AI: don't let a RemoveCounterAll sub-ability veto its own parent

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

@@ -158,7 +158,7 @@ public enum SpellApiToAi {
             .put(ApiType.Regenerate, RegenerateAi.class)
             .put(ApiType.Regeneration, AlwaysPlayAi.class)
             .put(ApiType.RemoveCounter, CountersRemoveAi.class)
-            .put(ApiType.RemoveCounterAll, CannotPlayAi.class)
+            .put(ApiType.RemoveCounterAll, CountersRemoveAllAi.class)
             .put(ApiType.RemoveFromCombat, RemoveFromCombatAi.class)
             .put(ApiType.RemoveFromGame, AlwaysPlayAi.class)
             .put(ApiType.RemoveFromMatch, AlwaysPlayAi.class)

forge-ai/src/main/java/forge/ai/ability/CountersRemoveAllAi.java

@@ -0,0 +1,26 @@
+package forge.ai.ability;
+
+import forge.ai.AiAbilityDecision;
+import forge.ai.AiPlayDecision;
+import forge.ai.SpellAbilityAi;
+import forge.game.player.Player;
+import forge.game.spellability.SpellAbility;
+
+/**
+ * The AI has no logic for choosing to remove all counters of a kind, so it still will not activate
+ * one on purpose. As a sub-ability it is a consequence of an effect the AI has already decided it
+ * wants - usually bookkeeping, like Oblivion Stone clearing the fate counters it just checked - so
+ * it must not veto its own parent.
+ */
+public class CountersRemoveAllAi extends SpellAbilityAi {
+
+    @Override
+    protected AiAbilityDecision canPlay(Player aiPlayer, SpellAbility sa) {
+        return new AiAbilityDecision(0, AiPlayDecision.CantPlayAi);
+    }
+
+    @Override
+    public AiAbilityDecision chkDrawback(Player aiPlayer, SpellAbility sa) {
+        return new AiAbilityDecision(100, AiPlayDecision.WillPlay);
+    }
+}

forge-gui-desktop/src/test/java/forge/ai/ability/RemoveCounterAllDrawbackTest.java

@@ -0,0 +1,47 @@
+package forge.ai.ability;
+
+import forge.ai.AITest;
+import forge.game.Game;
+import forge.game.phase.PhaseType;
+import forge.game.player.Player;
+import forge.game.zone.ZoneType;
+import org.testng.annotations.Test;
+
+import static junit.framework.Assert.assertEquals;
+
+/**
+ * RemoveCounterAll has no AI, so as a sub-ability it used to refuse and take its parent down with
+ * it. Oblivion Stone's wipe ends by clearing the fate counters it just checked, which meant the
+ * wipe itself could never be activated.
+ */
+public class RemoveCounterAllDrawbackTest extends AITest {
+
+    @Test
+    public void bookkeepingSubAbilityDoesNotVetoTheWipe() {
+        Game game = initAndCreateGame();
+        Player ai = game.getPlayers().get(1);
+        Player opp = game.getPlayers().get(0);
+        ai.setTeam(0);
+        opp.setTeam(1);
+
+        for (int i = 0; i < 8; i++) {
+            addCard("Wastes", ai);
+        }
+        fillLibrary(ai, 15);
+        fillLibrary(opp, 15);
+        // nothing of the AI's own is in range, so the wipe is pure upside
+        addCard("Grizzly Bears", opp);
+        addCard("Grizzly Bears", opp);
+        addCard("Grizzly Bears", opp);
+        addCard("Oblivion Stone", ai);
+
+        game.getPhaseHandler().devModeSet(PhaseType.MAIN2, ai);
+        game.getAction().checkStateEffects(true);
+        playUntilNextTurn(game);
+
+        assertEquals("it sacrificed Oblivion Stone to wipe", 1,
+                countCardsWithName(game, "Oblivion Stone", ZoneType.Graveyard));
+        assertEquals("the opponent's board is gone", 0,
+                countCardsWithName(game, "Grizzly Bears", ZoneType.Battlefield));
+    }
+}

forge-gui/res/cardsfolder/o/oblivion_stone.txt

@@ -1,8 +1,7 @@
 Name:Oblivion Stone
 ManaCost:3
 Types:Artifact
-A:AB$ PutCounter | Cost$ 4 T | ValidTgts$ Permanent | CounterType$ FATE | CounterNum$ 1 | SpellDescription$ Put a fate counter on target permanent.
+A:AB$ PutCounter | Cost$ 4 T | ValidTgts$ Permanent | CounterType$ FATE | CounterNum$ 1 | AILogic$ AtOppEOT | AITgts$ Permanent.YouCtrl+Other+nonLand | SpellDescription$ Put a fate counter on target permanent.
 A:AB$ DestroyAll | Cost$ 5 T Sac<1/CARDNAME> | ValidCards$ Permanent.nonLand+counters_LT1_FATE | SubAbility$ DBRemove | SpellDescription$ Destroy each nonland permanent without a fate counter on it, then remove all fate counters from all permanents.
 SVar:DBRemove:DB$ RemoveCounterAll | ValidCards$ Permanent | CounterType$ FATE | AllCounters$ True
-AI:RemoveDeck:All
 Oracle:{4}, {T}: Put a fate counter on target permanent.\n{5}, {T}, Sacrifice Oblivion Stone: Destroy each nonland permanent without a fate counter on it, then remove all fate counters from all permanents.