feat(combat): add saving throws (fort/ref/will, natural 1/20, effect modifiers)

src/pf1e_simulator/combat.py

@@ -189,6 +189,16 @@ class AttackResult:
     base_bonus: int = 0
 
 
+@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.
@@ -401,6 +411,22 @@ class CombatEngine:
             return damage
         return max(0, damage - dr.amount)
 
+    def resolve_save(
+        self, state: CombatantState, save_type: Literal["fort", "ref", "will"], dc: int
+    ) -> SaveResult:
+        """Roll a saving throw (fort/ref/will) against ``dc``.
+
+        PF1e: natural 1 = automatic failure, natural 20 = automatic success.
+        Effect modifiers (StatModifier with matching target) are applied via
+        ``resolve_modifiers`` — same bonus-type stacking rules as attacks.
+        """
+        roll = self._rng.d20()
+        base = getattr(state.combatant.saves, save_type)
+        bonus = resolve_modifiers(e for e in state.effects if e.target == save_type)
+        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 _roll_initiative(self) -> list[CombatantState]:
         rolls: dict[str, tuple[int, int]] = {}
         for state in self._states: