Improve rock attribution.

internal/game/tier456_test.go

@@ -588,6 +588,12 @@ func TestSnakeRecurringRocks(t *testing.T) {
 	if len(rocks) != 2 {
 		t.Fatalf("snake should volley on each friendly play: %+v", rocks)
 	}
+	// The set-aside Snake threw the rocks, not the pet (A/B) in play.
+	for _, r := range rocks {
+		if !strings.Contains(r.Text, "Snake") {
+			t.Fatalf("rock event should credit Snake as the source, got %q", r.Text)
+		}
+	}
 	if res.WinnerSeat != -1 {
 		t.Fatalf("expected draw, got %d", res.WinnerSeat)
 	}