feat(abilities): add Power Attack active feat (-X atk / +2X dmg, melee only)

Power Attack is the first active feat: a free-action toggle declared at
turn start. When state.power_attack is True and the combatant has the
POWER_ATTACK feature, melee attacks apply -X to the attack roll and
+2X to damage, where X = BAB//4 + 1 (min 1). Ranged attacks are
unaffected. The flag is cleared at the start of each turn via
_take_turn, like other per-turn state.

- abilities.py: POWER_ATTACK constant (AbilitySpec, no passive effects)
- combat.py: _has_feat helper, _power_attack_amt, resolve_attack
  applies penalty to attack total + crit confirm, bonus to damage
- tests/test_power_attack.py: 14 tests (amount at BAB 1/4/8/12, flag
  false, feat missing, attack penalty, damage bonus, ranged unaffected,
  flag cleared on turn)
- pyproject.toml: add SLF001 + RUF059 to test per-file-ignores (white-box
  testing accesses private helpers, partial tuple unpacking)
- README.md: document Power Attack in abilities.py section, 307 tests

README.md

@@ -379,9 +379,11 @@ dans la résolution) :
   à `resolve_attack` (attaque, dégâts, CA) et `resolve_save` (jets de
   sauvegarde) via `_stat_modifiers` qui collecte effets + conditions.
 - `abilities.py` — dons et capacités : `AbilitySpec` (dataclass avec
-  catégorie feat/class/racial/trait) et dons passifs prédéfinis (Weapon Focus,
+  catégorie feat/class/racial/trait), dons passifs prédéfinis (Weapon Focus,
   Toughness, Iron Will, Great Fortitude, Lightning Reflexes, Alertness,
-  Point-Blank Shot, Dodge). Les modificateurs sont collectés par
+  Point-Blank Shot, Dodge) et don actif Power Attack (−X attaque / +2X dégâts,
+  X = BAB//4 + 1, mêlée uniquement, declared as free action at turn start via
+  `state.power_attack`). Les modificateurs sont collectés par
   `_stat_modifiers` avec filtrage par arme (`weapon_filter`). Le champ
   `features` de `Combatant` contient les aptitudes permanentes.
 - `metrics.py` — statistiques en forme fermée : `win_rate`, `win_rate_sigma`,
@@ -399,7 +401,7 @@ dans la résolution) :
 La gate de validation complète (tests + lint + types) :
 
 ```bash
-uv run pytest -q          # 293 tests
+uv run pytest -q          # 307 tests
 uv run ruff check src tests
 uv run basedpyright src   # mode strict
 ```

pyproject.toml

@@ -47,7 +47,7 @@ allowed-confusables = ["σ"]
 [tool.ruff.lint.per-file-ignores]
 # Tests: assert is expected, magic numbers are fine, annotations are noisy,
 # parametrized golden tests legitimately take many arguments
-"tests/**" = ["S101", "PLR2004", "ANN", "PLR0913", "PLR0917", "ARG001"]
+"tests/**" = ["S101", "PLR2004", "ANN", "PLR0913", "PLR0917", "ARG001", "SLF001", "RUF059"]
 # rng.py: `random.Random` is used for reproducible Monte Carlo streams, not cryptography
 "src/pf1e_simulator/rng.py" = ["S311"]
 # cli.py: stdout printing is the point of a CLI

src/pf1e_simulator/abilities.py

@@ -139,5 +139,11 @@ DODGE = AbilitySpec(
     ),
 )
 
-# Skill Focus: +3 to a skill (not yet modeled — skills deferred)
+# Power Attack: active feat — declare at turn start, -X atk / +2X dmg on all
-# Defined as a placeholder for future expansion.
+# melee attacks this turn, where X = BAB//4 + 1 (min 1). No passive modifiers;
+# the engine checks for this feat and the ``power_attack`` flag on state.
+POWER_ATTACK = AbilitySpec(
+    name="Power Attack",
+    category="feat",
+    source_detail="feat lv1",
+)

src/pf1e_simulator/combat.py

@@ -162,6 +162,7 @@ class CombatantState:
     effects: list[StatModifier] = field(default_factory=list)
     conditions: list[Condition] = field(default_factory=list)
     moved_this_turn: bool = False
+    power_attack: bool = False
 
