fix(rules): Combat Casting's +4 no longer applies to the entangled concentration check (SRD combat-casting: the feat covers only casting defensively or while grappled)

src/pf1e_simulator/combat.py

@@ -3809,14 +3809,19 @@ class CombatEngine:
         damage_taken: int,
         *,
         dc_override: int | None = None,
+        combat_casting_applies: bool = True,
     ) -> 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
+        Combat Casting's +4 applies only when casting defensively or while
-        grappled/pinned, or while entangled, never for damage taken while
+        grappled (SRD feats/combat-casting.md: "a +4 bonus on concentration
-        casting. ``dc_override`` pins the DC (used by the entangled gate).
+        checks made to cast a spell or use a spell-like ability when
+        casting on the defensive or while grappled") - never for damage
+        taken while casting, never while entangled. ``combat_casting_applies``
+        is passed False by the situations outside the feat (entangled);
+        ``dc_override`` pins the DC (used by the entangled gate).
         """
         dc = (
             self._concentration_dc(caster, spell_level, damage_taken)
@@ -3824,7 +3829,9 @@ class CombatEngine:
             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)
+        has_combat_casting = (
+            combat_casting_applies and 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 = (
@@ -6168,9 +6175,14 @@ class CombatEngine:
         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).
+            # lost. Combat Casting's +4 does NOT apply: the feat covers only
+            # "casting on the defensive or while grappled" (SRD
+            # feats/combat-casting.md).
             dc = self._entangled_concentration_dc(spell_level)
-            if not self._check_concentration(caster, spell_level, 0, dc_override=dc):
+            if not self._check_concentration(
+                caster, spell_level, 0,
+                dc_override=dc, combat_casting_applies=False,
+            ):
                 self._log(
                     f"round {self._current_round} {caster.combatant.id}: "
                     f"casting while entangled: concentration failed (DC {dc}), "

tests/test_concentration.py

@@ -211,10 +211,12 @@ class TestEntangledCasting:
         engine, c = self._entangled_engine(11)
         assert engine._spell_cast_interrupted(c, 1, cast_defensively=False) is False
 
-    def test_combat_casting_helps_while_entangled(self) -> None:
+    def test_combat_casting_does_not_help_while_entangled(self) -> None:
-        # d20 7 + level 5 + wis 0 + 4 = 16 >= 16 -> PASS with the feat.
+        # SRD feats/combat-casting.md: the +4 covers only "casting on the
+        # defensive or while grappled" - NOT the entangled check. d20 7 +
+        # level 5 + wis 0 = 12 < DC 16 -> spell lost even with the feat.
         engine, c = self._entangled_engine(7, combat_casting=True)
-        assert engine._spell_cast_interrupted(c, 1, cast_defensively=False) is False
+        assert engine._spell_cast_interrupted(c, 1, cast_defensively=False) is True
 
     def test_entangled_carries_minus4_dex_skills(self) -> None:
         mods = {m.target: m.value for m in ENTANGLED.modifiers}