + ability_mod + armor_penalty + mod_bonus

    def _roll_initiative(self) -> list[CombatantState]:
        rolls: dict[str, tuple[int, int]] = {}
        for state in self._states:
            roll = self._rng.d20()
            rolls[state.combatant.id] = (roll, roll + state.combatant.initiative_mod)
        self._initiative_keys = {
            s.combatant.id: (
                rolls[s.combatant.id][1],
                s.combatant.initiative_mod,
                self._states.index(s),
            )
            for s in self._states
        }
        order = sorted(
            self._states,
            key=lambda s: self._initiative_keys[s.combatant.id],
            reverse=True,
        )
        for state in order:
            roll, total = rolls[state.combatant.id]
            self._log(
                f"initiative: {state.combatant.id} "
                f"d20={roll}+{state.combatant.initiative_mod}={total}"
            )
        return order

    def _build_round_order(self) -> list[CombatantState]:
        """Build initiative order for this round from current ``_states``.

        Summoned creatures (not present at the start of combat) inherit their
        caster's initiative key so they act immediately after the caster via
        stable sort.
        """

        def sort_key(s: CombatantState) -> tuple[float, int, int]:
            key = self._initiative_keys.get(s.combatant.id)
            if key is not None:
                return key
            caster_id = s.summon_caster_id
            if caster_id and caster_id in self._initiative_keys:
                ck = self._initiative_keys[caster_id]
                return (ck[0], ck[1], ck[2])
            return (0, 0, -999)

        return sorted(self._states, key=sort_key, reverse=True)

    def _expire_summons(self) -> None:
        """Decrement summon durations and remove expired summoned creatures."""
        expired: list[CombatantState] = []
        for state in list(self._states):
            if state.summon_duration > 0:
                state.summon_duration -= 1
                if state.summon_duration <= 0:
                    expired.append(state)
        for state in expired:
            self._log(
                f"round {self._current_round} {state.combatant.id}: summon expired"
            )
            self._states.remove(state)
            if state in self._pending_summons:
                self._pending_summons.remove(state)

    def _winner_side(self) -> str | None:
        active_sides = {s.side for s in self._states if s.active}
        if len(active_sides) == 1:
            return active_sides.pop()
        return None

    def threatened_squares(self, state: CombatantState) -> frozenset[Pos]:
        """Squares this combatant threatens with a melee weapon.

        (API publique, lecture pour politique LLM.) Natural reach (plain
        weapons and natural attacks) is a disk: every square up to the
        effective reach, adjacency included. A reach weapon threatens only
        the ring beyond the wielder's natural reach up to double it (PF1e
        reach dead zone). The union over usable melee weapons is returned.
        """
        if not state.active:
            return frozenset()
        melee = [w for w in state.usable_attacks() if w.kind == "melee"]
        if not melee:
            return frozenset()
        threatened: set[Pos] = set()
        for weapon in melee:
            threatened |= self._weapon_threatened_squares(state, weapon)
        return frozenset(threatened)

    def _weapon_threatened_squares(self, state: CombatantState, weapon: AttackSpec) -> set[Pos]:
        """Squares one melee weapon threatens: disk for natural reach, ring for reach weapons.

        The union over every occupied cell of the creature's footprint; the
        creature's own cells are never threatened.
        """
        inner_cells, outer_cells = _melee_reach_zone_cells(state, weapon)
        threatened: set[Pos] = set()
        for r, c in state.occupied_cells():
            threatened |= self._reach_band_cells((r, c), inner_cells, outer_cells)
        threatened -= state.occupied_cells()
        return threatened

    def _reach_band_cells(self, center: Pos, inner: int, outer: int) -> set[Pos]:
        """Cells whose 5-10-5 distance from ``center`` lies in ``[inner, outer]``.

        ``inner == 0`` gives the plain disk (the center itself is never
        included); ``inner > 0`` gives the reach-weapon ring dead-zone band.
        """
        r, c = center
        return {
            (r + dr, c + dc)
            for dr in range(-outer, outer + 1)
            for dc in range(-outer, outer + 1)
            if (dr, dc) != (0, 0)
            and inner <= self._grid.distance(center, (r + dr, c + dc)) <= outer
        }

    def enemies_threatening(self, state: CombatantState, pos: Pos) -> list[CombatantState]:
        """Active enemies whose threatened squares include pos (in self._states order).

        (API publique, lecture pour politique LLM.)
        """
        return [
            s
            for s in self._states
            if s is not state
            and s.active
            and s.side != state.side
            and pos in self.threatened_squares(s)
        ]

    def reachable_ft(self, state: CombatantState, budget: int | None = None) -> dict[Pos, int]:
        """Movement cost in feet from state's anchor to each reachable cell.

        (API publique, lecture pour politique LLM.) Same cost model as
        ``Grid.reachable``: 5-10-5 diagonals, terrain, elevation, blocked
        creatures excluded. ``budget`` is in feet; None = full field.
        """
        blocked = self._blocked(state)
        if budget is None:
            field = self._grid.reachable(state.pos, None, blocked)
        else:
            budget_cells = budget // _SQUARE_FT
            if budget_cells < 1:
                return {}
            field = self._grid.reachable(state.pos, budget_cells, blocked)
        return {pos: cost * _SQUARE_FT for pos, cost in field.items()}

    def movement_cost_ft(self, state: CombatantState, target: CombatantState) -> int | None:
        """Minimal movement cost in feet for ``state`` to reach a cell from which
        it can melee ``target``, or None if unreachable under its speed.

        (API publique, lecture pour politique LLM.) Uses the same cost model as
        ``_move_path``: a full Dijkstra field from the target's anchor (other
        active states' cells blocked), then the cheapest field value over
        ``state``'s footprint, compared against the combatant's effective
        (land-or-fly) speed. Read-only: never mutates state nor consumes RNG.
        """
        blocked = self._blocked(state, target)
        field = self._grid.reachable(target.pos, None, blocked)
        cost_cells = self._footprint_cost(state.occupied_cells(), field)
        if cost_cells is None:
            return None
        speed_cells = _speed_ft(state) // _SQUARE_FT
        if cost_cells > speed_cells:
            return None
        return cost_cells * _SQUARE_FT

    def _aoo_defense_block(
        self, attacker: CombatantState, target: CombatantState
    ) -> str | None:
        """Why an AoO cannot be executed against the target, or None.

        PF1e (CRB "Cover"): "You can't execute an attack of opportunity
        against an opponent with cover relative to you"; (CRB "Concealment"):
        "You can't execute an attack of opportunity against an opponent with
        total concealment" (miss chance >= 50%). A BLINDED attacker considers
        ALL its opponents to have total concealment (CRB "Conditions —
        Blinded": "All opponents are considered to have total concealment
        (50% miss chance) against the blinded character"), so its AoOs are
        suppressed too. Melee line: terrain cover only — creatures grant no
        melee cover.
        """
        concealment = self._concealment_chance(target)
        if self._has_condition_named(attacker, "blinded"):
            concealment = max(concealment, _TOTAL_CONCEALMENT_PCT)
        if concealment >= _TOTAL_CONCEALMENT_PCT:
            return "total concealment"
        if cover_bonus_cells(
            self._grid,
            attacker.occupied_cells(),
            target.occupied_cells(),
            ranged=False,
            occupied=frozenset(),
        ):
            return "cover"
        return None

    def _resolve_aoo(self, attacker: CombatantState, target: CombatantState) -> bool:
        """Resolve one attack of opportunity (single melee attack at normal bonus).

        AoOs are always taken (PF1e allows declining, but the simulator always strikes).
        A target with cover or total concealment relative to the attacker cannot be
        struck at all — the opportunity is suppressed without spending it.
        Returns True if the target dropped.
        """
        if self.has_condition_flag(attacker, "cant_aoo"):
            return False
        blocked = self._aoo_defense_block(attacker, target)
        if blocked is not None:
            self._log(
                f"round {self._current_round} {attacker.combatant.id}: "
                f"AoO vs {target.combatant.id} suppressed ({blocked})"
            )
            return False
        self._aoo_used[attacker.combatant.id] = self._aoo_used.get(attacker.combatant.id, 0) + 1
        weapon = next((w for w in attacker.usable_attacks() if w.kind == "melee"), None)
        if weapon is None:
            return False
        return self._resolve_swing(
            attacker, target, weapon, label="AoO"
        )

    def _check_move_aoo(
        self, mover: CombatantState, *, movement: bool = True
    ) -> bool:
        """Resolve AoOs provoked by leaving any threatened cell of the mover's footprint.

        Each enemy threatening a cell the mover occupies strikes once (capped
        by the per-round AoO allowance). PF1e (CRB "Attacks of Opportunity —
        Combat Reflexes and Additional Attacks of Opportunity"): "Moving out of
        more than one square threatened by the same opponent in the same round
        doesn't count as more than one opportunity for that opponent" — with
        ``movement`` the per-round per-opponent dedupe in
        ``_move_aoo_provoked`` skips a second movement-triggered strike from
        the same enemy. Stand-up (``movement=False``) is a separate trigger and
        always provokes, subject to the allowance. Returns True if the mover
        dropped.
        """
        provoked = self._move_aoo_provoked.setdefault(mover.combatant.id, set())
        for cell in mover.occupied_cells():
            for enemy in self.enemies_threatening(mover, cell):
                if movement and enemy.combatant.id in provoked:
                    continue
                if self._aoo_used.get(enemy.combatant.id, 0) >= self._aoo_allowance(enemy):
                    continue
                if movement:
                    provoked.add(enemy.combatant.id)
                self._resolve_aoo(enemy, mover)
                if not mover.active:
                    return True
        return False

    def _check_enter_aoo(self, mover: CombatantState, next_pos: Pos) -> bool:
        """Resolve AoOs provoked by ENTERING a hostile creature's square.

        PF1e (SRD "Movement, Position, and Distance" / "Moving Through a
        Square"): "You can move through a square occupied by a creature three
        size categories larger than you" / "a creature three size categories
        smaller than it" — the pass-through provokes an attack of opportunity
        from the occupant.  The strike fires when the mover's footprint at
        ``next_pos`` overlaps a hostile occupant's cells but the current
        footprint does not (a fresh entry, not an existing co-occupancy).
        Co-occupiable pairs (Tiny-or-smaller vs strictly larger, S4c) keep
        their no-AoO sharing behaviour.  Capped by the per-round AoO
        allowance; no per-opponent dedupe (``_move_aoo_provoked`` dedupes
        only leaving threatened cells).  Returns True if the mover dropped.
        """
        before = mover.occupied_cells()
        after = self._footprint_at(next_pos, mover)
        for s in self._states:
            if not s.active or s is mover or s.side == mover.side:
                continue
            if not _can_pass_through(mover.combatant.size, s.combatant.size):
                continue
            if _can_cooccupy(mover.combatant.size, s.combatant.size):
                continue  # S4c: sharing a square never provokes
            cells = s.occupied_cells()
            if not (after & cells):
                continue
            if before & cells:
                continue  # already co-occupying: no fresh entry
            if self._aoo_used.get(s.combatant.id, 0) >= self._aoo_allowance(s):
                continue
            self._resolve_aoo(s, mover)
            if not mover.active:
                return True
        return False

    def _check_provoked_aoo(self, attacker: CombatantState, weapon: AttackSpec) -> bool:
        """Check for ranged-AoO: firing a ranged-style weapon in a threatened square provokes.

        Ranged-style means projectile weapons and touch thrown/fired weapons
        (touch with a range increment); melee touch (no increment) does not provoke.
        Returns True if the attacker dropped (caller must stop attacking).
        """
        if not self._is_ranged_attack(weapon):
            return False
        for cell in attacker.occupied_cells():
            for enemy in self.enemies_threatening(attacker, cell):
                if self._aoo_used.get(enemy.combatant.id, 0) >= self._aoo_allowance(enemy):
                    continue
                self._resolve_aoo(enemy, attacker)
                if not attacker.active:
                    return True
        return False

    def _check_casting_aoo(self, caster: CombatantState, spell_level: int) -> bool:
        """Check for AoO from casting a spell in a threatened square.

        Returns True if the caster dropped or failed concentration (spell fizzles).
        """
        for cell in caster.occupied_cells():
            for enemy in self.enemies_threatening(caster, cell):
                if self._aoo_used.get(enemy.combatant.id, 0) >= self._aoo_allowance(enemy):
                    continue
                hp_before = caster.hp
                self._resolve_aoo(enemy, caster)
                if not caster.active:
                    self._log(
                        f"round {self._current_round} {caster.combatant.id}: "
                        f"casting interrupted by AoO from {enemy.combatant.id}"
                    )
                    return True
                # Concentration check if damaged
                dmg = hp_before - caster.hp
                if dmg > 0 and not self._check_concentration(caster, spell_level, dmg):
                    dc = self._concentration_dc(caster, spell_level, dmg)
                    self._log(
                        f"round {self._current_round} {caster.combatant.id}: "
                        f"concentration check failed (DC {dc}), spell fizzles"
                    )
                    return True
        return False

    def _concentration_dc(
        self, caster: CombatantState, spell_level: int, damage_taken: int
    ) -> int:
        """Concentration DC for the caster's current situation.

        - injured while casting: => 10 + damage_taken + spell_level
        - grappled or pinned:    => 10 + grappler's CMB + spell_level
        - casting defensively:   => 15 + 2 * spell_level
        """
        if caster.grappled_with is not None:
            grappler = next(
                (s for s in self._states if s.combatant.id == caster.grappled_with), None
            )
            cmb = self._maneuver_cmb(grappler) if grappler is not None else 0
            return 10 + cmb + spell_level
        if damage_taken > 0:
            return 10 + damage_taken + spell_level
        return 15 + 2 * spell_level

    def _entangled_concentration_dc(self, spell_level: int) -> int:
        """SRD Table 9-1: "Entangled while casting" => DC 15 + spell level."""
        return 15 + spell_level

    def _check_concentration(
        self,
        caster: CombatantState,
        spell_level: int,
        damage_taken: int,
        *,
        dc_override: int | None = None,
    ) -> bool:
        """Concentration check: DC depends on situation.

        PF1e (CRB): the check is d20 + caster level + the ability modifier
        used to determine bonus spells (Int/Wis/Cha) — NOT Constitution.
        Combat Casting's +4 applies only when casting defensively, while
        grappled/pinned, or while entangled, never for damage taken while
        casting. ``dc_override`` pins the DC (used by the entangled gate).
        """
        dc = (
            self._concentration_dc(caster, spell_level, damage_taken)
            if dc_override is None
            else dc_override
        )
        injured_while_casting = damage_taken > 0 and caster.grappled_with is None
        has_combat_casting = self._has_feat(caster, _COMBAT_CASTING_FEAT)
        bonus = 0 if injured_while_casting else (4 if has_combat_casting else 0)
        roll = self._rng.d20()
        total = (
            roll + caster.combatant.level + self._casting_ability_mod(caster) + bonus
        )
        return total >= dc
    def can_step5_to_attack(self, state: CombatantState, target: CombatantState) -> bool:
        """True if a 5-foot step toward ``target`` would put ``state`` in weapon range."""
        path = self._move_path(state, target)
        if not path:
            return False
        orig = state.pos
        state.pos = path[0]
        weapon = self.weapon_for(state, target)
        state.pos = orig
        return weapon is not None

    def _charge_speed_mult(self, state: CombatantState) -> int:
        """Charge speed multiplier: 2x normally; 1x for a creature restricted
        to a single standard action — PF1e (SRD "Charge"): "If you are able to
        take only a standard action on your turn, you can still charge, but
        you are only allowed to move up to your speed (instead of up to double
        your speed)" — staggered/disabled creatures and the surprise round
        (mirrors the Restricted Withdraw exception).
        """
        if self._surprise_round or self._is_staggered_limited(state):
            return 1
        return 2

    def can_charge(self, state: CombatantState, target: CombatantState) -> ChargeResult | None:
        """Return a ``ChargeResult`` if ``state`` can charge ``target`` this turn, else None.

        PF1e charge requirements (CRB):
        - Must have line of sight to the target at the start of the turn.
        - Must move at least 10 ft (2 squares) and at most double speed.
        - Must move in a straight line (Bresenham) to the closest attackable square.
        - The path must not pass through blocking terrain, difficult terrain, or creatures.
        - Must end adjacent to the target (within melee reach).
        - Only a single melee attack is allowed.

        Returns ``None`` only when the attacker has no usable melee weapon at all.
        Otherwise returns a ``ChargeResult``: ``weapon`` set and ``reason`` None on
        success, or ``weapon`` None with ``reason`` explaining the failure
        (``no_line_of_effect`` or ``no_charge_path``). ``distance_ft`` is the
        straight-line distance in feet to the chosen anchor on success, 0 on
        failure. Never mutates state nor consumes RNG.
        """
        if not has_line_of_effect_cells(
            self._grid, state.occupied_cells(), target.occupied_cells()
        ):
            return ChargeResult(weapon=None, distance_ft=0, reason="no_line_of_effect")
        speed_cells = _speed_ft(state) // _SQUARE_FT
        max_cells = self._charge_speed_mult(state) * speed_cells
        blocked = self._blocked(state, target)
        melee_weapons = [w for w in state.usable_attacks() if w.kind == "melee"]
        if not melee_weapons:
            return None
        for weapon in melee_weapons:
            inner_cells, reach_cells = _melee_reach_zone_cells(state, weapon)
            end = self._charge_end(
                state, target, reach_cells, max_cells, blocked, min_reach_cells=inner_cells
            )
            if end is not None:
                distance_ft = self._grid.distance(state.pos, end) * _SQUARE_FT
                return ChargeResult(weapon=weapon, distance_ft=distance_ft, reason=None)
        return ChargeResult(weapon=None, distance_ft=0, reason="no_charge_path")

    def _path_cost_5105(self, path: list[Pos]) -> int:
        """Total 5-10-5 movement cost of a path (diagonal parity threaded)."""
        total = 0
        diagonals_used = 0
        for frm, to in pairwise(path):
            total += self._grid.step_cost(frm, to, diagonals_used)
            if frm[0] != to[0] and frm[1] != to[1]:
                diagonals_used += 1
        return total

    def _charge_end(
        self,
        state: CombatantState,
        target: CombatantState,
        reach_cells: int,
        max_cells: int,
        blocked: frozenset[Pos],
        *,
        min_reach_cells: int = 0,
    ) -> Pos | None:
        """Find the closest anchor from which ``state`` can melee ``target`` via a charge.

        Scans anchors within reach of the target, picks the one whose Bresenham
        line from ``state.pos`` is the shortest valid charge path (>=2 cells,
        <=max_cells, no blocking terrain or creatures, footprint fits at the
        end, footprint-to-footprint distance within the weapon's reach band).
        Ties break toward lower distance from state.
        """
        target_cells = target.occupied_cells()
        candidates: list[tuple[int, Pos]] = []
        for end in self._charge_candidates(target, reach_cells, blocked, state.pos):
            footprint = self._footprint_at(end, state)
            if not self._cells_free(footprint, state):
                continue
            dist = min(
                self._grid.distance(cell_a, cell_b)
                for cell_a in footprint
                for cell_b in target_cells
            )
            if dist > reach_cells or dist < min_reach_cells:
                continue
            path = _bresenham_line(state.pos, end)
            if len(path) < _CHARGE_MIN_CELLS:
                continue
            if not self._charge_path_clear(path, state):
                continue
            # The charge budget is a movement budget: count it in 5-10-5
            # squares (diagonal parity threaded), not raw cells.
            if self._path_cost_5105(path) > max_cells:
                continue
            candidates.append((len(path), end))
        if not candidates:
            return None
        candidates.sort(key=lambda x: (x[0], self._grid.distance(state.pos, x[1])))
        return candidates[0][1]

    def _charge_candidates(
        self,
        target: CombatantState,
        reach_cells: int,
        blocked: frozenset[Pos],
        start: Pos,
    ) -> list[Pos]:
        """Anchors within reach of some target cell, passable, unoccupied, not the start."""
        result: set[Pos] = set()
        for tr, tc in target.occupied_cells():
            for dr in range(-reach_cells, reach_cells + 1):
                for dc in range(-reach_cells, reach_cells + 1):
                    if abs(dr) > reach_cells or abs(dc) > reach_cells:
                        continue
                    if dr == 0 and dc == 0:
                        continue
                    end = (tr + dr, tc + dc)
                    if end == start:
                        continue
                    if not self._grid.in_bounds(end) or not self._grid.passable(end):
                        continue
                    if end in blocked:
                        continue
                    result.add(end)
        return sorted(result)

    def _charge_path_clear(
        self, path: list[Pos], state: CombatantState
    ) -> bool:
        """True if the footprint fits at every anchor on the charge path."""
        for pos in path:
            if not self._cells_free(self._footprint_at(pos, state), state):
                return False
            terrain = self._grid.terrain_at(pos)
            if terrain.move_cost is not None and terrain.move_cost > 1:
                return False
        return True

    def _charge(
        self, attacker: CombatantState, target: CombatantState, weapon: AttackSpec
    ) -> None:
        """Execute a charge: move in a straight line, then make a single melee attack at +2.

        Sets a -2 AC penalty on the attacker that lasts until the start of their next turn
        (cleared in ``_take_turn``). Movement during a charge provokes AoOs step-by-step
        as for any move action. Like every other movement it is mutually exclusive
        with movement already spent this turn (``moved_this_turn``).
        """
        if attacker.moved_this_turn:
            return
        inner_cells, reach_cells = _melee_reach_zone_cells(attacker, weapon)
        speed_cells = _speed_ft(attacker) // _SQUARE_FT
        max_cells = self._charge_speed_mult(attacker) * speed_cells
        blocked = self._blocked(attacker, target)
        end = self._charge_end(
            attacker, target, reach_cells, max_cells, blocked, min_reach_cells=inner_cells
        )
        if end is None:
            return
        path = _bresenham_line(attacker.pos, end)
        start = attacker.pos
        actual_path: list[Pos] = []
        for step in path:
            if self._check_move_aoo(attacker):
                break
            if not attacker.active:
                break
            attacker.pos = step
            actual_path.append(step)
            self._check_reactions(
                ReactionEvent(kind="movement_step", actor=attacker)
            )
            if not attacker.active:
                break
        if actual_path:
            attacker.moved_this_turn = True
            coords = "->".join(f"({p[0]},{p[1]})" for p in (start, *actual_path))
            self._log(
                f"round {self._current_round} {attacker.combatant.id}: charge {coords}"
            )
        attacker.active_buffs.append(
            ActiveBuff(
                modifiers=(StatModifier(target="ac", value=-_CHARGE_AC_PENALTY),),
                rounds_left=1,
                source="charge",
            )
        )
        bonus = weapon.attack_bonus + _CHARGE_ATTACK_BONUS
        self._resolve_swing(
            attacker, target, weapon, label="charge", bonus_override=bonus
        )

    def _execute(self, state: CombatantState, action: Action) -> ActionResult:
        """Execute one action and return its explicit result.

