fix(rules): suppress attacks of opportunity through cover or total concealment

PF1e (CRB Cover): "You can't execute an attack of opportunity against an
opponent with cover relative to you"; (CRB Concealment): the same holds
against total concealment. _resolve_aoo now checks terrain cover
(cover_bonus_cells, melee line) and miss_chance >= 50 before striking,
logs the suppression and leaves the per-round budget unspent. Partial
concealment (blurred 20%) and normal attacks are unaffected.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/pf1e_simulator/combat.py

@@ -80,7 +80,10 @@ Phase 0 documented deviations from PF1e (conventions):
   (tracked in ``_move_aoo_provoked``, cleared at round start); the ranged,
   casting, stand-up and maneuver triggers are separate and each still
   provokes. AoOs always strike (PF1e allows declining, the simulator
-  does not). A 5-foot step never provokes AoOs (it is not a move action); the
+  does not) — except that an opponent with cover or total concealment
+  relative to the attacker cannot be struck at all (the opportunity is
+  suppressed, not spent; CRB "Cover"/"Concealment"). A 5-foot step never
+  provokes AoOs (it is not a move action); the
   withdraw action protects only the starting square (see below). A 5-foot
   step and any other movement (move, charge, withdraw) are mutually exclusive
   within the same turn (``moved_this_turn`` flag, cleared in ``_take_turn``).
@@ -2931,14 +2934,46 @@ class CombatEngine:
             return None
         return cost_cells * _SQUARE_FT
 
+    def _aoo_defense_block(
+        self, attacker: CombatantState, target: CombatantState
+    ) -> str | None:
+        """Why an AoO cannot be executed against the target, or None.
+
+        PF1e (CRB "Cover"): "You can't execute an attack of opportunity
+        against an opponent with cover relative to you"; (CRB "Concealment"):
+        "You can't execute an attack of opportunity against an opponent with
+        total concealment" (miss chance >= 50%). Melee line: terrain cover
+        only — creatures grant no melee cover.
+        """
+        if self._concealment_chance(target) >= _TOTAL_CONCEALMENT_PCT:
+            return "total concealment"
+        if cover_bonus_cells(
+            self._grid,
+            attacker.occupied_cells(),
+            target.occupied_cells(),
+            ranged=False,
+            occupied=frozenset(),
+        ):
+            return "cover"
+        return None
+
     def _resolve_aoo(self, attacker: CombatantState, target: CombatantState) -> bool:
         """Resolve one attack of opportunity (single melee attack at normal bonus).
 
         AoOs are always taken (PF1e allows declining, but the simulator always strikes).
+        A target with cover or total concealment relative to the attacker cannot be
+        struck at all — the opportunity is suppressed without spending it.
         Returns True if the target dropped.
         """
         if self.has_condition_flag(attacker, "cant_aoo"):
             return False
+        blocked = self._aoo_defense_block(attacker, target)
+        if blocked is not None:
+            self._log(
+                f"round {self._current_round} {attacker.combatant.id}: "
+                f"AoO vs {target.combatant.id} suppressed ({blocked})"
+            )
+            return False
         self._aoo_used[attacker.combatant.id] = self._aoo_used.get(attacker.combatant.id, 0) + 1
         weapon = next((w for w in attacker.usable_attacks() if w.kind == "melee"), None)
         if weapon is None: