Break a 9-clash pet deadlock by fainting both combatants.

internal/game/battle.go

@@ -440,6 +440,14 @@ func (g *Game) resolveBattle() {
 	// The exchange loop terminates: every clash kills at least one pet or
 	// is a detected stalemate, and summons/auras are finite. The guard is
 	// just insurance as effects get richer.
+	//
+	// clashStreak counts how many times the current pair has clashed without
+	// either fainting. Some effects (e.g. eat-an-apple-when-hurt) can make two
+	// pets un-killable, looping forever; if they trade blows deadlockLimit
+	// times in a row, both drop so the battle can proceed. It resets whenever
+	// the matchup changes (a fresh pet enters).
+	const deadlockLimit = 9
+	clashStreak := 0
 	for range 10_000 {
 		// Reveal until every side has a pet in play or runs out. Play
 		// effects queue up and resolve after all reveals (simultaneous).
@@ -525,6 +533,15 @@ func (g *Game) resolveBattle() {
 			}
 		}
 
+		// A fresh pet on either side is a new matchup, so the deadlock streak
+		// starts over.
+		for _, np := range newlyPlayed {
+			if np {
+				clashStreak = 0
+				break
+			}
+		}
+
 		// Battle over? A side that couldn't field a pet is out; no further
 		// effects resolve.
 		anyOut := false
@@ -657,9 +674,25 @@ func (g *Game) resolveBattle() {
 		if dealtB > 0 && ua.hasKnockout() {
 			ub.Damage = max(ub.Damage, ub.Power())
 		}
+		// Deadlock guard: if the pair keeps surviving, count the exchanges and
+		// force a mutual knockout once they hit the limit.
+		deadlocked := false
+		if ua.Alive() && ub.Alive() {
+			clashStreak++
+			if clashStreak >= deadlockLimit {
+				deadlocked = true
+				ua.Damage = max(ua.Damage, ua.Power())
+				ub.Damage = max(ub.Damage, ub.Power())
+			}
+		} else {
+			clashStreak = 0
+		}
 		clashTxt := fmt.Sprintf("%s's %s and %s's %s trade blows.",
 			pname(0), ua.Card.Name, pname(1), ub.Card.Name)
 		switch da, db := !ua.Alive(), !ub.Alive(); {
+		case deadlocked:
+			clashTxt = fmt.Sprintf("%s's %s and %s's %s are deadlocked after %d clashes — both faint.",
+				pname(0), ua.Card.Name, pname(1), ub.Card.Name, deadlockLimit)
 		case da && db:
 			clashTxt += " Both faint."
 		case da:

internal/game/battle_test.go

@@ -736,3 +736,28 @@ func TestSkunkStripFaintsDebuffedPet(t *testing.T) {
 		t.Fatalf("skunk should win once the stripped pet faints, got %d", res.WinnerSeat)
 	}
 }
+
+// Two pets that block every hit could clash forever; the deadlock rule makes
+// them both faint after 9 clashes so the battle can proceed.
+func TestBattleDeadlockBreaksAfterNineClashes(t *testing.T) {
+	g, _, _ := testGame(t)
+	wall := func(name string) Card {
+		return Card{
+			ID: g.newCardID(), Kind: KindPet, Name: name, Tier: 1, Power: 3, Suit: SuitRed,
+			Effects: []Effect{{Trigger: TriggerPlay, Action: ActionShieldSelf, Count: 20}},
+		}
+	}
+	res := forceBattle(t, g, []Card{wall("Wall")}, []Card{wall("Fort")})
+
+	clashes := eventsOfType(res, "clash")
+	if len(clashes) != 9 {
+		t.Fatalf("deadlock should resolve after 9 clashes, got %d", len(clashes))
+	}
+	last := clashes[len(clashes)-1]
+	if !last.Died[0] || !last.Died[1] {
+		t.Fatalf("the 9th clash should faint both pets: %+v", last)
+	}
+	if res.WinnerSeat != -1 {
+		t.Fatalf("a deadlock is a draw, got winner=%d", res.WinnerSeat)
+	}
+}