        Rejections (unsupported kinds, missing target) are logged and never
        reach the helpers; everything else dispatches exactly as before and
        reports ok.
        """
        kind = action.kind
        if kind in _UNSUPPORTED_ACTION_KINDS:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"{kind} rejected ({_REASON_UNSUPPORTED_KIND})"
            )
            return ActionResult(
                kind=kind, ok=False, reason=_REASON_UNSUPPORTED_KIND
            )
        target = next((s for s in self._states if s.combatant.id == action.target_id), None)
        rejection = self._target_rejection(state, kind, target, action)
        if rejection is not None:
            return rejection
        direct = self._execute_direct(state, target, action)
        if direct is not None:
            return direct
        override = self._dispatch_action(state, target, action)
        return override if override is not None else ActionResult(
            kind=kind, ok=True, reason=_REASON_OK
        )

    def _execute_direct(
        self, state: CombatantState, target: CombatantState | None, action: Action
    ) -> ActionResult | None:
        """Execute the kinds with a dedicated (non-target-dispatch) helper.

        delay/ready (U3/U4), the self-affecting defensive and prone actions
        (U5a/U5b) and the aid another / run pair (U5e) each own an explicit
        result; None means the action is not one of these kinds and the
        caller must fall through to ``_dispatch_action``.
        """
        kind = action.kind
        if kind == "delay":
            return self._execute_delay(state, target, action)
        if kind == "ready":
            return self._execute_ready(state, action)
        if kind in ("total_defense", "fight_defensively", "stand_up", "drop_prone"):
            return self._execute_self_action(state, kind)
        if kind == "aid_another":
            return self._execute_aid_another(state, target, action)
        if kind == "run":
            return self._execute_run(state, target, action)
        return None

    def _target_rejection(
        self,
        state: CombatantState,
        kind: str,
        target: CombatantState | None,
        action: Action,
    ) -> ActionResult | None:
        """U1 missing-target gate; move/5foot_step/run accept a destination instead
        (U5c / U5e); cast_spell accepts a target_pos instead (U7b)."""
        if target is not None or kind not in _TARGET_REQUIRED_ACTION_KINDS:
            return None
        if kind in ("move", "5foot_step", "run") and action.destination is not None:
            return None
        if kind == "cast_spell" and action.target_pos is not None:
            return None
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"{kind} rejected ({_REASON_MISSING_TARGET})"
        )
        return ActionResult(kind=kind, ok=False, reason=_REASON_MISSING_TARGET)

    def _execute_delay(
        self, state: CombatantState, target: CombatantState | None, action: Action
    ) -> ActionResult:
        """Execute the delay action (PF1e): forgo this turn, act later this round.

        With no target the combatant acts at the end of the round; with one it
        acts immediately before it. The new initiative total (target total
        minus 0.5, or the minimum total minus 0.5) is written into
        ``_initiative_keys`` so ``_build_round_order`` keeps the position for
        the following rounds. A second delay in the same round is rejected
        (``already_delayed``) to prevent an infinite delay loop.
        """
        kind = action.kind
        if state.delayed_this_round:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"{kind} rejected ({_REASON_ALREADY_DELAYED})"
            )
            return ActionResult(
                kind=kind, ok=False, reason=_REASON_ALREADY_DELAYED
            )
        key = self._initiative_keys.get(state.combatant.id)
        prior_index = key[2] if key is not None else self._states.index(state)
        if target is not None:
            target_key = self._initiative_keys.get(target.combatant.id)
            target_total = target_key[0] if target_key is not None else 0.0
            new_total = target_total - _DELAY_INITIATIVE_STEP
        else:
            totals = [k[0] for k in self._initiative_keys.values()]
            new_total = (
                min(totals) - _DELAY_INITIATIVE_STEP if totals else 0.0
            )
        self._initiative_keys[state.combatant.id] = (
            new_total,
            state.combatant.initiative_mod,
            prior_index,
        )
        state.delayed_this_round = True
        state.delay_before = target.combatant.id if target is not None else None
        if target is not None:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"{kind} before {target.combatant.id}"
            )
        else:
            self._log(f"round {self._current_round} {state.combatant.id}: {kind}")
        return ActionResult(kind=kind, ok=True, reason=_REASON_DELAYED)

    def _execute_ready(self, state: CombatantState, action: Action) -> ActionResult:
        """Execute the ready action (PF1e): spend the standard action preparing a
        payload that fires off-turn when its trigger event occurs.

        The payload is derived from the carrier fields like
        ``_execute_immediate`` (spell / maneuver / attack on ``target_id``;
        class-ability payloads are out of scope for U4). A new ready replaces
        any pending one. The engine fires it through ``_check_readied``, then
        the readied action is consumed. The turn loop keeps running (a policy
        may still spend the move action).
        """
        kind = action.kind
        state.readied = _ready_payload(action)
        state.readied_trigger = action.ready_trigger
        label = action.ready_trigger or "no trigger"
        self._log(
            f"round {self._current_round} {state.combatant.id}: {kind} ({label})"
        )
        return ActionResult(kind=kind, ok=True, reason=_REASON_READY)

    def _execute_self_action(self, state: CombatantState, kind: str) -> ActionResult:
        """Dispatch a target-free self-affecting action to its helper."""
        if kind == "total_defense":
            return self._execute_total_defense(state)
        if kind == "fight_defensively":
            return self._execute_fight_defensively(state)
        if kind == "stand_up":
            return self._execute_stand_up(state)
        return self._execute_drop_prone(state)

    def _execute_total_defense(self, state: CombatantState) -> ActionResult:
        """Execute the total defense action (PF1e): standard action granting a
        +4 dodge bonus to AC until the start of the combatant's next turn.
        PF1e (SRD "Total Defense"): "You can't make attacks of opportunity
        while using total defense" — the flag drops the AoO allowance to 0
        (see ``_aoo_allowance``) — and "You can't combine total defense with
        fighting defensively": the bonus is SET (never stacked on a prior
        +2) and a pending fighting-defensively declaration is voided (under
        total defense no attack is made, so its -4 is moot).
        """
        state.total_defense = True
        state.fight_defensively = False
        state.defensive_ac_bonus = _TOTAL_DEFENSE_AC_BONUS
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"total defense (+{_TOTAL_DEFENSE_AC_BONUS} AC)"
        )
        return ActionResult(kind="total_defense", ok=True, reason=_REASON_OK)

    def _execute_fight_defensively(self, state: CombatantState) -> ActionResult:
        """Execute the fighting defensively action (PF1e): standard action
        granting a +2 dodge bonus to AC until the start of the combatant's
        next turn, at the cost of -4 on attack and crit confirmation rolls.
        PF1e (SRD "Total Defense"): "You can't combine total defense with
        fighting defensively" — the declaration is rejected while total
        defense is active.
        """
        if state.total_defense:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"fight_defensively rejected ({_REASON_CANNOT_COMBINE})"
            )
            return ActionResult(
                kind="fight_defensively", ok=False, reason=_REASON_CANNOT_COMBINE
            )
        state.fight_defensively = True
        state.defensive_ac_bonus += _FIGHT_DEFENSIVELY_AC_BONUS
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"fighting defensively ({_FIGHT_DEFENSIVELY_ATTACK_PENALTY} attack, "
            f"+{_FIGHT_DEFENSIVELY_AC_BONUS} AC)"
        )
        return ActionResult(kind="fight_defensively", ok=True, reason=_REASON_OK)

    def _execute_stand_up(self, state: CombatantState) -> ActionResult:
        """Execute the stand up action (PF1e): move action that ends prone.

        Standing up provokes an AoO from each enemy threatening the
        combatant's squares (``_check_move_aoo`` with ``movement=False``:
        standing is a separate trigger, never deduped against a movement
        opportunity already taken this round);
        the AoOs resolve while the combatant is still prone (-4 AC). The
        prone condition is then removed from both representations: the
        duration-tracked ``active_conditions`` (trip/overrun) and the
        duration-less ``conditions`` list (drop_prone). If a provoked AoO
        takes the combatant out of the fight, the removal is a formality —
        inactive combatants do not act.
        """
        kind = "stand_up"
        if not self._has_condition_named(state, "prone"):
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"{kind} rejected ({_REASON_NOT_PRONE})"
            )
            return ActionResult(kind=kind, ok=False, reason=_REASON_NOT_PRONE)
        self._check_move_aoo(state, movement=False)
        state.active_conditions = [
            ac for ac in state.active_conditions if ac.condition.name != "prone"
        ]
        state.conditions = [c for c in state.conditions if c.name != "prone"]
        self._log(f"round {self._current_round} {state.combatant.id}: stands up")
        return ActionResult(kind=kind, ok=True, reason=_REASON_OK)

    def _execute_drop_prone(self, state: CombatantState) -> ActionResult:
        """Execute the drop prone action (PF1e): free action that goes prone.

        The prone condition is appended to the duration-less ``conditions``
        list (trip/overrun use the duration-tracked ``active_conditions``
        instead), so it persists until the combatant stands up. Both lists
        are read by ``_has_condition_named``, so the prone modifiers
        (-4 AC, -4 ranged attacks) apply immediately.
        """
        kind = "drop_prone"
        if self._has_condition_named(state, "prone"):
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"{kind} rejected ({_REASON_ALREADY_PRONE})"
            )
            return ActionResult(kind=kind, ok=False, reason=_REASON_ALREADY_PRONE)
        state.conditions.append(CONDITIONS_BY_NAME["prone"])
        self._log(f"round {self._current_round} {state.combatant.id}: drops prone")
        return ActionResult(kind=kind, ok=True, reason=_REASON_OK)

    def _execute_aid_another(
        self, state: CombatantState, target: CombatantState | None, action: Action
    ) -> ActionResult:
        """Execute the aid another action (PF1e, U5e simplification).

        The aider needs a usable melee weapon and makes an attack roll
        (d20 + the first usable melee weapon's bonus) against AC 10; natural
        20 always succeeds and natural 1 always fails (attack-roll
        convention). On success the target stacks +2 on its next attack roll
        (``aid_mode`` "attack" or None) or +2 AC against the next attack
        targeting it (``aid_mode`` "ac"); multiple aids add up. Documented
        simplifications: no adjacency/line-of-effect check on the ally, and
        any resolved target may be aided (the aider's side is not enforced).
        """
        kind = "aid_another"
        if target is None:
            return ActionResult(kind=kind, ok=False, reason=_REASON_MISSING_TARGET)
        weapon = next((w for w in state.usable_attacks() if w.kind == "melee"), None)
        if weapon is None:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"{kind} rejected ({_REASON_NO_WEAPON})"
            )
            return ActionResult(kind=kind, ok=False, reason=_REASON_NO_WEAPON)
        mode = "ac" if action.aid_mode == "ac" else "attack"
        roll = self._rng.d20()
        total = roll + weapon.attack_bonus
        success = (
            roll == _NATURAL_TWENTY
            or (roll != _NATURAL_ONE and total >= _AID_ANOTHER_DC)
        )
        if success:
            if mode == "ac":
                target.aid_ac_bonus += _AID_ANOTHER_BONUS
            else:
                target.aid_attack_bonus += _AID_ANOTHER_BONUS
            state.aid_grants.append((target.combatant.id, mode))
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"aid another {target.combatant.id} ({mode}) "
            f"d20={roll}+{weapon.attack_bonus}={total} vs AC {_AID_ANOTHER_DC} "
            f"-> {'success' if success else 'fail'}"
        )
        return ActionResult(kind=kind, ok=True, reason=_REASON_OK)

    def _expire_aid_grants(self, aider: CombatantState) -> None:
        """Remove this aider's unspent aid bonuses from its beneficiaries.

        PF1e (SRD "Aid Another"): the +2 lasts "as long as that attack comes
        before the beginning of your next turn" — your = the AIDER's turn, so
        expiry is tracked on the aider. Each grant subtracts its +2 from the
        beneficiary's pool (floor 0 — a bonus already consumed by an attack
        is untouched). Simplification: an aider removed before its next turn
        never expires its grants (the engine has no death hook for them).
        """
        for target_id, mode in aider.aid_grants:
            for state in self._states:
                if state.combatant.id != target_id:
                    continue
                if mode == "ac":
                    state.aid_ac_bonus = max(0, state.aid_ac_bonus - _AID_ANOTHER_BONUS)
                else:
                    state.aid_attack_bonus = max(
                        0, state.aid_attack_bonus - _AID_ANOTHER_BONUS
                    )
                break
        aider.aid_grants = []

    def _execute_run(
        self, state: CombatantState, target: CombatantState | None, action: Action
    ) -> ActionResult:
        """Execute the run action (PF1e, U5e): full-round movement at 4x speed.

        PF1e (SRD "Full-Round Actions — Run"): "When you run, you can move up
        to four times your speed in a straight line" — a run is NOT a ``move``:
        it cannot turn a corner. The path is the straight Bresenham line from
        the combatant's position toward an explicit destination (U5c) or the
        resolved target, walked under a 4x speed budget with the usual step-by-
        step AoO provocation, and truncated at the first obstacle (impassable
        terrain, a difficult-terrain cell, or a blocking creature) exactly like
        the charge's clear-path rule (``_run_line_path``). PF1e forbids running
        across difficult terrain (CRB "Movement, Position and Distance —
        Difficult Terrain": "You can't run or charge across difficult
        terrain"), so a difficult cell stops the run short. An auto-directed
        run advances until the obstacle and stops there (deterministic); a
        hostile creature (the target included) halts it one cell short, so it
        ends adjacent to the target. Friendly squares are still crossed, never
        ended on (SRD Movement, conformance L5). On completion the combatant is
        ``running`` until the start of its next turn, which denies it its
        Dexterity bonus to AC. An explicit destination that the straight line
        cannot honour within the 4x budget (blocked by terrain, difficult
        terrain, a creature, or out of range) is rejected with
        ``unreachable_destination``; with neither target nor destination the
        U1 gate rejects the action with ``missing_target``.
        """
        kind = "run"
        if state.moved_this_turn:
            # Defense in depth, mirroring the _move/_5foot_step no-op-ok
            # convention. Unreachable through the filtered path: run is a
            # full-round action, so no move-slot action can precede it in a
            # kept sequence (the budget filter would have dropped one).
            return ActionResult(kind=kind, ok=True, reason=_REASON_OK)
        if self.has_condition_flag(state, "cant_move"):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot move)")
            return ActionResult(kind=kind, ok=True, reason=_REASON_OK)
        # SRD "Conditions — Fatigued": "A fatigued character can neither run
        # nor charge" (same for exhausted/entangled via cant_charge).
        if self.has_condition_flag(state, "cant_charge"):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot run)")
            return ActionResult(kind=kind, ok=True, reason=_REASON_OK)
        if action.destination is not None:
            if action.destination == state.pos:
                path: list[Pos] = []  # already there: a valid zero-length run
            else:
                path = self._run_line_path(state, action.destination)
                if not path or path[-1] != action.destination:
                    path = []  # the straight line could not honour it
            if not path and action.destination != state.pos:
                self._log(
                    f"round {self._current_round} {state.combatant.id}: "
                    f"{kind} rejected ({_REASON_UNREACHABLE_DESTINATION})"
                )
                return ActionResult(
                    kind=kind, ok=False, reason=_REASON_UNREACHABLE_DESTINATION
                )
            self._walk_steps(state, path)
            state.moved_this_turn = True
        elif target is not None:
            path = self._run_line_path(state, target.pos)
            if self._walk_steps(state, path):
                state.moved_this_turn = True
        state.running = True
        self._log(f"round {self._current_round} {state.combatant.id}: run")
        return ActionResult(kind=kind, ok=True, reason=_REASON_OK)

    def _dispatch_action(
        self, state: CombatantState, target: CombatantState | None, action: Action
    ) -> ActionResult | None:
        """Route a validated action to its execution helper.

        Returns an explicit rejection when a destination-bearing movement
        cannot be honoured (U5c), an attack's chosen weapon is unavailable
        (U5d), or a spell's point target is off-map / without line of effect
        (U7b); None means the helper ran and the caller reports ok.
        """
        kind = action.kind
        if kind == "cast_spell":
            return self._execute_cast_spell(
                state, target, action.spell_name, target_pos=action.target_pos,
                metamagic=action.metamagic, cast_defensively=action.cast_defensively,
            )
        if kind == "maneuver":
            self._execute_maneuver(
                state, target, action.maneuver,
                direction=action.direction, trick_condition=action.trick_condition,
            )
        elif kind == "retrieve_weapon":
            self._retrieve_weapon(state, action.weapon_id)
        elif kind == "repair_weapon":
            self._repair_weapon(state, action.weapon_id)
        elif kind in ("channel_energy", "hex", "deed", "spell_combat", "inspire_courage"):
            self._execute_class_ability(state, target, action)
        elif kind == "charge":
            self._execute_charge(state, target)
        elif kind == "withdraw":
            self._withdraw(state, target)
        elif kind in ("attack", "full_attack"):
            return self._execute_attack(state, target, kind, action.weapon_id)
        elif kind == "immediate":
            self._execute_immediate(state, target, action)
        else:
            return self._execute_movement(state, target, action)
        return None

    def _execute_class_ability(
        self, state: CombatantState, target: CombatantState | None, action: Action
    ) -> None:
        """Dispatch a class-ability action by kind, reading its carrier field."""
        kind = action.kind
        if kind == "channel_energy":
            self._execute_channel_energy(
                state, target, action.channel_mode or "heal"
            )
        elif kind == "hex":
            self._execute_hex(state, target, action.hex_name)
        elif kind == "deed":
            self._execute_deed(state, target, action.deed_name)
        elif kind == "spell_combat":
            self._execute_spell_combat(state, target, action.spell_name)
        elif kind == "inspire_courage":
            self._execute_inspire_courage(state, target)

    def _execute_movement(
        self, state: CombatantState, target: CombatantState | None, action: Action
    ) -> ActionResult | None:
        """Execute a movement-style action (5foot_step, move, wait).

        With an explicit destination, move/5foot_step walk to that cell and
        report unreachable_destination when it cannot be honoured (U5c);
        without one they auto-path toward the target as before.
        """
        kind = action.kind
        if kind == "5foot_step":
            if action.destination is not None:
                return self._step5_to(state, action.destination)
            if target is None:
                return None
            self._step5(state, target)
        elif kind == "move":
            if action.destination is not None:
                return self._move_to(state, action.destination)
            if target is None:
                return None
            self._move(state, target)
        elif kind == "wait":
            self._log(f"round {self._current_round} {state.combatant.id}: wait")
        elif kind == "activate_power_attack":
            self._execute_activate_power_attack(state)
        return None

    def _execute_immediate(
        self, state: CombatantState, target: CombatantState | None, action: Action
    ) -> None:
        """Execute an immediate action (off-turn or in-turn).

        PF1e (SRD Immediate Actions): "Using an immediate action on your turn
        is the same as using a swift action and counts as your swift action
        for that turn." An immediate fired during the creature's OWN turn
        therefore spends the CURRENT turn's swift (``swift_used_this_turn``:
        swift actions later in the sequence are dropped, and no further
        immediate fires this round). Off-turn, the immediate consumes the
        NEXT turn's swift (``immediate_used``), which suppresses swift/free
        bonus actions on the following turn. The effect is resolved by the
        action's carrier fields: a spell, a maneuver, a class ability, or a
        single attack on ``target``.
        """
        if self._turn_actor is state:
            state.swift_used_this_turn = True
        else:
            state.immediate_used = True
        if action.spell_name is not None:
            self._execute_cast_spell(
                state, target, action.spell_name, target_pos=action.target_pos,
                metamagic=action.metamagic, cast_defensively=action.cast_defensively,
            )
        elif action.maneuver is not None:
            self._execute_maneuver(state, target, action.maneuver)
        elif action.class_ability is not None:
            self._execute_class_ability(state, target, action)
        elif target is not None:
            self._execute_attack(state, target, "attack")

    def _execute_activate_power_attack(self, state: CombatantState) -> None:
        """Activate Power Attack as a free action (requires the feat)."""
        if not self._has_feat(state, "Power Attack"):
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"activate_power_attack: no Power Attack feat"
            )
            return
        state.power_attack = True
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"Power Attack activated"
        )

    def _check_reactions(self, event: ReactionEvent) -> None:
        """Fire readied actions first, then offer the event to the reaction policy.

        A pending readied action fires independently of ``reaction_policy``;
        at most one trigger resolves per event (a fired readied action
        suppresses the policy loop). One immediate per event: the first active
        combatant (in state order) whose policy returns an action gets to act.
        PF1e (SRD "Immediate Actions"): "You also cannot use an immediate
        action if you are flat-footed" — flat-footed states are skipped.
        Reactions never cascade — while a reaction is executing, further
        events are ignored.
        """
        if self._in_reaction:
            return
        if self._check_readied(event):
            return
        if self._reaction_policy is None:
            return
        for state in self._states:
            if (
                not state.active
                or state.immediate_used
                or state.swift_used_this_turn
                or self._has_condition_named(state, "flat_footed")
            ):
                continue
            action = self._reaction_policy(self, state, event)
            if action is None:
                continue
            self._in_reaction = True
            self._execute(state, action)
            self._in_reaction = False
            return

    def _expire_readied_action(self, state: CombatantState) -> None:
        """PF1e (SRD "Ready — Initiative Consequences of Readying"): "If you
        come to your next action and have not yet performed your readied
        action, you don't get to take the readied action (though you can
        ready the same action again)." An untriggered readied action expires
        at the START of the combatant's next turn, before the policy runs (a
        forfeited turn still expires it)."""
        if state.readied is None:
            return
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            "ready expired (trigger never occurred)"
        )
        state.readied = None
        state.readied_trigger = None

    def _check_readied(self, event: ReactionEvent) -> bool:
        """Fire the first matching readied action; True when one fired.

        Any active combatant (in state order) whose pending trigger matches
        the event executes its payload off-turn with no swift cost. The
        pending action is cleared BEFORE the payload runs, so a readied
        action is one-shot and never re-fires on its own events; the payload's
        own events are additionally suppressed by ``_in_reaction``.
        """
        for state in self._states:
            payload = state.readied
            if not state.active or payload is None:
                continue
            if not self._ready_trigger_matches(state, event):
                continue
            trigger = state.readied_trigger
            state.readied = None
            state.readied_trigger = None
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"ready fires ({trigger})"
            )
            self._ready_shift_initiative(state, event.actor)
            target = next(
                (s for s in self._states if s.combatant.id == payload.target_id),
                None,
            )
            self._in_reaction = True
            self._dispatch_action(state, target, payload)
            self._in_reaction = False
            return True
        return False

    def _ready_shift_initiative(
        self, state: CombatantState, trigger_actor: CombatantState
    ) -> None:
        """Move the readier's initiative to the count it acted on (PF1e).

        PF1e (SRD "Ready — Initiative Consequences of Readying"): "Your
        initiative result becomes the count on which you took the readied
        action" and you "act immediately ahead of the character whose action
        triggered your readied action" — for the rest of the encounter. The
        slot is written into ``_initiative_keys`` with the same tuple shape
        ``_execute_delay`` uses (a 0.5 step off the anchor total, keeping the
        readier's initiative modifier and prior list index) so
        ``_build_round_order`` holds the new position for every following
        round. The step is ADDED (not subtracted as for delay): a readied
        action interrupts and acts immediately AHEAD of the trigger, whereas a
        delay postpones to act after — the two intents are opposite.
        Deterministic: no RNG is consumed and the current round's order
        (already built) is untouched — only subsequent rounds reorder.
        """
        key = self._initiative_keys.get(state.combatant.id)
        prior_index = key[2] if key is not None else self._states.index(state)
        trigger_key = self._initiative_keys.get(trigger_actor.combatant.id)
        trigger_total = trigger_key[0] if trigger_key is not None else 0.0
        self._initiative_keys[state.combatant.id] = (
            trigger_total + _DELAY_INITIATIVE_STEP,
            state.combatant.initiative_mod,
            prior_index,
        )

    def _ready_trigger_matches(
        self, state: CombatantState, event: ReactionEvent
    ) -> bool:
        """True when the event matches the combatant's pending readied trigger.