     @property
     def active(self) -> bool:
@@ -266,6 +267,7 @@ class CombatEngine:
         """Execute one combatant's full turn; return True if the battle is over."""
         state.effects.clear()
         state.moved_this_turn = False
+        state.power_attack = False
         actions = self._policy(self, state)
         before = len(self._transcript)
         for action in actions:
@@ -378,6 +380,16 @@ class CombatEngine:
                 mods.append(m)
         return mods
 
+    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 _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 resolve_attack(
         self,
         attacker: CombatantState,
@@ -394,7 +406,8 @@ class CombatEngine:
         base_bonus = bonus_override if bonus_override is not None else weapon.attack_bonus
         atk_mods = self._stat_modifiers(attacker, "attack", weapon_name=weapon.name)
         attack_mod = resolve_modifiers(atk_mods)
-        total = roll + base_bonus + penalty + flank + attack_mod
+        pa_amt = self._power_attack_amt(attacker) if weapon.kind == "melee" else 0
+        total = roll + base_bonus + penalty + flank + attack_mod - pa_amt
         ac = target.combatant.ac.total + resolve_modifiers(self._stat_modifiers(target, "ac"))
         occupied = frozenset(
             s.pos for s in self._states if s.active and s is not attacker and s is not target
@@ -413,11 +426,12 @@ class CombatEngine:
         if hit:
             if roll != _NATURAL_ONE and roll >= weapon.crit_range:
                 confirm = self._rng.d20()
-                confirm_total = confirm + base_bonus + penalty + flank + attack_mod
+                confirm_total = confirm + base_bonus + penalty + flank + attack_mod - pa_amt
                 crit = confirm != _NATURAL_ONE and confirm_total >= ac
             dmg_mods = self._stat_modifiers(attacker, "damage", weapon_name=weapon.name)
             damage = sum(c.formula.roll(self._rng) for c in weapon.damage) + weapon.damage_bonus
             damage += resolve_modifiers(dmg_mods)
+            damage += pa_amt * 2 if weapon.kind == "melee" else 0
             if crit:
                 damage *= weapon.crit_mult
             damage = self._apply_dr(damage, weapon, target)

