XP-System korrigiert: Level 2 gratis nach erster Welle, 1-1-Carousel-XP banken

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

backend/tests/test_game.py

@@ -192,3 +192,17 @@ def test_pve_freezes_streak_and_pays_no_win_bonus(art, cfg):
     while game.round["stage"] == 1 and not game.over:
         game.step()
     assert game.player.streak == 0
+
+
+def test_natural_level_progression(art, cfg):
+    """Ohne XP-Kauf: Level 1 bei 1-2, Level 4 bei 2-1, Level 5 mit 6/20 bei 3-2."""
+    game = Game(art, cfg, seed=6)
+    assert game.player.level == 1 and game.player.xp == 2  # 1-1-XP gebankt
+    checks = {}
+    while not game.over and game.round["label"] != "3-3":
+        checks[game.round["label"]] = (game.player.level, game.player.xp)
+        game.step()
+    assert checks["1-2"][0] == 1
+    assert checks["1-3"][0] == 3  # gratis Level 2 + kaskadierte XP
+    assert checks["2-1"] == (4, 0)
+    assert checks["3-2"] == (5, 6)