        Firing requires the event actor to be an ENEMY of the readier
        (different side); ``enemy_hits_ally`` additionally requires the
        damage target to share the readier's side. ``enemy_enters_reach``
        fires on any enemy movement step — documented simplification: reach
        is not re-computed per step.
        """
        trigger = state.readied_trigger
        if trigger is None:
            return False
        hostile = event.actor.side != state.side
        if trigger == "enemy_enters_reach":
            return hostile and event.kind == "movement_step"
        if trigger == "enemy_casts":
            return hostile and event.kind == "spell_cast"
        if trigger == "enemy_attacks":
            return hostile and event.kind == "attack_resolved"
        return (
            hostile
            and event.kind == "damage_taken"
            and event.target is not None
            and event.target.side == state.side
        )

    def _execute_cast_spell(
        self,
        state: CombatantState,
        target: CombatantState | None,
        spell_name: str | None,
        *,
        target_pos: tuple[int, int] | None = None,
        metamagic: tuple[str, ...] = (),
        cast_defensively: bool = False,
    ) -> ActionResult | None:
        """Cast the carried spell; an explicit ``target_pos`` (U7b) is
        validated first — an off-map point or one without line of effect
        from the caster is rejected without casting. ``metamagic`` (B7)
        selects the feats applied to THIS cast; ``cast_defensively`` (B24)
        trades the casting AoO for a concentration check."""
        if self.has_condition_flag(state, "cant_attack"):
            # PF1e (CRB): a nauseated creature cannot cast spells or
            # concentrate; the cant_attack flag blocks the cast entirely.
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"cast_spell rejected (cannot attack)"
            )
            return None
        if target_pos is not None:
            rejection = self._point_target_rejection(state, target_pos)
            if rejection is not None:
                return rejection
        if spell_name is None:
            return None
        return self._cast_spell(
            state, target, spell_name, center_pos=target_pos,
            metamagic=metamagic, cast_defensively=cast_defensively,
        )

    def _point_target_rejection(
        self, state: CombatantState, target_pos: tuple[int, int]
    ) -> ActionResult | None:
        """U7b gate: a point-targeted area must be in bounds and reachable."""
        if self._grid.in_bounds(target_pos) and has_line_of_effect_cells(
            self._grid, state.occupied_cells(), frozenset({target_pos})
        ):
            return None
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"cast_spell rejected ({_REASON_INVALID_DESTINATION})"
        )
        return ActionResult(
            kind="cast_spell", ok=False, reason=_REASON_INVALID_DESTINATION
        )

    def _execute_maneuver(
        self,
        state: CombatantState,
        target: CombatantState | None,
        maneuver: str | None,
        *,
        direction: tuple[int, int] | None = None,
        trick_condition: TrickCondition | None = None,
    ) -> None:
        """Execute a combat maneuver (trip, disarm, bull_rush, sunder, grapple,
        escape, overrun, dirty_trick, steal, reposition, drag)."""
        if target is None or not target.active:
            return
        if self.has_condition_flag(state, "cant_attack"):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot attack)")
            return
        if maneuver == "escape":
            self._maneuver_escape(state, target)
            return
        if maneuver not in (
            "trip", "disarm", "bull_rush", "sunder", "grapple",
            "overrun", "dirty_trick", "steal", "reposition", "drag",
        ):
            return
        # PF1e (SRD Trip / Bull Rush / Overrun; APG Reposition / Drag): "You
        # can only [affect] an opponent who is no more than one size category
        # larger than you." The attempt is illegal outright: no roll, no
        # provoked AoO.
        if maneuver in _SIZE_RESTRICTED_MANEUVERS and (
            _size_rank(target.combatant.size) - _size_rank(state.combatant.size)
            >= _MANEUVER_MAX_SIZE_DIFF
        ):
            self._log(
                f"round {self._current_round} {state.combatant.id}: {maneuver} vs "
                f"{target.combatant.id} rejected (target too large)"
            )
            return

        # PF1e (CRB, Combat Maneuver): attempting the maneuver provokes an
        # attack of opportunity from the target — resolved BEFORE the CMB
        # check — unless the attacker holds the Improved feat for it. Damage
        # taken from that AoO is applied as a penalty to the maneuver check
        # (CRB: "apply that amount as a penalty to the attack roll to perform
        # the maneuver"); being knocked below 0 hp by it forfeits the
        # maneuver.
        aoo_damage = 0
        if not self._has_feat(state, _IMPROVED_MANEUVER_FEATS[maneuver]):
            hp_before = state.hp
            self._maneuver_provoked_aoo(state, target)
            aoo_damage = max(0, hp_before - state.hp)
            if not state.active:
                return

        # PF1e (CRB Power Attack): the -X penalty applies to all melee attack
        # rolls AND combat maneuver checks while the feat is active. The
        # escape option that substitutes an Acrobatics/Escape Artist skill
        # check is not penalized (a skill check is not a CMB check) — see
        # _maneuver_escape.
        pa_amt = self._power_attack_amt(state)
        # PF1e (SRD Conditions - Grappled / Pinned): a grappled or pinned
        # creature takes a -2 penalty on "all attack rolls AND combat
        # maneuver checks, except for those made to escape or break a
        # grapple". Escape returned to its own handler above; initiating a
        # grapple is the exempt check. _maneuver_cmb stays a pure stat
        # (the concentration DC reads the grappler's CMB, not a check).
        grapple_penalty = (
            _GRAPPLED_CMB_PENALTY
            if maneuver != "grapple"
            and (
                self._has_condition_named(state, "grappled")
                or self._has_condition_named(state, "pinned")
            )
            else 0
        )
        attacker_cmb = self._maneuver_cmb(state) - pa_amt - grapple_penalty
        target_cmd = self._maneuver_cmd(target)
        roll = self._rng.d20()
        # PF1e (SRD Combat Maneuvers): "If your target is immobilized,
        # unconscious, or otherwise incapacitated, your maneuver
        # automatically succeeds (treat as if you rolled a natural 20 on
        # the attack roll)." The engine's incapacitated notion is the
        # helpless set (helpless/paralyzed/asleep/unconscious, CRB
        # "Conditions"); the natural 20 also feeds the margin-based
        # outcomes (bull rush / overrun / reposition / drag / dirty trick).
        if self._is_helpless(target):
            roll = _NATURAL_TWENTY
        # PF1e (CRB Combat Maneuvers): the provoked-AoO damage rides the
        # check total (floored at 0); natural 20/1 keep their rules below.
        total = max(0, roll + attacker_cmb - aoo_damage)
        if aoo_damage:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"maneuver AoO dealt {aoo_damage} damage "
                f"(-{aoo_damage} on the check)"
            )
        m = _ManeuverRoll(
            roll=roll, attacker_cmb=attacker_cmb, total=total,
            target_cmd=target_cmd,
            # PF1e: the CMB check is an attack roll — natural 20 always
            # succeeds, natural 1 always fails.
            success=roll == _NATURAL_TWENTY
            or (roll != _NATURAL_ONE and total >= target_cmd),
        )

        handlers: dict[str, Callable[[], None]] = {
            "trip": lambda: self._maneuver_trip(state, target, m),
            "disarm": lambda: self._maneuver_disarm(state, target, m),
            "bull_rush": lambda: self._maneuver_bull_rush(state, target, m, direction=direction),
            "sunder": lambda: self._maneuver_sunder(state, target, m),
            "grapple": lambda: self._maneuver_grapple(state, target, m),
            "overrun": lambda: self._maneuver_overrun(state, target, m),
            "dirty_trick": lambda: self._maneuver_dirty_trick(
                state, target, m, trick_condition=trick_condition
            ),
            "steal": lambda: self._maneuver_steal(state, target, m),
            "reposition": lambda: self._maneuver_reposition(state, target, m, direction=direction),
            "drag": lambda: self._maneuver_drag(state, target, m, direction=direction),
        }
        handlers[maneuver]()

    def _maneuver_provoked_aoo(
        self, state: CombatantState, target: CombatantState
    ) -> None:
        """Resolve the single AoO a combat maneuver provokes from its target.

        The target strikes only if it threatens the attacker, is able to
        make AoOs (``_resolve_aoo`` honours ``cant_aoo``) and has per-round
        AoO allowance left — same budget as movement/ranged provocation.
        """
        if not self.threatened_squares(target) & state.occupied_cells():
            return
        if self._aoo_used.get(target.combatant.id, 0) >= self._aoo_allowance(target):
            return
        self._resolve_aoo(target, state)

    def _retrieve_weapon(self, state: CombatantState, weapon_id: str | None) -> None:
        """Pick a stolen or dropped weapon back up.

        Removes ``weapon_id`` from ``weapon_stolen`` (steal maneuvers) or
        ``weapon_dropped`` (disarm maneuvers — SRD Disarm: the disarmed
        creature "drops one item it is carrying"; retrieving a dropped item
        is a move action). No-op (with a log line) when ``weapon_id`` is
        None or the id was never stolen or dropped. Once restored, the
        weapon is usable again via ``usable_attacks()``.
        """
        if weapon_id is None:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"retrieve: nothing to retrieve"
            )
            return
        if weapon_id in state.weapon_stolen:
            state.weapon_stolen.remove(weapon_id)
        elif weapon_id in state.weapon_dropped:
            state.weapon_dropped.remove(weapon_id)
        else:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"retrieve {weapon_id}: nothing to retrieve"
            )
            return
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"retrieve {weapon_id} (restored)"
        )

    def _repair_weapon(self, state: CombatantState, weapon_id: str | None) -> None:
        """Repair a broken weapon: remove it from ``weapon_broken`` and reset damage.

        No-op (with a log line) when ``weapon_id`` is None or the weapon was never
        damaged. Also removes the transient ``disarmed`` condition originating
        from the sunder that broke the weapon, so the repaired weapon is fully
        usable again.
        """
        if weapon_id is None:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"repair: nothing to repair"
            )
            return
        if weapon_id not in state.weapon_damage:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"repair {weapon_id}: nothing to repair"
            )
            return
        state.weapon_damage.pop(weapon_id, None)
        state.weapon_broken.discard(weapon_id)
        state.active_conditions = [
            c for c in state.active_conditions
            if not (c.condition.name == "disarmed" and c.source == "maneuver: sunder")
        ]
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"repair {weapon_id} (restored)"
        )

    def _maneuver_cmb(self, state: CombatantState) -> int:
        # PF1e (SRD Combat Maneuvers): "Creatures that are size Tiny or
        # smaller use their Dexterity modifier in place of their Strength
        # modifier to determine their CMB."
        ability_mod = (
            state.combatant.abilities.dex_mod
            if state.combatant.size.lower() in _TINY_OR_SMALLER_SIZES
            else state.combatant.abilities.str_mod
        )
        return (
            state.combatant.cmb
            or (state.combatant.bab + ability_mod + self._size_mod(state))
        )

    def _maneuver_cmd(self, target: CombatantState) -> int:
        if target.combatant.cmd:
            return target.combatant.cmd
        # PF1e (SRD Combat Maneuvers): "CMD = 10 + Base attack bonus +
        # Strength modifier + Dexterity modifier + special size modifier" —
        # the Tiny-or-smaller Dex-for-Str substitution is CMB-only, so the
        # ability component is computed here instead of via _maneuver_cmb.
        # A pre-baked CMB on a Tiny-or-smaller creature ALREADY carries that
        # substitution (SRD: they "use their Dexterity modifier in place of
        # their Strength modifier to determine their CMB"), so it must never
        # seed the CMD base — the extra Dexterity below would be double-
        # counted and Strength lost. Use the raw CMD formula for those sizes.
        if target.combatant.size.lower() in _TINY_OR_SMALLER_SIZES:
            target_base = (
                target.combatant.bab
                + target.combatant.abilities.str_mod
                + self._size_mod(target)
            )
        else:
            target_base = target.combatant.cmb or (
                target.combatant.bab
                + target.combatant.abilities.str_mod
                + self._size_mod(target)
            )
        # PF1e (SRD Combat Maneuver Defense): "A creature can also add any
        # circumstance, deflection, dodge, insight, luck, morale, profane,
        # and sacred bonuses to AC to its CMD. [...] A flat-footed creature
        # does not add its Dexterity bonus to its CMD." A Dexterity penalty
        # is not a bonus, so it still applies when flat-footed.
        dex_mod = target.combatant.abilities.dex_mod
        if self.has_condition_flag(target, "denies_dex_to_ac"):
            dex_mod = min(0, dex_mod)
        # PF1e (SRD Combat Maneuvers): "Any penalties to a creature's AC also
        # apply to its CMD." — negative AC modifiers ride the CMD whatever
        # their bonus type; only positive ones are restricted to the eight
        # SRD-listed types.
        ac_mods = [
            m
            for m in self._stat_modifiers(target, "ac")
            if m.bonus_type in _CMD_AC_BONUS_TYPES or m.value < 0
        ]
        # A combat maneuver is a melee attack roll (SRD: "Combat maneuvers are
        # attack rolls"), so the prone defender's -4 melee AC penalty applies.
        if self._has_condition_named(target, "prone"):
            ac_mods.append(StatModifier(target="ac", value=-4))
        ac_bonuses = resolve_modifiers(ac_mods)
        # defensive_ac_bonus (total defense / fight defensively) is a dodge
        # bonus and aid_ac_bonus a circumstance bonus to AC — both types the
        # SRD lets a creature add to its CMD.
        return (
            10 + target_base + dex_mod + ac_bonuses
            + target.defensive_ac_bonus + target.aid_ac_bonus
        )

    def _maneuver_trip(
        self, state: CombatantState, target: CombatantState, m: _ManeuverRoll
    ) -> None:
        if not m.success:
            self._maneuver_fail(state, target, "trip", m)
            # PF1e (SRD Trip): "If your attack fails by 10 or more, you are
            # knocked prone instead."
            if m.total <= m.target_cmd - _TRIP_RETALIATION_MARGIN:
                state.active_conditions.append(
                    ActiveCondition(
                        condition=CONDITIONS_BY_NAME["prone"],
                        rounds_left=1,
                        source="maneuver: trip retaliation",
                    )
                )
                self._log(
                    f"round {self._current_round} {state.combatant.id}: "
                    f"trip backfire -> attacker prone"
                )
            return
        target.active_conditions.append(
            ActiveCondition(
                condition=CONDITIONS_BY_NAME["prone"],
                rounds_left=1,
                source="maneuver: trip",
            )
        )
        self._log(
            f"round {self._current_round} {state.combatant.id}: trip vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> SUCCESS (prone)"
        )

    def _maneuver_disarm(
        self, state: CombatantState, target: CombatantState, m: _ManeuverRoll
    ) -> None:
        if not m.success:
            self._maneuver_fail(state, target, "disarm", m)
            # PF1e (SRD Disarm): "If your attack fails by 10 or more, you
            # drop the weapon that you were using to attempt the disarm."
            if m.total <= m.target_cmd - _DISARM_RETALIATION_MARGIN:
                own = next(
                    (w for w in state.usable_attacks() if w.kind == "melee"), None
                )
                if own is not None:
                    state.weapon_dropped.add(own.id)
                    self._log(
                        f"round {self._current_round} {state.combatant.id}: "
                        f"disarm backfire -> drops {own.name}"
                    )
            return
        # PF1e (SRD Disarm): "If your attack is successful, your target drops
        # one item it is carrying of your choice" — the weapon lands on the
        # ground (unusable until a retrieve_weapon move action picks it back
        # up), NOT a synthetic -4 attack penalty. The engine chooses the
        # target's first usable melee weapon (the wielded weapon, same choice
        # as the AoO machinery).
        weapon = next((w for w in target.usable_attacks() if w.kind == "melee"), None)
        if weapon is None:
            self._log(
                f"round {self._current_round} {state.combatant.id}: disarm vs "
                f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
                f"CMD {m.target_cmd} -> SUCCESS (no weapon to drop)"
            )
            return
        target.weapon_dropped.add(weapon.id)
        self._log(
            f"round {self._current_round} {state.combatant.id}: disarm vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> SUCCESS ({weapon.name} dropped)"
        )

    def _maneuver_bull_rush(
        self,
        state: CombatantState,
        target: CombatantState,
        m: _ManeuverRoll,
        *,
        direction: tuple[int, int] | None = None,
    ) -> None:
        if not m.success:
            self._maneuver_fail(state, target, "bull_rush", m)
            return
        # PF1e (SRD Bull Rush): "your target is pushed back 5 feet. For every
        # 5 by which your attack exceeds your opponent's CMD you can push the
        # target back an additional 5 feet." A natural-20 auto-success below
        # CMD still gets only the base 5 ft, hence the margin floor of 0.
        distance = 1 + max(0, m.total - m.target_cmd) // _BULL_RUSH_EXTRA_PER_MARGIN
        if direction is not None:
            pushed = False
            for _ in range(distance):
                new_pos = (target.pos[0] + direction[0], target.pos[1] + direction[1])
                if not self._cells_free(self._footprint_at(new_pos, target), target):
                    break
                target.pos = new_pos
                pushed = True
        else:
            pushed = self._bull_rush_push(state, target, distance)
        outcome = "SUCCESS (pushed)" if pushed else "SUCCESS (no space)"
        self._log(
            f"round {self._current_round} {state.combatant.id}: bull rush vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> {outcome}"
        )

    def _maneuver_sunder(
        self, state: CombatantState, target: CombatantState, m: _ManeuverRoll
    ) -> None:
        if not m.success:
            self._maneuver_fail(state, target, "sunder", m)
            return
        weapon = next((w for w in target.usable_attacks() if w.kind == "melee"), None)
        if weapon is None:
            self._log(
                f"round {self._current_round} {state.combatant.id}: sunder vs "
                f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
                f"CMD {m.target_cmd} -> SUCCESS (no weapon to damage)"
            )
            return
        dmg = state.combatant.abilities.str_mod + 2
        target.weapon_damage[weapon.id] = target.weapon_damage.get(weapon.id, 0) + dmg
        if target.weapon_damage[weapon.id] >= _WEAPON_DURABILITY:
            target.weapon_broken.add(weapon.id)
            target.active_conditions.append(
                ActiveCondition(
                    condition=Condition(
                        name="disarmed",
                        modifiers=(StatModifier(target="attack", value=-4),),
                    ),
                    rounds_left=1,
                    source="maneuver: sunder",
                )
            )
            self._log(
                f"round {self._current_round} {state.combatant.id}: sunder vs "
                f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
                f"CMD {m.target_cmd} -> SUCCESS (weapon destroyed)"
            )
            return
        self._log(
            f"round {self._current_round} {state.combatant.id}: sunder vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> SUCCESS ({dmg} damage to weapon)"
        )

    def _nearest_anchor_adjacent_to(
        self, grappler: CombatantState, target: CombatantState
    ) -> Pos | None:
        """Closest free anchor where ``target``'s footprint is adjacent to
        ``grappler``'s occupied cells (SRD "Grapple" pull-to-adjacent).

        Candidates are scored by 5-10-5 distance from the target's current
        anchor; ties break on (row, col) for determinism. The target's own
        current cells are excluded from the occupancy check (it is the thing
        being moved), walls/out-of-bounds are never candidates, and adjacency
        means the two footprints' cells are exactly one square apart.
        """
        grappler_cells = grappler.occupied_cells()
        best: tuple[int, Pos] | None = None
        for row in range(self._grid.height):
            for col in range(self._grid.width):
                anchor: Pos = (row, col)
                footprint = self._footprint_at(anchor, target)
                if not all(
                    self._grid.passable(cell) for cell in footprint
                ):
                    continue
                blocked = self._blocked(grappler, target)
                if footprint & (blocked | grappler_cells):
                    continue
                if not any(
                    self._grid.distance(g, t) == 1
                    for g in grappler_cells
                    for t in footprint
                ):
                    continue
                dist = self._grid.distance(anchor, target.pos)
                if best is None or (dist, anchor) < (best[0], best[1]):
                    best = (dist, anchor)
        return None if best is None else best[1]

    def _maneuver_grapple(
        self, state: CombatantState, target: CombatantState, m: _ManeuverRoll
    ) -> None:
        if not m.success:
            self._maneuver_fail(state, target, "grapple", m)
            return
        # PF1e (SRD "Grapple"): "If you successfully grapple a creature that
        # is not adjacent to you, move that creature to an adjacent open
        # space (if no space is available, your grapple fails)."
        if self.creature_distance(state, target) > 1:
            anchor = self._nearest_anchor_adjacent_to(state, target)
            if anchor is None:
                self._log(
                    f"round {self._current_round} {state.combatant.id}: grapple vs "
                    f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
                    f"CMD {m.target_cmd} -> FAILED (no adjacent space)"
                )
                return
            start = target.pos
            target.pos = anchor
            self._log(
                f"round {self._current_round} {state.combatant.id}: grapple pulls "
                f"{target.combatant.id} ({start[0]},{start[1]})->"
                f"({anchor[0]},{anchor[1]})"
            )
        target.active_conditions.append(
            ActiveCondition(
                condition=CONDITIONS_BY_NAME["grappled"],
                rounds_left=10,
                source=f"maneuver: grapple by {state.combatant.id}",
            )
        )
        target.grappled_with = state.combatant.id
        state.grappled_with = target.combatant.id
        self._log(
            f"round {self._current_round} {state.combatant.id}: grapple vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> SUCCESS (grappled)"
        )

    def _maneuver_fail(
        self, state: CombatantState, target: CombatantState, maneuver: str,
        m: _ManeuverRoll,
    ) -> None:
        self._log(
            f"round {self._current_round} {state.combatant.id}: {maneuver} vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> FAILED"
        )

    def _maneuver_overrun(
        self, state: CombatantState, target: CombatantState, m: _ManeuverRoll
    ) -> None:
        if not m.success:
            self._maneuver_fail(state, target, "overrun", m)
            self._overrun_fail_stop(state, target)
            return
        # PF1e (CRB "Overrun"): a successful maneuver moves you through the
        # target's square; the target is knocked prone only if the attack
        # exceeds its CMD by 5 or more.
        knocked_prone = m.total - m.target_cmd >= _OVERRUN_PRONE_MARGIN
        if knocked_prone:
            target.active_conditions.append(
                ActiveCondition(
                    condition=CONDITIONS_BY_NAME["prone"],
                    rounds_left=1,
                    source="maneuver: overrun",
                )
            )
        beyond = self._beyond_cell(state.pos, target.pos)
        moved_through = self._cells_free(self._footprint_at(beyond, state), state)
        if moved_through:
            state.pos = beyond
        achieved = ", ".join(
            label
            for label, flag in (("prone", knocked_prone), ("moved through", moved_through))
            if flag
        )
        outcome = f"SUCCESS ({achieved})" if achieved else "SUCCESS"
        self._log(
            f"round {self._current_round} {state.combatant.id}: overrun vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> {outcome}"
        )

    def _overrun_fail_stop(
        self, state: CombatantState, target: CombatantState
    ) -> None:
        """Park a failed overrun on the open approach cell in front of the target.