tests/test_power_attack.py

@@ -0,0 +1,236 @@
+"""Tests for Power Attack active feat: -X attack / +2X damage toggle."""
+
+from __future__ import annotations
+
+from pf1e_simulator.abilities import POWER_ATTACK
+from pf1e_simulator.combat import CombatantState, CombatEngine
+from pf1e_simulator.dice import parse_dice
+from pf1e_simulator.grid import Grid
+from pf1e_simulator.map import MapSpec, TerrainType
+from pf1e_simulator.models import (
+    AbilityScores,
+    ACProfile,
+    AttackSpec,
+    Combatant,
+    DamageComponent,
+    Saves,
+)
+from pf1e_simulator.rng import ScriptedRng
+
+
+def _make_fighter(
+    cid: str = "fighter",
+    *,
+    bab: int = 4,
+    attack_bonus: int = 5,
+    damage_bonus: int = 2,
+    features: list[object] | None = None,
+) -> Combatant:
+    attack = AttackSpec(
+        id=f"{cid}-w",
+        name="longsword",
+        kind="melee",
+        attack_bonus=attack_bonus,
+        damage=[DamageComponent(formula=parse_dice("1d8"), types=["slashing"])],
+        damage_bonus=damage_bonus,
+    )
+    return Combatant(
+        id=cid,
+        name=cid,
+        level=4,
+        size="Medium",
+        abilities=AbilityScores(
+            str_score=16, dex_score=12, con_score=14,
+            int_score=10, wis_score=10, cha_score=10,
+        ),
+        hp_max=30,
+        ac=ACProfile(total=18, touch=12, flat_footed=16),
+        bab=bab,
+        initiative_mod=2,
+        speed_land_ft=30,
+        saves=Saves(fort=6, ref=2, will=2),
+        attacks=[attack],
+        features=features or [],  # type: ignore[arg-type]
+    )
+
+
+def _make_foe(cid: str = "foe") -> Combatant:
+    attack = AttackSpec(
+        id=f"{cid}-w",
+        name="club",
+        kind="melee",
+        attack_bonus=3,
+        damage=[DamageComponent(formula=parse_dice("1d6"), types=["bludgeoning"])],
+    )
+    return Combatant(
+        id=cid,
+        name=cid,
+        level=1,
+        size="Medium",
+        abilities=AbilityScores(
+            str_score=10, dex_score=10, con_score=10,
+            int_score=10, wis_score=10, cha_score=10,
+        ),
+        hp_max=20,
+        ac=ACProfile(total=15, touch=10, flat_footed=13),
+        bab=1,
+        initiative_mod=0,
+        speed_land_ft=30,
+        saves=Saves(fort=2, ref=1, will=0),
+        attacks=[attack],
+    )
+
+
+def _make_engine(
+    fighter: Combatant, foe: Combatant, queue: list[int]
+) -> tuple[CombatEngine, CombatantState, CombatantState]:
+    f = CombatantState(combatant=fighter, side="players", pos=(0, 0), hp=fighter.hp_max)
+    t = CombatantState(combatant=foe, side="monsters", pos=(0, 0), hp=foe.hp_max)
+    legend = {".": TerrainType(type="floor", move_cost=1)}
+    spec = MapSpec(name="test", terrain=tuple(["." * 8] * 8), legend=legend)
+    grid = Grid.from_spec(spec)
+    engine = CombatEngine(ScriptedRng(queue), grid, [f, t])
+    return engine, f, t
+
+
+class TestPowerAttackAmount:
+    """Given: a combatant with Power Attack feat and various BAB values
+    When: _power_attack_amt is called with power_attack=True
+    Then: returns X = BAB//4 + 1 (min 1). At BAB +4 and every +4, X increases by 1."""
+
+    def test_bab_1_gives_x1(self) -> None:
+        fighter = _make_fighter(bab=1, features=[POWER_ATTACK])
+        engine, f, _ = _make_engine(fighter, _make_foe(), [10])
+        f.power_attack = True
+        assert engine._power_attack_amt(f) == 1
+
+    def test_bab_4_gives_x2(self) -> None:
+        fighter = _make_fighter(bab=4, features=[POWER_ATTACK])
+        engine, f, _ = _make_engine(fighter, _make_foe(), [10])
+        f.power_attack = True
+        assert engine._power_attack_amt(f) == 2
+
+    def test_bab_8_gives_x3(self) -> None:
+        fighter = _make_fighter(bab=8, features=[POWER_ATTACK])
+        engine, f, _ = _make_engine(fighter, _make_foe(), [10])
+        f.power_attack = True
+        assert engine._power_attack_amt(f) == 3
+
+    def test_bab_12_gives_x4(self) -> None:
+        fighter = _make_fighter(bab=12, features=[POWER_ATTACK])
+        engine, f, _ = _make_engine(fighter, _make_foe(), [10])
+        f.power_attack = True
+        assert engine._power_attack_amt(f) == 4
+
+    def test_flag_false_returns_zero(self) -> None:
+        fighter = _make_fighter(bab=4, features=[POWER_ATTACK])
+        engine, f, _ = _make_engine(fighter, _make_foe(), [10])
+        f.power_attack = False
+        assert engine._power_attack_amt(f) == 0
+
+    def test_feat_missing_returns_zero(self) -> None:
+        fighter = _make_fighter(bab=4)
+        engine, f, _ = _make_engine(fighter, _make_foe(), [10])
+        f.power_attack = True
+        assert engine._power_attack_amt(f) == 0
+
+
+class TestPowerAttackOnAttackRoll:
+    """Given: an attacker with Power Attack active
+    When: resolve_attack is called
+    Then: the attack total is reduced by X."""
+
+    def test_bab_4_attack_reduced_by_2(self) -> None:
+        fighter = _make_fighter(bab=4, features=[POWER_ATTACK])
+        foe = _make_foe()
+        engine, f, t = _make_engine(fighter, foe, [15, 4])
+        f.power_attack = True
+        result = engine.resolve_attack(f, t, fighter.attacks[0])
+        assert result.total == 15 + 5 - 2  # 18
+
+    def test_bab_8_attack_reduced_by_3(self) -> None:
+        fighter = _make_fighter(bab=8, features=[POWER_ATTACK])
+        foe = _make_foe()
+        engine, f, t = _make_engine(fighter, foe, [15, 4])
+        f.power_attack = True
+        result = engine.resolve_attack(f, t, fighter.attacks[0])
+        assert result.total == 15 + 5 - 3  # 17
+
+    def test_no_power_attack_normal_total(self) -> None:
+        fighter = _make_fighter(bab=4, features=[POWER_ATTACK])
+        foe = _make_foe()
+        engine, f, t = _make_engine(fighter, foe, [15, 4])
+        result = engine.resolve_attack(f, t, fighter.attacks[0])
+        assert result.total == 15 + 5  # 20
+
+
+class TestPowerAttackOnDamage:
+    """Given: an attacker with Power Attack active who hits
+    When: resolve_attack resolves damage
+    Then: damage is increased by 2X."""
+
+    def test_bab_4_damage_increased_by_4(self) -> None:
+        fighter = _make_fighter(bab=4, features=[POWER_ATTACK])
+        foe = _make_foe()
+        engine, f, t = _make_engine(fighter, foe, [15, 4])
+        f.power_attack = True
+        result = engine.resolve_attack(f, t, fighter.attacks[0])
+        assert result.hit is True
+        assert result.damage == 4 + 2 + 4  # 10
+
+    def test_bab_8_damage_increased_by_6(self) -> None:
+        fighter = _make_fighter(bab=8, features=[POWER_ATTACK])
+        foe = _make_foe()
+        engine, f, t = _make_engine(fighter, foe, [15, 4])
+        f.power_attack = True
+        result = engine.resolve_attack(f, t, fighter.attacks[0])
+        assert result.hit is True
+        assert result.damage == 4 + 2 + 6  # 12
+
+    def test_no_power_attack_normal_damage(self) -> None:
+        fighter = _make_fighter(bab=4, features=[POWER_ATTACK])
+        foe = _make_foe()
+        engine, f, t = _make_engine(fighter, foe, [15, 4])
+        result = engine.resolve_attack(f, t, fighter.attacks[0])
+        assert result.hit is True
+        assert result.damage == 4 + 2  # 6
+
+
+class TestPowerAttackOnlyMelee:
+    """Given: an attacker with Power Attack active using a ranged weapon
+    When: resolve_attack is called
+    Then: Power Attack does not apply (melee only)."""
+
+    def test_ranged_attack_unaffected(self) -> None:
+        fighter = _make_fighter(bab=4, features=[POWER_ATTACK])
+        fighter_ranged = fighter.model_copy(update={
+            "attacks": [AttackSpec(
+                id="fighter-w",
+                name="bow",
+                kind="ranged",
+                attack_bonus=5,
+                damage=[DamageComponent(formula=parse_dice("1d8"), types=["piercing"])],
+                range_increment_ft=60,
+            )],
+        })
+        foe = _make_foe()
+        engine, f, t = _make_engine(fighter_ranged, foe, [15, 4])
+        f.power_attack = True
+        result = engine.resolve_attack(f, t, fighter_ranged.attacks[0])
+        assert result.total == 15 + 5  # 20, no PA penalty
+        if result.hit:
+            assert result.damage == 4  # no PA bonus
+
+
+class TestPowerAttackClearedOnTurn:
+    """Given: a combatant with power_attack=True
+    When: _take_turn starts
+    Then: power_attack is cleared to False."""
+
+    def test_cleared_at_turn_start(self) -> None:
+        fighter = _make_fighter(bab=4, features=[POWER_ATTACK])
+        foe = _make_foe()
+        engine, f, t = _make_engine(fighter, foe, [10, 10])
+        f.power_attack = True
+        engine._take_turn(f)
+        assert f.power_attack is False