Fix AI freeze when declaring attackers with unpayable attack costs (Card-Forge#9998)

Author: vanja-ivancevic

forge-ai/src/main/java/forge/ai/AiController.java

@@ -1324,6 +1324,10 @@ public void declareAttackers(Player attacker, Combat combat) {
         // Check if we can reinforce with Banding creatures
         aiAtk.reinforceWithBanding(combat);
 
+        // Per CR 508.1d, the decision to pay attack costs (e.g. Propaganda)
+        // is made at declaration time. Remove attackers the AI can't pay for.
+        removeUnpayableAttackers(combat);
+
         // if invalid: just try an attack declaration that we know to be legal
         if (!CombatUtil.validateAttackers(combat)) {
             combat.clearAttackers();
@@ -1343,6 +1347,22 @@ public void declareAttackers(Player attacker, Combat combat) {
         }
     }
 
+    private void removeUnpayableAttackers(Combat combat) {
+        for (Card attacker : new ArrayList<>(combat.getAttackers())) {
+            Cost attackCost = CombatUtil.getAttackCost(game, attacker, combat.getDefenderByAttacker(attacker));
+            if (attackCost == null) {
+                continue;
+            }
+            SpellAbility fakeSA = new SpellAbility.EmptySa(attacker, attacker.getController());
+            fakeSA.setCardState(attacker.getCurrentState());
+            fakeSA.setPayCosts(attackCost);
+            fakeSA.setSVar("X", "0");
+            if (!ComputerUtilCost.canPayCost(attackCost, fakeSA, player, true)) {
+                combat.removeFromCombat(attacker);
+            }
+        }
+    }
+
     private List<SpellAbility> singleSpellAbilityList(SpellAbility sa) {
         if (sa == null) {
             return null;