        PF1e (SRD Overrun): "If your overrun attempt fails, you stop in the
        space directly in front of the opponent, or the nearest open space
        in front of the creature if there are other creatures occupying that
        space." An already-adjacent attacker is in front: no move, no log.
        """
        ar, ac = state.pos
        tr, tc = target.pos
        steps = max(abs(tr - ar), abs(tc - ac))
        if steps <= 1:
            return
        dr = 1 if tr - ar > 0 else (-1 if tr - ar < 0 else 0)
        dc = 1 if tc - ac > 0 else (-1 if tc - ac < 0 else 0)
        for i in range(steps - 1, 0, -1):
            cell = (ar + dr * i, ac + dc * i)
            if self._cells_free(self._footprint_at(cell, state), state):
                start = state.pos
                state.pos = cell
                self._log(
                    f"round {self._current_round} {state.combatant.id}: "
                    f"overrun blocked, stopped ({start[0]},{start[1]})->"
                    f"({cell[0]},{cell[1]})"
                )
                return

    def _maneuver_dirty_trick(
        self,
        state: CombatantState,
        target: CombatantState,
        m: _ManeuverRoll,
        *,
        trick_condition: str | None = None,
    ) -> None:
        # ``trick_condition`` is typed ``str`` here (not the TrickCondition
        # Literal) because the APG RAW list is enforced at RUNTIME by
        # ``_DIRTY_TRICK_CONDITIONS`` — untrusted policy payloads must be
        # rejected, not just statically annotated away.
        if not m.success:
            self._maneuver_fail(state, target, "dirty_trick", m)
            return
        condition_name = trick_condition or "dazzled"
        if condition_name not in _DIRTY_TRICK_CONDITIONS:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"dirty trick unknown condition {condition_name!r}"
            )
            return
        condition = CONDITIONS_BY_NAME[condition_name]
        # PF1e (APG Dirty Trick): "This condition lasts for 1 round. For
        # every 5 by which your attack exceeds your opponent's CMD, the
        # penalty lasts 1 additional round."
        rounds = 1 + max(0, m.total - m.target_cmd) // _DIRTY_TRICK_EXTRA_ROUND_MARGIN
        target.active_conditions.append(
            ActiveCondition(
                condition=condition,
                rounds_left=rounds,
                source="maneuver: dirty trick",
            )
        )
        self._log(
            f"round {self._current_round} {state.combatant.id}: dirty trick vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> SUCCESS ({condition_name} {rounds}r)"
        )

    def _maneuver_steal(
        self, state: CombatantState, target: CombatantState, m: _ManeuverRoll
    ) -> None:
        if not m.success:
            self._maneuver_fail(state, target, "steal", m)
            return
        # PF1e (APG Steal): "Items held in the hands (such as wielded weapons
        # or wands) also cannot be taken with the steal maneuver—you must use
        # the disarm combat maneuver instead." The model carries no non-held
        # items, so every stealable target is held: a success takes nothing.
        self._log(
            f"round {self._current_round} {state.combatant.id}: steal vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> SUCCESS (nothing stealable — wielded "
            f"weapons require disarm)"
        )

    def _maneuver_reposition(
        self,
        state: CombatantState,
        target: CombatantState,
        m: _ManeuverRoll,
        *,
        direction: tuple[int, int] | None = None,
    ) -> None:
        if not m.success:
            self._maneuver_fail(state, target, "reposition", m)
            return
        # PF1e (APG Reposition): "you may move your target 5 feet to a new
        # location. For every 5 by which your attack exceeds your opponent's
        # CMD, you can move the target an additional 5 feet" — the walk stops
        # at the first obstacle ("You cannot move a creature into a square
        # that is occupied by a solid object or obstacle").
        distance = 1 + max(0, m.total - m.target_cmd) // _REPOSITION_EXTRA_PER_MARGIN
        step = direction
        if step is None:
            # First free neighbor (the attacker's own square is occupied, so
            # it can never be picked here).
            for dr, dc in _NEIGHBOR_OFFSETS:
                cand = (target.pos[0] + dr, target.pos[1] + dc)
                if self._cells_free(self._footprint_at(cand, target), target):
                    step = (dr, dc)
                    break
        moved = False
        if step is not None:
            for _ in range(distance):
                pos = (target.pos[0] + step[0], target.pos[1] + step[1])
                if not self._cells_free(self._footprint_at(pos, target), target):
                    break
                target.pos = pos
                moved = True
        outcome = f"SUCCESS (moved to {target.pos})" if moved else "SUCCESS (no space)"
        self._log(
            f"round {self._current_round} {state.combatant.id}: reposition vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> {outcome}"
        )

    def _maneuver_drag(
        self,
        state: CombatantState,
        target: CombatantState,
        m: _ManeuverRoll,
        *,
        direction: tuple[int, int] | None = None,
    ) -> None:
        if not m.success:
            self._maneuver_fail(state, target, "drag", m)
            return
        # PF1e (APG Drag): "both you and your target are moved 5 feet back,
        # with your opponent occupying your original space and you in the
        # space behind that in a straight line. For every 5 by which your
        # attack exceeds your opponent's CMD, you can drag the target back an
        # additional 5 feet" — the line stops at the first obstacle.
        distance = 1 + max(0, m.total - m.target_cmd) // _DRAG_EXTRA_PER_MARGIN
        dragged = 0
        for _ in range(distance):
            ar, ac = state.pos
            tr, tc = target.pos
            adjacent = max(abs(tr - ar), abs(tc - ac)) == 1
            if not adjacent:
                break
            if direction is not None:
                beyond = (tr + direction[0], tc + direction[1])
            else:
                beyond = self._beyond_cell(state.pos, target.pos)
            if not self._cells_free(self._footprint_at(beyond, target), target):
                break
            target_old = target.pos
            target.pos = beyond
            state.pos = target_old
            dragged += 1
        outcome = "SUCCESS (dragged)" if dragged else "SUCCESS (no space)"
        self._log(
            f"round {self._current_round} {state.combatant.id}: drag vs "
            f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
            f"CMD {m.target_cmd} -> {outcome}"
        )

    def _maneuver_escape(
        self, state: CombatantState, target: CombatantState
    ) -> None:
        escape_cmb = self._maneuver_cmb(state)
        escape_skill = (
            self._skill_static_bonus(state, "escape_artist")
            if hasattr(state.combatant, "skills") and "escape_artist" in state.combatant.skills
            else 0
        )
        escape_bonus = max(escape_cmb, escape_skill)
        target_cmd = self._maneuver_cmd(target)
        roll = self._rng.d20()
        total = roll + escape_bonus
        # PF1e (SRD Combat Maneuvers): "Rolling a natural 20 while attempting
        # a combat maneuver is always a success (except when attempting to
        # escape from bonds)" — escaping a grapple is a combat maneuver, not
        # bonds, so the natural 20 auto-succeeds here too.
        success = roll == _NATURAL_TWENTY or (roll != _NATURAL_ONE and total >= target_cmd)
        if success:
            target.active_conditions = [
                ac for ac in target.active_conditions if ac.condition.name != "grappled"
            ]
            target.conditions = [c for c in target.conditions if c.name != "grappled"]
            state.active_conditions = [
                ac for ac in state.active_conditions if ac.condition.name != "grappled"
            ]
            state.conditions = [c for c in state.conditions if c.name != "grappled"]
            target.grappled_with = None
            state.grappled_with = None
        else:
            self._log(
                f"round {self._current_round} {state.combatant.id}: escape vs "
                f"{target.combatant.id} d20={roll}+{escape_bonus}={total} "
                f"CMD {target_cmd} -> FAILED"
            )

    def _execute_channel_energy(
        self,
        state: CombatantState,
        target: CombatantState | None,
        channel_mode: Literal["heal", "harm"],
    ) -> None:
        """Execute channel energy (positive energy, burst 30ft, 2d6).

        Heal mode heals all living creatures in the burst; harm mode damages
        all undead creatures in the burst — the target's side does not matter
        (PF1e Channel Energy: positive energy heals living creatures and
        damages undead creatures within 30 feet). Damaged creatures get a
        Will save (DC 10 + half the channeler's level + her Cha modifier)
        for half damage (CRB Channel Energy).
        """
        if not state.spend_resource("channel_energy", 1):
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"channel energy failed (no resources)"
            )
            return
        if target is None or not target.active:
            return

        # Channel energy affects all creatures within 30ft (6 cells)
        radius_cells = 30 // _SQUARE_FT  # 6 cells
        affected = self._creatures_in_range(state.pos, radius_cells)

        if not affected:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"channel energy - no targets in range"
            )
            return

        wanted_type = "living" if channel_mode == "heal" else "undead"
        hit = [s for s in affected if s.combatant.creature_type == wanted_type]

        # 2d6 damage/healing
        dmg = 1 + self._rng.roll_die(11)  # 2d6

        # PF1e (CRB, Channel Energy): creatures damaged by the channel get a
        # Will save (DC 10 + half the channeler's level + her Charisma
        # modifier) for half damage. Charisma is used RAW even when the
        # caster's spellcasting ability is another one (channeling is a
        # Charisma class feature). Heal mode grants no save.
        channel_dc = 10 + state.combatant.level // 2 + (
            (state.combatant.abilities.cha_score - 10) // 2
        )

        for affected_state in hit:
            if channel_mode == "heal":
                self._channel_heal(state, affected_state, dmg)
            else:
                self._channel_damage(state, affected_state, dmg, channel_dc)

        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"channel energy ({channel_mode}) {dmg} -> {len(hit)} targets"
        )

    def _channel_heal(
        self, state: CombatantState, affected_state: CombatantState, dmg: int
    ) -> None:
        dmg = self._bitter_reduced(state, affected_state, dmg)
        old_hp = affected_state.hp
        affected_state.hp = min(affected_state.hp + dmg, affected_state.combatant.hp_max)
        # PF1e (CRB, Stable Characters and Recovery): "If any sort of healing
        # cures the dying character of even 1 point of damage, he becomes
        # stable and stops losing hit points."
        if affected_state.hp < 0:
            affected_state.stabilized_hp = affected_state.hp
        actual = affected_state.hp - old_hp
        self._stats[state.combatant.id].damage_dealt += actual
        self._stop_bleeding(affected_state)
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"channel energy heals {affected_state.combatant.id} +{actual} HP"
        )

    def _channel_damage(
        self, state: CombatantState, affected_state: CombatantState, dmg: int, dc: int
    ) -> None:
        """Apply channel energy damage: Will save (DC from the channeler) for half."""
        save = self.resolve_save(affected_state, "will", dc)
        dealt = dmg // 2 if save.success else dmg
        hp_before = affected_state.hp
        affected_state.hp -= dealt
        self._stats[state.combatant.id].damage_dealt += dealt
        self._stats[affected_state.combatant.id].damage_taken += dealt
        self._log(
            f"round {self._current_round} {state.combatant.id}: channel energy "
            f"damages {affected_state.combatant.id} {dealt} "
            f"(Will DC{dc} d20={save.roll}+{save.total - save.roll}={save.total} "
            f"{'SAVED half' if save.success else 'FAILED full'}) "
            f"({hp_before}->{affected_state.hp})"
        )
        if affected_state.dead:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"{affected_state.combatant.id} dead"
            )
        self._check_reactions(
            ReactionEvent(
                kind="damage_taken",
                actor=state,
                target=affected_state,
                damage=dealt,
            )
        )

    def _execute_hex(
        self, state: CombatantState, target: CombatantState | None, hex_name: str | None
    ) -> None:
        """Execute a witch hex (evil_eye, slumber, cackle).

        APG Cackle is a free action with no hex resource cost, so it is
        dispatched before the resource/target gate; evil_eye and slumber are
        standard actions that each spend one use."""
        if hex_name == "cackle":
            self._hex_cackle(state)
            return
        if not state.spend_resource("hexes", 1):
            self._log(
                f"round {self._current_round} {state.combatant.id}: hex failed (no resources)"
            )
            return
        if target is None or not target.active:
            return
        if hex_name not in ("evil_eye", "slumber"):
            self._log(
                f"round {self._current_round} {state.combatant.id}: unknown hex {hex_name}"
            )
            return

        hex_dc = 10 + state.combatant.level // 2 + (state.combatant.abilities.int_score - 10) // 2

        if hex_name == "evil_eye":
            self._hex_evil_eye(state, target, hex_dc)
        else:
            self._hex_slumber(state, target, hex_dc)

    _EVIL_EYE_ROUNDS = 3
    _EVIL_EYE_SAVED_ROUNDS = 1

    def _hex_evil_eye(
        self, state: CombatantState, target: CombatantState, hex_dc: int
    ) -> None:
        """Evil Eye (APG): -2 on one chosen option for 3 rounds; a Will save
        reduces it to 1 round (never negates). Simplification: the chosen
        option is attack rolls — the engine's other hex targets are not
        selectable per cast."""
        save_result = self.resolve_save(target, "will", hex_dc)
        rounds = self._EVIL_EYE_SAVED_ROUNDS if save_result.success else self._EVIL_EYE_ROUNDS
        target.active_buffs.append(
            ActiveBuff(
                modifiers=(StatModifier(target="attack", value=-2),),
                rounds_left=rounds,
                source=f"hex: evil_eye by {state.combatant.id}",
            )
        )
        self._log(
            f"round {self._current_round} {state.combatant.id}: evil eye on "
            f"{target.combatant.id} -> -2 attack ({rounds}r)"
        )

    def _hex_slumber(
        self, state: CombatantState, target: CombatantState, hex_dc: int
    ) -> None:
        """Slumber (APG): the target remains asleep for a number of rounds
        equal to the witch's level; a successful Will save negates.
        Simplification documented in README: the RAW ending of the hex when
        the target takes damage is not modeled (no wake-on-damage hook)."""
        save_result = self.resolve_save(target, "will", hex_dc)
        if save_result.success:
            self._log(
                f"round {self._current_round} {state.combatant.id}: slumber on "
                f"{target.combatant.id} -> SAVED"
            )
            return
        rounds = state.combatant.level
        target.active_conditions.append(
            ActiveCondition(
                condition=CONDITIONS_BY_NAME["asleep"],
                rounds_left=rounds,
                source=f"hex: slumber by {state.combatant.id}",
            )
        )
        self._log(
            f"round {self._current_round} {state.combatant.id}: slumber on "
            f"{target.combatant.id} -> asleep ({rounds}r)"
        )

    _CACKLE_RANGE_FT = 30

    def _hex_cackle(self, state: CombatantState) -> None:
        """Cackle (APG): a free action that extends the duration of every
        evil eye, fortune or misfortune hex on all creatures within 30 ft by
        1 round. Fortune/misfortune are not implemented, so the extension
        covers evil_eye buffs; each buff list is rebuilt in a single pass so
        an extended hex is never re-extended."""
        extended = 0
        for other in self._states:
            if not other.active:
                continue
            if self.creature_distance(state, other) * _SQUARE_FT > self._CACKLE_RANGE_FT:
                continue
            other.active_buffs[:] = [
                ActiveBuff(
                    modifiers=buff.modifiers,
                    rounds_left=buff.rounds_left + 1,
                    source=buff.source,
                )
                if buff.source.startswith("hex: evil_eye")
                else buff
                for buff in other.active_buffs
            ]
            extended += sum(
                1 for buff in other.active_buffs if buff.source.startswith("hex: evil_eye")
            )
        if extended:
            self._log(
                f"round {self._current_round} {state.combatant.id}: cackle extends "
                f"{extended} evil eye hex(es)"
            )
        else:
            self._log(
                f"round {self._current_round} {state.combatant.id}: cackle - no hex "
                f"to extend"
            )

    def _execute_deed(
        self, state: CombatantState, target: CombatantState | None, deed_name: str | None
    ) -> None:
        """Execute a gunslinger deed (up_close_and_deadly, quick_clear)."""
        if deed_name not in ("up_close_and_deadly", "quick_clear"):
            return
        if deed_name == "up_close_and_deadly":
            # Up Close and Deadly: +1d6 damage within 30ft
            if target is None or not target.active:
                return
            dist_ft = self.creature_distance(state, target) * _SQUARE_FT
            if dist_ft > _UP_CLOSE_RANGE_FT:
                self._log(
                    f"round {self._current_round} {state.combatant.id}: deed Up Close "
                    f"and Deadly - target out of range"
                )
                return
            if not state.spend_resource("grit", 1):
                self._log(
                    f"round {self._current_round} {state.combatant.id}: deed failed (no grit)"
                )
                return
            # Apply +1d6 damage to next attack this round
            state.deed_up_close_and_deadly = True
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"deed Up Close and Deadly activated (+1d6 dmg within 30ft)"
            )
        elif deed_name == "quick_clear":
            # PF1e (Ultimate Combat, Deeds — Quick Clear): "As a standard
            # action, you can spend 1 point from your grit pool to remove the
            # broken condition from a single firearm you are holding, as long
            # as that condition was gained by a firearm misfire." The move
            # variant (clear ALL misfired firearms as part of a move action)
            # is not modeled: the deed always targets one firearm.
            broken_firearm = next(
                (
                    weapon.id
                    for weapon in state.combatant.attacks
                    if weapon.firearm and weapon.id in state.weapon_broken
                ),
                None,
            )
            if broken_firearm is None:
                self._log(
                    f"round {self._current_round} {state.combatant.id}: "
                    f"deed Quick Clear - no misfire to clear"
                )
                return
            if not state.spend_resource("grit", 1):
                self._log(
                    f"round {self._current_round} {state.combatant.id}: deed failed (no grit)"
                )
                return
            state.weapon_broken.discard(broken_firearm)
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"deed Quick Clear - {broken_firearm} cleared"
            )

    def _execute_spell_combat(
        self, state: CombatantState, target: CombatantState | None, spell_name: str | None
    ) -> None:
        """Execute Spell Combat (cast spell + full attack in same round).

        PF1e (CRB, Magus Spell Combat): as a full-round action the magus casts
        a standard-action spell and makes all of his melee attacks at -2. The
        penalty rides the full-attack chain to every swing and crit confirm,
        and — "any attack roll made as part of this spell also takes this
        penalty" — the spell's own melee/ranged touch attack too.
        Simplification: the spell may target any resolved enemy (the RAW
        spellcasting-as-move restriction and arcane pool cost are not modeled).
        Spell Combat requires a casting time of 1 standard action; the policy
        only proposes such spells, and a one-round spell would simply resolve
        on the caster's next turn via ``PendingCast``.
        """
        if target is None or not target.active or spell_name is None:
            return
        if not state.spend_resource("arcane_pool", 1):
            # Arcane pool not tracked yet, allow for now
            pass
        # Cast the spell — PF1e (CRB, Magus Spell Combat): "any attack roll
        # made as part of this spell also takes this penalty", so the -2 rides
        # the spell's touch attack too.
        self._cast_spell(
            state, target, spell_name, attack_penalty=_SPELL_COMBAT_ATTACK_PENALTY
        )
        # Then make a full attack at -2 (Spell Combat penalty)
        self._execute_attack(
            state, target, "full_attack", attack_penalty=_SPELL_COMBAT_ATTACK_PENALTY
        )

    def _execute_inspire_courage(
        self, state: CombatantState, target: CombatantState | None
    ) -> None:
        """Execute Inspire Courage (30ft radius, costs bardic_rounds).

        PF1e (CRB, Bardic Performance — Inspire Courage): +1 competence bonus
        on attack rolls and weapon damage rolls, and a +1 morale bonus on
        saving throws against charm and fear effects. Simplifications: the
        scaling (+1 per four bard levels) is not modeled (flat +1), and the
        engine has no "charm" descriptor, so mind_affecting stands in for it
        (documented over-coverage: compulsion effects also count). The save
        bonus is carried by two conditional modifiers (fear /
        mind_affecting); a save with both descriptors still totals +1 because
        morale does not stack with itself.
        """
        if not state.spend_resource("bardic_rounds", 1):
            self._log(
                f"round {self._current_round} {state.combatant.id}: inspire courage "
                f"failed (no bardic rounds)"
            )
            return
        if target is None:
            target = state
        # Apply to all allies within 30ft (6 cells)
        radius_cells = 30 // _SQUARE_FT
        affected: list[CombatantState] = []
        for state_other in self._states:
            if not state_other.active:
                continue
            if state_other.side == state.side:
                dist = self.creature_distance(state, state_other)
                if dist <= radius_cells:
                    affected.append(state_other)

        if not affected:
            self._log(
                f"round {self._current_round} {state.combatant.id}: inspire courage - "
                f"no allies in range"
            )
            return

        # Apply +1 competence attack/damage and +1 morale vs charm/fear saves
        for ally in affected:
            ally.active_buffs.append(
                ActiveBuff(
                    modifiers=(
                        StatModifier(target="attack", value=1, bonus_type="competence"),
                        StatModifier(target="damage", value=1, bonus_type="competence"),
                        StatModifier(
                            target="will", value=1, bonus_type="morale",
                            condition="fear",
                        ),
                        StatModifier(
                            target="will", value=1, bonus_type="morale",
                            condition="mind_affecting",
                        ),
                    ),
                    rounds_left=1,
                    source=f"inspire courage by {state.combatant.id}",
                )
            )
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"inspire courage +1 competence attack/damage, +1 morale vs "
            f"charm/fear saves to {len(affected)} allies"
        )
    def _execute_attack(
        self,
        state: CombatantState,
        target: CombatantState | None,
        kind: str,
        weapon_id: str | None = None,
        *,
        attack_penalty: int = 0,
    ) -> ActionResult | None:
        """Execute an attack / full_attack (U5d: optional explicit weapon).

        With ``weapon_id`` the attack is made with THAT weapon; a choice that
        is unknown, broken, stolen, or unable to strike the target is logged
        and rejected with ``weapon_unavailable`` (no attack is made). Without
        it the ``weapon_for`` auto-selection is unchanged. ``attack_penalty``
        is applied to every roll of the action (Spell Combat's -2). Returns an
        explicit rejection, or None when the helper ran (or silently no-oped)
        and the caller reports ok.
        """
        if self.has_condition_flag(state, "cant_attack"):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot attack)")
            return None
        if target is None:
            return None
        chosen: AttackSpec | None = None
        if weapon_id is not None:
            chosen = self._chosen_weapon(state, target, weapon_id)
            if chosen is None:
                self._log(
                    f"round {self._current_round} {state.combatant.id}: "
                    f"{kind} rejected ({_REASON_WEAPON_UNAVAILABLE})"
                )
                return ActionResult(
                    kind=kind, ok=False, reason=_REASON_WEAPON_UNAVAILABLE
                )
        if kind == "attack":
            weapon = chosen if chosen is not None else self.weapon_for(state, target)
            if weapon is None:
                return None
            self._single_attack(state, target, weapon)
        elif kind == "full_attack":
            if chosen is not None:
                self._full_attack_weapon(
                    state, target, chosen, attack_penalty=attack_penalty
                )
            else:
                self._full_attack(state, target, attack_penalty=attack_penalty)
        return None

    def _chosen_weapon(
        self, attacker: CombatantState, target: CombatantState, weapon_id: str
    ) -> AttackSpec | None:
        """The usable weapon ``weapon_id``, if it can strike ``target`` (U5d).

        None when the id is unknown or the weapon is broken/stolen (not in
        ``usable_attacks()``), or when it cannot reach the target / lacks
        line of effect.
        """
        for weapon in attacker.usable_attacks():
            if weapon.id == weapon_id:
                if self._weapon_usable_against(attacker, target, weapon):
                    return weapon
                return None
        return None

    def _execute_charge(self, state: CombatantState, target: CombatantState | None) -> None:
        if target is None or not target.active:
            return
        if self.has_condition_flag(state, "cant_charge"):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot charge)")
            return
        result = self.can_charge(state, target)
        if result is None or result.weapon is None:
            return
        self._charge(state, target, result.weapon)

    def _casting_ability_mod(self, caster: CombatantState) -> int:
        """Modifier of the casting ability (the one used for bonus spells)."""
        ability_name = caster.combatant.casting_ability.lower()
        ability_score = getattr(caster.combatant.abilities, f"{ability_name}_score")
        return (ability_score - 10) // 2

    def _spell_dc(
        self,
        caster: CombatantState,
        spell: SpellSpec,
        *,
        slot_level: int | None = None,
        metamagic: tuple[str, ...] = (),
    ) -> int:
        """Spell save DC: 10 + spell level + casting ability modifier.

        PF1e (SRD, Metamagic Feats): a metamagic spell occupies a higher
        slot but its save DC uses the spell's BASE level - "An empowered
        spell uses up a spell slot two levels higher than the spell's
        actual level" while "Saving throws and opposed rolls are not
        affected" (feats/empower-spell.md). The one exception is Heighten
        Spell: "Unlike other metamagic feats, Heighten Spell actually
        increases the effective level of the spell [...] All effects
        dependent on spell level (such as saving throw DCs [...]) are
        calculated according to the heightened level"
        (feats/heighten-spell.md) - so ``slot_level`` (the level the spell
        is cast at) feeds the DC only when Heighten Spell is applied.
        """
        if "Heighten Spell" in metamagic and slot_level is not None:
            return 10 + slot_level + self._casting_ability_mod(caster)
        return 10 + spell.level + self._casting_ability_mod(caster)

    def _spell_snapshot(self, state: CombatantState, spell_name: str) -> dict[str, object]:
        """One per-spell dict for the Observation, enriched from the registry."""
        spell = self._spell_registry.get(spell_name)
        if spell is None:
            return {
                "name": spell_name,
                "level": None,
                "school": "",
                "range_ft": 0,
                "save": "none",
                "dc": None,
                "summary": "",
                "half_on_save": False,
                "save_negates": False,
                "area": None,
                "cast_time": "standard",
            }
        half_on_save = _spell_half_on_save(spell)
        return {
            "name": spell.name,
            "level": spell.level,
            "school": spell.school,
            "range_ft": spell_range_ft(spell, state.combatant.level),
            "save": spell.save,
            "dc": self._spell_dc(state, spell),
            "summary": _spell_summary(spell),
            "half_on_save": half_on_save,
            "save_negates": spell.save != "none" and not half_on_save,
            "area": _spell_area_dict(spell),
            "cast_time": spell.cast_time,
        }

    def _cast_spell(
        self,
        caster: CombatantState,
        target: CombatantState | None,
        spell_name: str,
        *,
        center_pos: tuple[int, int] | None = None,
        metamagic: tuple[str, ...] = (),
        cast_defensively: bool = False,
        attack_penalty: int = 0,
    ) -> ActionResult | None:
        """Cast ``spell_name``.

