feat(abilities): add passive feats system (Weapon Focus, Iron Will, Dodge, Point-Blank Shot)

src/pf1e_simulator/abilities.py

@@ -0,0 +1,143 @@
+"""PF1e abilities: feats, class features, racial traits, character traits.
+
+All four categories share the same mechanical representation via ``AbilitySpec``.
+What differs is the ``category`` (for stacking and display) and ``source_detail``.
+
+This step defines passive feats — permanent stat modifiers that the engine
+collects alongside effects and conditions via ``_stat_modifiers``. Active feats
+(Power Attack, Rage) and conditional feats (Sneak Attack) will be added in
+later steps.
+
+Sources: PRPG Core Rulebook, Feats chapter.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Literal
+
+from pf1e_simulator.effects import StatModifier
+
+Category = Literal["feat", "class", "racial", "trait"]
+
+
+@dataclass(frozen=True)
+class AbilitySpec:
+    """One feat, class feature, racial trait, or character trait.
+
+    ``effects`` are the StatModifiers this ability grants. For passive feats,
+    these are always-on modifiers. For conditional feats, ``condition`` on
+    each StatModifier gates applicability (evaluated by the engine).
+    """
+
+    name: str
+    category: Category
+    source_detail: str = ""
+    effects: tuple[StatModifier, ...] = ()
+
+
+# ── Passive combat feats ─────────────────────────────────────────────────────
+# Weapon Focus: +1 attack with a specific weapon (untyped, CRB)
+def weapon_focus(weapon_name: str) -> AbilitySpec:
+    return AbilitySpec(
+        name=f"Weapon Focus ({weapon_name})",
+        category="feat",
+        source_detail="feat lv1",
+        effects=(
+            StatModifier(target="attack", value=1, weapon_filter=weapon_name),
+        ),
+    )
+
+
+# Toughness: +1 HP per Hit Die (approximated as +level HP, untyped, CRB)
+# For simplicity at this stage, we model it as a flat HP bonus.
+# The engine doesn't yet compute per-HD bonuses, so the caller sets the value.
+def toughness(level: int) -> AbilitySpec:
+    return AbilitySpec(
+        name="Toughness",
+        category="feat",
+        source_detail="feat lv1",
+        effects=(
+            StatModifier(target="hp", value=level),
+        ),
+    )
+
+
+# Iron Will: +2 will saves (untyped, CRB)
+IRON_WILL = AbilitySpec(
+    name="Iron Will",
+    category="feat",
+    source_detail="feat lv1",
+    effects=(
+        StatModifier(target="will", value=2),
+    ),
+)
+
+# Great Fortitude: +2 fortitude saves (untyped, CRB)
+GREAT_FORTITUDE = AbilitySpec(
+    name="Great Fortitude",
+    category="feat",
+    source_detail="feat lv1",
+    effects=(
+        StatModifier(target="fort", value=2),
+    ),
+)
+
+# Lightning Reflexes: +2 reflex saves (untyped, CRB)
+LIGHTNING_REFLEXES = AbilitySpec(
+    name="Lightning Reflexes",
+    category="feat",
+    source_detail="feat lv1",
+    effects=(
+        StatModifier(target="ref", value=2),
+    ),
+)
+
+# Alertness: +2 Perception and Sense Motive (untyped, CRB)
+# Modeled as +2 will (Wisdom-based) since skills aren't implemented
+ALERTNESS = AbilitySpec(
+    name="Alertness",
+    category="feat",
+    source_detail="feat lv1",
+    effects=(
+        StatModifier(target="will", value=2),
+    ),
+)
+
+# Point-Blank Shot: +1 attack and +1 damage with ranged weapons within 30 ft.
+# Untyped, conditional (CRB).
+POINT_BLANK_SHOT = AbilitySpec(
+    name="Point-Blank Shot",
+    category="feat",
+    source_detail="feat lv1",
+    effects=(
+        StatModifier(
+            target="attack", value=1, condition="target_within_30ft_ranged"
+        ),
+        StatModifier(
+            target="damage", value=1, condition="target_within_30ft_ranged"
+        ),
+    ),
+)
+
+# Precise Shot: no -4 penalty for shooting into melee (CRB)
+# This is a behavioral flag, not a stat modifier — it will be handled
+# as a SpecialBehavior in a later step. Defined here for completeness.
+PRECISE_SHOT = AbilitySpec(
+    name="Precise Shot",
+    category="feat",
+    source_detail="feat lv1",
+)
+
+# Dodge: +1 dodge bonus to AC (dodge type, stacks, CRB)
+DODGE = AbilitySpec(
+    name="Dodge",
+    category="feat",
+    source_detail="feat lv1",
+    effects=(
+        StatModifier(target="ac", value=1, bonus_type="dodge"),
+    ),
+)
+
+# Skill Focus: +3 to a skill (not yet modeled — skills deferred)
+# Defined as a placeholder for future expansion.