diff --git a/scripts/live/book_execute.py b/scripts/live/book_execute.py
index 39c1b44..6bfe49f 100644
--- a/scripts/live/book_execute.py
+++ b/scripts/live/book_execute.py
@@ -314,6 +314,11 @@ def _run():
 
         try:
             if do_execute and order is not None and not solo_protezione:
+                # U1/U2 si uniscono dopo questo rilascio: `set_open_cap` e' di U1 (execution.py,
+                # stesso file, non toccato qui). hasattr perche' oggi DeribitTrader non lo ha
+                # ancora — l'hasattr si toglie al merge, quando entrambi vivono nello stesso ramo.
+                if hasattr(trader, "set_open_cap"):
+                    trader.set_open_cap(inst, r["cap_per_asset"] * r.get("scala", 1.0), mark)
                 try:
                     fills = trader.rebalance_signed(inst, net, mark, min_usd=min_order)
                 except RebalanceParziale as rp:
diff --git a/tests/test_book_u2.py b/tests/test_book_u2.py
index f4f8a28..845406f 100644
--- a/tests/test_book_u2.py
+++ b/tests/test_book_u2.py
@@ -399,3 +399,61 @@ def test_parse_cron_log_legge_il_fill_di_un_RebalanceParziale(monkeypatch, capsy
     assert len(runs) == 1 and len(runs[0].fills) == 1
     f = runs[0].fills[0]
     assert f.asset == "BTC" and f.side == "sell" and abs(f.qty - 0.002) < 1e-9
+
+
+# ---------------------------------------------------------------------------
+# set_open_cap (da U1, stesso rilascio): chiamato SOLO se il trader lo espone (hasattr — U1 e
+# U2 si uniscono dopo questo rilascio), subito prima di rebalance_signed.
+# ---------------------------------------------------------------------------
+def test_set_open_cap_chiamato_se_il_trader_lo_espone(monkeypatch):
+    mod = carica_script("scripts/live/book_execute.py")
+
+    class _TraderConCap:
+        def __init__(self):
+            self.cap_visti = []
+        def set_open_cap(self, inst, cap_usd, mark):
+            self.cap_visti.append((inst, cap_usd, mark))
+        def rebalance_signed(self, inst, net, mark, min_usd=5.0):
+            return []
+        def position_usd(self, inst):
+            return 0.0
+        def ensure_disaster_sl(self, inst, sl_pct):
+            return {"state": "ok", "stop": 1.0, "amount": 0.0}
+
+    trader = _TraderConCap()
+    canned = _canned_report(cap_per_asset=300.0, scala=1.25)
+    monkeypatch.setattr(mod, "book_report", lambda **k: canned)
+    monkeypatch.setattr(mod, "notify", lambda t, d=None: None)
+    monkeypatch.setattr(mod, "DeribitTrader", lambda *a, **k: trader)
+    monkeypatch.setattr(mod, "load_config",
+                        lambda: dict(execution_enabled=True, min_order_usd=5.0,
+                                     disaster_sl_pct=0.30, max_data_age_days=2.0,
+                                     skh_feed_max_age_min=30.0))
+    monkeypatch.setattr(sys, "argv", ["book_execute.py", "--execute"])
+
+    mod._run()
+    assert trader.cap_visti == [("BTC_USDC-PERPETUAL", 300.0 * 1.25, 60000.0)]   # solo BTC ha un ordine
+
+
+def test_set_open_cap_non_richiesto_se_il_trader_non_lo_espone(monkeypatch):
+    """hasattr: un trader senza set_open_cap (oggi, prima del merge con U1) non deve rompersi."""
+    mod = carica_script("scripts/live/book_execute.py")
+
+    class _TraderSenzaCap:
+        def rebalance_signed(self, inst, net, mark, min_usd=5.0):
+            return []
+        def position_usd(self, inst):
+            return 0.0
+        def ensure_disaster_sl(self, inst, sl_pct):
+            return {"state": "ok", "stop": 1.0, "amount": 0.0}
+
+    canned = _canned_report()
+    monkeypatch.setattr(mod, "book_report", lambda **k: canned)
+    monkeypatch.setattr(mod, "notify", lambda t, d=None: None)
+    monkeypatch.setattr(mod, "DeribitTrader", lambda *a, **k: _TraderSenzaCap())
+    monkeypatch.setattr(mod, "load_config",
+                        lambda: dict(execution_enabled=True, min_order_usd=5.0,
+                                     disaster_sl_pct=0.30, max_data_age_days=2.0,
+                                     skh_feed_max_age_min=30.0))
+    monkeypatch.setattr(sys, "argv", ["book_execute.py", "--execute"])
+    mod._run()      # non deve sollevare AttributeError