Add a regression test for the optional trigger life gate

Bringer of the Black Dawn's upkeep tutor, asserting both directions: it fires
at 20 life and declines at 5, where paying 2 would drop it to 3.

Drop this commit if you would rather not carry the test.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: liamiak1

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

@@ -0,0 +1,62 @@
+package forge.ai.ability;
+
+import forge.ai.AITest;
+import forge.ai.SpellApiToAi;
+import forge.game.Game;
+import forge.game.ability.ApiType;
+import forge.game.card.Card;
+import forge.game.player.Player;
+import forge.game.spellability.SpellAbility;
+import forge.game.trigger.Trigger;
+import forge.game.zone.ZoneType;
+import org.testng.AssertJUnit;
+import org.testng.annotations.Test;
+
+/**
+ * An optional trigger must respect the AI's life-cost safety, the way the activated path already
+ * does (the gate lives in SpellAbilityAi.doTrigger). Exercised with Bringer of the Black Dawn's
+ * "upkeep: you may pay 2 life, tutor" trigger, asserting both directions: it fires when the AI can
+ * spare the life, and declines when paying would drop it below the safety threshold (the bug).
+ */
+public class TriggerLifeGateTest extends AITest {
+
+    @Test
+    public void optionalPayLifeTriggerRespectsLifeSafety() {
+        AssertJUnit.assertTrue("should tutor when it can spare the life",
+                tutors(bringerSetup(20)));
+        AssertJUnit.assertFalse("should not pay 2 life down to 3 to tutor",
+                tutors(bringerSetup(5))); // 5 - 2 = 3, below the threshold of 4
+    }
+
+    private Player bringerSetup(int life) {
+        Game game = initAndCreateGame();
+        Player ai = game.getPlayers().get(1);
+        addCard("Bringer of the Black Dawn", ai);
+        addCardToZone("Griselbrand", ai, ZoneType.Library);
+        for (int i = 0; i < 6; i++) addCardToZone("Forest", ai, ZoneType.Library);
+        ai.setLife(life, null);
+        return ai;
+    }
+
+    private boolean tutors(Player ai) {
+        Card bringer = null;
+        for (Card c : ai.getCardsIn(ZoneType.Battlefield)) {
+            if (c.getName().equals("Bringer of the Black Dawn")) {
+                bringer = c;
+                break;
+            }
+        }
+        AssertJUnit.assertNotNull(bringer);
+        SpellAbility sa = null;
+        for (Trigger t : bringer.getTriggers()) {
+            SpellAbility ability = t.ensureAbility();
+            if (ability != null && ability.getApi() == ApiType.ChangeZone) {
+                sa = ability;
+                break;
+            }
+        }
+        AssertJUnit.assertNotNull("no tutor trigger on Bringer", sa);
+        sa.setActivatingPlayer(ai);
+        return SpellApiToAi.Converter.get(sa).doTrigger(ai, sa, false);
+    }
+}