fix(rules): cover grants a Reflex-save bonus against area effects (SRD cover.md 'Cover and Reflex Saves': +2 vs standard cover - half the AC value, so +1 partial/+2 standard/+4 improved; soft cover grants none) - _area_save adds terrain cover//2 from the effect's point of origin (burst center, caster square for cone/line) to Reflex rolls; resolve_save gains an explicit flat_bonus

src/pf1e_simulator/combat.py

@@ -3385,6 +3385,7 @@ class CombatEngine:
         dc: int,
         *,
         save_descriptors: frozenset[str] = frozenset(),
+        flat_bonus: int = 0,
     ) -> SaveResult:
         """Roll a saving throw (fort/ref/will) against ``dc``.
 
@@ -3393,13 +3394,16 @@ class CombatEngine:
         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.
+        ``flat_bonus`` is an untyped situational bonus added to the total
+        (used for the cover bonus on Reflex saves, CRB "Cover and Reflex
+        Saves"); natural 1/20 still override the roll regardless of it.
         """
         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
+        total = roll + base + bonus + flat_bonus
         success = roll != _NATURAL_ONE and (roll == _NATURAL_TWENTY or total >= dc)
         return SaveResult(success=success, roll=roll, total=total, dc=dc)
 
@@ -7083,13 +7087,21 @@ class CombatEngine:
         total_damage = 0
         total_conditions = 0
         total_buffs = 0
+        # Reflex-save cover is measured from the effect's point of origin:
+        # the burst center, or the caster's square for a cone/line (CRB
+        # "Cover and Reflex Saves": the bonus applies "against attacks that
+        # originate or burst out from a point on the other side of the cover
+        # from you").
+        origin_cells = (
+            frozenset({center}) if effect.shape == "burst" else caster.occupied_cells()
+        )
 
         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,
+                save_type=save_type, origin_cells=origin_cells,
             )
             for sub_effect in effect.effects:
                 target_live = self._stats[affected_state.combatant.id]
@@ -7182,29 +7194,66 @@ class CombatEngine:
         saved: bool,
         dc: int = 15,
         save_type: SaveType = "none",
+        origin_cells: frozenset[Pos] = frozenset(),
     ) -> 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
+        (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.
+        other creature in the area - and every creature of a point-targeted
+        burst (no primary target, U7b) - rolls its own.
+
+        PF1e (CRB "Cover and Reflex Saves"): cover grants a Reflex bonus
+        against effects that burst from a point on the other side of the
+        cover - half the AC value (+1 partial / +2 standard / +4 improved);
+        soft cover from creatures grants none (CRB "Soft Cover"). The bonus
+        is measured from the effect's origin to the rolling creature.
+        Documented simplification: the primary target's reused save was
+        rolled on the generic spell path before the area resolved; for a
+        target-centered burst the origin IS its own square (bonus 0), so the
+        reuse only under-protects a cone/line primary standing behind cover
+        from the caster.
         """
         if save_type == "none":
             return False
         if affected_state is target:
             return saved
+        flat_bonus = (
+            self._reflex_cover_bonus(origin_cells, affected_state)
+            if save_type == "ref"
+            else 0
+        )
         save_result = self.resolve_save(
             affected_state,
             save_type,
             dc,
             save_descriptors=save_descriptors_for_effects(effect.effects),
+            flat_bonus=flat_bonus,
         )
         return save_result.success
 
+    def _reflex_cover_bonus(self, origin_cells: frozenset[Pos], state: CombatantState) -> int:
+        """Reflex-save cover bonus from an area effect's origin (terrain only).
+
+        CRB "Cover and Reflex Saves": "Cover grants you a +2 bonus on Reflex
+        saves against attacks that originate or burst out from a point on the
+        other side of the cover from you" - the Reflex bonus is half the AC
+        bonus (partial +2 AC/+1 Ref, standard +4/+2, improved +8/+4). CRB
+        "Soft Cover": creatures "provide no bonus on Reflex saves", so the
+        interposed-creature set is empty here.
+        """
+        cover = cover_bonus_cells(
+            self._grid,
+            origin_cells,
+            state.occupied_cells(),
+            ranged=True,
+            occupied=frozenset(),
+        )
+        return cover // 2
+
     def _apply_metamagic(
         self, spell: SpellSpec, metamagic_feats: tuple[str, ...]
     ) -> tuple[SpellEffect, ...]: