fix(rules): total defense and fighting defensively cannot be combined (SRD Total Defense) - no stacking, second declaration rejected

src/pf1e_simulator/combat.py

@@ -1064,7 +1064,7 @@ ACTION_RESULT_REASONS: frozenset[str] = frozenset({
     "downgraded:surprise",
     "delayed", "already_delayed", "ready",
     "not_prone", "already_prone", "unreachable_destination",
-    "weapon_unavailable", "invalid_destination",
+    "weapon_unavailable", "invalid_destination", "cannot_combine",
 })
 _REASON_OK = "ok"
 _REASON_UNSUPPORTED_KIND = "unsupported_kind"
@@ -1086,6 +1086,7 @@ _REASON_INVALID_DESTINATION = "invalid_destination"
 _REASON_NO_WEAPON = "no_weapon"
 _REASON_OUT_OF_RANGE = "out_of_range"
 _REASON_NO_LINE_OF_EFFECT = "no_line_of_effect"
+_REASON_CANNOT_COMBINE = "cannot_combine"
 
 # Action kinds that are declared but have no engine dispatch (U1 surfaces
 # them as explicit rejections instead of silent no-ops).
@@ -4115,10 +4116,14 @@ class CombatEngine:
         +4 dodge bonus to AC until the start of the combatant's next turn.
         PF1e (SRD "Total Defense"): "You can't make attacks of opportunity
         while using total defense" — the flag drops the AoO allowance to 0
-        (see ``_aoo_allowance``).
+        (see ``_aoo_allowance``) — and "You can't combine total defense with
+        fighting defensively": the bonus is SET (never stacked on a prior
+        +2) and a pending fighting-defensively declaration is voided (under
+        total defense no attack is made, so its -4 is moot).
         """
         state.total_defense = True
-        state.defensive_ac_bonus += _TOTAL_DEFENSE_AC_BONUS
+        state.fight_defensively = False
+        state.defensive_ac_bonus = _TOTAL_DEFENSE_AC_BONUS
         self._log(
             f"round {self._current_round} {state.combatant.id}: "
             f"total defense (+{_TOTAL_DEFENSE_AC_BONUS} AC)"
@@ -4129,7 +4134,18 @@ class CombatEngine:
         """Execute the fighting defensively action (PF1e): standard action
         granting a +2 dodge bonus to AC until the start of the combatant's
         next turn, at the cost of -4 on attack and crit confirmation rolls.
+        PF1e (SRD "Total Defense"): "You can't combine total defense with
+        fighting defensively" — the declaration is rejected while total
+        defense is active.
         """
+        if state.total_defense:
+            self._log(
+                f"round {self._current_round} {state.combatant.id}: "
+                f"fight_defensively rejected ({_REASON_CANNOT_COMBINE})"
+            )
+            return ActionResult(
+                kind="fight_defensively", ok=False, reason=_REASON_CANNOT_COMBINE
+            )
         state.fight_defensively = True
         state.defensive_ac_bonus += _FIGHT_DEFENSIVELY_AC_BONUS
         self._log(