        ``center_pos`` (U7b) centers a top-level ``AreaEffect`` on that cell
        instead of the target creature's position. It is honoured only for
        spells carrying an area; every other effect still resolves on the
        target. A cast with no resolved target requires ``center_pos`` and an
        area effect — the primary save is skipped and each creature in the
        area rolls its own. ``metamagic`` (B7) lists the feats applied to
        THIS cast (only feats the caster knows apply, and the spell then
        occupies — and must have — a slot of base level + adjustment).
        ``cast_defensively`` (B24) skips the casting AoO for a concentration
        check. ``attack_penalty`` folds into this cast's touch attack rolls
        (PF1e CRB Magus Spell Combat: "any attack roll made as part of this
        spell also takes this penalty"). Returns an explicit rejection
        (``no_slot``) when the required slot is unavailable; None means the
        cast proceeded through the gates.
        """
        spell = self._spell_registry.get(spell_name)
        if spell is None:
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"cast {spell_name} -> UNKNOWN SPELL"
            )
            return None
        # PF1e (CRB, Metamagic Feats): metamagic is chosen per cast and only
        # the feats the caster actually knows can be applied (B7).
        known = set(caster.combatant.metamagic_feats)
        applied = tuple(f for f in metamagic if f in known)
        used_level = spell.level + sum(
            _METAMAGIC_SLOT_ADJUST.get(f, 0) for f in applied
        )
        has_area = any(isinstance(e, AreaEffect) for e in spell.effects)
        if self._spell_cast_rejected(
            caster, target, spell, spell_name, center_pos, has_area=has_area
        ):
            return None
        # PF1e (CRB): a caster cannot cast without an available slot of the
        # spell's level (metamagic-inflated, B7); cantrips (level 0) are cast
        # freely. The slot is spent up-front — a later failed concentration
        # check or missed touch attack still burns it.
        if used_level > 0 and not caster.spend_spell_slot(used_level):
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"cast {spell_name} -> NO SPELL SLOT (level {used_level})"
            )
            return ActionResult(
                kind="cast_spell", ok=False, reason="no_slot",
                detail=f"level {used_level}",
            )
        # PF1e (SRD "Holding the Charge"): "If you cast another spell, the
        # touch spell dissipates."
        if caster.held_charge is not None:
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"held charge of {caster.held_charge.spell_name} dissipates "
                f"(casting {spell_name})"
            )
            caster.held_charge = None
        # PF1e (CRB, Concentration, B24): grappled/defensive/threatened casts
        # must clear their interruption gate before the spell is delivered.
        if self._spell_cast_interrupted(
            caster, used_level, cast_defensively=cast_defensively
        ):
            return None
        if spell.cast_time == "one_round":
            # PF1e (SRD "Casting Time"): "A spell that takes 1 round to cast
            # is a full-round action. It comes into effect just before the
            # beginning of your turn in the round after you began casting the
            # spell." The slot is spent and the start-of-casting gates have
            # run; delivery (touch attack, SR, saves, effects — "You make all
            # pertinent decisions about a spell [...] when the spell comes
            # into effect") is deferred to _resolve_pending_cast.
            caster.pending_cast = PendingCast(
                spell_name=spell_name,
                target_id=target.combatant.id if target is not None else None,
                center_pos=center_pos,
                metamagic=applied,
                slot_level=used_level,
                cast_defensively=cast_defensively,
                hp_at_cast=caster.hp,
            )
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"begins casting {spell_name} (1 round)"
            )
            return None
        # PF1e (CRB): hostile touch delivery needs a melee touch attack (B14)
        # and spell resistance can still turn the spell away. A confirmed
        # touch crit doubles the spell's damage (CRB "Range — Touch").
        self._deliver_cast(
            caster, target, spell, spell_name, center_pos,
            metamagic=applied, slot_level=used_level,
            attack_penalty=attack_penalty,
        )
        return None

    def _deliver_cast(
        self,
        caster: CombatantState,
        target: CombatantState | None,
        spell: SpellSpec,
        spell_name: str,
        center_pos: tuple[int, int] | None,
        *,
        metamagic: tuple[str, ...],
        slot_level: int,
        attack_penalty: int = 0,
    ) -> None:
        """Post-gate delivery: touch attack, spell resistance, then effects.

        Shared by the immediate cast path and the resolution of a pending
        one-round cast (SRD "Casting Time").
        """
        has_area = any(isinstance(e, AreaEffect) for e in spell.effects)
        blocked, delivery_crit = self._spell_delivery_blocked(
            caster, target, spell, spell_name, has_area=has_area,
            attack_penalty=attack_penalty,
            metamagic=metamagic, slot_level=slot_level,
        )
        if blocked:
            return
        self._apply_and_log_cast(
            caster, target, spell, spell_name, center_pos,
            metamagic=metamagic, slot_level=slot_level, spell_crit=delivery_crit,
            attack_penalty=attack_penalty,
        )

    def _spell_cast_interrupted(
        self, caster: CombatantState, spell_level: int, *, cast_defensively: bool
    ) -> bool:
        """Pre-delivery interruption gate (B24).

        PF1e (CRB, Concentration): while grappled the caster must pass
        DC 10 + grappler's CMB + spell level to cast at all; casting
        defensively forgoes the provocation but requires DC 15 + 2x spell
        level (Combat Casting's +4 applies to both); otherwise casting in a
        threatened square provokes the AoO (with the injured-casting check).
        True = the spell is lost (the slot is already spent).
        """
        if caster.grappled_with is not None or cast_defensively:
            if not self._check_concentration(caster, spell_level, 0):
                dc = self._concentration_dc(caster, spell_level, 0)
                situation = (
                    "while grappled" if caster.grappled_with is not None else "defensively"
                )
                self._log(
                    f"round {self._current_round} {caster.combatant.id}: "
                    f"casting {situation}: concentration failed (DC {dc}), spell lost"
                )
                return True
            return False
        if self._has_condition_named(caster, "entangled"):
            # PF1e (SRD Table 9-1 Concentration Check DCs): "Entangled while
            # casting" requires a DC 15 + spell level check or the spell is
            # lost. Combat Casting's +4 applies (not an injury check).
            dc = self._entangled_concentration_dc(spell_level)
            if not self._check_concentration(caster, spell_level, 0, dc_override=dc):
                self._log(
                    f"round {self._current_round} {caster.combatant.id}: "
                    f"casting while entangled: concentration failed (DC {dc}), "
                    f"spell lost"
                )
                return True
        return self._check_casting_aoo(caster, spell_level)

    def _spell_delivery_blocked(
        self,
        caster: CombatantState,
        target: CombatantState | None,
        spell: SpellSpec,
        spell_name: str,
        *,
        has_area: bool,
        attack_penalty: int = 0,
        metamagic: tuple[str, ...] = (),
        slot_level: int | None = None,
    ) -> tuple[bool, bool]:
        """Delivery gates: a hostile touch spell must land its melee touch
        attack (B14) and a hostile ranged touch spell (ray) must land its
        ranged touch attack (cover, concealment and crits included), then
        spell resistance must be overcome. Returns ``(blocked, crit)``:
        True blocked = no effect; ``crit`` is True when a damage-dealing
        touch delivery was confirmed on a natural 20 (the spell's damage
        dice are then doubled). A MISSED melee touch does not expend the
        spell - SRD "Holding the Charge": "you can hold the charge
        indefinitely. You can continue to make touch attacks round after
        round" - so the caster keeps a HeldCharge (the slot stays spent).
        A missed ranged touch IS expended (SRD: "ranged touch attacks
        cannot be held until a later turn")."""
        crit = False
        deals_damage = any(isinstance(e, DamageEffect) for e in spell.effects)
        # PF1e multi-projectile rays (Scorching Ray): each projectile rolls its
        # own ranged touch attack, resolved per-projectile in
        # _apply_damage_effect, so the single delivery attack is skipped here.
        per_projectile_attack = _spell_declares_projectiles(spell)
        if (
            target is not None
            and spell.range == "touch"
            and target.side != caster.side
        ):
            hit, crit = self._spell_touch_attack_hits(
                caster, target,
                attack_penalty=attack_penalty, deals_damage=deals_damage,
            )
            if not hit:
                caster.held_charge = HeldCharge(
                    spell_name=spell_name,
                    target_id=target.combatant.id,
                    metamagic=metamagic,
                    slot_level=spell.level if slot_level is None else slot_level,
                )
                self._log(
                    f"round {self._current_round} {caster.combatant.id}: "
                    f"holds the charge of {spell_name}"
                )
                return True, False
        if (
            target is not None
            and spell.requires_ranged_touch
            and not has_area
            and not per_projectile_attack
            and target.side != caster.side
        ):
            hit, ranged_crit = self._spell_ranged_touch_attack_hits(
                caster, target,
                attack_penalty=attack_penalty, deals_damage=deals_damage,
            )
            if not hit:
                return True, False
            crit = ranged_crit
        if (
            target is not None
            and not has_area
            and spell.spell_resistance
            and not self._check_spell_resistance(caster, target)
        ):
            return True, False
        return False, crit

    def _spell_touch_attack_hits(
        self,
        caster: CombatantState,
        target: CombatantState,
        *,
        attack_penalty: int = 0,
        deals_damage: bool = False,
    ) -> tuple[bool, bool]:
        """Melee touch attack to deliver a touch-range spell (B14).

        PF1e (CRB): d20 + caster's melee attack bonus vs the target's touch
        AC, PLUS the target's cover bonus (a touch attack is an attack roll —
        CRB "Cover") and subject to the target's concealment miss chance (CRB
        "Concealment"); a spell that deals damage threatens on a natural 20
        and deals double damage on a successful confirmation (CRB "Cast a
        Spell — Touch Attacks": "You can score critical hits with either type
        of attack as long as the spell deals damage"; CRB "Range — Touch").
        ``attack_penalty`` folds into the bonus (Spell Combat: "any attack
        roll made as part of this spell also takes this penalty"). Engine
        simplification (documented): the bonus is BAB + Strength modifier —
        Weapon Finesse and other situational touch bonuses are not modeled;
        natural 20 hits and natural 1 misses per the engine's attack-roll
        convention. The touch AC reuses the resolve_attack denies-Dex path
        (flat-footed/running target, invisible attacker).
        Returns ``(hit, crit)``.
        """
        roll = self._rng.d20()
        bonus = caster.combatant.bab + caster.combatant.abilities.str_mod + attack_penalty
        denies_dex = (
            self.has_condition_flag(target, "denies_dex_to_ac")
            or target.running
            or self._has_condition_named(caster, "invisible")
        )
        if denies_dex:
            ac = target.combatant.ac.touch - max(0, target.combatant.abilities.dex_mod)
        else:
            ac = target.combatant.ac.touch
        ac += self._attack_cover_bonus(caster, target, ranged=False)
        return self._resolve_touch_delivery(
            caster, target, label="touch attack",
            roll=roll, bonus=bonus, ac=ac, deals_damage=deals_damage,
        )

    def _spell_ranged_touch_attack_hits(
        self,
        caster: CombatantState,
        target: CombatantState,
        *,
        attack_penalty: int = 0,
        deals_damage: bool = False,
    ) -> tuple[bool, bool]:
        """Ranged touch attack to deliver a ray spell.

        PF1e (CRB, Magic — Ranged Touch Attacks): d20 + caster's ranged attack
        bonus vs the target's touch AC, PLUS the target's ranged cover bonus
        (terrain + soft cover, CRB "Cover") and subject to the concealment
        miss chance (CRB "Concealment"); a ray that deals damage can score a
        critical hit (CRB "Cast a Spell — Touch Attacks"). The spell's range
        is a single absolute value so there is no range-increment penalty.
        ``attack_penalty`` folds into the bonus (Spell Combat: "any attack
        roll made as part of this spell also takes this penalty"). Engine
        simplification (documented): the bonus is BAB + Dexterity modifier —
        size modifier, Weapon Finesse and other situational bonuses are not
        modeled; natural 20 hits and natural 1 misses per the engine's
        attack-roll convention. The touch AC reuses the resolve_attack
        denies-Dex path (flat-footed/running target, invisible attacker).
        Returns ``(hit, crit)``.
        """
        roll = self._rng.d20()
        bonus = caster.combatant.bab + caster.combatant.abilities.dex_mod + attack_penalty
        denies_dex = (
            self.has_condition_flag(target, "denies_dex_to_ac")
            or target.running
            or self._has_condition_named(caster, "invisible")
        )
        if denies_dex:
            ac = target.combatant.ac.touch - max(0, target.combatant.abilities.dex_mod)
        else:
            ac = target.combatant.ac.touch
        ac += self._attack_cover_bonus(caster, target, ranged=True)
        return self._resolve_touch_delivery(
            caster, target, label="ranged touch attack",
            roll=roll, bonus=bonus, ac=ac, deals_damage=deals_damage,
        )

    def _resolve_touch_delivery(
        self,
        caster: CombatantState,
        target: CombatantState,
        *,
        label: str,
        roll: int,
        bonus: int,
        ac: int,
        deals_damage: bool,
    ) -> tuple[bool, bool]:
        """Finish a touch-attack roll: hit check, crit threat/confirm (only
        when the spell deals damage, CRB "Cast a Spell — Touch Attacks"), then
        the concealment miss chance (a blinded caster faces total concealment,
        same max(target, 50) convention as _resolve_hit_damage)."""
        hit = roll == _NATURAL_TWENTY or (roll != _NATURAL_ONE and roll + bonus >= ac)
        self._log(
            f"round {self._current_round} {caster.combatant.id}: {label} vs "
            f"{target.combatant.id} d20={roll}+{bonus}={roll + bonus} AC {ac} "
            f"-> {'HIT' if hit else 'MISS'}"
        )
        if not hit:
            return False, False
        crit = False
        if deals_damage and roll == _NATURAL_TWENTY:
            confirm = self._rng.d20()
            crit = confirm == _NATURAL_TWENTY or (
                confirm != _NATURAL_ONE and confirm + bonus >= ac
            )
            self._log(
                f"round {self._current_round} {caster.combatant.id}: {label} "
                f"crit confirm d20={confirm}+{bonus}={confirm + bonus} AC {ac} "
                f"-> {'CRIT' if crit else 'no crit'}"
            )
        concealment = self._concealment_chance(target)
        blinded = self._has_condition_named(caster, "blinded")
        miss_chance = max(concealment, _TOTAL_CONCEALMENT_PCT) if blinded else concealment
        if miss_chance > 0:
            pct = self._rng.d100()
            missed = pct <= miss_chance
            source = "attacker blinded" if blinded else "concealment"
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"{source} vs {target.combatant.id}: "
                f"d100({pct}) {'<=' if missed else '>'} {miss_chance}% "
                f"— {'spell lost' if missed else 'spell delivered'}"
            )
            if missed:
                return False, False
        return True, crit

    def _spell_cast_rejected(
        self,
        caster: CombatantState,
        target: CombatantState | None,
        spell: SpellSpec,
        spell_name: str,
        center_pos: tuple[int, int] | None,
        *,
        has_area: bool,
    ) -> bool:
        """Pre-cast gates: resolvable target (or U7b point cast of an area
        spell), spell range and line of effect. True = not castable."""
        if target is None:
            point_ok = self._point_cast_castable(
                caster, spell, spell_name, center_pos, has_area=has_area
            )
            return not point_ok
        if not target.active:
            return True
        dist_ft = self.creature_distance(caster, target) * _SQUARE_FT
        if dist_ft > spell_range_ft(spell, caster.combatant.level):
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"cast {spell_name} -> OUT OF RANGE"
            )
            return True
        if not has_line_of_effect_cells(
            self._grid, caster.occupied_cells(), target.occupied_cells()
        ):
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"cast {spell_name} -> NO LINE OF EFFECT"
            )
            return True
        return False

    def _point_cast_castable(
        self,
        caster: CombatantState,
        spell: SpellSpec,
        spell_name: str,
        center_pos: tuple[int, int] | None,
        *,
        has_area: bool,
    ) -> bool:
        """U7b point cast (no resolved target): needs an area spell centered
        on ``center_pos``, within the spell's range of the caster."""
        if center_pos is None or not has_area:
            return False
        point_dist = min(
            self._grid.distance(cell, center_pos)
            for cell in caster.occupied_cells()
        ) * _SQUARE_FT
        if point_dist > spell_range_ft(spell, caster.combatant.level):
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"cast {spell_name} -> OUT OF RANGE"
            )
            return False
        return True

    def _apply_and_log_cast(
        self,
        caster: CombatantState,
        target: CombatantState | None,
        spell: SpellSpec,
        spell_name: str,
        center_pos: tuple[int, int] | None,
        *,
        metamagic: tuple[str, ...] = (),
        slot_level: int | None = None,
        spell_crit: bool = False,
        attack_penalty: int = 0,
    ) -> None:
        """Resolve save, apply effects and log a spell cast (post-gates).

        ``metamagic`` holds the feats chosen for THIS cast (already filtered
        to known ones, B7); ``slot_level`` is the spell's level in the slot
        used - it drives the slot cost and the concentration checks, but NOT
        the save DC: metamagic other than Heighten Spell does not raise the
        DC (SRD feats/empower-spell.md: "Saving throws and opposed rolls are
        not affected"; feats/heighten-spell.md: only Heighten Spell
        "increases the effective level of the spell", and its DC is computed
        from the heightened level). ``spell_crit`` is a confirmed
        touch-delivery critical: the spell's damage dice are doubled (CRB
        "Range — Touch": "deals double damage on a successful critical hit").
        ``attack_penalty`` (Spell Combat) folds into each projectile's ranged
        touch attack for multi-projectile ray spells.
        """
        dc = self._spell_dc(caster, spell, slot_level=slot_level, metamagic=metamagic)
        save_result = (
            self.resolve_save(
                target, spell.save, dc, save_descriptors=spell_save_descriptors(spell)
            )
            if spell.save != "none" and target is not None
            else None
        )
        caster_live = self._stats[caster.combatant.id]
        target_live = (
            self._stats[target.combatant.id] if target is not None else caster_live
        )
        # Apply only the metamagic feats chosen for this cast (B7)
        metamagic_effects = self._apply_metamagic(spell, metamagic)
        # PF1e multi-projectile rays (Scorching Ray): the delivery gate skipped
        # its single ranged touch attack, so each projectile rolls its own here
        # — only against a hostile target (a friendly ray needs no attack).
        per_projectile_attack = (
            spell.requires_ranged_touch
            and _spell_declares_projectiles(spell)
            and target is not None
            and target.side != caster.side
        )
        hp_before = target.hp if target is not None else caster.hp
        parts = self._apply_spell_effects_from_list(
            metamagic_effects, target, save_result, caster_live, target_live,
            caster=caster, spell_name=spell.name,
            empower="Empower Spell" in metamagic,
            maximize="Maximize Spell" in metamagic,
            dc=dc, center_pos=center_pos, save_type=spell.save,
            crit=spell_crit, ranged_touch=per_projectile_attack,
            attack_penalty=attack_penalty, spell_resistance=spell.spell_resistance,
        )
        save_str = _save_label(save_result)
        if target is None and center_pos is not None:
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"cast {spell_name} at ({center_pos[0]},{center_pos[1]}) "
                f"DC{dc} {save_str} "
                f"-> {'; '.join(parts)}"
            )
        elif target is not None:
            self._log(
                f"round {self._current_round} {caster.combatant.id}: "
                f"cast {spell_name} vs {target.combatant.id} "
                f"DC{dc} {save_str} "
                f"-> {'; '.join(parts)} "
                f"({hp_before}->{target.hp})"
            )
            if target.dead:
                self._log(
                    f"round {self._current_round} {caster.combatant.id}: "
                    f"{target.combatant.id} dead"
                )
        self._check_reactions(
            ReactionEvent(kind="spell_cast", actor=caster, target=target)
        )

    def _apply_spell_effects(
        self,
        spell: SpellSpec,
        target: CombatantState,
        save_result: SaveResult | None,
        caster_live: _LiveStats,
        target_live: _LiveStats,
    ) -> list[str]:
        """Legacy wrapper for compatibility."""
        return self._apply_spell_effects_from_list(
            spell.effects, target, save_result, caster_live, target_live,
            caster=target, spell_name=spell.name, save_type=spell.save
        )

    def _apply_spell_effects_from_list(
        self,
        effects: tuple[SpellEffect, ...],
        target: CombatantState | None,
        save_result: SaveResult | None,
        caster_live: _LiveStats,
        target_live: _LiveStats,
        *,
        caster: CombatantState,
        spell_name: str,
        empower: bool = False,
        maximize: bool = False,
        dc: int = 15,
        center_pos: tuple[int, int] | None = None,
        save_type: SaveType = "none",
        crit: bool = False,
        ranged_touch: bool = False,
        attack_penalty: int = 0,
        spell_resistance: bool = True,
    ) -> list[str]:
        saved = save_result is not None and save_result.success
        return [
            self._apply_single_spell_effect(
                effect, target, caster_live, target_live,
                caster=caster, spell_name=spell_name,
                empower=empower, maximize=maximize, saved=saved,
                dc=dc, center_pos=center_pos, save_type=save_type,
                crit=crit, ranged_touch=ranged_touch, attack_penalty=attack_penalty,
                spell_resistance=spell_resistance,
            )
            for effect in effects
        ]

    def _apply_single_spell_effect(
        self,
        effect: SpellEffect,
        target: CombatantState | None,
        caster_live: _LiveStats,
        target_live: _LiveStats,
        caster: CombatantState,
        *,
        spell_name: str,
        empower: bool = False,
        maximize: bool = False,
        saved: bool,
        dc: int = 15,
        center_pos: tuple[int, int] | None = None,
        save_type: SaveType = "none",
        crit: bool = False,
        ranged_touch: bool = False,
        attack_penalty: int = 0,
        spell_resistance: bool = True,
    ) -> str:
        if isinstance(effect, AreaEffect):
            return self._apply_area_effect(
                effect, target, caster_live, target_live,
                caster=caster, spell_name=spell_name, saved=saved,
                empower=empower, maximize=maximize, dc=dc,
                center_pos=center_pos, save_type=save_type,
                spell_resistance=spell_resistance,
            )
        if isinstance(effect, SummonEffect):
            return self._apply_summon_effect(effect, caster, caster_live, spell_name)
        if target is None:
            return ""
        return self._apply_targeted_spell_effect(
            effect, target, caster_live, target_live,
            caster=caster, saved=saved, empower=empower, maximize=maximize,
            spell_name=spell_name, crit=crit, ranged_touch=ranged_touch,
            attack_penalty=attack_penalty,
        )

    def _apply_targeted_spell_effect(
        self,
        effect: DamageEffect | ConditionEffect | HealEffect | BuffEffect | PenaltyEffect,
        target: CombatantState,
        caster_live: _LiveStats,
        target_live: _LiveStats,
        *,
        caster: CombatantState,
        saved: bool,
        empower: bool,
        maximize: bool,
        spell_name: str,
        crit: bool = False,
        ranged_touch: bool = False,
        attack_penalty: int = 0,
    ) -> str:
        if isinstance(effect, DamageEffect):
            return self._apply_damage_effect(
                effect, target, caster_live, target_live,
                saved=saved, empower=empower, maximize=maximize, caster=caster,
                crit=crit, ranged_touch=ranged_touch, attack_penalty=attack_penalty,
                spell_name=spell_name,
            )
        if isinstance(effect, ConditionEffect):
            return self._apply_condition_effect(
                effect, target, saved=saved, spell_name=spell_name,
                caster_level=caster.combatant.level,
            )
        if isinstance(effect, HealEffect):
            return self._apply_heal_effect(
                effect, target, caster_level=caster.combatant.level,
                empower=empower, maximize=maximize, saved=saved,
                healer=caster,
            )
        if isinstance(effect, PenaltyEffect):
            return self._apply_penalty_effect(
                effect, target, caster=caster, saved=saved,
                empower=empower, maximize=maximize, spell_name=spell_name,
            )
        return self._apply_buff_effect(
            effect, target, spell_name=spell_name,
            caster_level=caster.combatant.level,
        )

    def _apply_damage_effect(
        self,
        effect: DamageEffect,
        target: CombatantState,
        caster_live: _LiveStats,
        target_live: _LiveStats,
        *,
        saved: bool,
        empower: bool,
        maximize: bool,
        caster: CombatantState,
        crit: bool = False,
        ranged_touch: bool = False,
        attack_penalty: int = 0,
        spell_name: str = "",
    ) -> str:
        # PF1e (CRB, Magic — Caster Level): per-level spell damage is resolved
        # against the caster's level at cast time; the scaled formula then
        # flows through crits, energy resistance and metamagic unchanged.
        formula = effect.effective_formula(caster.combatant.level)
        # PF1e multi-projectile spells (SRD Magic Missile: "one missile, plus
        # one additional missile per two caster levels beyond 1st [...]
        # maximum of five"; Scorching Ray: "one ray, plus one additional ray
        # for every four levels beyond 3rd [...] maximum of three"): each
        # projectile rolls its own damage and, for a ray, its own attack.
        count = (
            effect.projectiles.count_for(caster.combatant.level)
            if effect.projectiles is not None
            else 1
        )
        total = 0
        for _ in range(count):
            dmg = self._resolve_one_projectile(
                effect, formula, target, caster,
                saved=saved, empower=empower, maximize=maximize,
                crit=crit, ranged_touch=ranged_touch, attack_penalty=attack_penalty,
            )
            if dmg is None:
                continue  # this ray missed — no damage, no stat/reaction
            caster_live.damage_dealt += dmg
            target_live.damage_taken += dmg
            self._check_reactions(
                ReactionEvent(
                    kind="damage_taken", actor=caster, target=target, damage=dmg
                )
            )
            total += dmg
            # PF1e: if the target drops mid-sequence the remaining projectiles
            # are lost (the engine's existing multi-attack convention).
            if not target.active:
                break
        # PF1e recurring damage (S2c, Acid Arrow): a landed hit leaves acid
        # that keeps burning for rounds_for(caster_level) rounds. Only attached
        # while the target is still standing (a dead target has no turns).
        if effect.recurring is not None and target.active:
            self._attach_recurring_damage(effect.recurring, target, caster, spell_name)
        return f"{total} damage"

    def _resolve_one_projectile(
        self,
        effect: DamageEffect,
        formula: DiceExpr,
        target: CombatantState,
        caster: CombatantState,
        *,
        saved: bool,
        empower: bool,
        maximize: bool,
        crit: bool,
        ranged_touch: bool,
        attack_penalty: int,
    ) -> int | None:
        """Resolve one projectile's hit + damage; None when the ray misses.

        Rolls the projectile's own ranged touch attack (when the spell is a
        ray), then its own damage dice through maximize / crit / save /
        empower / energy resistance, and applies the damage to the target.
        """
        proj_crit = crit
        if ranged_touch:
            # Each ray rolls its own ranged touch attack (cover, concealment
            # and critical threat included).
            hit, proj_crit = self._spell_ranged_touch_attack_hits(
                caster, target,
                attack_penalty=attack_penalty, deals_damage=True,
            )
            if not hit:
                return None
        raw = formula.roll(self._rng)
        if maximize:
            raw = formula.max_value()
        if proj_crit:
            # PF1e (CRB "Range — Touch"): a touch/ranged-touch spell that
            # deals damage threatens on a natural 20 and deals double
            # damage on a successful critical hit.
            raw *= 2
        if saved and effect.half_on_save:
            dmg = max(0, raw // 2)
        elif saved and effect.save_negates:
            dmg = 0
        else:
            dmg = raw
        if empower:
            dmg = int(dmg * 1.5)
        dmg = self._apply_energy_resistance(dmg, frozenset(effect.types), target)
        target.hp -= dmg
        return dmg

    def _attach_recurring_damage(
        self,
        spec: RecurringDamageSpec,
        target: CombatantState,
        caster: CombatantState,
        spell_name: str,
    ) -> None:
        """Add a recurring-damage source to a target that just took the hit."""
        rounds = spec.rounds_for(caster.combatant.level)
        if rounds <= 0:
            return
        target.recurring_damage.append(
            RecurringDamage(
                formula=spec.formula,
                types=frozenset(spec.types),
                rounds_left=rounds,
                source=f"acid: {spell_name}",
            )
        )

    def _apply_condition_effect(
        self,
        effect: ConditionEffect,
        target: CombatantState,
        *,
        saved: bool,
        spell_name: str,
        caster_level: int = 0,
    ) -> str:
        duration = effect.duration_rounds
        if effect.duration_rounds_per_level > 0:
            duration = max(1, caster_level * effect.duration_rounds_per_level)
            if effect.max_duration_rounds > 0:
                duration = min(duration, effect.max_duration_rounds)
        if saved and effect.save_negates:
            # PF1e partial save (SRD spells/fear.md): a successful save does
            # not always spare the target — it may impose a weaker condition
            # (Fear: shaken for 1 round instead of panicked).
            if effect.save_partial is not None:
                name, partial_duration = effect.save_partial
                applied = self._impose_condition(target, name, partial_duration, spell_name)
                if not applied:
                    return ""
                return f"{name} ({partial_duration}r) (partial save)"
            return f"{effect.condition_name} negated"
        return self._impose_condition(
            target, effect.condition_name, duration, spell_name
        )

    def _impose_condition(
        self,
        target: CombatantState,
        condition_name: str,
        duration_rounds: int,
        spell_name: str,
    ) -> str:
        """Append a timed condition to the target; handle the bleeding DoT."""
        cond = CONDITIONS_BY_NAME.get(condition_name)
        if cond is None:
            return ""
        target.active_conditions.append(
            ActiveCondition(
                condition=cond,
                rounds_left=duration_rounds,
                source=f"spell: {spell_name}",
            )
        )
        if condition_name == "bleeding":
            # The bleeding condition's damage-over-time is engine-driven
            # (CombatantState.bleed_damage, CRB Conditions — bleeding); the
            # SRD Bleed cantrip (spells/bleed.md) deals 1 bleed damage/round.
            target.bleed_damage = max(target.bleed_damage, 1)
        return f"{condition_name} ({duration_rounds}r)"

    def _bitter_reduced(
        self, healer: CombatantState, target: CombatantState, amount: int
    ) -> int:
        """PF1e (Drawback "Bitter"): "When you receive healing from an ally's
        class feature, spell, or spell-like ability, reduce the amount of that
        healing by 1 hit point." Applies only to ally-sourced healing (an
        ally is another creature on the same side); self-healing is untouched.
        """
        if (
            amount > 0
            and healer is not target
            and healer.side == target.side
            and self._has_feat(target, "Bitter")
        ):
            return amount - 1
        return amount

    def _apply_heal_effect(
        self,
        effect: HealEffect,
        target: CombatantState,
        *,
        caster_level: int,
        empower: bool,
        maximize: bool,
        saved: bool,
        healer: CombatantState | None = None,
    ) -> str:
        formula = effect.effective_formula(caster_level)
        heal = formula.roll(self._rng)
        if maximize:
            heal = formula.max_value()
        if empower:
            heal = int(heal * 1.5)
        if target.combatant.creature_type == "undead":
            # PF1e (SRD "Cure Light Wounds"): "Since undead are powered by
            # negative energy, this spell deals damage to them instead of
            # curing their wounds. An undead creature can apply spell
            # resistance, and can attempt a Will save to take half damage."
            # SR is resolved upstream (_spell_delivery_blocked); the rolled
            # save halves here. Cure damage is spell energy: never reduced by
            # DR, and it does not stop bleeding or stabilize. Bitter reduces
            # healing, not this damage.
            dmg = heal // 2 if saved else heal
            target.hp -= dmg
            return f"{dmg} damage (undead)"
        if healer is not None:
            heal = self._bitter_reduced(healer, target, heal)
        old_hp = target.hp
        target.hp = min(target.hp + heal, target.combatant.hp_max)
        # PF1e (CRB, Stable Characters and Recovery): "If any sort of healing
        # cures the dying character of even 1 point of damage, he becomes
        # stable and stops losing hit points."
        if target.hp < 0:
            target.stabilized_hp = target.hp
        actual = target.hp - old_hp
        self._stop_bleeding(target)
        return f"+{actual} HP"

    def _apply_buff_effect(
        self,
        effect: BuffEffect,
        target: CombatantState,
        *,
        spell_name: str,
        caster_level: int,
    ) -> str:
        # PF1e caster-level scaling on buff values (SRD shield of faith
        # "+2 deflection, +1 per six caster levels (maximum +5)"): the flat
        # extra is added to EVERY modifier of the buff.
        modifiers = effect.modifiers
        if effect.scaling_flat is not None:
            extra = min(
                effect.scaling_flat.max_amount,
                (caster_level // effect.scaling_flat.per_levels)
                * effect.scaling_flat.amount,
            )
            if extra > 0:
                modifiers = tuple(
                    StatModifier(
                        target=mod.target,
                        value=mod.value + extra,
                        bonus_type=mod.bonus_type,
                        condition=mod.condition,
                        weapon_filter=mod.weapon_filter,
                    )
                    for mod in modifiers
                )
        target.active_buffs.append(
            ActiveBuff(
                modifiers=modifiers,
                rounds_left=effect.duration_rounds,
                source=f"spell: {spell_name}",
            )
        )
        return f"buff {len(modifiers)} mods ({effect.duration_rounds}r)"

    def _apply_penalty_effect(
        self,
        effect: PenaltyEffect,
        target: CombatantState,
        *,
        caster: CombatantState,
        saved: bool,
        empower: bool,
        maximize: bool,
        spell_name: str,
    ) -> str:
        """Apply a rolled ability penalty (SRD Ray of Enfeeblement).

        The penalty is rolled (maximized/empowered like spell damage), halved
        on a successful save, and applied as negative untyped StatModifiers on
        the listed targets for ``duration_rounds_per_level`` rounds per caster
        level. A penalty of 0 or less has no effect.
        """
        formula = effect.effective_formula(caster.combatant.level)
        if maximize:
            penalty = formula.max_value()
        else:
            penalty = formula.roll(self._rng)
            if empower:
                penalty = int(penalty * 1.5)
        if saved and effect.half_on_save:
            penalty //= 2
        if penalty <= 0:
            return "no penalty"
        duration = max(1, caster.combatant.level * effect.duration_rounds_per_level)
        target.active_buffs.append(
            ActiveBuff(
                modifiers=tuple(
                    StatModifier(target=t, value=-penalty, bonus_type="")
                    for t in effect.targets
                ),
                rounds_left=duration,
                source=f"spell: {spell_name}",
            )
        )
        return f"-{penalty} {'/'.join(effect.targets)} ({duration}r)"

    def _apply_area_effect(
        self,
        effect: AreaEffect,
        target: CombatantState | None,
        caster_live: _LiveStats,
        target_live: _LiveStats,
        *,
        caster: CombatantState,
        spell_name: str,
        saved: bool,
        empower: bool = False,
        maximize: bool = False,
        dc: int = 15,
        center_pos: tuple[int, int] | None = None,
        save_type: SaveType = "none",
        spell_resistance: bool = True,
    ) -> str:
        """Apply an area effect to all creatures within its template.

        PF1e (CRB, Magic - Aiming a Spell): a burst/spread centers on
        ``center_pos`` when given (U7b point targeting), otherwise on the
        resolved target's position; a cone or line starts at the CASTER's
        square and is aimed at that same resolved cell (the cone "shoots
        away from you in a quarter-circle in the direction you designate",
        the line "shoots away from you in a line in the direction you
        designate"). Every creature whose occupied cells intersect the
        template is subject to the effect.
        """
        center = _burst_center(target, center_pos)
        if center is None:
            return "no targets in area"
        affected = self._area_creatures(effect, caster, center)

        if not affected:
            return "no targets in area"

        total_damage = 0
        total_conditions = 0
        total_buffs = 0

        for affected_state in affected:
            if spell_resistance and not self._check_spell_resistance(caster, affected_state):
                continue
            creature_saved = self._area_save(
                affected_state, target, effect, saved=saved, dc=dc,
                save_type=save_type,
            )
            for sub_effect in effect.effects:
                target_live = self._stats[affected_state.combatant.id]
                result = self._apply_single_spell_effect(
                    sub_effect, affected_state, caster_live, target_live,
                    caster=caster, spell_name=spell_name, saved=creature_saved,
                    empower=empower, maximize=maximize,
                )
                if "damage" in result:
                    total_damage += int(result.split()[0])
                elif "damage" not in result and result:
                    if "negated" not in result and "buff" not in result:
                        total_conditions += 1
                    elif "buff" in result:
                        total_buffs += 1

        return (
            f"area: {len(affected)} targets, {total_damage} total damage, "
            f"{total_conditions} conditions, {total_buffs} buffs"
        )

    def _area_creatures(
        self, effect: AreaEffect, caster: CombatantState, aim: tuple[int, int]
    ) -> list[CombatantState]:
        """Creatures intersecting the template of an area effect.

        Burst: circle of ``radius_ft`` around the resolved center ``aim``
        (unchanged behaviour). Cone/line: the template originates at the
        caster's anchor cell and opens toward ``aim`` (PF1e CRB "Aiming a
        Spell" — see ``areas.py``); a creature is affected when ANY of its
        occupied cells lies inside the template.

        ``effect.targets`` restricts the selection (SRD bless/bane bursts):
        "allies" keeps only creatures on the caster's side (the caster
        included — SRD bless "The caster and all allies"), "enemies" keeps
        only the opposite side, "all" keeps everyone.
        """
        span_cells = effect.radius_ft // _SQUARE_FT
        if effect.shape == "burst":
            affected = self._creatures_in_range(aim, span_cells)
        else:
            origin = caster.pos
            if effect.shape == "cone":
                cells = cone_cells(self._grid, origin, aim, span_cells)
            else:
                cells = line_cells(self._grid, origin, aim, span_cells)
            affected = [
                state
                for state in self._states
                if state.active and state.occupied_cells() & cells
            ]
        if effect.targets == "allies":
            return [s for s in affected if s.side == caster.side]
        if effect.targets == "enemies":
            return [s for s in affected if s.side != caster.side]
        return affected

    def _creatures_in_range(
        self, center: tuple[int, int], radius_cells: int
    ) -> list[CombatantState]:
        """Return active creatures within radius_cells of center."""
        affected: list[CombatantState] = []
        for state in self._states:
            if not state.active:
                continue
            dist = min(
                self._grid.distance(center, cell) for cell in state.occupied_cells()
            )
            if dist <= radius_cells:
                affected.append(state)
        return affected

    def _area_save(
        self,
        affected_state: CombatantState,
        target: CombatantState | None,
        effect: AreaEffect,
        *,
        saved: bool,
        dc: int = 15,
        save_type: SaveType = "none",
    ) -> bool:
        """Save result for one creature in an area effect.

        PF1e (CRB): every creature in the area rolls the save the SPELL lists
        (Will / Fortitude / Reflex) — "save negates" and "save for half" both
        grant it; whether a success negates or halves is decided per sub-effect
        (``save_negates`` / ``half_on_save``), never by skipping the roll.
        The resolved primary target re-uses its already-rolled save; every
        other creature in the area — and every creature of a point-targeted
        burst (no primary target, U7b) — rolls its own.
        """
        if save_type == "none":
            return False
        if affected_state is target:
            return saved
        save_result = self.resolve_save(
            affected_state,
            save_type,
            dc,
            save_descriptors=save_descriptors_for_effects(effect.effects),
        )
        return save_result.success

    def _apply_metamagic(
        self, spell: SpellSpec, metamagic_feats: tuple[str, ...]
    ) -> tuple[SpellEffect, ...]:
        """Apply the feats chosen for THIS cast to the spell's effects (B7)."""
        if not metamagic_feats:
            return spell.effects
        has_extend = "Extend Spell" in metamagic_feats
        return tuple(
            self._metamagic_transform_sub(effect, has_extend=has_extend)
            for effect in spell.effects
        )

    def _metamagic_transform_sub(
        self, effect: SpellEffect, *, has_extend: bool
    ) -> SpellEffect:
        """Apply Extend Spell to one effect (recursing into AreaEffect sub-effects)."""
        if isinstance(effect, (DamageEffect, HealEffect)):
            return effect
        if isinstance(effect, ConditionEffect):
            duration = effect.duration_rounds * 2 if has_extend else effect.duration_rounds
            per_level = (
                effect.duration_rounds_per_level * 2
                if has_extend
                else effect.duration_rounds_per_level
            )
            max_rounds = (
                effect.max_duration_rounds * 2
                if has_extend
                else effect.max_duration_rounds
            )
            partial = effect.save_partial
            if partial is not None and has_extend:
                partial = (partial[0], partial[1] * 2)
            return ConditionEffect(
                condition_name=effect.condition_name,
                duration_rounds=duration,
                save_negates=effect.save_negates,
                save_partial=partial,
                duration_rounds_per_level=per_level,
                max_duration_rounds=max_rounds,
            )
        if isinstance(effect, BuffEffect):
            duration = effect.duration_rounds * 2 if has_extend else effect.duration_rounds
            return BuffEffect(
                modifiers=effect.modifiers,
                duration_rounds=duration,
                scaling_flat=effect.scaling_flat,
            )
        if isinstance(effect, PenaltyEffect):
            duration = (
                effect.duration_rounds_per_level * 2
                if has_extend
                else effect.duration_rounds_per_level
            )
            return PenaltyEffect(
                formula=effect.formula,
                scaling_flat=effect.scaling_flat,
                targets=effect.targets,
                duration_rounds_per_level=duration,
                half_on_save=effect.half_on_save,
            )
        if isinstance(effect, AreaEffect):
            return AreaEffect(
                shape=effect.shape,
                radius_ft=effect.radius_ft,
                effects=tuple(
                    self._metamagic_transform_sub(sub, has_extend=has_extend)
                    for sub in effect.effects
                ),
                save_for_half=effect.save_for_half,
                targets=effect.targets,
            )
        return effect


    def _apply_summon_effect(
        self,
        effect: SummonEffect,
        state: CombatantState,
        _caster_live: _LiveStats,
        _spell_name: str,
    ) -> str:
        """Apply a summoning effect - create a summoned creature."""
        # PF1e (SRD spells/summon-monster-1.md): "Duration 1 round/level (D)"
        # - a per-level duration resolves against the caster's level at cast
        # time, mirroring the ConditionEffect convention; a fixed duration is
        # the pre-conformance fallback.
        duration = effect.duration_rounds
        if effect.duration_rounds_per_level > 0:
            duration = max(
                1, state.combatant.level * effect.duration_rounds_per_level
            )
        # Load the summoned creature
        try:
            summoned_combatant = load_combatant(Path(effect.creature))
        except CombatantLoadError:
            return f"summon failed: could not load {effect.creature}"

        # Find a valid adjacent position for the summoned creature
        center = state.pos
        spawn_pos = None
        for dr in (-1, 0, 1):
            for dc in (-1, 0, 1):
                if dr == 0 and dc == 0:
                    continue
                pos = (center[0] + dr, center[1] + dc)
                if self._cells_free(self._footprint_at(pos, state), state):
                    spawn_pos = pos
                    break
            if spawn_pos:
                break

        if not spawn_pos:
            return "summon failed: no space"

        # Create summoned creature state
        summoned_state = CombatantState(
            combatant=summoned_combatant,
            side=state.side,
            pos=spawn_pos,
            hp=summoned_combatant.hp_max,
        )

        # Insert into initiative order right after caster
        caster_idx = next(i for i, s in enumerate(self._states) if s is state)
        self._states.insert(caster_idx + 1, summoned_state)

        # Set expiration
        summoned_state.summon_duration = duration
        summoned_state.summon_caster_id = state.combatant.id
        self._apply_simple_monster_death(summoned_state)

        self._stats[summoned_state.combatant.id] = _LiveStats()
        self._pending_summons.append(summoned_state)

        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"summon {summoned_combatant.id} at {spawn_pos} ({duration}r)"
        )
        return f"summoned {summoned_combatant.id}"

    def _resolve_swing(
        self,
        attacker: CombatantState,
        target: CombatantState,
        weapon: AttackSpec,
        *,
        label: str,
        bonus_override: int | None = None,
        attack_penalty: int = 0,
    ) -> bool:
        """Resolve one swing, log it, update stats. Return True if target dropped.

        ``attack_penalty`` is folded into the attack bonus (and thus the crit
        confirmation): Spell Combat's -2 (PF1e, Magus Spell Combat) rides the
        full-attack chain to every swing.
        """
        live = self._stats[attacker.combatant.id]
        target_live = self._stats[target.combatant.id]
        hp_before = target.hp
        override = bonus_override
        if weapon.secondary:
            # PF1e (CRB "Natural Attacks"): secondary natural attacks are at
            # base attack bonus -5; the Multiattack feat reduces this to -2.
            penalty = 2 if self._has_feat(attacker, "Multiattack") else 5
            base = weapon.attack_bonus if override is None else override
            override = base - penalty
        if attack_penalty:
            base = weapon.attack_bonus if override is None else override
            override = base + attack_penalty
        result = self.resolve_attack(attacker, target, weapon, bonus_override=override)
        live.hits += int(result.hit)
        live.crits += int(result.crit)
        live.damage_dealt += result.damage
        target_live.damage_taken += result.damage
        outcome = "CRIT" if result.crit else "HIT" if result.hit else "MISS"
        flank_str = f"+{result.flank_bonus}(flank)" if result.flank_bonus else ""
        high_ground_str = (
            f"+{result.high_ground_bonus}(high)" if result.high_ground_bonus else ""
        )
        melee_str = f"{result.melee_penalty}(melee)" if result.melee_penalty else ""
        bonus_str = (
            f"{result.base_bonus}{result.penalty:+d}{flank_str}{high_ground_str}{melee_str}"
            if result.penalty
            else f"{result.base_bonus}{flank_str}{high_ground_str}{melee_str}"
        )
        line = (
            f"round {self._current_round} {attacker.combatant.id}: {label} "
            f"vs {target.combatant.id} "
            f"d20={result.roll}+{bonus_str}={result.total} "
            f"AC {result.ac} -> {outcome}"
        )
        if result.hit:
            line += f" {result.damage} damage ({hp_before}->{target.hp})"
            if self._is_paralyzing_touch(attacker, weapon):
                duration = 1 + self._rng.roll_die(4)
                if not self._has_condition_named(target, "paralyzed"):
                    target.active_conditions.append(
                        ActiveCondition(
                            condition=CONDITIONS_BY_NAME["paralyzed"],
                            rounds_left=duration,
                            source=f"monster ability: paralyzing touch by {attacker.combatant.id}",
                        )
                    )
                line += f" paralyzed ({duration}r)"
        self._log(line)
        if target.dead:
            self._log(
                f"round {self._current_round} {attacker.combatant.id}: "
                f"{target.combatant.id} dead"
            )
            return True
        if not target.active:
            self._log(
                f"round {self._current_round} {attacker.combatant.id}: "
                f"{target.combatant.id} down"
            )
            return True
        self._check_reactions(
            ReactionEvent(
                kind="attack_resolved",
                actor=attacker,
                target=target,
                damage=result.damage,
            )
        )
        return False

    def _attack(
        self,
        attacker: CombatantState,
        target: CombatantState,
        weapon: AttackSpec,
        *,
        attack_penalty: int = 0,
    ) -> None:
        for swing in range(1, weapon.count + 1):
            if not attacker.active:
                return
            if self._check_provoked_aoo(attacker, weapon):
                return
            label = weapon.name if weapon.count == 1 else f"{weapon.name} #{swing}"
            if self._resolve_swing(
                attacker, target, weapon, label=label, attack_penalty=attack_penalty
            ):
                return

    def _single_attack(
        self, attacker: CombatantState, target: CombatantState, weapon: AttackSpec
    ) -> None:
        if not attacker.active:
            return
        if self._check_provoked_aoo(attacker, weapon):
            return
        self._resolve_swing(attacker, target, weapon, label=weapon.name)

    def _full_attack(
        self,
        attacker: CombatantState,
        target: CombatantState,
        *,
        attack_penalty: int = 0,
    ) -> None:
        melee_weapons = [
            w
            for w in attacker.usable_attacks()
            if w.kind == "melee" and self._melee_weapon_usable(attacker, target, w)
        ]
        if not melee_weapons:
            # No melee weapon reaches: fall back to weapon_for (ranged/touch),
            # preserving the pre-L3 single-weapon behavior.
            weapon = self.weapon_for(attacker, target)
            if weapon is None:
                return
            self._full_attack_weapon(
                attacker, target, weapon, attack_penalty=attack_penalty
            )
            return
        for weapon in melee_weapons:
            if not attacker.active or not target.active:
                return
            self._full_attack_weapon(
                attacker, target, weapon, attack_penalty=attack_penalty
            )

    def _full_attack_weapon(
        self,
        attacker: CombatantState,
        target: CombatantState,
        weapon: AttackSpec,
        *,
        attack_penalty: int = 0,
    ) -> None:
        """Resolve one weapon's full-attack swings (count swings or BAB iteratives)."""
        if weapon.count > 1:
            self._attack(attacker, target, weapon, attack_penalty=attack_penalty)
            return
        if weapon.natural:
            # PF1e (CRB "Natural Attacks"): "You do not receive additional
            # natural attacks for a high base attack bonus." One swing per
            # natural weapon, at its own attack bonus.
            self._attack(attacker, target, weapon, attack_penalty=attack_penalty)
            return
        n = min(
            _MAX_ITERATIVES,
            1 + max(0, (attacker.combatant.bab - 1) // _ITERATIVE_PENALTY),
        )
        for i in range(n):
            if not attacker.active:
                return
            if not target.active:
                return
            if self._check_provoked_aoo(attacker, weapon):
                return
            label = weapon.name if n == 1 else f"{weapon.name} #{i + 1}"
            bonus = weapon.attack_bonus - _ITERATIVE_PENALTY * i
            if self._resolve_swing(
                attacker, target, weapon, label=label, bonus_override=bonus,
                attack_penalty=attack_penalty,
            ):
                return

    def _melee_weapon_usable(
        self, attacker: CombatantState, target: CombatantState, weapon: AttackSpec
    ) -> bool:
        """True if ``weapon`` (a melee weapon) can reach ``target`` with clear LoE."""
        if not has_line_of_effect_cells(
            self._grid, attacker.occupied_cells(), target.occupied_cells()
        ):
            return False
        dist_ft = self.creature_distance(attacker, target) * _SQUARE_FT
        inner_cells, outer_cells = _melee_reach_zone_cells(attacker, weapon)
        return inner_cells * _SQUARE_FT <= dist_ft <= outer_cells * _SQUARE_FT

    def _step5(self, state: CombatantState, target: CombatantState) -> None:
        if state.moved_this_turn:
            return
        if self.has_condition_flag(state, "cant_move"):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot move)")
            return
        # SRD "Take 5-Foot Step": "You can only take a 5-foot-step if your
        # movement isn't hampered by difficult terrain or darkness." — a step
        # out of OR into a difficult cell is blocked (darkness not modeled).
        if self._footprint_touches_difficult(self._footprint_at(state.pos, state)):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot step)")
            return
        path = self._move_path(state, target)
        start = state.pos
        if self._footprint_touches_difficult(self._footprint_at(path[0], state)):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot step)")
            return
        state.pos = path[0]
        state.moved_this_turn = True
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"5ft step ({start[0]},{start[1]})->({path[0][0]},{path[0][1]})"
        )

    def _step5_to(self, state: CombatantState, destination: Pos) -> ActionResult:
        """5-foot step to an explicit adjacent cell — never provokes (U5c)."""
        kind = "5foot_step"
        if state.moved_this_turn:
            return ActionResult(kind=kind, ok=True, reason=_REASON_OK)
        if self.has_condition_flag(state, "cant_move"):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot move)")
            return ActionResult(kind=kind, ok=True, reason=_REASON_OK)
        adjacent = self._grid.distance(state.pos, destination) == 1
        free = self._cells_free(self._footprint_at(destination, state), state)
        # PF1e (SRD Measuring Distance): "You can't move diagonally past a
        # corner (even by taking a 5-foot step)."
        diagonal = state.pos[0] != destination[0] and state.pos[1] != destination[1]
        corner_clear = not diagonal or self._grid.diagonal_allowed(state.pos, destination)
        # SRD "Take 5-Foot Step": "You can only take a 5-foot-step if your
        # movement isn't hampered by difficult terrain or darkness." — a step
        # out of OR into a difficult cell is blocked (darkness not modeled).
        step_clear = not (
            self._footprint_touches_difficult(self._footprint_at(state.pos, state))
            or self._footprint_touches_difficult(self._footprint_at(destination, state))
        )
        if not adjacent or not free or not corner_clear or not step_clear:
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"{kind} rejected ({_REASON_UNREACHABLE_DESTINATION})"
            )
            return ActionResult(
                kind=kind, ok=False, reason=_REASON_UNREACHABLE_DESTINATION
            )
        start = state.pos
        state.pos = destination
        state.moved_this_turn = True
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"5ft step ({start[0]},{start[1]})->({destination[0]},{destination[1]})"
        )
        return ActionResult(kind=kind, ok=True, reason=_REASON_OK)

    def _move(self, state: CombatantState, target: CombatantState) -> None:
        if state.moved_this_turn:
            return
        if self.has_condition_flag(state, "cant_move"):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot move)")
            return
        path = self._move_path(state, target, friendly_passable=True)
        start = state.pos
        actual_path = self._walk_steps(state, path)
        if actual_path:
            state.moved_this_turn = True
            coords = "->".join(f"({p[0]},{p[1]})" for p in (start, *actual_path))
            self._log(f"round {self._current_round} {state.combatant.id}: move {coords}")

    def _move_to(self, state: CombatantState, destination: Pos) -> ActionResult:
        """Move action to an explicit cell within speed (U5c).

        Validated against the Dijkstra cost field from the combatant's position
        under its speed budget; walked step-by-step with the same AoO
        machinery as the auto-pathed move.
        """
        kind = "move"
        if state.moved_this_turn:
            return ActionResult(kind=kind, ok=True, reason=_REASON_OK)
        if self.has_condition_flag(state, "cant_move"):
            self._log(f"round {self._current_round} {state.combatant.id}: wait (cannot move)")
            return ActionResult(kind=kind, ok=True, reason=_REASON_OK)
        if not self._destination_reachable(state, destination, friendly_passable=True):
            self._log(
                f"round {self._current_round} {state.combatant.id}: "
                f"{kind} rejected ({_REASON_UNREACHABLE_DESTINATION})"
            )
            return ActionResult(
                kind=kind, ok=False, reason=_REASON_UNREACHABLE_DESTINATION
            )
        path = self._descend_path(state, destination, friendly_passable=True)
        self._walk_steps(state, path)
        state.moved_this_turn = True
        self._log(
            f"round {self._current_round} {state.combatant.id}: "
            f"move -> ({destination[0]},{destination[1]})"
        )
        return ActionResult(kind=kind, ok=True, reason=_REASON_OK)

    def _destination_reachable(
        self,
        state: CombatantState,
        destination: Pos,
        *,
        speed_factor: int = 1,
        friendly_passable: bool = False,
        avoid_difficult: bool = False,
    ) -> bool:
        """True when destination is passable, unoccupied and within this speed.

        ``speed_factor`` widens the budget (run: 4x speed, U5e).
        ``friendly_passable`` routes the cost field around allies' squares
        (move/run may cross them, SRD Movement); the destination itself must
        still be completely free. ``avoid_difficult`` removes difficult cells
        from the cost field, mirroring the descent constraint of a run
        (CRB: "You can't run or charge across difficult terrain") so the
        reachability verdict and the walked path agree.
        """
        speed_cells = int(
            _speed_ft(state)
            // _SQUARE_FT
            * self._get_speed_mult(state)
            * speed_factor
        )
        if speed_cells <= 0:
            return destination == state.pos
        if not self._cells_free(self._footprint_at(destination, state), state):
            return False
        if avoid_difficult and self._footprint_touches_difficult(
            self._footprint_at(destination, state)
        ):
            return False
        blocked = self._blocked_hostile(state) if friendly_passable else self._blocked(state)
        if avoid_difficult:
            blocked = blocked | self._difficult_cells()
        field = self._grid.reachable(state.pos, speed_cells, blocked)
        return destination in field

    def _difficult_cells(self) -> frozenset[Pos]:
        """Every passable cell on the grid whose terrain costs more than one."""
        return frozenset(
            (row, col)
            for row in range(self._grid.height)
            for col in range(self._grid.width)
            if self._is_difficult_cell((row, col))
        )

    def _walk_steps(
        self, state: CombatantState, path: list[Pos]
    ) -> list[Pos]:
        """Walk a precomputed path cell by cell, resolving AoOs and reactions."""
        actual_path: list[Pos] = []
        for step in path:
            if self._check_move_aoo(state):
                break
            if not state.active:
                break
            # SRD "Moving Through a Square": "Creatures moving through squares
            # occupied by other creatures provoke attacks of opportunity from
            # those creatures." — resolved BEFORE the step is committed, so a
            # mover dropped by the entry AoO never lands on the square.
            if self._check_enter_aoo(state, step):
                break
            if not state.active:
                break
            state.pos = step
            actual_path.append(step)
            self._check_reactions(ReactionEvent(kind="movement_step", actor=state))
            if not state.active:
                break
        return actual_path

    def _move_path(
        self, state: CombatantState, target: CombatantState, *, friendly_passable: bool = False
    ) -> list[Pos]:
        """Full movement path toward the target, up to the combatant's speed.

        Greedy walk of the anchor over the Dijkstra cost field from the target,
        requiring the whole footprint to fit at each step.
        """
        return self._descend_path(state, target.pos, friendly_passable=friendly_passable)

    def _descend_path(
        self,
        state: CombatantState,
        anchor: Pos,
        *,
        speed_factor: int = 1,
        avoid_difficult: bool = False,
        friendly_passable: bool = False,
    ) -> list[Pos]:
        """Greedy walk of the anchor over the cost field from ``anchor``.

        ``speed_factor`` widens the movement budget (run: 4x speed, U5e).
        ``avoid_difficult`` excludes difficult-terrain cells from the walk
        (PF1e: a run cannot cross difficult terrain), so the walk stops in
        front of the obstacle. ``friendly_passable`` lets the walk CROSS
        same-side creatures' squares (move/run, PF1e SRD Movement) while the
        tail is trimmed so the movement never ENDS on an occupied cell.
        """
        speed_mult = self._get_speed_mult(state)
        speed_cells = int(
            _speed_ft(state)
            // _SQUARE_FT
            * speed_mult
            * speed_factor
        )
        if speed_cells <= 0:
            return []
        blocked = self._blocked_hostile(state) if friendly_passable else self._blocked(state)
        to_target = self._grid.reachable(anchor, None, blocked)
        if self._footprint_cost(state.occupied_cells(), to_target) is None:
            return []
        path: list[Pos] = []
        current = state.pos
        budget = speed_cells
        diagonals_used = 0
        while budget > 0:
            best = self._best_move_step(
                state, current, to_target, budget, diagonals_used,
                avoid_difficult=avoid_difficult, friendly_passable=friendly_passable,
            )
            if best is None:
                break
            _, step_cost, nxt = best
            # PF1e 5-10-5: the diagonal cost alternates 1-2-1-2, so the
            # running diagonal count must follow the walk (grid.reachable
            # already tracks it; the greedy descent must too).
            if current[0] != nxt[0] and current[1] != nxt[1]:
                diagonals_used += 1
            current = nxt
            path.append(current)
            budget -= step_cost
        if friendly_passable:
            while path and not self._cells_free(self._footprint_at(path[-1], state), state):
                path.pop()
        return path

    def _run_line_path(self, state: CombatantState, goal: Pos) -> list[Pos]:
        """Straight-line run path toward ``goal``, truncated at the first obstacle.

        PF1e (SRD "Full-Round Actions — Run"): "When you run, you can move up
        to four times your speed in a straight line" — a run CANNOT turn a
        corner the way a Dijkstra ``move`` does. The path is the Bresenham
        line from the combatant's anchor toward ``goal``, walked under the 4x
        speed budget and stopped at the first obstacle, mirroring the charge's
         straight-line clear-path logic (CRB "Charge"): impassable terrain, a
         difficult-terrain cell (CRB "Difficult Terrain": "You can't run or
         charge across difficult terrain"), or a blocking creature. A hostile
         creature (including the target itself) halts the walk one cell short,
         so an auto-directed run ends adjacent to the target — except one the
         mover may pass through (three size categories apart, SRD "Moving
         Through a Square"), which is crossed with an entry AoO and never
         ended on. Friendly squares
        are still crossed (SRD Movement, conformance L5) but never ended on —
        the tail is trimmed like ``_descend_path``.
        """
        speed_mult = self._get_speed_mult(state)
        budget = int(
            _speed_ft(state) // _SQUARE_FT * speed_mult * _RUN_SPEED_FACTOR
        )
        if budget <= 0:
            return []
        path: list[Pos] = []
        current = state.pos
        diagonals_used = 0
        for nxt in _bresenham_line(state.pos, goal):
            footprint = self._footprint_at(nxt, state)
            if self._footprint_touches_difficult(footprint):
                break
            if not self._cells_walkable(footprint, state):
                break
            step = self._grid.step_cost(current, nxt, diagonals_used)
            if step > budget:
                break
            path.append(nxt)
            if current[0] != nxt[0] and current[1] != nxt[1]:
                diagonals_used += 1
            current = nxt
            budget -= step
        while path and not self._cells_free(self._footprint_at(path[-1], state), state):
            path.pop()
        return path

    def _best_move_step(
        self,
        state: CombatantState,
        current: Pos,
        to_target: dict[Pos, int],
        budget: int,
        diagonals_used: int,
        *,
        avoid_difficult: bool = False,
        friendly_passable: bool = False,
    ) -> tuple[int, int, Pos] | None:
        """Pick the adjacent anchor that best descends the cost field toward the target."""
        current_cost = self._footprint_cost(self._footprint_at(current, state), to_target)
        if current_cost is None:
            return None
        best: tuple[int, int, Pos] | None = None
        row, col = current
        fits = self._cells_walkable if friendly_passable else self._cells_free
        for d_row, d_col in _STEP_DELTAS:
            nxt = (row + d_row, col + d_col)
            # PF1e (CRB, Measuring Distance): "You can't move diagonally past
            # a corner (even by taking a 5-foot step)" — same corner rule the
            # explicit step (``_step5_to``) and flee (``_best_flee_step``)
            # paths already enforce.
            if not self._grid.diagonal_allowed(current, nxt):
                continue
            footprint = self._footprint_at(nxt, state)
            if not fits(footprint, state):
                continue
            if avoid_difficult and self._footprint_touches_difficult(footprint):
                continue
            nxt_cost = self._footprint_cost(footprint, to_target)
            if nxt_cost is None or nxt_cost >= current_cost:
                continue
            # Friendly square: enter it only to cross it — a free cell must
            # descend from it, so the walk never dead-ends on an ally
            # (movement may not END on an occupied cell).
            if (
                friendly_passable
                and not self._cells_free(footprint, state)
                and not self._has_free_descent(state, nxt, to_target, nxt_cost)
            ):
                continue
            step = self._grid.step_cost(current, nxt, diagonals_used)
            if step > budget:
                continue
            score = step + nxt_cost
            if best is None or score < best[0]:
                best = (score, step, nxt)
        return best

    def _has_free_descent(
        self,
        state: CombatantState,
        pos: Pos,
        to_target: dict[Pos, int],
        pos_cost: int,
    ) -> bool:
        """True if a fully free anchor that descends the field is reachable from ``pos``.

        The free anchor may sit beyond a CHAIN of occupied anchors: crossing a
        creature three size categories away (SRD "Moving Through a Square")
        walks through several non-free cells before emerging on the far side,
        so a one-step lookahead is not enough. The chain must strictly
        descend the cost field at every hop, so the walk never dead-ends on
        an occupied cell (movement may not END there).
        """
        seen: set[Pos] = {pos}
        frontier: list[tuple[Pos, int]] = [(pos, pos_cost)]
        while frontier:
            current, current_cost = frontier.pop()
            row, col = current
            for d_row, d_col in _STEP_DELTAS:
                nxt = (row + d_row, col + d_col)
                footprint = self._footprint_at(nxt, state)
                cost = self._footprint_cost(footprint, to_target)
                if cost is None or cost >= current_cost:
                    continue
                if self._cells_free(footprint, state):
                    return True
                if nxt not in seen:
                    seen.add(nxt)
                    frontier.append((nxt, cost))
        return False

    def _footprint_touches_difficult(self, footprint: frozenset[Pos]) -> bool:
        """True if any footprint cell is difficult terrain (move cost > 1)."""
        return any(self._is_difficult_cell(cell) for cell in footprint)

    def _is_difficult_cell(self, pos: Pos) -> bool:
        """True for a passable cell whose terrain costs more than one square."""
        if not self._grid.in_bounds(pos):
            return False
        terrain = self._grid.terrain_at(pos)
        return terrain.move_cost is not None and terrain.move_cost > 1

    def _flee_path(self, state: CombatantState, threat: CombatantState) -> list[Pos]:
        """Movement path away from ``threat``, up to double speed.

        A staggered/disabled creature taking Restricted Withdraw (SRD "Full-Round
        Actions": "you can withdraw as a standard action. In this case, you may
        move up to your speed") gets a single-speed budget instead.

        Uses the Dijkstra cost field from the threat and greedily picks the
        step that maximizes distance (cost) from the threat each cell.
        """
        speed_mult = self._get_speed_mult(state)
        withdraw_mult = 1 if self._is_staggered_limited(state) else 2
        max_cells = int(
            withdraw_mult * (_speed_ft(state) // _SQUARE_FT) * speed_mult
        )
        if max_cells <= 0:
            return []
        blocked = self._blocked(state)
        from_threat = self._grid.reachable(threat.pos, None, blocked)
        if self._footprint_cost(state.occupied_cells(), from_threat) is None:
            return []
        path: list[Pos] = []
        current = state.pos
        budget = max_cells
        diagonals_used = 0
        while budget > 0:
            best = self._best_flee_step(
                state, current, from_threat, budget, diagonals_used
            )
            if best is None:
                break
            _, step_cost, nxt = best
            if current[0] != nxt[0] and current[1] != nxt[1]:
                diagonals_used += 1
            current = nxt
            path.append(current)
            budget -= step_cost
        return path

    def _best_flee_step(
        self,
        state: CombatantState,
        current: Pos,
        from_threat: dict[Pos, int],
        budget: int,
        diagonals_used: int,
    ) -> tuple[int, int, Pos] | None:
        """Pick the adjacent anchor that maximizes distance from the threat."""
        current_cost = self._footprint_cost(self._footprint_at(current, state), from_threat)
        if current_cost is None:
            return None
        best: tuple[int, int, Pos] | None = None
        row, col = current
        for d_row, d_col in _STEP_DELTAS:
            nxt = (row + d_row, col + d_col)
            footprint = self._footprint_at(nxt, state)
            if not self._cells_free(footprint, state):
                continue
            if not self._grid.diagonal_allowed(current, nxt):
                continue
            nxt_cost = self._footprint_cost(footprint, from_threat)
            if nxt_cost is None or nxt_cost <= current_cost:
                continue
            step = self._grid.step_cost(current, nxt, diagonals_used)
            if step > budget:
                continue
            score = -(nxt_cost * 100) + step
            if best is None or score < best[0]:
                best = (score, step, nxt)
        return best

    def _withdraw(self, state: CombatantState, threat: CombatantState | None) -> None:
        """Full-round action: move up to 2x speed away from the nearest enemy.

        Restricted Withdraw (SRD "Full-Round Actions"): a staggered/disabled
        creature takes this as a standard action and moves up to its speed
        (single, not double — see ``_flee_path``).

        The starting square is not threatened — no AoO when leaving it.
        Subsequent squares provoke AoOs normally (step-by-step, as for move).
        Like every other movement it is mutually exclusive with movement
        already spent this turn (``moved_this_turn``).
        """
        if state.moved_this_turn:
            return
        if threat is None:
            return
        path = self._flee_path(state, threat)
        if not path:
            return
        start = state.pos
        actual_path: list[Pos] = []
        for i, step in enumerate(path):
            if i > 0 and self._check_move_aoo(state):
                break
            if not state.active:
                break
            state.pos = step
            actual_path.append(step)
            self._check_reactions(ReactionEvent(kind="movement_step", actor=state))
            if not state.active:
                break
        if actual_path:
            state.moved_this_turn = True
            coords = "->".join(f"({p[0]},{p[1]})" for p in (start, *actual_path))
            self._log(
                f"round {self._current_round} {state.combatant.id}: withdraw {coords}"
            )

    def _log(self, line: str) -> None:
        self._transcript.append(line)


    def _size_mod(self, state: CombatantState) -> int:
        """Size modifier for CMB/CMD: Medium=0, Small=-1, Large=1, etc."""
        return _SIZE_MODIFIERS.get(state.combatant.size.lower(), 0)

    def _bull_rush_push(
        self, attacker: CombatantState, target: CombatantState, distance: int
    ) -> bool:
        """Push target up to ``distance`` cells away from attacker.

        The push stops at the first obstacle; returns True if the target
        moved at least one cell.
        """
        # Calculate direction away from attacker
        ar, ac = attacker.pos
        tr, tc = target.pos
        dr = tr - ar
        dc = tc - ac
        # Normalize to single step
        if dr != 0:
            dr = 1 if dr > 0 else -1
        if dc != 0:
            dc = 1 if dc > 0 else -1
        moved = False
        for _ in range(distance):
            new_pos = (target.pos[0] + dr, target.pos[1] + dc)
            if not self._cells_free(self._footprint_at(new_pos, target), target):
                break
            target.pos = new_pos
            moved = True
        return moved

    def _beyond_cell(self, attacker_pos: Pos, target_pos: Pos) -> Pos:
        """The 1-cell position on the far side of the target from the attacker."""
        ar, ac = attacker_pos
        tr, tc = target_pos
        dr = 1 if tr - ar > 0 else (-1 if tr - ar < 0 else 0)
        dc = 1 if tc - ac > 0 else (-1 if tc - ac < 0 else 0)
        return (tr + dr, tc + dc)

    def _cell_free(self, pos: Pos, mover: CombatantState) -> bool:
        """True if pos is in bounds and not occupied by any active state but mover."""
        if not (0 <= pos[0] < self._grid.height and 0 <= pos[1] < self._grid.width):
            return False
        return not any(s.pos == pos for s in self._states if s.active and s is not mover)
def _find_heal_spell(engine: CombatEngine, spells_known: list[str]) -> str | None:
    """Find a heal spell in known spells."""
    for name in spells_known:
        spell = engine.spell_registry.get(name)
        if spell and any(isinstance(e, HealEffect) for e in spell.effects):
            return name
    return None


def _find_ally_needing_heal(engine: CombatEngine, caster: CombatantState) -> CombatantState | None:
    """Find an ally below 50% HP."""
    for ally_state in engine.states:
        below_half = ally_state.hp < ally_state.combatant.hp_max // 2
        if ally_state.side == caster.side and ally_state.active and below_half:
            return ally_state
    return None


def _find_offensive_spell(
    engine: CombatEngine, spells_known: list[str], caster: CombatantState, target: CombatantState
) -> str | None:
    """Find an offensive spell that can reach the target."""
    dist_ft = engine.creature_distance(caster, target) * _SQUARE_FT
    for name in spells_known:
        spell = engine.spell_registry.get(name)
        if not spell:
            continue
        # Check for damage effect
        has_damage = any(isinstance(e, DamageEffect) for e in spell.effects)
        if not has_damage:
            continue
        max_range = spell_range_ft(spell, caster.combatant.level)
        if dist_ft <= max_range and has_line_of_effect_cells(
            engine.grid, caster.occupied_cells(), target.occupied_cells()
        ):
            return name
    return None


def _find_buff_spell(engine: CombatEngine, spells_known: list[str]) -> str | None:
    """Find a buff spell."""
    for name in spells_known:
        spell = engine.spell_registry.get(name)
        if spell and any(isinstance(e, BuffEffect) for e in spell.effects):
            return name
    return None


def _has_slot(engine: CombatEngine, caster: CombatantState, spell_name: str) -> bool:
    """True if the caster still has a spell slot of the given spell's level."""
    spell = engine.spell_registry.get(spell_name)
    return spell is not None and caster.spell_slots_left.get(spell.level, 0) > 0


def _is_castable_this_turn(engine: CombatEngine, spell_name: str) -> bool:
    """False only for long casting times (more than 1 round): the budget filter
    would drop the cast, so the policy must never propose it."""
    spell = engine.spell_registry.get(spell_name)
    return spell is None or spell.cast_time != "long"


def _choose_spell_action(
    engine: CombatEngine, state: CombatantState, target: CombatantState
) -> tuple[Action, ...] | None:
    """Select and return a spell action if appropriate, else None.

    Long-casting-time spells are never selected (they cannot be scheduled
    within a turn); the heal -> offensive -> buff order is unchanged.
    """
    caster = state
    spells_known = caster.combatant.spells
    if not spells_known:
        return None

    # 1. Heal spell if ally below 50% HP
    heal_spell = _find_heal_spell(engine, spells_known)
    if (
        heal_spell
        and _is_castable_this_turn(engine, heal_spell)
        and _has_slot(engine, caster, heal_spell)
    ):
        ally = _find_ally_needing_heal(engine, caster)
        if ally and ally.hp < ally.combatant.hp_max // 2:
            return (Action(kind="cast_spell", target_id=ally.combatant.id, spell_name=heal_spell),)

    # 2. Offensive spell if enemy in range
    offensive_spell = _find_offensive_spell(engine, spells_known, caster, target)
    if (
        offensive_spell
        and _is_castable_this_turn(engine, offensive_spell)
        and _has_slot(engine, caster, offensive_spell)
    ):
        return (
            Action(kind="cast_spell", target_id=target.combatant.id, spell_name=offensive_spell),
        )

    # 3. Buff spell
    buff_spell = _find_buff_spell(engine, spells_known)
    if (
        buff_spell
        and _is_castable_this_turn(engine, buff_spell)
        and _has_slot(engine, caster, buff_spell)
    ):
        return (Action(kind="cast_spell", target_id=caster.combatant.id, spell_name=buff_spell),)

    return None


# PF1e (SRD Conditions, nauseated): "The only action such a character can
# take is a single move action per turn" — genuine move actions only: the
# 5-foot step and dropping prone are free actions, not move actions, and
# run/charge/withdraw are full-round.
_NAUSEA_MOVE_KINDS: frozenset[str] = frozenset(
    {"move", "stand_up", "retrieve_weapon", "repair_weapon"}
)

# Casting-time plumbing for the budget filters: a cast_spell action consumes
# the slot its spell's CastTime maps to. The pure filters take a resolver so
# tests can drive them without a registry; the engine binds its own.
CastTimeResolver = Callable[[Action], CastTime]


def _default_cast_time(_action: Action) -> CastTime:
    return "standard"


def _cast_time_slot(cast_time: CastTime) -> _ActionEconomySlot:
    """Budget slot consumed by a cast_spell of the given casting time.

    PF1e (CRB, Magic — Casting Time): a standard/swift casting time takes
    that kind of action; an immediate action is off-turn and consumes the
    next swift (handled via immediate_used, so it is budget-free here); a
    free-action cast is free. one_round occupies the full-round slot (it IS
    a full-round action, SRD "Casting Time") and additionally defers the
    spell's effect to the start of the caster's next turn via
    ``PendingCast``. A long casting
    time (more than 1 round: 3 rounds, 10 minutes, 1 hour, ...) cannot be
    scheduled by the turn budget at all — the
    engine drops such casts before the filter runs, so reaching this
    function with "long" is a programming error.
    """
    if cast_time == "standard":
        return "standard"
    if cast_time == "swift":
        return "swift"
    if cast_time in ("immediate", "free"):
        return "free"
    if cast_time in ("full_round", "one_round"):
        return "full_round"
    msg = f"long casting time cannot be scheduled by the budget filter: {cast_time!r}"
    raise ValueError(msg)


def _effective_slot(
    action: Action, cast_time: CastTimeResolver, *, free_draw: bool = False
) -> _ActionEconomySlot:
    """The budget slot an action consumes, resolving cast_spell by cast time
    and the cackle hex by its APG free-action cost.

    ``free_draw`` (SRD "Move Actions": "If you have a base attack bonus of +1
    or higher, you may draw a weapon as a free action combined with a regular
    move") makes retrieve_weapon occupy the free slot instead of the move
    slot — the caller sets it only when the turn's sequence carries a move
    action and the actor's BAB is at least +1.
    """
    if action.kind == "cast_spell":
        return _cast_time_slot(cast_time(action))
    if action.kind == "hex" and action.hex_name == "cackle":
        return "free"
    if action.kind == "deed" and action.deed_name == "quick_clear":
        # PF1e (Ultimate Combat, Deeds — Quick Clear): a STANDARD action
        # (unlike the swift grit deeds); the kind-level deed slot stays swift.
        return "standard"
    if action.kind == "retrieve_weapon" and free_draw:
        return "free"
    return _action_economy_slot(action.kind)


def _without_swift_bonus(
    actions: tuple[Action, ...],
    *,
    cast_time: CastTimeResolver = _default_cast_time,
) -> tuple[Action, ...]:
    """Drop swift/free bonus actions (deed, inspire_courage, swift).

    An immediate action consumes the combatant's next swift action; the
    policy-returned sequence is filtered so no swift bonus fires that turn —
    including a swift-action cast_spell, which occupies the same slot. The
    check is by effective slot so the standard-action Quick Clear deed
    (Ultimate Combat) survives.
    """
    return tuple(
        a
        for a in actions
        if _effective_slot(a, cast_time) != "swift"
    )


def _dropped_kinds(
    before: tuple[Action, ...], after: tuple[Action, ...]
) -> tuple[str, ...]:
    """Kinds present in ``before`` but absent from the filtered ``after``."""
    kept = {a.kind for a in after}
    return tuple(a.kind for a in before if a.kind not in kept)


def _staggered_filter(
    actions: tuple[Action, ...],
    *,
    cast_time: CastTimeResolver = _default_cast_time,
    free_draw: bool = False,
) -> tuple[Action, ...]:
    """Staggered: one move OR one standard action, plus every swift and free.

    PF1e (CRB, Conditions — Staggered): "A staggered creature may take a
    single move action or standard action each round (but not both, nor can
    he take full-round actions). A staggered creature can still take free,
    swift, and immediate actions." So the filter walks the sequence in order
    and keeps every swift and free action, the FIRST move-or-standard action,
    and drops full-round actions plus any SECOND move-or-standard. A leading
    ``full_attack`` (already in range) is downgraded to a single standard
    ``attack`` that consumes the one move-or-standard slot; a further
    full-round action (charge, run, a full-round/one-round cast,
    spell_combat) is dropped. Exceptions (SRD "Full-Round Actions — Restricted
    Withdraw", SRD "Charge — restricted"): "If you are limited to taking only
    a standard action each round you can withdraw as a standard action. In
    this case, you may move up to your speed" / "If you are able to take only
    a standard action on your turn, you can still charge, but you are only
    allowed to move up to your speed" — ``withdraw`` and ``charge`` are kept
    as the one standard action and their movement budgets halve to single
    speed (``_flee_path``, ``_charge_speed_mult``).
    """
    kept: list[Action] = []
    slot_used = False  # the single move-OR-standard slot is spent
    for action in actions:
        if action.kind == "full_attack":
            # A full attack is a full-round action; staggered it collapses to
            # a single standard attack (the kept move-or-standard action).
            if not slot_used:
                kept.append(Action(kind="attack", target_id=action.target_id))
                slot_used = True
            continue
        slot = _effective_slot(action, cast_time, free_draw=free_draw)
        if slot == "full_round":
            if action.kind in ("withdraw", "charge") and not slot_used:
                # Restricted Withdraw / Restricted Charge: standard action.
                kept.append(action)
                slot_used = True
            continue
        if slot in ("standard", "move"):
            if slot_used:
                continue
            kept.append(action)
            slot_used = True
        else:  # swift / free — always allowed while staggered (CRB)
            kept.append(action)
    return tuple(kept)


def _surprise_filter(
    actions: tuple[Action, ...],
    *,
    cast_time: CastTimeResolver = _default_cast_time,
    free_draw: bool = False,
) -> tuple[Action, ...]:
    """Surprise round: one standard OR move action, plus every free action.

    PF1e (SRD "Surprise"): "combatants who started the battle aware of their
    opponents each take a standard or move action during the surprise round.
    You can also take free actions during the surprise round." The rule text
    grants neither a swift action nor a full-round action, so swift and
    full-round kinds are dropped — with the same conventions as
    ``_staggered_filter``: a ``full_attack`` collapses to a single standard
    ``attack``, and ``withdraw`` / ``charge`` survive as the standard-action
    Restricted Withdraw / Restricted Charge (SRD "Full-Round Actions",
    "Charge": legal "if you are able to take only a standard action on your
    turn", at single speed).
    """
    kept: list[Action] = []
    slot_used = False  # the single standard-or-move slot is spent
    for action in actions:
        if action.kind == "full_attack":
            if not slot_used:
                kept.append(Action(kind="attack", target_id=action.target_id))
                slot_used = True
            continue
        slot = _effective_slot(action, cast_time, free_draw=free_draw)
        if slot == "full_round":
            if action.kind in ("withdraw", "charge") and not slot_used:
                kept.append(action)
                slot_used = True
            continue
        if slot in ("standard", "move"):
            if slot_used:
                continue
            kept.append(action)
            slot_used = True
        elif slot == "free":
            kept.append(action)
    return tuple(kept)


def _nauseated_filter(actions: tuple[Action, ...]) -> tuple[Action, ...]:
    """PF1e (CRB) nauseated: a single move action per turn, nothing else.

    The sequence collapses to its first move-like action; standard actions
    (attack, cast_spell, maneuver, ...) and full-round actions are dropped.
    """
    for action in actions:
        if action.kind in _NAUSEA_MOVE_KINDS:
            return (action,)
    return ()


# X4 general per-turn action economy (CRB, "Actions in Combat"): one standard
# action + one move action (or one full-round action in place of both), plus
# one swift action; free and conditional actions never consume the budget.
# A move action may also be taken INSTEAD of the standard one (conversion:
# when the move slot is spent and the standard is free, a second move
# consumes the standard). Every Action kind is classified into exactly one
# slot (exhaustive over the Action.kind Literal, locked by
# tests/test_conformance_action_economy.py):
# - standard: attack, maneuver, channel_energy, hex, delay, ready,
#   total_defense, aid_another; cast_spell occupies the slot its spell's
#   CastTime maps to (_cast_time_slot) — standard by default
# - move: move, stand_up, retrieve_weapon (drawing a weapon is a move action),
#   repair_weapon
# - swift: swift, deed, inspire_courage (the engine's swift bonus kinds)
# - full-round: full_attack, charge, withdraw, full_round, spell_combat
#   (spell + full attack in one round), run (4x-speed movement, PF1e
#   full-round); consumes the standard AND the move slot
# - free/conditional (everything else, no budget): wait, free, immediate
#   (off-turn it consumes the NEXT swift via immediate_used; on your own turn
#   it consumes THIS turn's swift via swift_used_this_turn — SRD Immediate
#   Actions), 5foot_step (free step, mutually exclusive with other movement via
#   moved_this_turn), drop_prone, activate_power_attack and fight_defensively
#   (mode declarations applied to the attack that follows them, like the
#   Power Attack toggle), summon is not a kind (summons arrive via cast_spell).
_ACTION_ECONOMY_STANDARD_KINDS: frozenset[str] = frozenset({
    "attack", "cast_spell", "maneuver", "channel_energy", "hex",
    "delay", "ready", "total_defense", "aid_another",
})
_ACTION_ECONOMY_MOVE_KINDS: frozenset[str] = frozenset({
    "move", "stand_up", "retrieve_weapon", "repair_weapon",
})
_ACTION_ECONOMY_SWIFT_KINDS: frozenset[str] = frozenset(
    {"swift", "deed", "inspire_courage"}
)
_ACTION_ECONOMY_FULL_ROUND_KINDS: frozenset[str] = frozenset({
    "full_attack", "charge", "withdraw", "full_round", "spell_combat", "run",
})
_ACTION_ECONOMY_FREE_KINDS: frozenset[str] = frozenset({
    "wait", "free", "immediate", "5foot_step", "drop_prone",
    "activate_power_attack", "fight_defensively",
})

_ActionEconomySlot = Literal["standard", "move", "swift", "full_round", "free"]


def _action_economy_slot(kind: str) -> _ActionEconomySlot:
    """The budget slot one action kind consumes (free if none applies)."""
    if kind in _ACTION_ECONOMY_STANDARD_KINDS:
        return "standard"
    if kind in _ACTION_ECONOMY_MOVE_KINDS:
        return "move"
    if kind in _ACTION_ECONOMY_SWIFT_KINDS:
        return "swift"
    if kind in _ACTION_ECONOMY_FULL_ROUND_KINDS:
        return "full_round"
    return "free"


def _action_economy_filter(
    actions: tuple[Action, ...],
    *,
    cast_time: CastTimeResolver = _default_cast_time,
    free_draw: bool = False,
) -> tuple[Action, ...]:
    """Degrade a policy sequence to the legal PF1e action economy.

    Greedy in-order walk: each action is kept while its budget slot is free
    (one standard, one move, one swift; a full-round action is only legal
    while BOTH the standard and the move slot are still free and consumes
    them all). A cast_spell's slot is its spell's casting time resolved by
    ``cast_time`` (long casts are dropped by the engine BEFORE this filter —
    _cast_time_slot raises for them). PF1e (CRB, "Actions in Combat"): a
    move action can be taken "instead of" the standard one — when the move
    slot is already spent and the standard slot is still free, a further
    move action converts the standard slot (so (move, stand_up) and
    (move, move) are legal). The kept sequence is therefore the earliest
    order-stable legal prefix-subsequence; every skipped action is
    deterministic. ``free_draw`` makes retrieve_weapon a free action (SRD
    "Move Actions", BAB +1 combined with a move — see _effective_slot).
    """
    kept: list[Action] = []
    spent: dict[_ActionEconomySlot, bool] = {
        "standard": False,
        "move": False,
        "swift": False,
        "full_round": False,
        "free": False,
    }
    for action in actions:
        slot = _effective_slot(action, cast_time, free_draw=free_draw)
        if slot == "free":
            kept.append(action)
            continue
        if slot == "full_round":
            if spent["standard"] or spent["move"]:
                continue
            spent["standard"] = True
            spent["move"] = True
            kept.append(action)
            continue
        if slot == "move" and spent["move"]:
            slot = "standard"  # conversion: a move action consumes the standard slot
        if spent[slot]:
            continue
        spent[slot] = True
        kept.append(action)
    return tuple(kept)


def _dropped_kinds_multiset(
    before: tuple[Action, ...], after: tuple[Action, ...]
) -> tuple[str, ...]:
    """One dropped-kind entry per dropped action instance (in order).

    Unlike ``_dropped_kinds`` (set membership, which cannot report dropping
    the second of two same-kind actions), this consumes the kept instances
    first and reports every surplus — the budget filter regularly drops a
    duplicate standard/move/swift action.
    """
    remaining: dict[str, int] = {}
    for action in after:
        remaining[action.kind] = remaining.get(action.kind, 0) + 1
    dropped: list[str] = []
    for action in before:
        count = remaining.get(action.kind, 0)
        if count > 0:
            remaining[action.kind] = count - 1
        else:
            dropped.append(action.kind)
    return tuple(dropped)


def _ready_payload(action: Action) -> Action:
    """Derive the concrete payload of a ready action from its carrier fields.

    Mirrors ``_execute_immediate``: ``spell_name`` casts, ``maneuver``
    performs the maneuver (carrying direction/trick_condition), anything
    else attacks ``target_id``. Class-ability payloads are out of scope for U4.
    """
    if action.spell_name is not None:
        return Action(
            kind="cast_spell",
            target_id=action.target_id,
            spell_name=action.spell_name,
            target_pos=action.target_pos,
            metamagic=action.metamagic,
            cast_defensively=action.cast_defensively,
        )
    if action.maneuver is not None:
        return Action(
            kind="maneuver",
            target_id=action.target_id,
            maneuver=action.maneuver,
            direction=action.direction,
            trick_condition=action.trick_condition,
        )
    return Action(kind="attack", target_id=action.target_id)


Policy = Callable[[CombatEngine, CombatantState], tuple[Action, ...]]

LLMPolicy = Callable[[Observation, CombatantState], tuple[Action, ...]]

ReactionPolicy = Callable[
    [CombatEngine, CombatantState, ReactionEvent], Action | None
]


def default_policy(engine: CombatEngine, state: CombatantState) -> tuple[Action, ...]:
    """Full-attack the nearest enemy; cast spells; charge, 5ft-step, or approach if out of range.

    Decision order:
    1. Channel energy (oni) if resource available and an ally is hurt or enemies are grouped.
    2. Hex (nairda) if resource available and the target is within close range.
    3. Heal spell if an ally is below 50% HP and a heal spell is available.
    4. Offensive spell if an enemy is in range and spell slots available.
    5. Buff spell if no immediate threat and spell slots available.
    6. Full-attack if a weapon is usable against the nearest enemy this turn (no move needed).
    7. Charge if a straight-line charge path exists (2x speed, +2 attack, -2 AC).
    8. 5-foot step then full-attack if a single step brings the target into weapon range.
    9. Move toward the target then single attack (standard + move economy).
    10. Wait if nothing is possible.

    Class-ability bonus actions (deed for tammara, inspire_courage for misty) are
    prepended to the normal action sequence whenever their resource is available.

    Precedence for replacement (standard) abilities: channel_energy and hex are
    evaluated first and replace the whole turn when their resource is available
    and their condition is met; otherwise the normal spell/melee flow runs and the
    swift/free abilities are combined with it. This keeps each class able to act
    each turn while reserving standard-action class abilities for their triggers.

    Never casts a spell if threatened without Concentration check (handled in _cast_spell).
    """
    target = engine.nearest_enemy(state)
    if target is None:
        return (Action(kind="wait"),)
    # Must flee: withdraw from the nearest enemy
    if engine.has_condition_flag(state, "must_flee"):
        return (Action(kind="withdraw", target_id=target.combatant.id),)

    # Channel energy (oni): standard action that heal/harms in a 30ft burst.
    channel_mode = _emit_channel_energy(engine, state)
    if channel_mode is not None:
        return (
            Action(
                kind="channel_energy",
                target_id=target.combatant.id,
                channel_mode=channel_mode,
            ),
        )

    # Hex (nairda): standard action when the target is within close range.
    if _emit_hex(engine, state, target):
        return (Action(kind="hex", target_id=target.combatant.id, hex_name="evil_eye"),)

    normal = _normal_actions(engine, state, target)

    # Misty spell_combat (main) + inspire_courage (swift): replaces the normal action.
    spell_combat = _spell_combat_actions(engine, state, target)
    if spell_combat is not None:
        return spell_combat

    # Deed (tammara) and inspire_courage (misty melee fallback): swift/free bonuses.
    swift_bonus = _swift_bonus_actions(engine, state, target)
    return (*swift_bonus, *normal) if swift_bonus else normal


def _normal_actions(
    engine: CombatEngine, state: CombatantState, target: CombatantState
) -> tuple[Action, ...]:
    """The spell/melee action sequence (without swift/free class-ability add-ons)."""
    if state.combatant.spells:
        spell_action = _choose_spell_action(engine, state, target)
        if spell_action is not None:
            return spell_action
    return _melee_action(engine, state, target)


_GROUPED_ENEMY_COUNT = 2
_HEX_RANGE_FT = 25


def _emit_channel_energy(
    engine: CombatEngine, state: CombatantState
) -> Literal["heal", "harm"] | None:
    """Channel mode when oni should channel (heal living / harm undead)."""
    if state.resources_left.get("channel_energy", 0) <= 0:
        return None
    if _find_ally_needing_heal(engine, state) is not None:
        return "heal"
    radius_cells = 30 // _SQUARE_FT
    grouped_undead_enemies = [
        s
        for s in engine.states
        if s.side != state.side
        and s.active
        and s.combatant.creature_type == "undead"
        and engine.creature_distance(state, s) <= radius_cells
    ]
    return "harm" if len(grouped_undead_enemies) >= _GROUPED_ENEMY_COUNT else None


def _emit_hex(
    engine: CombatEngine, state: CombatantState, target: CombatantState | None
) -> bool:
    """True when nairda should hex: resource available and target within close range."""
    if state.resources_left.get("hexes", 0) <= 0:
        return False
    if target is None or not target.active:
        return False
    return engine.creature_distance(state, target) * _SQUARE_FT <= _HEX_RANGE_FT


def _spell_combat_actions(
    engine: CombatEngine, state: CombatantState, target: CombatantState
) -> tuple[Action, ...] | None:
    """Misty's spell_combat (main) + inspire_courage (swift), or None if no offensive spell."""
    if state.resources_left.get("bardic_rounds", 0) <= 0:
        return None
    offensive = _find_offensive_spell(engine, state.combatant.spells, state, target)
    if offensive is None:
        return None
    return (
        Action(kind="inspire_courage", target_id=target.combatant.id),
        Action(kind="spell_combat", target_id=target.combatant.id, spell_name=offensive),
    )


def _swift_bonus_actions(
    engine: CombatEngine, state: CombatantState, target: CombatantState
) -> tuple[Action, ...]:
    """Swift/free class-ability actions (deed, inspire_courage) to prepend to the turn."""
    bonus: list[Action] = []

    # Deed (tammara): swift/free action, emitted alongside the normal action only
    # when the target is within Up Close and Deadly range (30 ft).
    if (
        state.resources_left.get("grit", 0) > 0
        and engine.creature_distance(state, target) * _SQUARE_FT <= _UP_CLOSE_RANGE_FT
    ):
        bonus.append(
            Action(
                kind="deed",
                target_id=target.combatant.id,
                deed_name="up_close_and_deadly",
            )
        )

    # Inspire courage (misty melee fallback): combined with the normal action.
    if state.resources_left.get("bardic_rounds", 0) > 0:
        bonus.append(Action(kind="inspire_courage", target_id=target.combatant.id))

    return tuple(bonus)


def _melee_action(
    engine: CombatEngine, state: CombatantState, target: CombatantState
) -> tuple[Action, ...]:
    """Choose a non-spell action: full-attack, charge, step, or approach."""
    if engine.weapon_for(state, target) is not None:
        return (Action(kind="full_attack", target_id=target.combatant.id),)
    charge = engine.can_charge(state, target)
    if charge is not None and charge.weapon is not None:
        return (Action(kind="charge", target_id=target.combatant.id),)
    if engine.can_step5_to_attack(state, target):
        return (
            Action(kind="5foot_step", target_id=target.combatant.id),
            Action(kind="full_attack", target_id=target.combatant.id),
        )
    return (
        Action(kind="move", target_id=target.combatant.id),
        Action(kind="attack", target_id=target.combatant.id),
    )